Experimental Characterization of Membrane Fouling under ... · This research work on reverse osmosis water treatment systems is divided into two main parts: (1) the experimental characterization

Experimental Characterization of Membrane Fouling under Intermittent Operation and Its Application to the

Optimization of Solar Photovoltaic Powered Reverse Osmosis Drinking Water Treatment Systems

by

Marina Freire-Gormaly

A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy

Department of Mechanical and Industrial Engineering University of Toronto

© Copyright by Marina Freire-Gormaly 2018

ii

Experimental Characterization of Membrane Fouling under

Intermittent Operation and Its Application to the Optimization of

Solar Photovoltaic Powered Reverse Osmosis Drinking Water

Treatment Systems

Marina Freire-Gormaly

Doctor of Philosophy

Department of Mechanical and Industrial Engineering

University of Toronto

2018

Abstract

This thesis presents a novel experimental characterization of reverse osmosis membrane

fouling from the intermittent operation of solar powered water treatment systems. This thesis also

depicts the development of an analytical membrane fouling model and a design framework to

configure location-customized solar photovoltaic reverse osmosis systems.

The World Health Organization estimates that 760 million people worldwide lack access

to clean drinking water. The regions with the highest water scarcity are usually off-grid, remote

and have high solar insolation. Therefore, the use of solar powered reverse osmosis water treatment

systems is a viable solution. However, to minimize the costs, these systems are configured with

minimal battery storage and operated intermittently with extended shutdown periods. Literature

lacks an experimental characterization of the effect of this intermittent operation on membrane

fouling and an associated design optimization framework.

iii

This research work on reverse osmosis water treatment systems is divided into two main

parts: (1) the experimental characterization of membrane fouling under intermittent operation, and

(2) the development of an analytical membrane fouling model and a design optimization

framework for these systems.

A new fully-instrumented experimental lab-scale system was designed, built,

commissioned and operated with triplicate measurements of membrane permeability and

membrane salt rejection for the experimental characterization. A new pilot-scale experimental

system was also designed, built and operated. The membrane fouling was characterized

experimentally for intermittent and continuous operation. The effect of anti-scalant and rinsing

was also investigated. Two types of experimental water was tested: an experimental MilliQ-based

matrix and an experimental groundwater-based matrix. The groundwater was from Nobleton,

Ontario. In addition, membrane autopsy was performed using scanning electron microscopy.

An analytical membrane fouling model was developed based on the experimental results.

Furthermore, a novel design framework was developed using this new analytical membrane

fouling model. This design optimization framework can be used for the configuration of

community-specific solar photovoltaic reverse osmosis systems that are reliable throughout the

system life at a minimal cost. The design optimization framework can be adapted for other modular

systems such as renewable power systems for off-grid communities, remote First Nations, Métis,

and Inuit communities, or remote mining sites.

iv

Dedication

I dedicate this work to my friend, Susan Lee, whose enthusiasm for my research, curiosity

and encouragement was invaluable. Although she didn’t see the work to completion, dying of brain

cancer in late 2016, her spirit of generosity and social consciousness continue to inspire me.

I also dedicate this work to my great-aunt Andrea. Although she only saw me start my

doctoral research, and thought it was ‘real swish,’ her kind and friendly nature taught me the

importance of learning from everyone I meet.

v

Acknowledgments

I have been very fortunate to work with Prof. Amy Bilton for this doctoral program. Her

mentorship, leadership and work-ethic has been instrumental. I greatly appreciate her guidance,

assistance troubleshooting the experimental equipment and systematic approach to everything. Her

dedication to global engineering research, teaching and her students is inspirational. Working with

her, helping set-up the lab and seeing it grow over the past years has been an incredible experience.

I also sincerely appreciate the guidance and expertise provided by my committee members,

Dean Cristina Amon and Prof. Robert C. Andrews. Their review, in-depth critique of my research

and discussions over the past years have been incredibly helpful. I also would like to thank Prof.

Robert C. Andrews for lending his RO experimental equipment. This helped me immensely to set-

up the experimental systems in this thesis. Prof. A. H. M. Anwar Sadmani and Dr. Gwen Woods-

Chabane for their helpful guidance explaining the RO experimental equipment and answering any

questions I had during my doctoral studies.

I also greatly appreciate the expertise provided by my external committee members, Prof.

John H. Lienhard and Prof. Murray Metcalfe.

Jeff Vandenberg from the Toronto Regional Conservation Authority graciously taught me

how to use his water collection equipment and allowed me to collect water at the Nobleton, Ontario

deep water well. I also appreciate Prof. Christopher M. Yip’s generosity sharing his fridge for the

groundwater storage. I am grateful to George Kretschmann from Geology, who provided

invaluable technical support on the scanning electron microscopy and electron dispersive

spectroscopy.

The financial support from the Natural Sciences and Engineering Research Council

(NSERC) of Canada for the NSERC Discovery Grant and experimental equipment infrastructure

financially supported through the Canada Foundation for Innovation and the Ontario Research

Fund were invaluable. I am also very thankful for the NSERC CGS-D scholarship, the Department

of Mechanical and Industrial Engineering at the University of Toronto for the fellowship and

Conference Travel Grant, and to the Province of Ontario for the Queen Elizabeth II/Dupont

Graduate Scholarship in Science and Technology, the Hatch Graduate Scholarship for Sustainable

vi

Energy, the Paul Cadario Doctoral Fellowship in Global Engineering, the Mary Gertrude L'Anson

Scholarship and the Ontario Society of Professional Engineers (OSPE) Personal Scholarship.

I had the privilege of working with extremely helpful and dedicated undergraduate

researchers, Youngmok (Justin) Ko, Rashmi Satharakulasinghe, Francis Cruz, Daniel Powell,

Caiden Chi, and an M.Eng. researcher, Ravier Weekes. Their enthusiasm and support made

working in the lab a joy.

The Water and Energy Research Lab was a dynamic, supportive and innovative team. I am

really thankful to Shakya Sur and Ahmed Mahmoud for helping out with driving a van or vehicle

for water collection trips. As well, my trustworthy water moving crew labmates, who never

hesitated to come over and help move containers off the van and into the fridge. The lab group

was a great place of comradery and I appreciate the conversations, discussions, helpful critiques

of my presentations and the endless support of all of my labmates.

I am thankful for the support my mom, dad, sister, Marianne, and brother-in-law, Ray

provided throughout my studies. I also appreciate my friends and extended family for supporting

me and listening about my adventures in the lab. I also appreciate Dr. Faizul Mohee’s

encouragement all along the way. Whether it was listening to my practice presentations, providing

a sounding board for ideas, reading my drafts or encouraging me to take a break once in a while, I

greatly appreciate all of their support.

vii

Table of Contents

Dedication ...................................................................................................................................... iv

Acknowledgments............................................................................................................................v

Table of Contents .......................................................................................................................... vii

List of Tables ............................................................................................................................... xiii

List of Figures .............................................................................................................................. xiv

Chapter 1 ..........................................................................................................................................1

Introduction .................................................................................................................................1

1.1 Motivation ............................................................................................................................1

1.2 Problem Statement ...............................................................................................................4

1.3 Research Objectives and Goals ............................................................................................4

1.4 Research Scope ....................................................................................................................5

1.5 Thesis Contributions ............................................................................................................6

1.6 Research Program ................................................................................................................8

1.7 Thesis Organization .............................................................................................................9

Chapter 2 ........................................................................................................................................11

Background and Literature Review ..........................................................................................11

2.1 Renewable Powered Reverse Osmosis Desalination .........................................................11

2.1.1 Reverse Osmosis Water Treatment ........................................................................12

2.1.2 Overview of Renewable Powered RO Systems .....................................................13

2.2 Reverse Osmosis Membrane Fouling ................................................................................15

2.2.1 Biofouling ..............................................................................................................15

2.2.2 Scaling....................................................................................................................16

2.2.3 Pre-treatment to Minimize RO Membrane Fouling ...............................................16

2.2.4 Experimental Studies on RO Membrane Fouling ..................................................17

2.2.5 RO Membrane Fouling Models and Mechanisms .................................................18

viii

2.3 Design Approaches for Solar Powered RO Systems .........................................................19

2.4 Summary and Research Needs...........................................................................................20

Chapter 3 ........................................................................................................................................22

Experimental Systems and Methods .........................................................................................22

3.1 Introduction ........................................................................................................................22

3.2 Lab-scale Systems ..............................................................................................................22

3.2.1 Initial Lab-scale System Setup...............................................................................22

3.2.2 Improved Lab-scale System Setup.........................................................................25

3.2.3 Lab-scale Instrumentation ......................................................................................28

3.2.4 Experimental Water Tank ......................................................................................31

3.3 Pilot-scale System ..............................................................................................................32

3.3.1 Pilot-scale System Setup ........................................................................................32

3.3.2 Pilot-scale Instrumentation ....................................................................................35

3.4 Experimental Methods .......................................................................................................37

3.4.1 Experiment Water Preparation ...............................................................................37

3.4.2 Operating Conditions .............................................................................................40

3.4.3 Cartridge Filter Replacement .................................................................................43

3.4.4 Lab-scale System Procedures ................................................................................43

3.4.4.1 Membrane Coupon Preparation ...............................................................43

3.4.4.2 Membrane Autopsy .................................................................................44

3.4.5 Pilot-scale System Procedures ...............................................................................45

3.4.5.1 Membrane Preparation ............................................................................45

3.4.5.2 Membrane Autopsy .................................................................................45

3.4.6 Membrane Characterization ...................................................................................46

3.4.6.1 Pure Water Permeability ..........................................................................46

3.4.6.2 Scanning Electron Microscopy ................................................................47

ix

3.4.6.3 ATP Surface Deposit Analysis ................................................................48

3.5 Conclusion .........................................................................................................................48

Chapter 4 ........................................................................................................................................49

Membrane Fouling under Intermittent Operation with the Initial Lab-scale System and

using the Experimental MilliQ-based Matrix ...........................................................................49

4.1 Introduction ........................................................................................................................49

4.2 Experimental Program .......................................................................................................49

4.3 System Operating Conditions ............................................................................................50

4.4 Effect of Intermittent Operation vs. Continuous Operation...............................................50

4.5 Discussion ..........................................................................................................................55

4.6 Conclusions ........................................................................................................................57

Chapter 5 ........................................................................................................................................58

Membrane Fouling Characterization at the Lab-scale using the Experimental MilliQ-based

Matrix ........................................................................................................................................58

5.1 Introduction ........................................................................................................................58

5.2 System Operating Conditions ............................................................................................58

5.3 Experimental Program .......................................................................................................60

5.4 Effect of Anti-scalant Pre-treatment ..................................................................................61

5.5 Effect of Intermittent Operation vs. Continuous Operation...............................................62

5.6 Effect of Anti-scalant F135 for Intermittent Operation with no Rinse ..............................63

5.7 Effect of Rinsing with Anti-scalant F135 for Intermittent Operation................................64

5.8 Combined Comparison of the Effect of Operational Conditions on Membrane

Permeability .......................................................................................................................65

5.9 Combined Comparison of the Effect of Operational Conditions on Salt Rejection ..........67

5.10 Combined Comparison of the Effect of Operational Conditions on the Membrane

Autopsies............................................................................................................................68

5.11 Conclusions ........................................................................................................................71

Chapter 6 ........................................................................................................................................73

x

Membrane Fouling Characterization at the Lab-scale and Pilot-scale using the

Experimental Groundwater-based Matrix .................................................................................73

6.1 Introduction ........................................................................................................................73

6.2 Experimental Hypotheses ..................................................................................................73

6.2.1 Effect of Intermittent vs. Continuous Operation on Membrane Fouling with

Anti-scalant Usage at the Lab-scale .......................................................................73

6.2.2 Effect of Permeate Rinsing on Membrane Fouling with Anti-scalant Usage at

the Lab-scale ..........................................................................................................74

6.2.3 Effect of Experimental System on Membrane Fouling .........................................75

6.3 Experimental Program to Test Hypotheses........................................................................75

6.4 Experimental Results .........................................................................................................76

6.4.1 Lab-scale Membrane Permeability Decline ...........................................................76

6.4.2 Lab-scale Salt Rejection ........................................................................................80

6.4.3 Lab-scale Membrane Autopsy ...............................................................................81

6.4.4 Discussion for the Lab-scale Experimental Results ...............................................84

6.4.4.1 Effect of Intermittent vs. Continuous Operation on Membrane

Fouling with Anti-scalant Usage .............................................................84

6.4.4.2 Effect of Effect of Permeate Rinsing on Membrane Fouling with

Anti-scalant Usage ...................................................................................85

6.4.5 Pilot-scale Membrane Permeability Decline .........................................................86

6.4.6 Pilot-scale Membrane Autopsy ..............................................................................89

6.4.7 Discussion for the Pilot-scale.................................................................................91

6.4.7.1 Effect of Experimental System on Membrane Fouling ...........................91

6.5 Discussion of Potential Fouling Mechanisms ....................................................................92

6.6 Conclusions ........................................................................................................................93

Chapter 7 ........................................................................................................................................95

Design Optimization Framework for Solar Powered Reverse Osmosis Systems

Considering Membrane Fouling from Intermittent Operation ..................................................95

7.1 Introduction ........................................................................................................................95

xi

7.2 Design Optimization Framework Approach ......................................................................96

7.3 Design Optimization Framework .......................................................................................99

7.3.1 Optimization Setup ................................................................................................99

7.3.2 Simulation Model.................................................................................................101

7.3.2.1 Power System Model .............................................................................104

7.3.2.2 Water Treatment System Model ............................................................106

7.3.2.3 Analytical Membrane Fouling Model ...................................................107

7.3.3 Cost Model ...........................................................................................................109

7.3.3.1 Power System Cost Model ....................................................................112

7.3.3.2 Water Treatment System Cost Model ...................................................114

7.4 Optimization Results and Discussion ..............................................................................116

7.4.1 Effect of System Size on Optimal System Cost...................................................116

7.4.2 Effect of System Size on System Configuration..................................................119

7.4.3 Effect of System Reliability on Optimal System Configuration .........................120

7.4.4 Effect of Membrane Permeability Decline on System Reliability .......................121

7.4.5 Effect of Geographic Location on Optimal System Configuration .....................124

7.5 Conclusions ......................................................................................................................127

Chapter 8 ......................................................................................................................................128

Summary and Conclusions ......................................................................................................128

8.1 Summary ..........................................................................................................................128

8.1.1 Initial Experimental Characterization of Intermittent Operation .........................129

8.1.2 Improved Experimental Characterization of Intermittent Operation at the Lab-

scale......................................................................................................................129

8.1.3 Experimental Characterization of Intermittent Operation using Groundwater ....130

8.1.4 Design Optimization of Solar Powered Water Treatment Systems Considering

Membrane Fouling ...............................................................................................131

8.2 Conclusions ......................................................................................................................131

xii

8.3 Recommendations for Future Work.................................................................................134

8.4 List of Published Papers from this Thesis........................................................................136

8.5 List of Conference Proceedings from this Thesis ............................................................136

References ....................................................................................................................................138

xiii

List of Tables

Table 1-1: Water salinity ranges in terms of the total dissolved solids, adapted from [15]. .......... 2

Table 3-1: Water chemistry of La Mancalona, Mexico groundwater, Nobleton, Ontario

groundwater, the experimental MilliQ-based matrix and the experimental groundwater-based

matrix. ........................................................................................................................................... 38

Table 3-2: Filmtec BW30 membrane characteristics. ................................................................... 47

Table 4-1: List of experiments and operating conditions. ............................................................ 50



Table 7-1: List of design variables.............................................................................................. 100

Table 7-2: List of genetic algorithm parameters. ........................................................................ 101

Table 7-3: Membrane fouling parameters for cases investigated. .............................................. 108

Table 7-4: Individual component costs for the solar powered water treatment system. ............. 110

Table 7-5: Water cost (USD/m3) for various system sizes (1, 5, 10 m3/day) and LOWP (1%, 5%,

10%). Shows decreasing water costs for reduced system reliability (increasing LOWP). ......... 119

Table 7-6: Effect of changing the design goal LOWP for a 10 m3/day system for La Mancalona,

Mexico. ....................................................................................................................................... 121

Table 7-7: Effect of considering membrane fouling on the optimal system configuration for a

design goal loss of water probability of 1%. ............................................................................... 122

Table 7-8: Effect of geographic location on the optimal system configuration for a design goal

loss of water probability (LOWP) of 1%. For all the shown design configurations the optimal

operating condition was Case 3 (with anti-scalant and with rinsing) and the optimization found

the optimal system cost at the maximum membrane life of five years. ...................................... 126

xiv

List of Figures

Figure 1-1: The world map of a) water scarcity [1], and b) average solar irradiance [24]. Regions

with high water scarcity also tend to have high solar irradiance. ................................................... 3

Figure 1-2: Flowchart of the research program conducted in this thesis with the associated

chapter numbers. ............................................................................................................................. 9

Figure 2-1: Reverse osmosis membrane resistance as a function of time. ................................... 13

Figure 2-2: Simple PVRO system schematic for remote communities. ....................................... 14

Figure 3-1: Initial experimental lab-scale system schematic including instrumentation. ............. 24

Figure 3-2: Physical initial experimental lab-scale setup corresponding to the lab-scale schematic

in Figure 3-1. ................................................................................................................................. 25

Figure 3-3: Improved experimental lab-scale system schematic with instrumentation. ............... 26

Figure 3-4: Physical experimental lab-scale reverse osmosis system. ......................................... 27

Figure 3-5: Electrical system diagram with sensors, actuators, DAQ and user interface. ............ 29

Figure 3-6: User-interface for data monitoring in Labview.......................................................... 30

Figure 3-7: User control interface in Labview. ............................................................................. 30

Figure 3-8: a) Isometric view of the experimental water tank; and b) cut-away view of the inner

components of the experimental water tank. ................................................................................ 32

Figure 3-9: Pilot-scale system schematic. ..................................................................................... 34

Figure 3-10: Physical setup of the pilot-scale system. .................................................................. 35

Figure 3-11: Labview continuous monitoring interface for the pilot-scale system. ..................... 36

Figure 3-12: Labview control interface for the pilot-scale system. .............................................. 37

xv

Figure 3-13: Nobleton deep well (Nobleton, Ontario) with the a) well's green access box and

b) portable variable frequency drive for the submersible pump located inside the well. ............. 40

Figure 3-14: Groundwater collection at the Nobleton deep well, Ontario. .................................. 40

Figure 3-15: Operating pressure for the a) intermittent experiments and b) the continuous

experiments for a representative three days of operation. ............................................................ 42

Figure 3-16: Location of SEM and ATP samples for the lab-scale samples. ............................... 44

Figure 3-17: Unraveled TW30-2514 membrane for removal of the membrane autopsy samples.

....................................................................................................................................................... 45

Figure 3-18: Pilot-scale membrane autopsy sample locations shown on the unraveled membrane.

....................................................................................................................................................... 46

Figure 3-19: Laser-cut holder for the aluminum disks containing the SEM samples (gold sputter

coated reverse osmosis membrane samples)................................................................................. 47

Figure 4-1: Membrane permeability as a function of operating time for the intermittent run. The

hours when the system was shutdown are not included. .............................................................. 51

Figure 4-2: Transmembrane pressure for the intermittent and continuous experimental run. ...... 52

Figure 4-3: Membrane permeability vs. operating time for the continuous run (averaged over 30

min intervals). ............................................................................................................................... 53

Figure 4-4: Comparison of initial continuous and intermittent experiments. ............................... 54

Figure 5-1: Experimental system operational conditions: a) permeability, b) pressure, c) recovery

ratio, d) salt rejection. ................................................................................................................... 59

Figure 5-2: Normalized membrane permeability for continuous operation with and without the

use of F135 anti-scalant. ............................................................................................................... 61

Figure 5-3: Normalized membrane permeability of continuous operation and intermittent

operation with F135 anti-scalant. .................................................................................................. 63

xvi

Figure 5-4: Normalized permeability decline for intermittent operated experiment both with and

without anti-scalant and without rinsing. ...................................................................................... 64

Figure 5-5: Normalized membrane permeability of decline for intermittent operated experiment

with anti-scalant when operated with rinsing and without rinsing. .............................................. 65

Figure 5-6: Comparative bar graph of the experimental conditions investigated, the permeability

shown is the permeability at the fourth hour of the day. .............................................................. 66

Figure 5-7: Comparative bar graph of the average salt rejection for the experimental conditions

investigated. .................................................................................................................................. 67

Figure 5-8: Comparative SEM images of the various operating conditions at x 1000

magnification: a) clean un-used membrane, b) continuous with anti-scalant, c) continuous

without anti-scalant, d) intermittent with anti-scalant and with rinse, e) intermittent with anti-

scalant and and no rinse, f) intermittent without anti-scalant. ...................................................... 68

Figure 5-9: Comparative SEM cross-sections of the various operating conditions at x 500



scalant and and no rinse, f) intermittent without anti-scalant and without rinse. ......................... 69

Figure 5-10: Concentration of ATP on the membrane surface for various operating conditions. 70

Figure 6-1: Normalized membrane permeability for F260 anti-scalant when operated

continuously and intermittently. ................................................................................................... 77

Figure 6-2: Normalized membrane permeability for intermittent operation and F260 anti-scalant

with and without rinse. The rinse significantly improved the membrane permeability. .............. 78

Figure 6-3: Normalized permeability for the various operating conditions investigated at the

fourth hour of each day for day-to-day comparison. .................................................................... 79

Figure 6-4: Salt rejection for the groundwater experiments with F260. ....................................... 80

Figure 6-5: Membrane autopsy of the lab-scale experiments at x 1000 magnification and the

length bar represents 20 µm (a-c). Also, the membrane autopsies are shown at x 3000

xvii

magnification and the length bar represents 5 µm (d-f). For the continuous with F260 anti-scalant

(a, d), intermittent with F260 anti-scalant and no rinse (b, e) and intermittent with F260 anti-

scalant and with rinse (c, f) experiments. ..................................................................................... 82

Figure 6-6: Concentration of ATP on the membrane surface for lab-scale operating conditions

with anti-scalant F260. .................................................................................................................. 83

Figure 6-7: a) Normalized membrane permeability with the pilot-scale system operated with the

F260 anti-scalant and no rinsing in intermittent operation. The circled permeability rose above

the declining trend due to several start-up attempts after the submersible pump failed. .............. 87

Figure 6-8: Normalized membrane permeability for intermittent operation and the F260 anti-

scalant without rinsing for both the pilot-scale system and the lab-scale system. ........................ 88

Figure 6-9: Pilot-scale SEM autopsy a) compared to lab-scale SEM autopsy b) for intermittent

operation with F260 and no rinse at x 1000 magnification. Pilot-scale SEM autopsy c) compared

to lab-scale SEM autopsy d) for intermittent operation with F260 and no rinse at x 3000

magnification. ............................................................................................................................... 89

Figure 6-10: Pilot-scale membrane ATP compared to the lab-scale for intermittent operation with

F260 and no rinse. ......................................................................................................................... 90

Figure 6-11: Schematic of the difference between the lab-scale system and the pilot-scale system

during extended shutdown periods. .............................................................................................. 92

Figure 6-12: Proposed fouling mechanism process for intermittent operation of reverse osmosis

membranes .................................................................................................................................... 93

Figure 7-1: Framework for performing the cost optimization of the PVRO system. ................... 96

Figure 7-2: Solar powered reverse osmosis water treatment system architecture. ....................... 97

Figure 7-3: PVRO operating costs and pre-treatment................................................................... 98

Figure 7-4: System simulation flowchart outlining the hourly and daily steps in the simulation to

determine the loss of water probability. ...................................................................................... 102

xviii

Figure 7-5: Power management strategy for the solar powered water treatment model. simulation

for a day of sample operation in Mexico for a 1 m3 system with 4 solar panels and 2.6 kWh of

energy storage. ............................................................................................................................ 106

Figure 7-6: Membrane fouling model based on experimental data [110,131]. ......................... 108

Figure 7-7: Normalized membrane permeability decline (KFF) vs. operating time in days for Case

1-4 used in the water treatment system model. ........................................................................... 109

Figure 7-8: Tank capacity and costs from a supplier of plastic drinking water tanks [144]. ...... 111

Figure 7-9: a) Annualized system cost vs. design goal LOWP for variable system size (m3/day)

and b) the actual LOWP compared to the design goal LOWP for a 10 year simulation period for

La Mancalona, Mexico. .............................................................................................................. 117

Figure 7-10: Water cost ($/m3) vs. the system size (m3/day) for La Mancalona, Mexico at various

design goal loss of water probabilities (1%, 5%, 10%). ............................................................. 118

Figure 7-11: System configuration varies with size of the system for a 10 year simulation period

and at 5% LOWP with experimental fouling and anti-scalant usage with daily rinsing. ........... 120

Figure 7-12: Actual loss of water probability (LOWP) when simulated vs. the Designed goal

LOWP for several system sizes ( a) 1 m3/day, b) 5 m3/day, c) 10 m3/day). The optimal system

design was determined considering no fouling then simulated for a 10 year period with

experimental fouling (with anti-scalant and rinsing) and Abbas et. al. [110] fouling. ............... 123

Figure 7-13: Several communities were selected for evaluating the optimization algorithm in four

countries (Mexico, Ghana, India and Bangladesh). .................................................................... 124

Figure 7-14: Annualized system cost (USD) vs. variable LOWP for three communities in India,

Ghana, and Bangladesh) for variable system sizes (m3/day) a) 1 m3/day, b) 5 m3/day, c)

10 m3/day and a 10 year simulation period. ................................................................................ 125

1

Chapter 1

Introduction

1.1 Motivation

Globally, over 760 million people lack access to clean drinking water (Figure 1-1a) and its

associated health benefits [1]. They rely instead on seasonally available water sources (e.g. ponds,

rivers, rain cisterns, wells) that are often contaminated with excess dissolved minerals, chemicals,

bacteria and other pollutants [1]. Furthermore, these communities have limited access to electricity

[2]. Connecting these communities to large water treatment plants and the central electricity grid

is not a viable option due to their remote locations. Diesel generators are a common power source

for remote communities [3]. However, the high cost of diesel and environmental pollution has

limited their use for water treatment [4]. A viable alternative is the use of solar power since

communities facing high water scarcity (Figure 1-1a) also tend to be in regions of high solar

insolation (Figure 1-1b). To date, researchers have developed non-diesel water treatment

technologies appropriate for off-grid locations, such as solar ultra-violet (UV) water purification

systems [5], solar thermal desalination systems [6–8], solar photovoltaic reverse osmosis (PVRO)

systems [9–11] and wind powered reverse osmosis systems [12]. For these solutions to be

economic, the technologies must be fine-tuned to the location-specific energy source, the water

demand and the water characteristics of the community [13]. As well, due to their remote location,

the water treatment systems require minimal operator intervention, and should be reliable over the

lifetime of the systems at a minimum cost.

Solar photovoltaic powered reverse osmosis (PVRO) systems are promising for small-scale

(also called community-scale) desalination applications due to their low-cost, small footprint,

water purification efficacy and simple design from modular components [14]. Desalination is the

2

process of removing salts from brackish or seawater sources to produce drinking water. For the in-

land water-stressed communities considered in this thesis, the groundwater is often brackish with

a high level of dissolved minerals from the local geology. The level of dissolved minerals is

quantified using the total dissolved solids (TDS) which is a bulk measurement of the water salinity.

The water salinity ranges of typical water sources are provided in Table 1-1.

Table 1-1: Water salinity ranges in terms of the total dissolved solids, adapted from [15].

Water type Salinity Range

(mg/L of TDS)

Drinking water <500

Freshwater 50 - 500

Brackish 1,000 - 10,000

Seawater 30,000 - 45,000

Community-scale PVRO systems have been deployed previously in remote communities

[11, 15, 16]. PVRO systems require minimal maintenance because their repair is challenging in

remote communities [17–20]. Furthermore, energy storage is a large component of the system cost

due to the need for frequent battery replacements. To reduce the energy storage costs, PVRO

systems are often operated intermittently to reduce the need for batteries [8]. This intermittent

operation is a unique aspect of these PVRO systems since industrial-scale reverse osmosis plants

are designed to operate continuously. The effectiveness of reverse osmosis membranes is reduced

by scaling, biofouling and chemical degradation [22]. These effects can be minimized by selecting

effective pre-treatment [7] and chemical cleaning methods [23]. For PVRO systems, chemical

cleaning methods are rarely performed [8]. In addition, for PVRO systems, the effect of

intermittent operation, anti-scalant and membrane rinsing on membrane fouling needs to be

quantified [8].

3

Figure 1-1: The world map of a) water scarcity [1], and b) average solar irradiance [24]. Regions

with high water scarcity also tend to have high solar irradiance.

Another challenge for remote communities is the system affordability. To reduce the cost

of PVRO systems, they can be designed from commercially available modular components. This

reduces the cost by facilitating construction, parts replacement and system troubleshooting.

Complex design decisions are required to determine the appropriate system architecture.

Furthermore, to predict the membrane permeability of the intermittently operated PVRO systems,

a detailed experimental characterization of the reverse osmosis membrane fouling under

intermittent operation is required. Since every community has their own unique needs, each

location requires a customized design for the best performance. The performance is greatly

affected by the variability in the water characteristics, the water demand, the membrane fouling,

and the solar energy availability. Typically, skilled engineers are required to analyze the location-

specific conditions for a community to make the appropriate design decisions. For small remote

communities this kind of detailed design is not economically possible. An automated design

optimization framework can facilitate these complex design decisions and make this technology

accessible to these resource-constrained communities.

Low High No Data

Average Solar Irradiance (W/m2)

| | |

175 200 225 [2]

a) b)

Average Solar Irradiance (W/m2)

175 200 225

4

1.2 Problem Statement

The literature lacks a fundamental understanding of how the intermittent operation from

extended shutdown periods affects the permeability of the reverse osmosis (RO) membrane. This

intermittent operation is common in solar powered reverse osmosis water treatment systems for

resource-constrained communities. Both the fouling behavior of reverse osmosis membranes

under extended shutdown periods and the operating conditions to mitigate this fouling need to be

better understood. In addition, the current design methods for PVRO systems lack an analytical

model describing the membrane fouling behavior caused by intermittent operation. Design

optimization frameworks for PVRO systems that consider the membrane fouling from intermittent

operation are required to increase adoption of this technology in remote communities.

1.3 Research Objectives and Goals

The goal of this research is to develop a fundamental understanding of reverse osmosis

membrane fouling for brackish water under intermittent operation with extended shutdown

periods. This intermittent operation is common for small-scale (1 - 10 m3/day) solar powered

reverse osmosis systems. The subsequent goal is to use the experimental findings to develop an

analytical model of the membrane permeability decline for use in the development of a design

optimization framework for these water treatment systems. To accomplish these goals, the research

objectives are as follows:

1. Development of an experimental system and protocol for the characterization of

intermittent operation for small-scale solar powered water treatment systems.

5

2. Experimental characterization of reverse osmosis membrane fouling by scaling for

intermittent operation compared to continuous operation when using anti-scalant pre-

treatment and shutdown procedures appropriate for remote locations.

3. Experimental characterization of reverse osmosis membrane fouling for intermittent

operation at the lab-scale and pilot-scale.

4. Development of a design optimization framework for small-scale PVRO brackish water

systems that considers membrane fouling from intermittent operation using an analytical

membrane fouling model.

1.4 Research Scope

The research conducted in this thesis focused on developing an improved understanding of

membrane fouling caused by intermittent operation of PVRO systems using experimental

characterization. As well, the research focused on the development of a design framework for these

systems considering the membrane fouling from intermittent operation. The characterization of

membrane fouling caused by intermittent operation focused on the effect of extended shutdown

periods, commonly experienced in PVRO systems with limited battery storage. The experimental

investigations concentrated on the characterization of the membrane fouling for two types of

experimental water. The first experimental water used MilliQ® (a high purity lab-grade water) as

the solvent and was termed ‘experimental MilliQ-based matrix.’ The second experimental water

used a local groundwater from Nobleton, Ontario as the solvent and was termed ‘experimental

groundwater-based matrix.’ The experimental waters were mixed with lab-grade chemicals to

mimic groundwater high in dissolved minerals, common of inland brackish desalination. Using

the experimental results, the research then focused on the development of a design optimization

framework for small-scale (1 - 10 m3/day) brackish water PVRO systems.

6

1.5 Thesis Contributions

The main contributions of this PhD research work were the experimental characterization of

membrane fouling from intermittent operation and the development of a novel design optimization

framework for PVRO systems that considers membrane fouling from intermittent operation. This

thesis resulted in the following contributions:

The experimental quantification of reverse osmosis membrane fouling under intermittent

operation and continuous operation was conducted, and compared to each other. It was the first

of its kind in literature. A fully instrumented and automated experimental system was

developed for quantifying the RO membrane fouling in triplicate. The experimental system

was designed, built, commissioned and operated to characterize the membrane fouling

resulting from extended shutdown periods overnight.

o Published Journal Paper: Freire-Gormaly, M., Bilton, A., (2017) An Experimental System

for Characterization of Membrane Fouling of Solar Photovoltaic Reverse Osmosis Systems

under Intermittent Operation, Desalination and Water Treatment, volume 73, pp.54-63.

The characterization of membrane fouling during extended shutdown periods for reverse

osmosis membranes in a controlled experimental system with anti-scalant pre-treatment and

rinsing with permeate water was performed. This was conducted using the experimental

MilliQ-based matrix. The membrane permeability and membrane autopsy using scanning

electron microscopy (SEM) showed that the use of anti-scalant and rinsing maintained high

membrane permeability.

7

o Published Journal Paper: Freire-Gormaly, M., Bilton, A., (2018) Experimental

Quantification of the Effect of Intermittent Operation on Membrane Performance of Solar

Powered Reverse Osmosis Desalination Systems, Desalination, volume 435, pp.188-197.

The characterization of reverse osmosis membrane fouling under intermittent operation was

carried out in controlled experiments using the lab-scale and pilot-scale experimental systems

with the experimental groundwater-based matrix. The experiments were operated with anti-

scalant pre-treatment and rinsing with permeate water prior to shut down. The lab-scale

membrane fouling results showed that the membrane permeability was maximized when the

system was operated intermittently with a daily permeate water rinse prior to shut down. The

lab-scale results also represented the pilot-scale experimental results.

o Journal Paper: Freire-Gormaly, M., Bilton, A., (In-Preparation) Experimental Lab-scale

and Pilot-scale Characterization of the Effect of Intermittent Operation on Membrane

Fouling for Solar Powered Reverse Osmosis Desalination Systems, Desalination.

A novel design optimization framework for PVRO systems was developed, which considered

the membrane fouling under intermittent operation. The framework configured the PVRO

system components (e.g. number of solar panels, number of RO membranes, size of the water

tank) and operating conditions (i.e. with or without rinse, with or without anti-scalant) for a

user-defined geographic location and water demand. It was found that lower reliability systems

reduced the annualized system costs. It was demonstrated that considering membrane fouling

was critical to design reliable and cost-optimal PVRO systems. The cost-optimal system

configurations were compared for several geographic locations (Mexico, Ghana, India and

Bangladesh). It was also shown that despite variations in solar insolation and water salinity

between these geographic locations, a similar system configuration met the water demands.

8

o Journal Paper: Freire-Gormaly, M., Bilton, A., (Under Review) Design of Solar

Powered Reverse Osmosis Desalination Systems Considering Membrane Fouling

caused by Intermittent Operation, Desalination, DES_2018_301

1.6 Research Program

The research in this thesis followed the methodology shown in Figure 1-2. The research

program comprised of experimental investigations and a design optimization of solar powered

reverse osmosis systems. Based on the results of the experimental program, an analytical model of

membrane fouling was developed, and a design optimization framework was implemented for

solar powered reverse osmosis water treatment systems. The experimental program allowed for

quantification of the effect intermittent operation had on membrane fouling. The experimental

results also allowed for identifying potential fouling mechanisms which are unique to intermittent

operation compared to continuous operation. As well, in resource-constrained communities,

minimal pre-treatment, operator intervention and brine volume are required since brine is typically

release to the environment with minimal post-treatment. Therefore, developing a design

framework to automatically configure the cost optimal system with the required reliability and

which considers the membrane fouling caused by intermittent operation was required.

9

Figure 1-2: Flowchart of the research program conducted in this thesis with the associated

chapter numbers.

1.7 Thesis Organization

This thesis is organized into eight chapters. The first chapter provides the motivation, the

problem statement, the objectives, and the contributions. The second chapter covers the

background and an extensive literature review of PVRO systems, membrane fouling and system

design optimization. The third chapter outlines the experimental methods and the experimental

equipment setup and instrumentation. The fourth chapter provides the initial experimental results

when the system was operated intermittently and continuously with extended shutdown periods

for the experimental MilliQ-based matrix. The fifth chapter presents the detailed experimental

results with an improved experimental system to characterize the membrane permeability for

intermittent operation with anti-scalant pre-treatment and rinsing with permeate water for the

experimental MilliQ-based matrix. The sixth chapter describes the experimental results with the

Develop Design Framework for PVRO

Design Optimization Framework

Experimental Characterization of Reverse Osmosis Fouling

Simulation

RO Fouling

Pre-treatment and Membrane Rinsing

Design Optimization Module

RO SystemOperation

PVRO System Costs

Improved Lab-scale

MilliQ-based matrix

Initial Lab-scale

MilliQ-based matrix

Ch. 7

Ch. 4 Ch. 5

Design, Build and Commission New Experimental Systems Ch. 3

Groundwater-based matrix

Pilot-scale Ch. 6

Groundwater-based matrix

10

improved experimental system and pilot-scale system using a second experimental water matrix

to characterize the membrane permeability for intermittent operation with anti-scalant pre-

treatment and rinsing with permeate water for the experimental groundwater-based matrix. The

seventh chapter presents the design optimization framework for cost-optimal PVRO systems that

are designed to meet a community’s water needs based on their geographic location and water

characteristics. The eighth chapter provides the conclusions of this thesis and the directions for

future work.

11

Chapter 2

Background and Literature Review

2.1 Renewable Powered Reverse Osmosis Desalination

Renewable powered reverse osmosis desalination has been a topic of intense research

due to the growing need for stand-alone water treatment systems for remote locations [25–34].

Several existing renewable powered reverse osmosis systems have been installed and studied

previously [20,35–38]. Studies on existing renewable powered reverse osmosis systems tend to

focus on either the pilot-scale implementation [39–42] or the design and cost optimization [43–

46]. All renewable powered desalination systems have inherent intermittent operation due to the

intermittent nature of the power source. For example, wind power is only available during wind

speeds within the cut-off range of the wind turbine. As well, solar power is only available during

daylight hours and varies with cloud cover. Some of these systems are designed for high solar

insolation locations and therefore use solar photovoltaics coupled with batteries as their main

source of power [33,43,47,48]. To reduce the costs of these systems, very little battery storage

is incorporated in the design leading to intermittently operated systems with extended shutdown

periods [33,43,47,48]. Many researchers claim intermittent operation leads to increased

membrane fouling rates [33,39,42,49] and high membrane fouling rates have been observed in

operating plants with several years of data [50]. However, no one to date validated this

experimentally and evaluated the effectiveness of simple treatments to alleviate membrane

fouling.

12

2.1.1 Reverse Osmosis Water Treatment

The reverse osmosis (RO) process produces fresh water by applying a pressure higher

than the osmotic pressure across a semi-permeable membrane [5,6,8,51,52]. Water passes

through the membrane producing permeate and leaves behind excess dissolved solids

constituting a concentrated brine (retentate). RO is one of the main commercial desalination

technologies due to its high energy efficiency, no thermal requirements, and modularity. Spiral

wound membranes are the most common RO membrane type in use. The permeate flow rate

across the membrane is proportional to the difference between the applied pressure and the

osmotic pressure, given by Equation 2-1:

(2-1)

where 𝑄𝑃 is the permeate flow rate (m3/s), 𝐾𝑊 =1

𝑅𝜇 is the membrane permeability for water

(ms-1bar-1), R is the membrane resistance as a function of fouling (m-3s2bar), µ is the dynamic

viscosity of water (m2/s), Amem is the membrane surface area (m2), KT is the water permeability

temperature correction factor, ∆�̅� is the average pressure applied across the membrane (bar), and

∆�̅� is the average osmotic pressure applied across the membrane (bar). The membrane flux

(Lm-2h-1) is given by 𝐽 =𝑄𝑃

𝐴𝑚𝑒𝑚 and is commonly reported to describe the amount of permeate

produced per unit of membrane area. The membranes can become fouled by particulates, scaling

or biological growth leading to a decline in the membrane permeability and an increase in

membrane resistance. A typical response of the membrane resistance is shown in Figure 2-1.

Some of the increase in membrane resistance can be reversed by cleaning, but some fouling is

irreversible. This leads to an overall decrease in membrane water permeability and increases the

energy requirements. Typically, small-scale RO plants do not have cleaning cycles due to the

𝑄𝑃 = 𝐾𝑊𝐴𝑚𝑒𝑚𝐾𝑇(∆�̅� − ∆�̅�)

13

high costs of cleaning chemicals and lack of facilities for chemical disposal in their remote

locations.

Figure 2-1: Reverse osmosis membrane resistance as a function of time.

2.1.2 Overview of Renewable Powered RO Systems

RO membrane desalination can be coupled with power systems to produce standalone,

modular water treatment systems. To reduce costs, numerous studies have looked at the overall

design and optimization of RO membrane systems [9,10,53–55] and investigated small scale

solar photovoltaic reverse osmosis (PVRO) systems that produced less than 10 m3/day of clean

drinking water [11,16,17,19,33,48,56]. Figure 2-2 shows a schematic of a basic PVRO system.

The feed water pump transports brackish water from an intake to a simple pre-treatment system,

typically a cartridge filter and anti-scalants [11]. A high-pressure pump provides the pressure

required to operate the RO membrane module. The PVRO system is powered by solar

photovoltaics and the power is distributed through the system using control electronics. The

permeate water is stored in a fresh water tank. In remote communities, the reject brine is typically

released slowly to the environment [16,33].

Mem

bra

ne

Res

ista

nce

(m

-1)

Operating Time (Days)

Rinitial

Rreversible

Rirreversible

Cleaning Cleaning

14

Figure 2-2: Simple PVRO system schematic for remote communities.

Membrane fouling is one of the major challenges to RO membrane systems and as a

result has been the subject of intense research over the past decades [40,57–65]. These studies

focused on lab-scale experiments to identify the onset of crystal nucleation and precipitation for

scaling [57–60] and the effects of biofilm on RO performance [61,64,65]. Membrane fouling is

a concern for small-scale systems in remote communities due to limited financial flexibility for

membrane replacement costs, chemical cleaning costs, limited operator knowledge and, lack of

access to resources to improve system performance by chemical or mechanical cleaning once

the system is operational.

Considering membrane fouling in the design of PVRO systems has been identified as a

major area for further research since existing design methods do not account for RO membrane

fouling, nor the effects of pretreatment [11]. An added challenge for small-scale PVRO systems

in remote communities is intermittent operation to reduce the need for batteries, which are an

expensive component of the system [8]. It is generally regarded that this intermittent operation

leads to premature fouling of the reverse osmosis membranes, however, this behavior has not

been characterized experimentally [8].

Brackish Water Intake

Control Electronics

Reject Brine

Fresh Water Tank

Reverse Osmosis ModuleFeed Water

Pump

High Pressure PumpPre-Treatment

Solar PV Array

15

2.2 Reverse Osmosis Membrane Fouling

Reverse osmosis membrane foulants can be categorized into several groups (biological,

mineral, particle, colloidal, organic and oxidant). For particle fouling, typically filtration with

5 µm sediment filters is sufficient to remove suspended solids. For colloidal fouling and organic

fouling coagulation and filtration are typically used as treatment methods. Oxidant fouling

occurs in the presence of free chlorine and oxidants, which can be present if chlorination or

ozonation are used to treat biological content. The reverse osmosis membrane is very sensitive

to oxidant foulants, and hence these pre-treatment methods are not recommended. Mineral

scaling and biofouling are the dominant sources of reverse osmosis membrane fouling in

operating plants [8]. Membrane fouling causes increased pressure requirements [8], energy

requirements [7], costs due to early replacement of membranes [15,66] and chemical costs for

cleaning [67]. High flux rates correspond to higher permeate volumes, however, exceeding the

critical flux rate leads to increased membrane fouling due to the boundary effects from

concentration polarization and hydrodynamic effects at the membrane interface [68]. High flux

rates result in high levels of scaling by locally exceeding the solubility limit of dissolved minerals

and by compacting dispersed foulants onto the membrane surface.

2.2.1 Biofouling

Biofouling is caused by the growth of biofilm on the membrane surface [65,67,69,70].

Biofouling has been associated with increasing membrane resistance, even with 99.99%

biological component removal from the feed water [71]. Studies on biofilm growth mechanisms

have been conducted in the literature [52,64,72–74]. These researchers performed modeling,

simulations and lab-scale experiments to quantify biofouling and the influence on system

parameters [52,64,72–74]. Radu et al. [64,72] presented a detailed biomass growth model in two-

dimensions and three-dimensions in small lab-scale channels. This work was extended to spiral-

16

wound elements by Vrouwenvelder et. al. [74]. None of the previous research has studied how

intermittent operation from extended shutdown periods affect the growth of biofilms in RO

systems.

2.2.2 Scaling

Scaling is caused by the precipitation of dissolved minerals onto the RO membrane and

system components [75]. Scaling in brackish water is a major concern due to the high levels of

dissolved calcium carbonate, silicates and other dissolved minerals often present in groundwater

due to the local geology. Several researchers have studied the scaling of RO membranes by

calcium carbonate [76–79], silica and iron oxides [80–82] for operational conditions analogous

to large-scale desalination plants. By treating fouling on early on-set, the amount of irreversible

fouling (fouling that cannot be cleaned) can be minimized [83]. None of the previous scaling

studies investigated how intermittent operation affects the crystal growth on RO membranes.

2.2.3 Pre-treatment to Minimize RO Membrane Fouling

Fouling of RO membranes can be reduced by adjusting the operating characteristics

(flux, recovery rate, feed channel pressure drop) or by using appropriate pre-treatment methods

selected based on the characteristics of the feed-water (e.g. anti-scalants, sand filtration,

coagulation and flocculation), and overall system design [84]. For small-scale RO systems in

remote communities, minimal operator intervention is required. Anti-scalants are a suitable

chemical pre-treatment for small-scale brackish water systems because they can be injected in-

line autonomously without operator intervention.

Anti-scalants shift the solubility curves of the sparingly soluble minerals to delay

precipitation [85]. The dose of anti-scalant and the chemical composition of anti-scalants for

optimal performance remains an area of active research [23,83,86–94]. Anti-scalants are

17

commonly used to minimize mineral scaling as they delay the onset of targeted mineral scales

[92,95,96]. Previous studies have outlined the mechanisms of scale formation [49,57,63,76,97]

and the effect of pH on scale formation [98] for continuously operated systems. These studies

were focused on the cleaning schedule for RO membrane modules in large-scale RO desalination

systems operated continuously. For small-scale brackish water systems, cleaning of the RO

modules is rarely incorporated in the design [99]. Recent studies have shown determining an

optimal cleaning schedule before implementation for small-scale renewable powered RO

systems is unreliable [18]. These previous studies did not consider the intermittency inherent

from small-scale renewable powered RO systems. Hence, characterization of scaling of RO

membranes in small-scale renewable powered RO systems operated intermittently is required.

2.2.4 Experimental Studies on RO Membrane Fouling

The existing experimental studies on membrane fouling have explored both biofouling

and scaling for industrial-scale desalination systems. RO membrane experiments on full-scale

membrane cartridges were conducted to observe the role monochloramine has on fouling rate

and fouling potential [100]. They demonstrated that monochloramine can reduce fouling rates,

but can also have a negative impact on the life of the membrane due to degradation of the

membrane polymer. Periodic cleaning of the RO membranes with air and water (air sparging)

has been shown to be effective in removal of biological fouling and organic nutrients [101].

Real-time monitoring systems and alarm systems for early identification of fouling [102,103]

have also been developed. However, these are complicated systems that were developed for use

in industrial-scale plants. The literature lacks experiments which characterize the effectiveness

of pre-treatment options on reducing membrane fouling rates of brackish RO systems operated

intermittently with extended shutdown periods.

18

2.2.5 RO Membrane Fouling Models and Mechanisms

Existing scaling models in literature [49,79,98,104–108] focus on single compound

scales, and are typically at the lab-scale. Some studies were conducted on modeling the

membrane fouling of full-scale system operation of spiral-wound modules over a period of

4 months [106]. Hoek et al. [106] developed a new semi-empirical model and found it was able

to predict the experimentally observed membrane fouling. Hoek et al. [106] also proposed a new

mechanism of cake-enhanced concentration polarization. However, this model was for

secondary wastewater effluent which had different fouling compounds than the brackish

groundwater considered in this thesis. Oh et al. developed a mathematical model of scale

formation which focused on two main mechanisms of scale formation, bulk crystallization and

surface crystallization [108]. Bulk crystallization is when crystals form in the feed solution and

deposit on the surface of the membrane resulting in reduced permeability. Surface crystallization

is when crystal growth occurs directly on the surface of the membrane. Concentration

polarization plays a key role in scale formation, increased concentration polarization leads to

surface crystallization as the dominant crystal growth mechanism. These previous studies

focused on modeling the various factors that affect scale formation (e.g. pH, cross-flow velocity,

pre-treatment) in continuous operation. None of the previous studies analyzed the effect of

intermittent operation on membrane scaling.

One fouling model studied the effect of both biofouling and scaling simultaneously [109]

and showed the presence of a biofilm can increase the concentration polarization and thereby

induce scaling. A study by Thompson et. al. [109] used a single model foulant (gypsum) and

focused on continuous operation. The literature lacks fouling models under intermittent

operating conditions for real groundwater which capture the effects of both scaling and

biofouling.

19

Although renewable powered RO systems have been in operation, very few long-term,

physics-based mathematical models of reverse osmosis membrane fouling have been proposed

in literature [110,111]. Recent studies have built upon this work by developing fouling models

using neural networks and machine-learning techniques [111–113]. These studies required

significant training data and were developed for industrial-scale continuously operated RO

systems. Despite these recent advances, mathematical fouling models are required for long-term

simulations of reverse osmosis systems operated intermittently.

2.3 Design Approaches for Solar Powered RO Systems

Researchers have formulated cost and energy optimization design approaches for small-

scale renewable powered reverse osmosis systems [25,50] and small-scale PVRO systems

[11,14,33,114,115]. Bilton et al. developed a modular design architecture for the cost-optimal

PVRO systems [11]. The computer-based approach configured systems from an inventory of

components by applying design principles to limit the design space and employing a genetic

algorithm to find the minimum cost solution. These previous design algorithms focused

predominantly on the costs of the system and detailed physics-based models of the components

[33,115]. The RO models in these existing design algorithms focus on the selection of the RO

modules and do not consider a detailed fouling model. Instead, some researchers have arbitrarily

assumed fixed fouling rates [25,115]. These researchers also considered the down time of

extended shutdown periods to size water storage and to over-size the required RO membrane

array [25,115]. None of the previous design optimization algorithms considered the impact RO

membrane fouling from intermittent operation has on the system life or cost.

Although membrane permeability decline has been predicted using neural networks for

large-scale continuously operated RO water treatment plants [111–113], only limited research

20

has been performed for predicting the membrane performance decline of small-scale PVRO

systems [18]. Previous optimization studies for PVRO systems do not consider how operating

conditions, such as the use of anti-scalant or permeate rinsing affect membrane permeability and

membrane replacement rates [14,114,116]. As a result, in the real operating system, as the

membrane permeability declines, water production would decrease and would not be able to

meet demand. These previous optimization studies therefore over-estimate the system reliability

and the community’s water demand would not be adequately met by these systems. An integrated

design framework for PVRO systems with extended shutdown periods that considers the impacts

of membrane fouling from intermittent operation, pre-treatment, and cost and energy

requirements is required.

2.4 Summary and Research Needs

This chapter provided a review of the existing literature on reverse osmosis membrane

fouling by biofouling and scaling; and methods of minimizing membrane fouling using pre-

treatment technology. A review of the experimental studies on RO membrane fouling and fouling

mechanisms was also provided. No previous studies have considered the impact intermittent

operation would have on membrane fouling. Also, none of the previous work investigated the

effect of simple interventions appropriate for remote areas, such as rinsing and anti-scalant, on

membrane fouling in intermittently operated RO systems. The existing literature provided

insight to the challenges of designing solar photovoltaic reverse osmosis systems, but none

completely solve the challenges of designing a system that will meet the water demands of a

community considering membrane fouling from intermittent operation.

The research undertaken in this thesis seeks to resolve some of these remaining

challenges to improve the provision of clean drinking water to off-grid remote communities.

This research seeks to develop an improved understanding of how reverse osmosis membranes

21

become fouled by the daily extended shutdown period common of intermittently operated

renewable powered and solar powered desalination systems. Then to use this new information

to develop a new design algorithm to design solar powered desalination systems that considers

the membrane permeability decline from membrane fouling caused by intermittent operation.

22

Chapter 3

Experimental Systems and Methods

Some of the content of this chapter has been previously published (full citation: Freire-Gormaly,

M., Bilton, A., (2017) An Experimental System for Characterization of Membrane Fouling of

Solar Photovoltaic Reverse Osmosis Systems under Intermittent Operation, Desalination and

Water Treatment, vol.73, pp.54-63 and in Freire-Gormaly, M., Bilton, A., (2017) Experimental

Quantification of the Effect of Intermittent Operation on Membrane Performance of Solar

Powered Reverse Osmosis Desalination Systems, Special Issue: Desalination, vol.435, pp.188-

197. It has been reproduced here. Permission to use this content was secured from the editor.

3.1 Introduction

This chapter outlines the experimental systems and methods used to quantify the reverse

osmosis membrane fouling under intermittent operation. There were three experimental systems

that were used. An initial lab-scale system, an improved lab-scale system and a pilot-scale

system. The initial lab-scale system is described. The detailed description of the improved lab-

scale system setup is provided. The instrumentation and data acquisition are also described. The

auxiliary system components are also described, for example the experimental water storage

tank. The pilot-scale system and its instrumentation are described. Finally, the experimental

methods are outlined.

3.2 Lab-scale Systems

3.2.1 Initial Lab-scale System Setup

As part of this research, a custom experimental lab-scale system was designed, built and

commissioned to allow for smaller water volumes than typically needed for real systems for the

experiments. The initial lab-scale system schematic (Figure 3-1) shows the various system

automation and monitoring equipment. The lab-scale system (Figure 3-2) allowed for testing

different two different operating conditions (continuous and intermittent operation). The system

23

was configured with the ability to perform automated rinsing and anti-scalant dosing. However,

the initial experiments did not use these features.

The system was designed to allow for continuous monitoring of the system operating

conditions including the pressure, conductivity and flow rates. This data was required to

determine the membrane permeability. The initial lab-scale system used an equalization tank

with a gravity fed float valve to maintain the recovery ratio at a consistent 75%. As well, the

system configuration was on a small portable stand to allow for transfer of the equipment through

the lab door.

The initial experimental setup allowed for triplicate measurements of the permeate flow

rates using three identical cross-flow cells (SEPA cells). The cross-flow cells permitted smaller

water volumes to be used per experiment than a spiral-wound membrane module since a much

smaller membrane area was used (0.0266 m2) for the cross-flow cells compared to the spiral

wound elements (7-34 m2). The online monitoring of the system operating conditions allowed

for detailed analysis of the system behaviour.

The initial experimental system was equipped with four analog flowmeters (FLR1000,

Omega Inc., Laval, Quebec) to measure the permeate flowrate for each SEPA CF module and to

measure the brine flowrate going to drain. The experimental system was also equipped with two

digital flowmeters (FPR301, Omega Inc., Laval, Quebec) to measure the feed flowrate and

recirculation flowrate. Four inline conductivity sensors (A1002, EC/pH Sensors, Boston MA)

measured the electrical conductivity, three for the permeate water (0-500 µS/cm) from each

SEPA cross-flow cell and one for the feed flow (0-5000 µS/cm).

24

Figure 3-1: Initial experimental lab-scale system schematic including instrumentation.

The initial experimental system used a variable frequency driven (VFD) high pressure

positive displacement pump (Hydracell Pump Model M03SASGSSSPA, Wanner Engineering

Inc., Minneapolis, MN) to maintain the desired feed flowrate. A pressure release valve (C46

Valve, Wanner Engineering Inc., Minneapolis, MN) and a pressure regulator were also used to

ensure the system pressure did not exceed safe operating pressures. To remove particulate matter,

a 5-inch tall, 3½-inch diameter filter housing with a spun polypropylene 5 µm cartridge filter

(Pentek, Upper Saddle River, NJ) was installed in front of the high pressure pump. The initial

experimental system did not have computer-based control of the variable-frequency drive. The

25

experimental system was manually started and shut down using the manual interface of the

variable frequency drive.

Figure 3-2: Physical initial experimental lab-scale setup corresponding to the lab-scale

schematic in Figure 3-1.

3.2.2 Improved Lab-scale System Setup

After the initial experiments were completed, the initial experimental lab-scale system

was improved to a new configuration which permitted more equal distribution of the feed flow

to the three cross-flow cells (Figure 3-3). The improved lab-scale system allowed for testing

different operating conditions (e.g. anti-scalant, intermittent operation, continuous operation,

rinsing before shutdown) and online continuous monitoring of the system parameters (e.g.

Feed WaterTank

Agitator

DAQ

Custom Electronics

LabVIEW User Interface

High Pressure

Pump

Equalization Tank

RO Module 3RO Module 2

RO Module 1

Chiller

26

pressure, conductivity, permeate flow rates). The experimental lab-scale system (Figure 3-4) also

had autonomous control systems to maintain a consistent recovery ratio using an automated

needle valve, and to maintain a consistent level in the equalization tank using a float-switch

coupled to a solenoid valve.

Figure 3-3: Improved experimental lab-scale system schematic with instrumentation.

To ensure the inlet pressure of the high-pressure pump did not drop below the rated

suction pressure, a submersible pump (Rule iL200 Marine 200 GPH Inline Submersible Pump

(12-Volt, Intermittent Duty), Xylem Inc., Beverly, MA) was used on the inlet of the feed water

inlet before the cartridge filter. This was an improvement compared to the initial lab-scale system

which was reliant on the suction of the pump. The equalization tank was used to vent air to

27

atmosphere and to enable recirculation of the brine and experiment water to reach high recovery

ratios typical of brackish water desalination systems. The float switch (.6A NO/NC POLY,

RSF88Y100R, Cynergy3 Components LLC, Garden Grove, CA) coupled with the actuation of

a solenoid valve (SV3201, Omega Inc., Laval, Quebec) was used to refill the equalization tank

with experiment water at the same rate of net water withdrawal (the three SEPA cross-flow

permeate flowrates plus the brine flowrate).

Figure 3-4: Physical experimental lab-scale reverse osmosis system.

RO Module 3

RO Module 2

RO Module 1

pH control

Conductivity Sensors

Flowmeters

VFD LabVIEW Interface

Custom Electronics

DAQ

Agitator

High Pressure Pump & Chiller

(Outside of View)

Automated Needle Valve

28

The experimental system also consisted of equipment for automated rinsing, anti-scalant

dosing, and start-up and shutdown procedures. A solenoid valve (SV3202, Omega Inc., Laval,

Quebec) and an automatic three-way control valve (Electric Actuated PVC 3-Way Ball Valves

- Multi-Voltage 5615, Valworx ®, Cornelius, NC) was installed for permeate rinses. An anti-

scalant dosing peristaltic pump (100.PH.030/4 Peristaltic Pump, Williamson Inc., Brighton,

Sussex) was installed for accurate dosage of anti-scalant pre-treatment.

3.2.3 Lab-scale Instrumentation

The lab-scale system was instrumented with continuous data collection and monitoring.

The lab-scale system was equipped with three analog flowmeters (Alicat Scientific L-10ccm-

D/5V) which allowed for high accuracy measurements at low flowrates in the range of

0-10 mL/min to measure the permeate flowrate for each SEPA cross-flow module. A single

analog flowmeter (Alicat Scientific L-100ccm-D/5V) was used to measure the brine flowrate in

the range of 25-100 mL/min. The lab-scale system was also equipped with two digital

flowmeters (FPR301, Omega Inc., Laval, Quebec) to measure the feed flowrate and recirculation

flowrate. Four inline conductivity sensors (A1002, EC/pH Sensors, Boston MA) measured the

electrical conductivity, three for the permeate water (0-500 µS/cm) from each SEPA cross-flow

cell and one for the feed flow (0-5000 µS/cm).

The high pressure before the SEPA cross-flow cells was measured using a high-pressure

transducer (P51-1000-S-A-I36-4.5V, SSI Technologies, Janesville, WI). The temperature of the

feed water was monitored using a thermistor (TH-44000-NPT Thermistor, Omega Inc., Laval,

Quebec). The feed water temperature was maintained in the equalization tank using an

immersion chiller (13271-500, VWR, Mississauga, Ontario) and a temperature controller

29

(61161-300, VWR, Mississauga, Ontario) set at 151oC, analogous to the source water

temperature of the target community.

The improved experimental lab-scale setup included continuous pH control through

automated acid (HCl) or base (KOH) addition and continuous pH monitoring. A data acquisition

system (DAQ NI USB-6343, National Instruments) and custom electronics were used to collect

the data. A diagram of the electrical connections is shown in Figure 3-5.

Figure 3-5: Electrical system diagram with sensors, actuators, DAQ and user interface.

Custom circuits were designed and soldered to interface the sensors with the data

acquisition system. Driver circuits were also designed for the dosing pump, feed pump, solenoid

valve, float switch and three-way control valve. Custom power circuits were also configured to

provide appropriate and well-conditioned power to all sensors and actuators.

30

Figure 3-6: User-interface for data monitoring in Labview.

Figure 3-7: User control interface in Labview.

31

The system control and monitoring were performed using a custom-made Labview

program. Figure 3-6 shows the user interface which provides online monitoring of the

conductivity, temperature, pressure, flow rates, and recovery ratio. User control was also

performed through a secondary interface (Figure 3-7). For example, the anti-scalant dosing pump

could be actuated, the three-way control valve could be activated, and the system could be turned

on or off using the variable frequency drive. In addition, automated scripts were written to

provide timing for the intermittent experiments presented below.

3.2.4 Experimental Water Tank

The experimental water tank (Figure 3-8) was equipped with UV disinfection,

temperature control, and continuous agitation to ensure a consistent source water for the

experiments. The UV disinfection system (Tank MasterTM TM22 UV Tank Storage Sanitizer,

Atlantic Ultraviolet Corp., Hauppauge, NY) provided continuous UV exposure to the water in

the tank. The temperature control was provided using a second immersion chiller (13271-500,

VWR, Mississauga, Ontario) and a temperature controller unit (61161-300, VWR, Mississauga,

Ontario) ensured the experiment water was maintained at a constant temperature (10oC)

throughout the experiment duration. Continuous agitation was provided using a mechanical

agitator (Arrow Model 1200, Arrow Engineering Ltd., Hillside, New Jersey). The continuous

agitation ensured the chiller did not become encrusted in ice and that there was an even

temperature in the tank and sufficient mixing to ensure the concentration was uniform throughout

the tank. The level of water in the tank was maintained above the minimum reach of the chiller

coil and agitator (approximately 80 L). All ports were covered to prevent dust or particles from

the ambient air entering the tank during operation of the experiments.

32

Figure 3-8: a) Isometric view of the experimental water tank; and b) cut-away view of the inner

components of the experimental water tank.

3.3 Pilot-scale System

3.3.1 Pilot-scale System Setup

In real systems implemented in the field, full-scale spiral wound reverse osmosis

elements are used. However, to limit the water requirements, the lab-scale system was

implemented with smaller membrane coupons. Therefore, to ensure the lab-scale experimental

system adequately represented the membrane fouling behavior of a real-system, the pilot-scale

system was built using a spiral-wound element and operated intermittently. The pilot-scale

system was designed to a size that would minimize the daily feed water requirements to a range

that would be practical to fulfill through local groundwater collection.

To keep the initial PVRO plant in La Mancalona, Mexico a cost-effective system, the

pilot-plant was not fully instrumented, therefore real operating data was unavailable. Although

an alternate option would be to perform experiments on a pilot-scale system in the target

Chiller Coil

Agitator

Tank LevelIndicator

a) b)

33

community, it was impractical to go to the field to perform controlled experiments. As well, the

PVRO plant in La Mancalona, Mexico is an operating drinking water plant for the community.

It would be an unnecessary burden on the community to disrupt the community’s only source of

clean drinking water to perform experiments. It was decided that this alternate option would not

be responsible engagement with the community.

The pilot-scale system was designed in a similar configuration to the real operating pilot-

plant and it mirrored the lab-scale system configuration (Figure 3-9). The main difference

between the pilot-scale and the lab-scale system was that the pilot-scale system was not run in

triplicate. If the pilot-scale system was run in triplicate the water volumes would be prohibitively

large. Instead, the pilot-scale system was run with a single spiral-wound membrane element

(Figure 3-10). Again, similar to the lab-scale system an equalization tank was used in the pilot-

scale system to achieve high recovery ratios, similar to those achieved in the field with a larger

spiral-wound element.

The pilot-scale system was pressurized with a high pressure pump (Hydracell Pump

Model M03SASGSSSPA, Wanner Engineering Inc., Minneapolis, MN) driven with a variable

frequency drive to maintain the desired feed flowrate. A pressure release valve (C46 Valve,

Wanner Engineering Inc., Minneapolis, MN) was used keep the system pressure below the safe

operating pressures. To remove particulate matter, a 10-inch tall x 3.5-inch diameter filter

housing with spun polypropylene 5 µm cartridge filter (Pentek, Upper Saddle River, NJ) was

installed in front of the high-pressure pump. A submersible pump (Rule iL200 Marine 200 GPH

Inline Submersible Pump, 12-Volt, Intermittent Duty, Xylem Inc., Beverly, MA) pumped the

feed water through the filter cartridge.

34

Figure 3-9: Pilot-scale system schematic.

The TW2514 RO spiral wound element (Dow Filmtec, The Dow Chemical Company)

was housed in an RO fiberglass pressure vessel (ROPV, Harbin ROPV Industrial Co., Ltd,

Nangang District, China). The temperature in the equalization tank was maintained using an

immersion chiller (13271-500, VWR, Mississauga, Ontario) and a temperature controller

(61161-300, VWR, Mississauga, Ontario) at (151oC) analogous to the source water temperature

of a brackish water RO system. A float switch (.6A NO/NC POLY, RSF88Y100R, Cynergy3

Components LLC, Garden Grove, CA) actuated a solenoid valve (SV3201, Omega Inc., Laval,

Quebec) to refill the equalization tank with water from the experiment water feed tank. The

equalization tank included continuous pH control using automated acid (HCl) and base (KOH)

addition using two peristaltic dosing pumps (100.PH.030/4 Peristaltic Pump, Williamson Inc.,

35

Brighton, Sussex). Anti-scalant dosing was provided using a peristaltic dosing pump

(100.PH.030/4 Peristaltic Pump, Williamson Inc., Brighton, Sussex).

Figure 3-10: Physical setup of the pilot-scale system.

3.3.2 Pilot-scale Instrumentation

The pilot-scale system also incorporated continuous data monitoring and autonomous

control of system operating parameters. The pilot-scale system used automated control of the

needle valve for maintaining the recovery ratio. Three analog flowmeters measured the feed flow

rate (500-2000 mL/min, FLR1010, Omega Inc., Laval, Quebec), permeate flowrate (200-1000

mL/min, FLR1009, Omega Inc., Laval, Quebec) and the brine flowrate (200-1000 mL/min,

High Pressure

Pump

Cartridge Filter

Equalization Tank

Flowmeters

Conductivity Sensor

RO Pressure Vessel

36

FLR1010, Omega Inc., Laval, Quebec). Two inline conductivity sensors (A1002, EC/pH

Sensors, Boston MA) measured the electrical conductivity, one for the permeate water (0-

500 µS/cm) and one for the feed water (0-10,000 µS/cm). The pressure was measured using a

high-pressure transducer (P51-1000-S-A-I36-4.5V, SSI Technologies, Janesville, WI). The

temperature of the feed water was monitored using a thermistor (TH-44000-NPT Thermistor,

Omega Inc., Laval, Quebec).

Figure 3-11: Labview continuous monitoring interface for the pilot-scale system.

New components were used for the pilot-scale system to ensure both the pilot-scale

system and the lab-scale system could be used alternatively. The only two components that were

shared between the lab-scale system and pilot-scale system were the NI-USB-6343 data

acquisition system and the experimental water tank storage container. The user-interface was

37

implemented in Labview to provide continuous monitoring of the system (Figure 3-11). The

Labview interface provided continuous feedback regarding the system operating conditions

(pressure, temperature, flow rates, recovery ratio). As well, the user-control in Labview (Figure

3-12) allowed for actuation of the various auxiliary systems (anti-scalant dosing pump and

submersible pump).

Figure 3-12: Labview control interface for the pilot-scale system.

3.4 Experimental Methods

The overall experimental method for both the lab-scale system and the pilot-scale system

were analogous. In the case of the lab-scale system there were some additional procedures that

needed to be performed for preparing the membrane coupons. The overlapping methods are

presented followed by the methods that were distinct for the lab-scale and the pilot-scale systems.

3.4.1 Experiment Water Preparation

The water used in the experiments was mixed to mimic brackish groundwater common

of communities requiring solar powered desalination. La Mancalona, Mexico is one of many

38

communities with similar water characteristics, socio-economic conditions, and high solar

insolation. The water from La Mancalona, Mexico was analyzed from a 2 L sample that was

shipped from the community (Table 3-1).

Table 3-1: Water chemistry of La Mancalona, Mexico groundwater, Nobleton, Ontario

groundwater, the experimental MilliQ-based matrix and the experimental groundwater-based

matrix.

Ions in the Water

La

Mancalona,

Mexico

(mg/L)

Nobleton,

Ontario

Deep Well

(mg/L)

Experimental

MilliQ-based

matrix

(mg/L)

Experimental

groundwater-

based matrix

(mg/L)

Sodium (Na+) 164 11 164 164

Magnesium (Mg2+

) 99 26 99 99

Calcium (Ca2+

) 502 64 502 502

Chloride (Cl-) 166 2.3 166 166

Sulfate (SO42-

) 1773 - 1713 1436

Potassium 6.4 - - -

Iron 5.9 - - -

Nitrate as Nitrogen 3.9 - - -

Silicon 23 22 - 22

Strontium 12 0.75 - 0.75

General Characteristics

pH 7.83 7.63 7 7

Alkalinity (As CaCO3) 142.5 1.2 - -

Conductivity 3770 550 4140 3740

Total Dissolved Solids 2262 340 2648 2393

Hardness 1661 270 1660 1660

Dissolved Organic Content 1.3 2.9 - 2.9

Total Ammonia-N 0.37 3.7 - 3.7

Orthophosphate - 0.31 - 0.31

Each lab-scale experiment required approximately 150 L of experiment water and the

pilot-scale experiment required approximately 600 L of experiment water. Due to the remote

location of the partner community, it was unfeasible to ship experimental water volumes to the

experimental lab-scale system. Instead, experimental water matrices were prepared using either

lab-grade MilliQ® water or the local Nobleton, Ontario groundwater as the solvent. For the

39

experimental MilliQ-based matrix, the MilliQ® lab-grade water was prepared using an Elix®

(EMD Millipore Ltd, Etobicoke, Ontario) water purification system and was mixed with

scientific grade inorganic salts. The resultant experimental MilliQ-based matrix was used to

mimic a brackish groundwater. Inorganic salts were added in the various proportions and

dissolved in the lab-grade water. The inorganic salts used were magnesium sulfate, sodium

chloride, and sodium sulfate from Fisher Scientific Company (Fisher Chemical, Fair Lawn, New

Jersey) and calcium sulfate from Anachemia, a VWR Company (VWR, Mississauga, Ontario).

The water analysis of the experimental MilliQ-based matrix mixed with the inorganic salts is

presented in Table 3-1.

The groundwater analysis from the community in La Mancalona, Mexico had a dissolved

organic content of 1.3 mg/L. Since the water volumes required for the experimental program

undertaken were too large to ship from the remote community in Mexico, a local groundwater

well with a similar dissolved organic content was identified from the Ontario government’s

provincial groundwater monitoring program through a partnership with the Toronto Regional

Conservation Authority. The Nobleton, Ontario deep well, (Figure 3-13) was selected since its

historical dissolved organic content was (1.1-3.3) mg/L and was in the closest range of dissolved

organic content of the wells in Ontario’s provincial groundwater monitoring program.

The groundwater was collected throughout the experimental program using several 20 L

water containers (Figure 3-14) to ensure fresh water was used in the experiments. The collected

water was stored in 20 L containers in a walk-in refrigerator at 4oC for a maximum of three

weeks. The water analysis of the Nobleton, Ontario groundwater is presented in Table 3-1 and

shows the concentrations of dissolved minerals and dissolved organic content. The water

chemistry of the experimental groundwater-based matrix that used the Nobleton, Ontario

groundwater as the solvent for inorganic salts is also presented in Table 3-1.

40

Figure 3-13: Nobleton deep well (Nobleton, Ontario) with the a) well's green access box and

b) portable variable frequency drive for the submersible pump located inside the well.

Figure 3-14: Groundwater collection at the Nobleton deep well, Ontario.

3.4.2 Operating Conditions

To evaluate the effects of intermittent operation on membrane fouling, separate

experiments were conducted. For each experiment, fresh membranes were prepared and used

41

following the method described in the respective sections for the lab-scale and pilot-scale. The

intermittent experiments were operated for 8 hours per day with 16 hours of shutdown. The start-

up procedure was to turn on the VFD and increase the VFD frequency to 15 Hz, then the needle

valve on the recirculation line was adjusted until the system operating pressure reached 20.7 bar

and the back pressure of the RO modules was slightly adjusted using the individual needle valves

on each cross-flow cell until the permeate flow rates were similar within ±5%. The recovery

ratio was also adjusted using the needle valve for the waste stream (Figure 3-1, Figure 3-3 and

Figure 3-7). After 8 hours of operation the system was shut down by reducing the frequency on

the VFD to zero. After 16 hours, the system was re-started by slowly increasing the VFD

frequency to 15 Hz. The needle valve on the recirculation line was not re-adjusted nor were the

needle valves on the individual RO modules.

A new set of membranes were prepared in the same process and used in the continuous

experiments. The continuously operated experiments were initiated using the same startup

procedure as the intermittent experiments and then were operated continuously. The runtime was

equal to or longer than the intermittent experiments to enable a fair comparison between the

operating modes. The system operating pressure vs time for three consecutive days of

intermittent operation and of continuous operation are shown in Figure 3-15.

The experimental systems were run with a recirculation loop to enable recovery ratios

representative of the full-scale system. The experimental recovery ratio was selected as 75%

since in full-scale PVRO systems, the brine waste is typically percolated to the environment [33]

and minimal volumes were preferred. In addition, when operating at higher recovery ratios, the

permeate water produced is much greater than at lower recovery ratios leading to lower specific

energy consumption. The experiments were then run in the various operating conditions.

42

Figure 3-15: Operating pressure for the a) intermittent experiments and b) the continuous

experiments for a representative three days of operation.

The three main operating conditions investigated were the use of anti-scalant (BWA

Additives Flocon 135 and Flocon 260) versus no anti-scalant, intermittent (8 hours on, 16 hours

off) vs. continuous (24 hours on) operation and rinsing of the system with lab-grade clean water

vs. no rinsing prior to shutdown. The rinsing volumes (8 L at the lab-scale, 21 L at the pilot-

0

5

10

15

20

0 8 16 24 32 40 48 56 64 72

Ap

plie

d P

ress

ure

(bar

)

Houra)

0

5

10

15

20

0 8 16 24 32 40 48 56 64 72

Ap

plie

d P

ress

ure

(bar

)

Hourb)

43

scale) were selected to be three times the system volume including the tubing, reverse osmosis

module(s), submersible pump and all the system components in-line to provide sufficient volume

of clean water to rinse the system components. In a real system, the rinse would be performed

with permeate water, however, for the experiments, lab-grade water was selected to reduce

variability from the collected experiment permeate water quality.

3.4.3 Cartridge Filter Replacement

During the experiments, the cartridge filters required daily monitoring and were replaced

daily throughout the experiments for both the lab-scale and pilot-scale system. This ensured that

the filters were not clogged during operation of the system. The high pressure pump would be at

risk of damage if the cartridge filter became too blocked with particulates. In an operating system

in the field, a larger cartridge filter would be used and a maintenance schedule would be followed

to prevent clogging.

3.4.4 Lab-scale System Procedures

The experimental method for the lab-scale system required some distinct methods from

the pilot-scale system. First, the membrane coupon preparation was required since membranes

for the lab-scale system were purchased in a flat-sheet roll. Second, after the experiment was

completed, the membrane autopsy was performed in a slightly distinct method.

3.4.4.1 Membrane Coupon Preparation

For each experiment, membrane coupons were cut using a die (Sterlitech Sepa CF Steel

Rule Die, 19 cm x 14 cm) from a membrane flat-sheet roll (40” x 60” Dow Filmtec BW30). The

membrane coupons were soaked in lab-grade water for 24 hours to wet the membranes and to

ensure uniform polymer swelling. The membranes were then placed in the cross-flow cells,

compressed in the pressure vessel to 68.9 bar and the system was operated at an applied pressure

44

of 20.7 bar (pre-compacted) for 24 hours using lab-grade water (MilliQ® water) in a closed loop

maintained at 10oC. After pre-compaction, the experiments were commenced by spiking the

experimental MilliQ-based matrix (5 L in the equalization tank) to the required conductivity to

represent the operating recovery ratio. The experiments were then run in the designated operating

condition.

3.4.4.2 Membrane Autopsy

Membrane autopsy was performed to characterize the dominant fouling mechanisms

using two techniques, adenosine triphosphate (ATP) and scanning electron microscopy (SEM),

described in more detail in Section 3.4.6. Each ATP sample and SEM sample were taken from

the same locations on the membrane coupon, as shown in Figure 3-16. This was done to ensure

the results would be comparable between experiments and various operating conditions.

Figure 3-16: Location of SEM and ATP samples for the lab-scale samples.

45

3.4.5 Pilot-scale System Procedures

The pilot-scale system methodology differed from the lab-scale system since the

membrane was a spiral-wound element. The spiral-wound element fit directly into the housing

and did not require cutting. For the pilot-scale experiment, a new Filmtec TW30-2514 was used.

The Filmtec TW30 used the same BW30 membrane but it was wrapped in tape instead of

fiberglass, which allowed for simple disassembly for the membrane autopsy.

3.4.5.1 Membrane Preparation

The TW30-2514 was prepared by performing pre-compaction. Prior to the start of pre-

compaction, the TW30-2514 was rinsed with 40 L of lab-grade water to remove the wetting

chemicals. Pre-compaction was performed by operating the reverse osmosis system at an applied

pressure of 20.7 bar (pre-compacted) for 24 hours using lab-grade water in a closed loop

maintained at 10oC.

3.4.5.2 Membrane Autopsy

After completion of the pilot-scale experiment, the TW30-2514 was immediately

removed from the high-pressure housing for analysis of the membrane surface using ATP and

SEM. The TW30-2514 spiral-wound membrane element was opened using a sharp knife to

unravel and reveal the membrane surface (Figure 3-17). The location of the ATP sample and

SEM sample on the unraveled membrane are shown in Figure 3-18.

Figure 3-17: Unraveled TW30-2514 membrane for removal of the membrane autopsy samples.

PermeateCollection Tube

Brine Outlet

Feed Inlet

46

Figure 3-18: Pilot-scale membrane autopsy sample locations shown on the unraveled

membrane.

3.4.6 Membrane Characterization

The reverse osmosis membranes investigated in this thesis were analyzed using three

main techniques (pure water permeability, scanning electron microscopy (SEM) and adenosine

triphosphate (ATP) surface deposit analysis). The pure water permeability was measured at the

beginning of the experiment. The membrane autopsy was performed using the other two

techniques, SEM and ATP. These three techniques are described in the subsequent sections.

3.4.6.1 Pure Water Permeability

The pure water permeability provides the maximum flux that the virgin membrane can

achieve. The pure water permeability for the virgin reverse osmosis membrane Filmtec BW30

was determined experimentally. Membranes were pre-compacted for 24 hours using MilliQ®

water at 20.7 bar to allow the permeate flow rate to reach a constant flow rate (±5%). The pure

water permeability was measured by performing pre-compaction followed by adjusting the

applied pressure from 0-20.7 bar in 3.4 bar increments and recording the corresponding permeate

flow rate. The pure water permeability was determined to be (0.57±0.05) L m-2 day-1 kPa-1 also

equivalently as (2.4±0.2) L m-2 h-1 bar-1. In comparison, Antony et. al. found the pure water

PermeateCollection Tube

Brine Outlet

Active Membrane Area

SEM Sample Location

ATP Sample Location

Cut Lines

14”

1cm

9”

2”Feed Inlet

47

permeability of Filmtec BW30 membranes to be (2.5±0.3) L m-2 h-1 bar -1 [117]. Table 3-2 lists

the membrane characteristics of the Filmtec BW30 membranes investigated in this thesis.

Table 3-2: Filmtec BW30 membrane characteristics.

Membrane Pure Water

Permeability

(L m-2 h-1 bar -1)

Contact angle (o) Zeta

potential

(mV)

Average

Roughness

(nm)

Filmtec BW30 2.5±0.3 [117] 61.42±0.56 [118] -8.0±1.2 [119] 45.9±0.2 [118]

3.4.6.2 Scanning Electron Microscopy

Membrane autopsy using SEM was also performed. SEM samples were analyzed to

observe the scales and deposits accumulated on the membrane surface. SEM was performed

using a JEOL JSM6610-Lv Scanning Electron Microscope (JEOL Ltd., Tokyo, Japan). First, the

samples were dried in ambient air for at least 24 hours and then gold sputter-coated to provide a

200 nm thick conductive layer for the SEM’s electron beam.

Figure 3-19: Laser-cut holder for the aluminum disks containing the SEM samples (gold

sputter coated reverse osmosis membrane samples).

48

The surface deposits were imaged to elucidate and evaluate the various fouling

mechanisms. Several aluminum sample holders were machined and a custom-built laser cut case

was made (Figure 3-19) to transport several sets of membrane samples simultaneously to the

SEM and to prevent ambient dust particles from settling on the dried membrane samples.

3.4.6.3 ATP Surface Deposit Analysis

After each experiment was completed, the membranes were immediately removed for

testing the adenosine triphosphate (ATP) on the membranes to evaluate the presence of

biological fouling. ATP is a measure of the living cells present on the membrane surface or in a

sample of water. The solid phase ATP content was measured using a luminometer (Kikkoman

Lumitester C-110, New Brunswick, Canada). Membrane coupons extracted from the membrane

were tested using the Deposit and Surface Analysis protocol [120].

3.5 Conclusion

In conclusion, the experimental systems and methods used in this thesis provided a means

of mimicking the real conditions of an operating plant in a controlled environment at the lab-

scale and at the pilot-scale. The experimental systems were equipped with continuous data

collection of the system parameters to ensure precise quantification of the membrane

permeability as a function of time. As well, the experimental systems were capable of

autonomous control for rinsing of the membranes, and maintenance of a consistent recovery ratio

during the experiments. The experimental methods outlined in this chapter highlight the key

aspects of the experimental program which was undertaken in this thesis.

49

Chapter 4

Membrane Fouling under Intermittent Operation with the Initial Lab-scale System and using the Experimental MilliQ-based Matrix

This work has been previously published (full citation: Freire-Gormaly, M., Bilton, A., (2017)

An Experimental System for Characterization of Membrane Fouling of Solar Photovoltaic

Reverse Osmosis Systems under Intermittent Operation, Desalination and Water Treatment,

vol.73, pp.54-63). It has been reproduced here. The experimental methods were described in

Chapter 3 to avoid repetition. Permission to use this content was secured from the editor.

4.1 Introduction

The initial experimental lab-scale system described in Chapter 3 was used to assess the

membrane permeability decline for the experimental MilliQ-based matrix. The experimental

MilliQ-based matrix was a solution of lab-grade water mixed with lab-grade chemicals to mimic

the concentration of groundwater representative of communities requiring solar powered reverse

osmosis water treatment systems. These initial experiments provided a quantification of the

membrane permeability decline for intermittently operated RO systems compared to

continuously operated RO systems.

4.2 Experimental Program

The experimental method described in Chapter 3 was followed for these experiments

with the experimental MilliQ-based matrix. The experimental MilliQ-based matrix consisted of

lab-grade (MilliQ®) water and lab-grade chemicals. The experiments were performed to test the

effect of the operating conditions (intermittent vs. continuous operation). Table 4-1 lists the

experimental program. The membrane permeability was determined using instrumentation

measurements and Equation 2-1.

50

Table 4-1: List of experiments and operating conditions.

Experimental System Base Water Operating

Condition

Anti-scalant

(AS) Use

Permeate

Rinse

Initial Lab-scale Lab-Grade Intermittent None None

Initial Lab-scale Lab-Grade Continuous None None

4.3 System Operating Conditions

The initial lab-scale system was operated using a recirculation loop and an automated

needle valve to maintain a high recovery ratio of 75%. The membranes were first run in a pre-

compaction cycle with lab grade water for twenty-four hours at 20.7 bar. The intermittent run

was operated for 8 hours per day with 16 hours of shutdown for three days. The start-up

procedure was to turn on the variable frequency drive and increase the operating frequency until

the system operating pressure reached 20.7 bar and slightly adjust the back pressure of the RO

modules until the permeate flow rates were within ±0.5mL/min and about 8 mL/min. The

recovery ratio was also adjusted using the needle valve for the waste stream. The intermittent

run was operated for three consecutive days. After 8 hours of operation, the system was shut

down by manually reducing the frequency on the variable frequency drive to zero. After 16

hours, the system was re-started by manually increasing the variable frequency drive to 15 Hz.

To compare the membrane fouling to a continuous run, the system was operated continuously

for 24 hours. This was also the runtime for the intermittent experiments to enable a fair

comparison between the two operating conditions. A new set of membranes were prepared and

used in the continuous run.

4.4 Effect of Intermittent Operation vs. Continuous Operation

The membrane permeability was calculated using the measured permeate flowrates, the

operating pressure, and feed water conductivity. The time-axis of the experimental results

51

represents the operating time of the experiment. The hours when the experimental system was

shut down were not included in the time-axis to clearly compare the two operating conditions.

Figure 4-1: Membrane permeability as a function of operating time for the intermittent run.

The hours when the system was shutdown are not included.

The permeability data set for the intermittent run, shown in Figure 4-1, was averaged for

each thirty minutes of operation. The pressure regulator was engaged during the intermittent

experimental run and continuous experimental run maintaining a consistent transmembrane

pressure (Figure 4-2). The recovery ratio was also maintained at an average recovery ratio of

75%. Overall, in Figure 4-1 there is a consistent trend of decreasing permeability. For the

intermittent run, there was a rapid decrease in membrane permeability that can be observed

immediately after the first time the system was shut down for 16 hours (shown in Figure 4-1 at

52

hour eight). The permeability decreased rapidly to below 4x10-7m-1s bar-1 by the end of 24 hours

of intermittent operation.

Figure 4-2: Transmembrane pressure for the intermittent and continuous experimental run.

There was a small initial increase in the membrane permeability after start-up and then a

decrease in permeability at the start of Day 3 for SEPA 2 and SEPA 3. Since the results in Figure

4-1 were averaged over thirty minutes, initial increases in membrane permeability after start-up

were not shown. The initial increase in permeability is anticipated to be due to the rapid removal

of salts that had accumulated on the surface of the membrane during the time when the system

was shut down. The slow decrease is likely due to fouling during the operating time from scaling.

The permeability in SEPA 1 dropped less rapidly than in SEPA 2 and SEPA 3 (Figure 4-1). This

indicates a lower rate of fouling on SEPA 1’s membrane. This could be due to unit to unit

variation or due to an unequal division of flow in the piping flow manifold. Further experiments

53

and refinements of the experimental system design were undertaken and are described in detail

in Chapter 5.

The initial continuous experimental run was operated for approximately 24 hours. Figure

4-3 shows the calculated membrane permeability for the continuous experimental run. The

membrane permeability decreased during continuous operation. The membrane permeability for

SEPA 2 and SEPA 3 show a similar trend of decline. SEPA 1 has a distinctive pattern of decline

with a sharp linear decrease starting at the sixth hour of the experiment, the permeability declined

at a steeper rate than SEPA 2 and 3 from this point onwards to a minimum at the 24th hour of the

experiment.

Figure 4-3: Membrane permeability vs. operating time for the continuous run (averaged over

30 min intervals).

The rapid sharp decline in permeability for SEPA 1 may have been caused from unequal

division of flow in the parallel manifold or from rapid fouling of the membrane in SEPA 1. In

54

subsequent experiments in Chapters 5 and 6, the improved lab-scale system was used which had

a larger footprint, improved parallel manifold of stainless steel and smaller needle valves for

improved control. The pressure throughout the experiment was very stable because the pressure

regulator was engaged from the beginning of the experiment, as shown in Figure 4-2. The needle

valves which pressurize the SEPA cells were set initially when all three SEPA cells had a similar

permeability and were not adjusted throughout the duration of the experiment.

A comparison of the initial intermittent and continuous run is shown in Figure 4-4.

Comparing the calculated permeability values, there is a difference between the two operating

conditions. This could be due to the severe pressure fluctuations observed for the intermittent

run compared to the continuous run (Figure 4-2).

Figure 4-4: Comparison of initial continuous and intermittent experiments.

55

Despite these variations, these initial results indicate that increased fouling due to scaling

for intermittent operation may not be as significant as anticipated. Previous experimental tests

showed even larger variations between the SEPA cells, and this current setup has resolved large

variations. However, small variations still exist between SEPA cells due to variability between

the membrane fouling rates. This variability originally motivated performing the experiments in

triplicate. Additional experiments with the improved experimental lab-scale setup (with

improvements to ensure a steady pressure) were performed and described in Chapter 5 to more

accurately quantify the difference in fouling rates between the intermittent and continuously

operated systems.

4.5 Discussion

This chapter presented an approach to evaluate the effects of intermittent operation with

extended shutdown periods on membrane fouling in PVRO systems, which had never been

previously quantified. To evaluate this effect, a custom experimental system was designed and

constructed. The system consisted of three stainless steel SEPA cross-flow reverse osmosis

membrane cells connected in parallel, and was equipped with computer-controlled valves and

pumps to autonomously test different operating conditions. The system was also instrumented

with pressure, flow, temperature, and conductivity sensors to characterize membrane

permeability decline.

These initial experiments had several challenges that were addressed before proceeding

with the experiments detailed in Chapter 5. The initial experiments had large pressure

fluctuations caused by the accumulation of air in the feed water line after the cartridge filter. To

resolve the accumulation of air in the feed water line, the improved experimental lab-scale

system used a submersible pump directly from the equalization tank to overcome the pressure

56

drop associated with the polyspun cartridge filter. As well, during the initial experiments, the

flowrate of the gravity fed float valve frequently fluctuated. To resolve this issue the gravity fed

float valve was replaced with a float switch which activated a solenoid valve directly from the

experiment water tank. As well, the Labview code which controlled the activation of the

automated needle valve was improved to take an average over 30 seconds of the instantaneous

recovery ratio and the valve was only adjusted if the recovery ratio fell outside of the upper and

lower limit (±5 % of the target recovery ratio). The Pelton wheel flowmeters were also replaced

with pressure-based flowmeters. Finally, the physical system setup was adapted to a larger

footprint and a new flow manifold was implemented with stainless steel tubing instead of flexible

stainless-steel tubing to ensure equal flow division of the feed flow to the three SEPA cross-flow

cells.

The initial experiments were conducted using the initial lab-scale system to evaluate the

effects of intermittent operation for brackish water without organic content. It was found in these

initial experiments that the intermittent operation did not have a significant impact on membrane

permeability. These experiments contradicted previous claims in literature that membrane

fouling is greatly accelerated by intermittent operation. However, it should be noted that these

experiments were only conducted for a short period of time and with pressure fluctuations. These

aspects were evaluated in more detail in the experimental results presented in Chapters 5 and 6.

Based on these initial experimental results, it is hypothesized that the intermittent

operation increased fouling by two main mechanisms: scaling and biofouling. Fouling by scaling

is hypothesized to be a dominant factor for the intermittent operation since the water in the SEPA

cross-flow cells remains stagnant over a 16-hour period. During this 16-hour period existing

nucleation sites would have substantial time for crystal growth. Although biological content was

kept to a minimum using the UV lamp in the experiment water tank, there was evidence when

57

the flowmeters were disassembled that there was minimal biological growth in the system from

slime build-up on the various internal components of the flowmeters. Further experiments

described in Chapter 5 were performed to evaluate the fouling mechanisms for intermittent

operation and the effects of intermittent operation over a longer operating period with the

improved experimental system.

4.6 Conclusions

These initial experiments were conducted using the initial lab-scale system to evaluate

the effect of intermittent operation compared to continuous operation for a lab-mixed brackish

water. The results showed that the intermittent operation did not cause a significant decline in

membrane permeability compared to the continuously operated experiment. Further experiments

described in Chapter 5 were performed using the improved experimental lab-scale system. The

experiments in Chapter 5 were performed to evaluate the effect of intermittent operation, anti-

scalant pre-treatment and rinsing of the membranes prior to shut down on the membrane

permeability over a longer operating period (three to six days).

58

Chapter 5

Membrane Fouling Characterization at the Lab-scale using the Experimental MilliQ-based Matrix

This work has been previously published (full citation: Freire-Gormaly, M., Bilton, A., (2017)

Experimental Quantification of the Effect of Intermittent Operation on Membrane Performance

of Solar Powered Reverse Osmosis Desalination Systems, Special Issue: Desalination, vol.435,

pp. 188-197.). The experimental methods were described in Chapter 3. The remaining parts of

the published work have been reproduced here. Permission to use this content will be secured

from the editor after final publication of the article.

5.1 Introduction

Experiments were performed using the improved lab-scale system to determine the effect

of various operating conditions (intermittent operation, anti-scalant pre-treatment and rinsing of

the membranes prior to shut down) on membrane permeability. The experiments in this chapter

were operated for a longer time period (three to six days) compared to the initial experiments

(three days) reported in Chapter 4. This chapter presents the results for the lab-scale experiments

when the experiments were performed with the experimental MilliQ-based matrix. These

experiments also investigated the effect of using anti-scalant pre-treatment. The graphs in do not

state the type of anti-scalant since all the graphs represent the results for anti-scalant F135.

5.2 System Operating Conditions

Consistent experimental conditions were applied in all of these experiments. The

pressure set at 20.7 bar and was maintained using a pressure regulator on the high-pressure pump.

The system was operated at a cross-flow velocity of 0.1 ms-1 to match the conditions in a pilot-

plant operating with a spiral-wound reverse osmosis element. The membrane flux ranged from

36.0 Lm-2h-1 at the beginning of the experiment to 13.5 Lm-2h-1 at the end of the experiments.

This is below the manufacturer’s recommended flux rate for a TW30-2514 spiral-wound RO

module (55 Lm-2h-1). The recovery ratio was set to 75% and was maintained using an automated

59

needle valve on the brine line. The high recovery ratio was selected to minimize the brine which

in a real operating pilot-plant would typically be percolated to the environment with minimal

treatment [33]. The equalization tank was refilled using a solenoid valve triggered by a float

switch to maintain a consistent conductivity and level in the tank. The system was instrumented

to allow for continuous data collection of the system conditions and for autonomous control of

the system’s recovery ratio.

Figure 5-1: Experimental system operational conditions: a) permeability, b) pressure, c)

recovery ratio, d) salt rejection.

System data from a sample day during a lab-scale experiment for intermittent operation

with anti-scalant and no rinse is shown in (Figure 5-1). There is good agreement between the

three SEPA cells, providing results in triplicate for each experiment (Figure 5-1a). Conditions

were consistent throughout the experiment, however, there were a few deviations. Pressure was

60

consistently maintained at 20.7 bar (Figure 5-1b). Despite the automated control on the system

to maintain the system conditions, there was some variability in the recovery ratio (Figure 5-1c)

due to the automated needle valve adjusting to the required recovery ratio.

5.3 Experimental Program

The experimental method described in Chapter 3 was followed for these experiments

with the experimental MilliQ-based matrix which consisted of lab-grade (MilliQ®) water as the

solvent for lab-grade chemicals. The experiments were performed to test the effect of the

operating conditions, pre-treatment, and a permeate rinse at shutdown. Table 5-1 lists the

experimental program for the results presented in this chapter. The pre-treatment investigated in

these experiments was a commercially available anti-scalant (Flocon 135, BWA Additives)

designed to minimize scale formation.


Experimental

System

Operating

Condition

Anti-scalant

(AS) Use

Permeate

Rinse

Improved Lab-scale Intermittent None None

Improved Lab-scale Continuous None None

Improved Lab-scale Continuous With F135 None

Improved Lab-scale Intermittent With F135 None

Improved Lab-scale Continuous With F135 None

Improved Lab-scale Intermittent With F135 With Rinse

The normalization of the membrane permeability was performed by dividing the

instantaneous membrane permeability by the average value over the first five minutes of the

experiment. This limited the effect of membrane to membrane variability. The time axis of the

experimental results represents the operating time of the experiment. The hours when the

experimental system was shutdown were not included in the time-axis to clearly compare the

various operating conditions.

61

5.4 Effect of Anti-scalant Pre-treatment

Pre-treatment methods in industrial-scale reverse osmosis systems can include several

steps. However, for resource-constrained communities, minimal pre-treatment is usually done to

minimize system complexity and cost. The results show the average membrane permeability of

the three SEPA cross-flow cells. Figure 5-2 compares the normalized permeability for

continuous experiments ‘with’ and ‘without’ anti-scalant F135 addition using the experimental

MilliQ-based matrix. The normalization exceeded one for ‘continuous with anti-scalant and no

rinse’ between hour zero and hour four likely due to the membranes compacting slightly during

operation. It should be noted that no rinsing was implemented in either case.

Figure 5-2: Normalized membrane permeability for continuous operation with and without the

use of F135 anti-scalant.

62

The experiment ‘with no anti-scalant’ decreased very rapidly when compared to ‘with

anti-scalant’ at the high recovery ratio of 75%. The effect of anti-scalant showed that anti-scalant

is required for operating these reverse osmosis systems at a high recovery ratio of 75%. As a

result, most of the other experiments were operated with anti-scalant since without it, the

experiment duration was too short to investigate simple remedial actions that could potentially

restore membrane permeability, such as rinsing with permeate water.

5.5 Effect of Intermittent Operation vs. Continuous Operation

The effect of intermittent operation versus continuous operation when no rinsing was

performed was investigated to determine the effect on the membrane permeability. The results

in Figure 5-3 show the average membrane permeability of the three SEPA cross-flow cells.

Figure 5-3 compares continuous to intermittent operation, in both experiments they were

operated with F135 anti-scalant and without rinsing.

The experimental results show that intermittent compared to continuous operation did

not cause a significant decrease in membrane permeability over this experiment duration at the

high recovery ratio (Figure 5-3). Although the permeability slightly increased at the start of the

8th hour of operation for the intermittently operated experiment, overall the permeability decline

of the intermittently operated experiment was comparable to the continuously operated

experiment. This is hypothesized to be a result of insignificant crystal growth on the membrane

surface during the extended shutdown period since anti-scalants were used. The increase in

membrane permeability at the start of the new day can be seen clearly in the intermittent

operation since these results are presented with the continuous data. The results in Chapter 4

were the average over thirty minutes of data and the system had several fluctuations in pressure

and flow rate that were resolved with the improved lab-scale system.

63

Figure 5-3: Normalized membrane permeability of continuous operation and intermittent

operation with F135 anti-scalant.

5.6 Effect of Anti-scalant F135 for Intermittent Operation with no Rinse

Intermittent operation with anti-scalant F135 maintained a consistently higher membrane

permeability than experiments operated without anti-scalant (Figure 5-4). The anti-scalant

reduced the onset of scale formation, thereby improving the membrane performance. There was

a visible improvement in membrane permeability at the start of the new day (at hour 8) for both

with and without anti-scalant usage. This is hypothesized to be a result of the local concentration

in the cross-flow reverse osmosis cell. At shutdown, the permeate water remaining in the tubing,

was able to flow back into the cross-flow cell through osmosis. At the membrane surface, there

64

is likely a localized decrease in salt concentration which permits some scales to dissolve and

become detached. As well, the start-up allows for a fast flow rate and air to scour the membrane

surface which can further contribute to the increased membrane permeability at the start of the

new day (at hour 8 and 16) (Figure 5-4).

Figure 5-4: Normalized permeability decline for intermittent operated experiment both with

and without anti-scalant and without rinsing.

5.7 Effect of Rinsing with Anti-scalant F135 for Intermittent Operation

Figure 5-5 compares the effect of permeate rinsing for intermittent operation with anti-

scalant addition. Rinsing had a significant improvement on the membrane permeability as a

function of time. Without rinsing the membrane, performance reduced significantly by the

65

second day of intermittent operation, but with rinsing, high permeability was still observed after

seven days of operation. This is hypothesized to be a result of the washing away of residual salts

and anti-scalant which otherwise remained on the surface of the membrane. For the case with

rinsing, the membrane sits in clean water overnight, potentially dissolving some mineral scaling.

Figure 5-5: Normalized membrane permeability of decline for intermittent operated experiment

with anti-scalant when operated with rinsing and without rinsing.

5.8 Combined Comparison of the Effect of Operational Conditions on Membrane Permeability

Figure 5-6 shows the average normalized permeability (for all three SEPA cells) at the

fourth hour for all the experimental conditions for each individual day. Each individual

experiment for the tested operating condition was ended when the permeate flow rate dropped

66

below 30% of the initial flow rate. The exception was for the intermittent operation with anti-

scalant and rinsing experiment which was ended once it was determined that it maintained high

membrane permeability well beyond the operating time of the other experiments. The trend of

consistent permeability for intermittent operation with anti-scalant and with rinse can be clearly

seen in the comparative bar graph. Figure 5-6 shows that for intermittent operation with anti-

scalant use and 8 L of permeate rinsing, the permeability declined only slightly to (87±9) %

while all the other operating conditions declined to zero except continuous operation with anti-

scalant and no rinse which reached (30±4) % by Day 5. The results also show that without anti-

scalant usage and without 8 L of permeate rinsing when operated continuously, the membrane

permeability decreased significantly by day 3 to (13±9) %. Intermittent operation with anti-

scalant use and rinsing provided consistent membrane permeability for six days of operation,

while all the other operating conditions, intermittent without rinsing and continuous operation

with or without anti-scalant decayed much more rapidly.

Figure 5-6: Comparative bar graph of the experimental conditions investigated, the

permeability shown is the permeability at the fourth hour of the day.

67

5.9 Combined Comparison of the Effect of Operational Conditions on Salt Rejection

The average salt rejection was examined for the operating conditions (Figure 5-7). For

these experimental conditions, a decreasing trend of salt rejection was observed except for

intermittent with anti-scalant and rinsing. The experimental conditions without anti-scalant (both

intermittent and continuous operation) showed the largest decline in salt rejection. The

significant decline in salt rejection when no anti-scalant was used is hypothesized to be a result

of the large amount of gypsum crystals which grew on the surface of the membranes, greatly

increasing the localized salt concentration on the feed side of the membrane. When the

experiment was operated intermittently with anti-scalant and with rinsing, the salt rejection was

maintained with minimal decline.

Figure 5-7: Comparative bar graph of the average salt rejection for the experimental conditions

investigated.

68

5.10 Combined Comparison of the Effect of Operational Conditions on the Membrane Autopsies

After each experiment, a membrane coupon was imaged using SEM (Figure 5-8 and

Figure 5-9). A summary of the surface features observed on the membrane coupons (Figure 5-8

and Figure 5-9) shows a visible reduction in surface scales when both anti-scalants were used

and rinsing for intermittent operation (Figure 5-8d). This coincides with the high permeability

still present for this case after the experiments.

Figure 5-8: Comparative SEM images of the various operating conditions at x 1000



scalant and and no rinse, f) intermittent without anti-scalant.

69

Mineral scales are minimal and were not the main cause of the decrease in membrane

permeability. However, in all other cases, where the permeability decreased, large crystals were

formed on the membrane surface, greatly reducing the membrane permeability. The membrane

coupon cross-sections (Figure 5-9) also show a visible reduction in the thickness of the surface

scales when anti-scalant F135 and rinsing was used for intermittent operation and a large increase

in scale thickness when compared to the clean membrane.

Figure 5-9: Comparative SEM cross-sections of the various operating conditions at x 500



scalant and and no rinse, f) intermittent without anti-scalant and without rinse.

70

The average ATP on the membrane surface for each of the experimental factors is shown

in Figure 5-10. The concentration of ATP (cATP), measured using the luminometer was

normalized to the concentration of ATP in the respective experiment feed water. The

concentration of ATP on the membrane surface after the experiments showed significantly lower

biological activity for intermittent operation than for continuous operation. During these

experiments, the experimental MilliQ-based matrix was used consisting of lab-grade chemicals

dissolved in lab-grade water. There was minimal organic content. Biological films nor cake

layers were observed in the SEM membrane autopsy (Figure 5-8). As a result, it is expected that

there was minimal biological fouling in these experiments. Further experiments presented in

Chapter 6 explored the effect a real groundwater with organic content had on the membrane

fouling results.

Figure 5-10: Concentration of ATP on the membrane surface for various operating conditions.

71

5.11 Conclusions

This chapter presented an experimental study on the effects of intermittent operation,

anti-scalant F135 addition, and permeate rinsing commonly seen in renewable energy powered

reverse osmosis systems. The comparison of intermittent operation and continuous operation,

as well as anti-scalant usage and membrane rinsing with permeate water showed that minimizing

membrane permeability decline is most dependent on performing a rinse of the membranes with

permeate water.

The experimental results showed that intermittent operation alone did not have a

significant negative impact on the membrane performance in the short-term (several days of

operation in the cross-flow unit). Anti-scalants were observed to improve the membrane

performance when used in isolation for intermittent operation. Rinsing the membranes with 8 L

of permeate water prior to shut down when anti-scalant was used had a significant improvement

on the membrane performance during intermittent operation. Membrane autopsy using scanning

electron microscopy showed the fewest scale deposits for intermittent operation with anti-scalant

and 8 L of permeate rinsing. For this case, on the sixth day of operation, the average normalized

permeability declined only slightly to (87±9) % for intermittent operation with anti-scalant and

with rinse; while all the other operating conditions declined to nearly zero except continuous

operation with anti-scalant (30±4) %.

This topic requires more investigation with a wider array of water sources. Further

experiments presented in Chapter 6 used an experiment water containing a real groundwater with

organic content. The experiments in this chapter were conducted with a lab-mixed brackish water

without organic content, over a short period of time, and in cross-flow cells with much smaller

membrane areas than in real systems. However, this work shows that systematic experimental

72

studies on conditions encountered for renewable powered desalination system are required for

cost-effective system operation. These experimental results represent an initial set of studies to

quantify the effect of intermittent operation and various simple interventions which may be taken

to improve the membrane performance for small-scale solar powered RO systems.

This chapter presented the results of experimental studies to be able to take into

consideration membrane fouling for intermittent operation for the system design of future

renewable powered reverse osmosis systems. This will enable the development of better design

algorithms that consider the membrane fouling in the design of solar powered water treatment

systems. The improved systems design considering membrane fouling was explored in Chapter 7

with the development of an optimization framework for PVRO systems. These results can also

be useful for other renewable powered desalination systems which exhibit intermittency due to

the inherent intermittent nature of the renewable power source (e.g. wind, tidal, wave).

73

Chapter 6

Membrane Fouling Characterization at the Lab-scale and Pilot-scale using the Experimental Groundwater-based Matrix

This work is in preparation for publication (full citation: Freire-Gormaly, M., Bilton, A., (2018)

Experimental Lab-scale and Pilot-scale Characterization of the Effect of Intermittent Operation

on Membrane Fouling for Solar Powered Reverse Osmosis Desalination Systems, Desalination).

It has been reproduced here. The experimental methods were described in Chapter 3 to avoid

repetition. Permission to use this content will be secured from the editor.

6.1 Introduction

Since systems in the field operate with brackish groundwater, the experiments in this

chapter were performed with a more realistic experiment water to elucidate the underlying

fouling mechanisms under intermittent operation. In addition, the effects of typical membrane

fouling mitigation used for PVRO systems, permeate rinsing and anti-scalants, were

experimentally evaluated using the experimental groundwater-based matrix. Furthermore, since

the previous experiments were performed at the lab-scale on smaller membrane coupons to

minimize water requirements, the agreement with larger spiral wound membranes was

experimentally investigated at the pilot-scale. Verification that the pilot-scale experiment match

the lab-scale system will allow for extrapolation of the lab-scale results to guide the design of

full-scale systems.

6.2 Experimental Hypotheses

6.2.1 Effect of Intermittent vs. Continuous Operation on Membrane Fouling with Anti-scalant Usage at the Lab-scale

The effect of intermittent operation compared to continuous operation is hypothesized to

increase the fouling rate, leading to lower membrane permeability compared to a continuously

operated RO system. The main mechanism is hypothesized to be due to the membrane being in

74

contact with stagnant water during the shutdown time, exacerbating biofouling, since biological

growth would have time to colonize. In addition, it is hypothesized that the anti-scalant may

increase the growth of biological content by providing food for micro-organisms [121]. The

extended duration of the shutdown period for 16 hours could also have an influence on

biological growth, since there would be large fluctuations in nutrient supply, this could cause

stress in the biofilm and result in detachment and starvation in parts of the biofilm [122]. It is

also hypothesized that the initial time post-shutdown may cause osmotic suck-back causing

water to flow from the permeate channel to the feed channel of the membrane. This could also

serve as a localized concentration reduction at the membrane interface immediately after shut

down. It is expected that this localized concentration reduction could reduce the likelihood of

significant crystal growth during shutdown.

6.2.2 Effect of Permeate Rinsing on Membrane Fouling with Anti-scalant Usage at the Lab-scale

The effect of permeate rinsing prior to shut down is hypothesized to reduce biofouling

caused by the presence of stagnant anti-scalant, which can act as a source of nutrients for

biological growth [121] since the stagnant water would be predominantly the rinse water. It is

expected that the permeate rinse will not be able to remove crystals firmly attached to the

membrane nor biofilm which may have securely adhered to the surface of the membrane.

Similarly, it is hypothesized that the permeate rinse would not be able to detach surface crystals,

or firmly attached biological growth. The permeate rinse is hypothesized to reduce the presence

of bulk crystals by providing a very low concentration stagnant water which could slightly

dissolve scales during the shutdown period.

75

6.2.3 Effect of Experimental System on Membrane Fouling

The effect of the lab-scale versus pilot-scale system on the normalized membrane

permeability decline is hypothesized to have a minimal effect. It is hypothesized that the two

experimental systems will behave analogously. This is anticipated because both experimental

systems were designed to operate at the same cross-flow velocity and operating conditions.

6.3 Experimental Program to Test Hypotheses

The experiments conducted to test the hypotheses are outlined in Table 6-1. These

experiments will be used to evaluate the effect of intermittent operation compared to continuous

operation at the lab-scale for the experimental groundwater-based matrix. As well, these

experiments will allow for analyzing the effect of a permeate rinse post-shutdown to restore the

membrane permeability for the intermittently operated lab-scale system. Finally, these

experiments will permit a comparison of the lab-scale experimental results to the pilot-scale

system results. This comparison is required for the design optimization to extrapolate the lab-

scale findings to full-scale RO spiral wound element modules.

The experimental method detailed in Chapter 3 was followed for these experiments. The

experimental MilliQ-based matrix used in these experiments was a real groundwater from the

Nobleton, Ontario deep well as the solvent for lab-grade chemicals. This was done to achieve a

water chemistry with dissolved organic content and dissolved minerals to represent brackish

groundwater commonly present in remote communities that require solar powered reverse

osmosis systems. The details about the water collection and groundwater analysis were presented

in Chapter 3, Section 3.8.1. The pre-treatment anti-scalant investigated for these experiments

was selected to be Flocon 260 (F260) from BWA Additives because it was designed to

counteract high foulant conditions and high scaling conditions. In contrast, the Flocon 135, used

76

in the experiments presented in Chapter 5, was designed solely for high scaling conditions. Since

the experiments in this chapter were performed with the experimental groundwater-based matrix

containing dissolved organic content, the F260 anti-scalant was better suited to counteract both

the mineral and organic foulants.

The membrane permeability was measured continuously during operation for all the

experiments conducted in this chapter. The salt rejection was also measured using the feed

conductivity and the permeate conductivity. The amount of biologic content was also measured

using an aggregate measure of the adenosine triphosphate (ATP) using the deposit surface

analysis of the reverse osmosis membrane after the experiment. Membrane autopsy using

scanning electron microscopy (SEM) was also conducted to visually compare the foulant

coverage and morphology on the membranes.

In all analyses, the membrane permeability was normalized using the same method as in

Chapter 5, by dividing by the average value of the membrane permeability over the first five

minutes of the experiment. This limited the effect of membrane to membrane variability.


Experimental

System

Operating

Condition

Anti-scalant

(AS) Use

Permeate

Rinse

Lab-scale Continuous With F260 None

Lab-scale Intermittent With F260 None

Lab-scale Intermittent With F260 With Rinse

Pilot-scale Intermittent With F260 None

6.4 Experimental Results

6.4.1 Lab-scale Membrane Permeability Decline

The effect of intermittent operation compared to continuous operation for the F260 anti-

scalant without rinsing (Figure 6-1) shows that there was some initial improvement in membrane

77

permeability at the beginning of each day (Day 3 - Day 7). These results (Figure 6-1) show that

without rinsing, anti-scalant pre-treatment alone cannot restore membrane permeability.

Continuous operation results in a similar decline in membrane permeability as intermittent

operation for the F260 anti-scalant, though there is a minimal increase in membrane permeability

at the beginning of each day. The membrane flux at the lab-scale ranged from 36.0 Lm-2h-1 at

the beginning of the experiment to 13.5 Lm-2h-1 at the end of the experiments. This range was

below the manufacturer’s recommended flux rate for a TW30-2514 spiral-wound RO module

(55 Lm-2h-1).

Figure 6-1: Normalized membrane permeability for F260 anti-scalant when operated

continuously and intermittently.

78

The experimental results show that when the F260 anti-scalant was used and a remedial

rinse with permeate water was performed at the end of the day, the membrane permeability was

effectively restored (Figure 6-2). The error region represents the 95% confidence interval of the

mean of three cross-flow cells. The normalized membrane permeability for intermittent with

rinse recovered 20% percent from the end of the previous day to the start of the next day for

Day 1 - Day 5. Similarly, the normalized membrane permeability for intermittent without rinse

recovered on average 20% from the end of the previous day to the start of the next day for

Day 2 - Day 7. In contrast from Day 1 to Day 2 for intermittent without rinse, the normalized

membrane permeability ended at Day 1 at 78% and started on Day 2 at 80%. This shows the first

day with no rinse had a large effect on the membrane permeability decline.

Figure 6-2: Normalized membrane permeability for intermittent operation and F260 anti-

scalant with and without rinse. The rinse significantly improved the membrane permeability.

79

The comparative graph for the operating conditions (intermittent, continuous) and pre-

treatment technologies (Figure 6-3) shows the effect intermittent operation had on the

normalized membrane permeability for each day of the experiments. The error represents the

95% confidence interval of the mean of three cross-flow cells. The daily value of the normalized

membrane permeability is from the fourth hour of operation and averaged between the three

cross-flow SEPA cells. The fourth hour of operation was selected to permit a comparison

between the daily decline of the normalized membrane permeability for the three experiments.

Figure 6-3: Normalized permeability for the various operating conditions investigated at the

fourth hour of each day for day-to-day comparison.

For the experiment with F260 anti-scalant and no rinsing, the membrane permeability

decreased at about the same rate as continuous operation when no rinsing was used for

intermittent operation. The only operating condition and pre-treatment that maintained

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1 2 3 4 5 6 7

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rmal

ized

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mea

bili

ty

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Continuous F260 Intermittent F260 No Rinse Intermittent F260 Rinse

80

membrane permeability above 70% of the initial membrane permeability was the use of the F260

anti-scalant and with rinsing at the end of each day prior to shutdown, indicating this would be

appropriate pre-treatment for real applications.

6.4.2 Lab-scale Salt Rejection

The effect the operating conditions (intermittent, continuous), pre-treatment (F260 anti-

scalant) and rinsing (no rinse, rinse) had on the average daily salt rejection can be seen in Figure

6-4. The average salt rejection for the three SEPA cross-flow cells was averaged over each day.

The error bars represent the standard deviation of the salt rejection over each day. The

experiments that were operated intermittently with the F260 anti-scalant and permeate rinsing

provided the highest salt rejection.

Figure 6-4: Salt rejection for the groundwater experiments with F260.

99.0

99.1

99.2

99.3

99.4

99.5

99.6

99.7

99.8

2 3 4 5 6 7

Salt

Rej

ecti

on

(%

)

Days

Continuous F260 Intermittent F260 No Rinse Intermittent F260 Rinse

81

The experiment operated with the F260 anti-scalant and no rinsing performed worse than

with the F260 anti-scalant and rinsing. In addition, the experiment with the F260 anti-scalant and

no rinsing had the largest variability over the span of each day. This is likely due to the extended

shutdown period where the concentration next to the membrane surface declines slightly due to

forward osmosis from the permeate collection tubing into the cross-flow cell. The continuous

operation with the F260 anti-scalant had the lowest salt rejection of the three experiments. This

is likely because there were no extended shutdown periods where the localized concentration

next to the membrane surface decreased below the feed water concentration.

6.4.3 Lab-scale Membrane Autopsy

The lab-scale membrane autopsy using SEM (Figure 6-5) shows different surface

features for the different operating conditions. The membrane that was operated continuously

with F260 anti-scalant (Figure 6-5a) had uniform small crystals dispersed evenly on the surface

(on average about 1 µm or less in diameter) of calcium, sulfur and magnesium, confirmed by X-

ray electron dispersive spectroscopy (EDS). The membrane that was operated intermittently with

F260 anti-scalant and no rinse (Figure 6-5b) had small and medium-sized crystals, however, the

texture was quite different, since there was a layer on top and under the crystals of varying sizes.

This is hypothesized to be a biofilm that occurred because the anti-scalant remaining in the cross-

flow cell after shutdown provided a source of food initially for bacterial growth [121]. Due to

forward osmotic flow driven by the concentration gradient, there is likely sufficient oxygen for

bacteria to survive temporarily after the system is shutdown.

82

Figure 6-5: Membrane autopsy of the lab-scale experiments at x 1000 magnification and the

length bar represents 20 µm (a-c). Also, the membrane autopsies are shown at x 3000

magnification and the length bar represents 5 µm (d-f). For the continuous with F260 anti-

scalant (a, d), intermittent with F260 anti-scalant and no rinse (b, e) and intermittent with F260

anti-scalant and with rinse (c, f) experiments.

a)

20 µm

b)

20 µm

c)

20 µm 5 µm

5 µm

5 µm

d)

e)

f)

83

For the membrane operated intermittently with F260 anti-scalant and with rinse (Figure

6-5c) the membrane had small and medium-sized crystals. There were some regions of the

membrane surface that were not covered in dense crystals. This shows the rinse was effective in

washing away the residual anti-scalant and groundwater from the membrane surface. The anti-

scalant did not act as a food source, and therefore the biological content was less prevalent and

the dominating source of fouling was by scaling.

The average concentration of ATP on the membrane surface from the three SEPA cross-

flow cells for each of the experimental factors tested with the groundwater is shown in Figure

6-6. The error bars represent the variability between the three membranes from the three SEPA

cross-flow cells. The concentration of ATP (cATP) on the membrane surface after the

experiments showed significantly lower biological activity for continuous operation than

intermittent operation.

Figure 6-6: Concentration of ATP on the membrane surface for lab-scale operating conditions

with anti-scalant F260.

0

1

2

3

Continuous Int+No Rinse Int+Rinse

Mem

bra

ne

cATP

no

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to

fe

ed w

ater

cAT

P (

x10

00

)

84

The highest biological activity was observed on the membrane operated intermittently

but without a rinse. This is hypothesized to be a result of the shutdown period providing

sufficient time for the biological colony to use the anti-scalant and dissolved organic content in

the water as sources of food. The permeate water in the tubing can also flow into the cross-flow

cells through forward osmosis due to the concentration gradient which may provide sufficient

oxygen for the colonies to replicate during the shutdown period. While in the case of the rinse

and anti-scalant use, the membrane surface is swept clean with permeate water prior to the

extended shutdown period. This rinse washes away residual anti-scalant or nutrients. The

continuously operated system is hypothesized to have the least biologic activity because the

system is never stagnant and there is a consistent cross-flow sweeping the surface of the

membrane. The biologic activity grows but reaches a steady-state due to detachment caused by

the turbulent flow induced by the feed spacers. This is consistent with a previous study, which

showed the attachment and detachment of biological growth reaches a steady state [72] .

6.4.4 Discussion for the Lab-scale Experimental Results

6.4.4.1 Effect of Intermittent vs. Continuous Operation on Membrane Fouling with Anti-scalant Usage

Overall, the membrane permeability declined slightly faster when operated intermittently

with anti-scalant F260 compared to when the system was operated continuously (Figure 6-1).

This is expected to be a result of two competing mechanisms of fouling from scaling and

biofouling. For the intermittent operation, the dominating fouling mechanism was expected to

be from biofouling, as intermittent operation had the highest membrane ATP measurements

(Figure 6-6) and the SEM autopsy showed the thickest film deposits (Figure 6-5b,e). In contrast,

for continuous operation the dominating mechanism is expected to be from scaling, as the SEM

85

membrane autopsy showed the most scale coverage (Figure 6-5a, d). As well, the ATP

measurements (Figure 6-6) were the lowest for continuous operation.

For intermittent operation with anti-scalant and no rinse, there was an initial spike in the

membrane permeability at the start of Day 3 - Day 7. This is likely a result of the back-flow from

forward osmosis which occurs when the system is shut down for extended periods of time. The

permeate water in the tubing can flow back into the cross-flow cell by forward osmosis. Thus,

locally decreasing the concentration of the water at the membrane surface and slightly dissolving

some crystals which may have adhered to the surface and slightly loosening the foulants. At

start-up there is also an initial sparging and scouring of the membrane surface since there are air

bubbles and turbulent flow during the initial start-up of the system. This resulted in lower levels

of mineral scaling for this case as shown in (Figure 6-5b,e). For intermittent operation with anti-

scalant F260 and no rinse, the start-up did not appear to contribute to an improved permeability

on the second day (Figure 6-2). This is likely due to the biological and organic fouling which

was initiated in the first shutdown period, further decreasing the permeability. On the subsequent

days, it is anticipated that this fouling does not substantially increase. As a result, the osmotic

suck-back and start-up scouring effects dominate, increasing the start-up permeability.

6.4.4.2 Effect of Effect of Permeate Rinsing on Membrane Fouling with Anti-scalant Usage

For intermittent operation with anti-scalant F260 and with rinse, the membrane

permeability was significantly higher than without rinse (Figure 6-2). This is likely because the

anti-scalant effectively binds to the foulants and the rinse effectively washes away the majority

of the scales and deposits from each day, as seen in the membrane autopsy (Figure 6-5c, f). The

biological content was also lower with rinse than without (Figure 6-6). This is likely due to the

rinse which washes away some organic content and residual anti-scalant which may otherwise

86

act as a source of nutrients after shutdown. The salt rejection was also the highest for intermittent

operation with rinse (Figure 6-4). Which indicates, the membrane performance was better than

without the rinse. Even with rinsing, over several days, the membrane permeability began to

decline. This is likely due to some securely attached scales and deposits that were not removed

with the rinsing of the membrane.

6.4.5 Pilot-scale Membrane Permeability Decline

The pilot-scale experimental system was operated intermittently with the Nobleton

groundwater augmented with lab-grade chemicals using the F260 anti-scalant and no rinse

(Figure 6-7). The error bounds shown in the pilot-scale results are different from the lab-scale

error. In the lab-scale results, the error bounds are the standard deviation of the calculated

membrane permeability of the three cross-flow cells. While for the pilot-scale, the error was

calculated based on the accuracy and variation in the conductivity, pressure, and temperature

measurements. This difference was because the pilot-scale experiment was operated only once

since the water volumes required were prohibitively large. The membrane flux at the pilot-scale

ranged from 36.9 Lm-2h-1 at the beginning of the experiment to 13.8 Lm-2h-1 at the end of the

experiment which was below the manufacturer’s recommended flux (55 Lm-2h-1). The

membrane permeability was determined using the fully instrumented experimental system. It

was noted that the trend of declining permeability was slightly interrupted on the third day of

operation (circled in a dotted blue region in Figure 6-7a).

87

Figure 6-7: a) Normalized membrane permeability with the pilot-scale system operated with

the F260 anti-scalant and no rinsing in intermittent operation. The circled permeability rose

above the declining trend due to several start-up attempts after the submersible pump failed.

On the third day, the experiment was very difficult to start, and the submersible pump

failed. This caused air to enter the system and a loss of pressurization. As a result of the air and

turbulence next to the membrane, scales may have been scoured from the surface, thereby

increasing the overall permeability. The remaining days of operation were started without issue.

The normalized membrane permeability shows the general trend of a small increase in

membrane permeability initially at the start of each day. As well, the normalized membrane

permeability is comparable with experimental results from the lab-scale experimental system

(Figure 6-1). The comparison graph (Figure 6-8) shows the membrane permeability has a similar

88

trend of decreasing permeability and daily increase in membrane permeability after the extended

shutdown period for both the pilot-scale system and the lab-scale system.

Figure 6-8: Normalized membrane permeability for intermittent operation and the F260 anti-

scalant without rinsing for both the pilot-scale system and the lab-scale system.

The membrane permeability for the pilot-scale system however, shows a lower daily

increase at the start-up of the system. For the pilot-scale system, the normalized permeability

increased on average by (12±6) % from the shutdown time of the previous day. Compared to the

lab-scale system, where the normalized permeability increased on average by (23±12) % from

the shutdown time of the previous day.

89

6.4.6 Pilot-scale Membrane Autopsy

The surface coverage of the pilot-scale and lab-scale systems operated intermittently with

F260 and no rinse were compared using SEM as shown in Figure 6-9a-d. The pilot-scale SEM

surface appears to have several cracks.

Figure 6-9: Pilot-scale SEM autopsy a) compared to lab-scale SEM autopsy b) for intermittent

operation with F260 and no rinse at x 1000 magnification. Pilot-scale SEM autopsy c)

compared to lab-scale SEM autopsy d) for intermittent operation with F260 and no rinse at

x 3000 magnification.

This is expected to be a result of the unraveling process and drying of the spiral-wound

membrane. It is not expected that the cracking occurred during operation, since the salt-rejection

remained high, above 99.5%, throughout the experiment. The features of the membranes for both

the pilot-scale and lab-scale are similar since they both appear to have a layer on top and under

5 µm

c)a)

b)

20 µm 5 µm

d)

20 µm

90

the crystals (Figure 6-9c, d). The scales on the surface of the SEM in both the pilot-scale system

and lab-scale system were confirmed to have the same composition of calcium, sulfur, and

magnesium using EDS. The features of the membranes and the similar scales indicates similar

fouling mechanisms between the lab-scale system and the pilot-scale system.

The normalized concentration of ATP on the membrane surface for the pilot-scale with

intermittent operation and with F260 anti-scalant and no rinse is compared to the lab-scale in

Figure 6-10. The normalized concentration of ATP on the pilot-scale membrane was

significantly lower than the lab-scale membrane. This could be due to the size of the sample that

was used in the pilot-scale membrane autopsy (4.5 in2) compared to the lab-scale membrane

autopsy for ATP (0.5 in2).

Figure 6-10: Pilot-scale membrane ATP compared to the lab-scale for intermittent operation

with F260 and no rinse.

In addition, the membrane sample for the pilot was across the full width of the spiral

wound element, spanning from the inlet to the outlet. This cross-width sample contained regions

which were visibly fouled (dark yellow and orange) upon visual inspection and regions that

appeared non-fouled upon visual inspection. The outlet regions of the spiral wound membrane

0

1

2

3

Pilot Lab-scale

Mem

bra

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cATP

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ater

cAT

P (

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91

sample were fouled the most, and therefore may have been a more representative region to select

the membrane sample for ATP analysis from the pilot-scale membrane.

6.4.7 Discussion for the Pilot-scale

6.4.7.1 Effect of Experimental System on Membrane Fouling

Despite similar fouling structures observed from the membrane autopsy (Figure 6-10),

the comparison graph (Figure 6-8) shows the membrane permeability for the pilot-scale system

had a smaller daily increase at the start-up of the system. This is likely due to differences in the

membrane structure and the ratio of permeate water flow reversal which would occur through

osmosis to membrane surface area during shutdown by osmotic suck-back. In the TW30-2514

spiral-wound element in the pilot-scale system, the membrane area is 6503.2 cm2 compared to

the cross-flow membrane area in the lab-scale system, which is 138.7 cm2. This corresponds to

approximately 46 times the area. By contrast, in the pilot-scale system the permeate water tubing

is only about three times the volume of the permeate water tubing of the lab-scale system. This

corresponds to a larger permeate water volume to membrane area ratio for the lab-scale system

(8x10-5 m) compared to the pilot-scale system (1x10-5 m), approximately an order of magnitude

greater.

The osmotic suck-back due to forward osmosis after shutdown during the extended

shutdown periods likely has a lower impact on decreasing the localized concentration on the feed

side for the pilot-scale RO membrane compared to the lab-scale membrane. As well, the

construction of the spiral-wound elements is designed such that only the final fractions of the

membrane sleeves are close to the permeate collection tube. Therefore, unlike the lab-scale

system, there is not a significant amount of permeate water that interacts with the membrane and

that can provide a decreased salt concentration during the extended shutdown periods. A

92

schematic presentation of the difference between the lab-scale and pilot-scale systems during the

extended shutdown periods is shown in Figure 6-11.

Figure 6-11: Schematic of the difference between the lab-scale system and the pilot-scale

system during extended shutdown periods.

6.5 Discussion of Potential Fouling Mechanisms

The results indicate the permeability decline under intermittent operation can be

maintained by using anti-scalant pre-treatment and a permeate rinse prior to shut down. The use

of a simple rinse with permeate water can improve and maintain the membrane permeability

above continuous operation, as discussed in Section 6.4.2. This is explained using the following

mechanistic diagram (Figure 6-12).

Intermittent operation has several steps between operating days. First, in step one, the

extended shutdown period allows sufficient time for forward osmotic flow to permeate into the

cross-flow cell changing the localized salt concentration and loosening scales and deposits from

the membrane surface (Figure 6-12a). Second, in step two, the extended shutdown period allows

for osmotic suck-back and a decreased concentration on the feed side of the membrane (Figure

Feed Spacer

Permeate Spacer

Membrane

Feed Channel

Direction of Osmotic Suck-Back

Legend:

Permeate Collection

Lab-scalePermeate Collection Tube

Pilot-scale

93

6-12b). The experimental system minimized bacterial content using UV-disinfection in the

experiment water tank, however, if there was bacterial growth inside the cross-flow reverse

osmosis SEPA cell, the bacteria would experience nutrient deficiency due to the stagnant water

overnight. Third, in step three, after the extended shutdown period, the system is re-started.

During start-up, very turbulent flow and air enters the system as the water is pressurized by the

high-pressure pump. It is anticipated that this provides sparging and scouring of the membrane

surface and lifts away some foulants and scales which become loosened from the surface during

the extended shutdown period (Figure 6-12c).

Figure 6-12: Proposed fouling mechanism process for intermittent operation of reverse osmosis

membranes

6.6 Conclusions

This chapter presented an experimental study on the effects of intermittent operation with

anti-scalant addition and permeate rinsing on membrane permeability decline when the improved

1 2 3Flow reversal by osmosis during extended shutdown periods

Decreased concentration at the membrane surface and flow reversal loosens foulants accumulated on membrane surface

Startup introduces air and turbulent flow at the membrane surface and helps remove loosened foulants accumulated on membrane surface

Permeate water

Membrane

Feed water

Legend:

Foulant

Scale

Permeate water flow direction

Feed water flow direction

Step: a) b) c)Step: Step:

94

experimental system was operated with a local groundwater augmented with lab-grade

chemicals. The comparison of intermittent operation and continuous operation with anti-scalant

usage and membrane rinsing with permeate water was consistent with the experimental MilliQ-

based matrix results from Chapter 5, the membrane permeability decline can be minimized by

rinsing with permeate water prior to the extended shut down period. The experimental results

showed that intermittent operation alone did not have a significant negative impact on the

membrane performance in the short-term (several days of operation in the cross-flow unit). This

trend remained consistent for the groundwater results compared to the earlier results presented

in Chapter 5 for the experimental MilliQ-based matrix. As well, in both Chapter 5 and Chapter 6,

the membrane permeability was maximized when the system was operated intermittently with a

daily permeate water rinse prior to the extended shutdown period. The pilot-scale system results

compared to the improved experimental system showed that the lab-scale system adequately

represented the normalized membrane permeability decline of a full-scale spiral wound reverse

osmosis membrane module. The discussion on fouling mechanisms provided potential

mechanisms that occur during the extended shut down periods.

95

Chapter 7

Design Optimization Framework for Solar Powered Reverse Osmosis Systems Considering Membrane Fouling from Intermittent Operation

This work is under peer-review for publication (full citation: Freire-Gormaly, M., Bilton, A.,

(Under Review) Design of Solar Powered Reverse Osmosis Desalination Systems Considering

Membrane Fouling caused by Intermittent Operation, Desalination, DES_2018_301). It has

been reproduced here. Permission to use this content will be secured from the editor.

7.1 Introduction

In the previous chapters, the experimental results showed that rinsing the membranes

with permeate water prior to the extended shutdown periods improved the membrane

permeability. Previous optimization studies in the literature for solar powered water treatment

systems do not consider how operating conditions, such as intermittent operation, the use of anti-

scalant or permeate rinsing affect membrane permeability and membrane replacement rates

[14,114,116]. As a result, in the real application of these solar powered water treatment systems,

as the membrane permeability declines, water production would decrease and would not be able

to meet demand. These previous optimization studies therefore over-estimate the system

reliability.

Membrane fouling needs to be considered in the design of PVRO systems to improve the

long-term reliability of these systems. If systems are designed without considerations of

membrane fouling, PVRO systems may be cost-optimally designed for ideal conditions (low

membrane resistance) and be under-sized once fouling occurs. When fouling occurs, membrane

permeability decreases as a function of time and a larger system would be required to meet the

demands of the community.

96

The design optimization framework in this chapter incorporates a membrane fouling

model of the membrane permeability decline for intermittently operated systems towards the

development of a design algorithm. The analytical membrane fouling model for intermittent

operation was developed from the experimental characterization outlined in Chapter 5. The

sensitivity of the system design to the daily water demand, system reliability and membrane

fouling model were also investigated. Several case studies were performed to test the application

of the design framework for several geographic locations to configure the solar powered water

treatment system from commercially available components.

7.2 Design Optimization Framework Approach

For a water treatment system to be practical for remote communities, the system must be

cost-effective and require minimal operator intervention. To determine the ideal design and

operating conditions, an optimization structure, shown in Figure 7-1, was developed. The

approach uses a genetic algorithm combined with a simulation model and a cost model

implemented in Matlab 2016a (MathWorks®, Natick, MA, USA).

Figure 7-1: Framework for performing the cost optimization of the PVRO system.

Genetic Algorithm Optimizer

Hourly Simulation

Model

Design Variables

Water Demand Constraint

System Cost

Minimum Water Production per

day

System Cost Model

System Model

97

The simulation model consists of an hourly simulation for a ten-year period to adequately

evaluate the performance of the solar powered reverse osmosis system configuration. A ten-year

simulation period was selected based on a sensitivity analysis to the simulation duration

described in Section 7.3.2. At each time step, the water produced was determined considering

membrane fouling as a function of time. This approach ensures the system size is sufficient to

provide the community’s daily water demands once membrane fouling occurs.

The technologies investigated were all market available components and included spiral-

wound membranes, pressure vessel housings, pumps, a polycarboxylic anti-scalant, and solar

photovoltaic panels. The polycarboxylic anti-scalant was selected since very small volumes are

required and they are environmentally benign [123]. The solar powered reverse osmosis system

architecture investigated in this chapter is shown in Figure 7-2.

Figure 7-2: Solar powered reverse osmosis water treatment system architecture.

The system architecture consists of a set of components for the power sub-system and

the water treatment sub-system. The water treatment components include a high pressure pump,

reverse osmosis pressure vessel, reverse osmosis membranes, pre-treatment, and water storage

Water Storage Tank

Solar Panels

Battery Storage

Control Electronics

Motor

Pump RO Pressure Vessel

Pre-Treatment

Well

RO Membrane

Brine DisposalCartridge Filter

& Anti-scalant Dosing

98

tank. A representative inventory of modular components was compiled with parameters

extracted from manufacturer data. The inventory of components is described in more detail in

Section 7.3.3.

In addition to the physical system configuration, the operating conditions influence the

rate of membrane fouling and the overall water production of the system. The operating

conditions included in the fouling model (Figure 7-3) were the use of an anti-scalant (with or

without anti-scalant) and the use of clean water for rinsing the membranes prior to extended

shutdown periods. Only intermittent operation was considered, since it had been previously

shown that continuous operation is uneconomic for resource-constrained communities [124].

Figure 7-3: PVRO operating costs and pre-treatment.

A multi-objective optimization was performed to investigate the cost-reliability trade-off

of the various operating conditions. The system was designed to minimize the annualized cost

such that the system could meet the community’s daily water demands with a given reliability

constraint. The reliability of the system was quantified using a loss of water probability (LOWP)

metric which is the number of hours that the community’s water demand was not met divided

by the total number of hours in the simulation. The trade-off between the costs of more expensive

Pre-Treatment and Membrane Cleaning

F135

No-F135

Rinse

No-Rinse

RO System Operating Cost

F135$1.60/lb

Rinse Volume Accounted

Cartridge Filters

99

operating conditions and the benefits for improved membrane permeability were evaluated. For

example, the use of anti-scalants versus no anti-scalants and the benefits of improved membrane

permeability were investigated in the simulation-based optimization framework.

7.3 Design Optimization Framework

The optimization framework described above (Figure 7-1) relied on a physical system

simulation and a cost model. The simulation model used an experimentally derived model of the

membrane fouling under the various operating conditions (Figure 7-3). The following sections

describe the optimization framework, the cost models and how the membrane fouling model was

incorporated into the optimization framework.

7.3.1 Optimization Setup

The optimization problem addressed is the minimization of the annualized system cost

of a solar powered reverse osmosis system design subject to a reliability constraint (loss of water

probability which quantifies the system’s ability to meet the community’s water demands) and

constraints on the optimization design variables. The solar powered reverse osmosis system is a

modular system composed of discrete components (pumps, reverse osmosis membranes,

pressure vessels, storage tanks, solar panels) which makes their optimization difficult. As well,

the cost function to determine the annualized system cost over a 25-year lifetime and the

reliability constraint are non-linear. This results in a mixed integer nonlinear program (MINLP).

Several approaches exist to optimize MINLPs, for example, piecewise linear modeling, spatial

branch-and-bound, and search heuristics [125]. The genetic algorithm [126] is an example of a

search heuristic method for MINLPs and it is a global optimization technique. The genetic

algorithm was used to determine the minimum annualized system cost subject to a reliability

constraint, loss of water probability (LOWP, defined in Equation 7-1). The system reliabilities

100

considered were between 1% LOWP - 10% LOWP. The optimization problem was solved using

eight design variables listed in Table 7-1. The number of batteries was not selected as a design

variable, because only minimal energy storage was required for the solar powered system to

operate during the day with extended shutdown periods at night.

Table 7-1: List of design variables.

Design Variable Number Design Variable Name

1 Use of F135 Anti-scalant

2 Rinsing

3 Length of Membrane Life

4 Number of RO Membranes

5 Diameter of RO Membranes

6 Length of RO Membranes

7 Permeate Water Tank Size

8 Number of Solar PV Panels

The genetic algorithm was selected because it required only an initial population of

potential solutions and a fitness evaluation of the population. The genetic algorithm then mutates

the population towards the Pareto front. Genetic crossovers and mutations occur over several

generations until the optimal design variables which satisfy the reliability constraint are

identified. The genetic algorithm was coupled with a penalty function to evaluate whether or not

the reliability constraint was met.

The genetic algorithm requires the selection of several parameters including the

population size, elite count, cross-over fraction, function tolerance, constraint tolerance, the

number of stalled generations for convergence, and the maximum generations. To determine

these parameters a tuning procedure was performed by changing each parameter individually by

10% to evaluate the effect on the optimal system design. Table 7-2 lists the tuned parameters

that were used for the remainder of analysis in this chapter.

101

Table 7-2: List of genetic algorithm parameters.

Parameter Value

Population size 150

Elite count 1

Crossover fraction 0.3

Function tolerance 0.01

Constraint tolerance 1E-10

Number of stalled generations for convergence 50

Maximum number of generations 150

7.3.2 Simulation Model

The simulation model predicts the water production of a full-scale system using the

power system model coupled to a water treatment system model. The simulation that was

performed for the solar powered reverse osmosis system is outlined in Figure 7-4. The water

treatment system model estimates the membrane fouling as a function of time and the water

produced based on the energy produced by the power system model. Water is stored and

withdrawn from a tank to accommodate for fluctuations in weather and water demand. The

simulation was run hourly for ten years with solar insolation data (global horizontal irradiance

which includes cloud cover) from the geographic location to characterize the system reliability

using the LOWP.

During each hour of the simulation (Figure 7-4), an energy balance was performed on

the power system and the water production was calculated. First, the solar power produced over

the given day was calculated. Second, the total number of hours the water treatment system can

run in the given day was calculated. Third, the water production in the given hour was calculated

considering membrane fouling. Fourth, the water level in the water storage tank at the given hour

was calculated considering the water production and the water demand in that hour.

102

Figure 7-4: System simulation flowchart outlining the hourly and daily steps in the simulation

to determine the loss of water probability.

103

There was a check to determine if the maximum tank level was exceeded. If the

maximum tank level was reached, a flag was reset to the maximum tank level, so that the tank

would not be overfilled. There was also a check to ensure the tank level did not drop below

empty. If the tank was empty, the water demand of the community in that hour was not met, and

the counter for the LOWP was incremented. If it was the time to rinse the system (one operating

condition required a daily rinse prior to the extended shutdown period) the rinse volume was

removed from the tank. Finally, the time was incremented to the subsequent hour. To end the

simulation, the day must meet the total number of days for the simulation (3650 days). The last

step in the simulation was to calculate the actual LOWP for the system design. This value was

used by the genetic algorithm’s penalty function to determine the lowest cost system that met

the desired loss of water probability constraint.

To limit the computational effort, the sensitivity of simulation duration was investigated

(5 to 25 years) for the system size of 5 m3/day and LOWP of 1%. Simulation durations longer

than ten years did not result in a new system configuration and the computational time was 2.5

times longer. Therefore, a simulation length of ten years was selected to ensure the membrane

life was tested beyond two maximum membrane replacements and sufficient inter-annual

variations were considered. The following sections provide the details of the individual models

and the associated assumptions.

In the simulation, the loss of water probability is used as the metric for the system

reliability. The loss of water probability was defined as follows:

𝐿𝑂𝑊𝑃 = 𝑁𝑤𝑎𝑡𝑒𝑟

𝑁𝑠𝑖𝑚 (7-1)

where Nwater is the total number of hours during the simulation that the water demand was not

met in hours, and Nsim is the total number of hours for the simulation. A custom MATLAB

104

program was used for performing the simulations. The details of the individual technology

models are presented in the following individual technology modeling sections.

7.3.2.1 Power System Model

The power for the water treatment system is provided by a solar array with minimal

battery storage. The batteries are sized to provide sufficient power to allow the system to operate

at a constant flow rate and pressure once the system is turned on. Although some previously

installed solar powered reverse osmosis systems operate with variable flow and variable pressure

[50,127], several existing plants operate at a constant flow rate and a set pressure point

[33,34,128]. The solar powered reverse osmosis system configuration investigated in this chapter

is simulated to operate at a constant feed flow rate and a set pressure point.

The solar photovoltaic system model uses solar radiation data from the geographic

location of interest to determine the power produced. For all scenarios, the hourly solar radiation

data was calculated from the global horizontal insolation data from the National Renewable

Energy Laboratory’s (NREL) National Solar Radiation Data Base (NSRDB) [24,129]. The

global horizontal insolation data includes the cloud attenuation [24,129]. Using the hourly solar

insolation data, the power produced by the solar photovoltaic system at a given hourly time step

is given by:

𝑃𝑠𝑜𝑙𝑎𝑟 = 𝑁𝑝𝑎𝑛𝑒𝑙𝜂𝑝𝑎𝑛𝑒𝑙𝜂𝑚𝑝𝑝𝑡𝐼𝑠𝑜𝑙𝑎𝑟𝐴 (7-2)

where Psolar is the power generated by the solar panels in kW, Npanel is the number of solar panels,

which is a design variable, ηpanel is the efficiency of the panel, ηmppt is the efficiency of the

maximum power tracking power electronics (98%), Isolar is the incident radiation from the sun

in kW/m2, and A is the area of the panel in m2. The panel efficiency, ηpanel, and the panel area in

m2, A, are a function of the panel that was modelled. A single solar panel type was used in the

105

design for ease of construction, assembly and maintenance. As a conservative estimate, the panel

was assumed to be mounted horizontally.

The amount of power required by the pump is determined by:

𝑃𝑝𝑢𝑚𝑝 = 𝐹𝑐𝑜𝑛𝑣𝑒𝑟𝑡𝑃𝑓×𝑄𝑓,𝑚𝑒𝑚𝑏

𝜂𝑝𝑢𝑚𝑝 (7-3)

where Ppump is the power required by the high pressure pump in kW, Fconvert is the unit conversion

factor, Pf is the reverse osmosis membrane feed pressure in bar, Qf,memb is the feed flow rate

based on the membrane configuration selected in the design in m3/hour, ηpump is the efficiency

of the high pressure pump.

The solar powered water treatment system is designed to operate at a single operating

point (pressure and flow rate) for several hours a day. Therefore, a small amount of battery

capacity was included in the power system model. It is assumed that the battery is charged in the

morning and then the system will turn on and run at a constant rate. The amount of battery storage

required (Estorage,reqd) was determined based on the ten-year simulation for each individual design

to determine the maximum required energy storage to account for the periods of time when there

was insufficient solar power available to operate the system at the set operating point. To provide

a conservative estimate of the battery storage requirements, no excess energy from the previous

day was used in the subsequent day. A sample day of operation of the solar powered system is

shown in Figure 7-5 with the hourly solar panel power production, battery state of charge and

system power requirements.

To take into account round trip losses from storing the energy in the battery [130], the

total power of the solar system with battery storage is given by:

𝑃𝑠𝑦𝑠𝑡𝑒𝑚 = 𝑃𝑠𝑜𝑙𝑎𝑟𝜂𝑟𝑡𝑏𝑎𝑡𝑡 (7-4)

106

where Psystem is the power produced at a given time step in kW, Psolar is the solar power and ηrtbatt

is the round-trip battery efficiency [130].

Figure 7-5: Power management strategy for the solar powered water treatment model.

simulation for a day of sample operation in Mexico for a 1 m3 system with 4 solar panels and

2.6 kWh of energy storage.

7.3.2.2 Water Treatment System Model

The water treatment system model determines the water production for a given energy input.

The water production (Qp) in m3/hr for each hour was determined based on the membrane

selected in the design vector, the membrane fouling and the operating pressure. The water

production is given by:

𝑄𝑝 = 𝐾𝐹𝐹𝐾𝑊𝐾𝑇𝐴𝑚𝑒𝑚(𝑃 − 𝜋) (7-5)

107

where KFF is the fouling factor, KW is the membrane permeability to water (m hr-1bar-1), KT is the

temperature correction factor, Amem is the membrane area (m2), P is the average operating

pressure in bar, and π is the average osmotic pressure of the water being treated in bar.

Experiments were performed to determine the membrane permeability as a function of

time for various operating conditions (anti-scalant use and rinsing) [131] described in Chapter 5

for an intermittently operated reverse osmosis membrane water treatment system. The system

was operated for 8 hours per day at a fixed operating pressure and was shut down for the

remaining 16 hours of the day. The improved lab-scale experimental system, described

previously [132] and in Chapter 3, was operated using the experimental MilliQ-based matrix to

test a water matrix containing high-levels of dissolved minerals common of brackish water in

remote regions facing high water scarcity. One such community, La Mancalona, is located in the

Yucatan Peninsula (GPS coordinates: Latitude: 18.81°N, Longitude: 89.29°W) was selected

because it is representative of other communities with high solar insolation served by brackish

groundwater. As well, La Mancalona currently has an operating solar powered water treatment

system [33] and is a partner community for the research in this thesis.

7.3.2.3 Analytical Membrane Fouling Model

An analytical membrane fouling model was developed for the different operating

methods for the reverse osmosis water treatment systems. The analytical model was based on

the experimental results [131] and built on the mathematical form for fouling [110]. The

analytical membrane fouling model of the normalized membrane permeability decline (fouling)

per day uses an exponential function, and is defined as follows:

𝐾𝐹𝐹 = 𝑎𝑒𝑏

(𝑑𝑎𝑦+𝑐) (7-6)

108

where day is the number of days since the start of use of the new membranes. The parameters,

a, b, c for the four cases investigated are included in Table 7-3. Additionally, for the daily

behavior of the membrane fouling, a linear fit was determined from the experimental data and

included in Table 7-3 as d. The daily decrease in the membrane permeability (KFF) and the hourly

decline of the membrane permeability each day are shown for two representative days of Case 3

(Figure 7-6). The daily exponential fouling model for Case 1-4 are shown in Figure 7-7.

Table 7-3: Membrane fouling parameters for cases investigated.

Case Description a b c d

1 No AS & No Rinse 0.0048 46 7.7 -0.042

2 AS & No Rinse 0.063 20 6.1 -0.042

3 AS & Rinse 0.54 3.8 6.0 -0.027

4 AS & No Rinse [110] 0.68 79 200 -0.042

Figure 7-6: Membrane fouling model based on experimental data [110,131].

0.70

0.75

0.80

0.85

0.90

0.95

1.00

0 8

No

rmal

ized

Mem

bra

ne

Perm

eab

ilty

Operating Time (t in hours)

Daily Decline

Hourly Decline

𝐾𝐹𝐹 = 𝑎𝑒𝑏

( 𝑎𝑦 𝑐)

𝐾𝐹𝐹, 𝑜𝑢𝑟𝑙𝑦, 𝑎𝑦1 = 𝐾𝐹𝐹,

𝐾𝐹𝐹, 𝑜𝑢𝑟𝑙𝑦, 𝑎𝑦 = 𝐾𝐹𝐹,

1 Operating Time (day in days)2

109

Figure 7-7: Normalized membrane permeability decline (KFF) vs. operating time in days for

Case 1-4 used in the water treatment system model.

The anti-scalant usage of the full-scale system was determined based on the amount of

feed water used per day and the required anti-scalant dose from the water characteristics. The

anti-scalant dose was calculated using the anti-scalant manufacturer’s dose calculation software

Flodose (BWA Water Additives, Version 4.0). This dose rate was used to determine the cost of

using anti-scalant over the system life.

7.3.3 Cost Model

The total cost of the solar powered water treatment system was determined based on the

cost of individual components selected in the design and the operating costs required to run the

system. The power system cost model is described first, followed by the water treatment cost

model. Table 7-4 provides the individual costs of the system components (e.g. pump, filters).

The costs of the water tanks (Figure 7-8) shows that larger tanks tend to cost more, yet there are

certain sizes which break this trend due to economies of scale. In this analysis it was assumed

that only one tank could be selected for simplicity. The cost models for each individual

subsystem are outlined below.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0 30 60 90 120 150 180

No

rmal

ized

Mem

bra

ne

Per

mea

bilt

y

Operating Time (days)

Case 1

Case 2

Case 3

Case 4

110

Table 7-4: Individual component costs for the solar powered water treatment system.

Subsystem Description USD Product

Power

PV Panel 340.73 Sunmodule Plus SW280 [133]

PV BOS Structural 12%*Wdc Market Price [134]

PV BOS Electrical 27%*Wdc Market Price [134]

Lead-Acid Batteries 80/kWh Market Price [135]

Water

Treatment Membranes

2.5” x 14” 151.00 TW30-2514 [136]

2.5” x 21” 160.00 TW30-2521 [136]

2.5” x 40” 208.00 BW30-2540 [136]

4” x 14” 245.00 TW30-4014 [136]

4” x 21” 255.00 TW30-4021 [136]

4” x 40” 285.00 BW30-4040 [136]

Pressure Vessels

2.5x14 FRP 1000 psi 320.41 ROPV - MHFG-2514-14-1000 [137]



4x14 SS 300 psi 104.00 AMI PV4014SSAU-316 [136]

4x21 SS 300 psi 155.00 AMI PV4021SSAU-316 [136]

4x 40, 1 FRP 300 psi 180.00 Codeline 40E30N-1 [138]

4x40, 2 FRP 300 psi 257.78 Codeline 40E30N-2 [138]

4x 40, 3 FRP 300 psi 273.33 Codeline 40E30N-3W [138]

Pumps

Less than 1 Lpm 700.00 Danfoss APP 0.8 [11]

Less than 2 Lpm 4239.00 Danfoss APP 1.8 [11]

Less than 4.8 Lpm 4782.00 Danfoss APP 2.5 [11]

Motors

Less than 1 Lpm 845.00 Leeson 116698.00 [11]

Less than 2 Lpm 1319.00 Leeson G141121.00 [11]

Less than 4.8 Lpm 2141.00 Leeson 170615.60 [11]

Filter

Filter Housing 65.54 Pentek 20" Housing [139]

Filter Cartridge 20.00 Pentek 20" Filter [136]

Anti-scalant

Peristaltic Pump 42.51 Williamson [140]

Container 14.99 Aquapak [141]

Flocon 135 1.6/lb BWA Additives [142]

To compare the various system configurations on an equal basis, the annualized cost

method was used for a 25-year system life. The annualized system cost (Asystem) was determined

111

for each system configuration based on the cost of the power system (Cpower) and the cost of the

water system (CRO) which were annualized using the annualization factor (Fequiv, annual). The

Fequiv,annual is given by:

𝐹𝑒𝑞𝑢𝑖𝑣,𝑎𝑛𝑛𝑢𝑎𝑙 =𝑖(1 𝑖)𝑙𝑖𝑓𝑒

(1 𝑖)𝑙𝑖𝑓𝑒−1 (7-7)

where i is the discount rate of 12% [143], and life is the system life of 25 years.

Figure 7-8: Tank capacity and costs from a supplier of plastic drinking water tanks [144].

The annualized system cost is given by:

𝐴𝑠𝑦𝑠𝑡𝑒𝑚 = 𝐴𝑝𝑜𝑤𝑒𝑟 𝐴𝑅𝑂 (7-8)

where Apower is the power system costs (capital and replacement). The power system cost was

converted to annual costs using:

𝐴𝑝𝑜𝑤𝑒𝑟 = 𝐶𝑝𝑜𝑤𝑒𝑟(𝐹𝑒𝑞𝑢𝑖𝑣,𝑎𝑛𝑛𝑢𝑎𝑙) (7-9)

where Cpower is the cost of the power system and Fequiv,annual is the equivalent annual cost factor.

0

2000

4000

6000

8000

10000

12000

0 20 40 60 80

Tan

k C

ost

(U

SD)

Tank Capacity (m3)

112

The capital costs of the reverse osmosis system were converted to annualized costs (ARO)

as follows:

𝐴𝑅𝑂 = 𝐶𝑅𝑂(𝐹𝑒𝑞𝑢𝑖𝑣,𝑎𝑛𝑛𝑢𝑎𝑙) 𝐴𝑅𝑂,𝑅𝑒𝑝𝑙 (7-10)

Where CRO is the capital cost of the water system, Fequiv,annual is given by Equation (7-7) and

ARO,Repl is the annual replacement cost of the components for the reverse osmosis water treatment

system, given in Equation (7-22).

7.3.3.1 Power System Cost Model

The power system cost (Cpower) can be broken into contributions from the solar system

(Csolar), the battery system (Cbatt) and the balance of system costs (CBOS). The power system cost

(Cpower) was calculated as follows:

𝐶𝑝𝑜𝑤𝑒𝑟 = 𝐶𝑠𝑜𝑙𝑎𝑟 𝐶𝐵𝑂𝑆 𝐶𝑏𝑎𝑡𝑡 (7-11)

The cost of the solar photovoltaic system (Csolar) considers the use of a single brand of solar

panels at a set power rating per panel and it was calculated as follows:

𝐶𝑠𝑜𝑙𝑎𝑟 = 𝑁𝑝𝑎𝑛𝑒𝑙𝑠𝐶𝑃𝑎𝑛𝑒𝑙 (7-11)

where Npanels is the number of panels and CPanel is the cost of the solar panel [145].

The balance of system costs (CBOS) of the solar photovoltaic system were calculated as

follows:

𝐶𝐵𝑂𝑆 = 𝐶𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝐶𝑠𝑡𝑟𝑢𝑐𝑡𝑢𝑟𝑎𝑙 (7-12)

where Celectrical is the balance of system costs for the electrical components of the solar

photovoltaic system and Cstructural is the balance of system costs for the structural components.

113

The balance of system costs for the electrical components (Celectrical) were determined as

follows:

𝐶𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 = 0. 7(𝑊 𝑐,𝑠𝑜𝑙𝑎𝑟) (7-13)

where the Wdc,solar is the rated DC power rating of the solar photovoltaic system. The factor of

27% is based on U.S. photovoltaic solar costs from NREL [134] for the conductors, switches,

grounding equipment, fuses and breakers required for setting up a solar photovoltaic power

system.

The balance of system costs for the structural components (Cstructural) was determined as:

𝐶𝑠𝑡𝑟𝑢𝑐𝑡𝑢𝑟𝑎𝑙 = 0. (𝑊 𝑐,𝑠𝑜𝑙𝑎𝑟) (7-14)

where the Wdc,solar is the rated DC power rating of the solar photovoltaic system. The factor of

12% is based on U.S. photovoltaic solar costs from NREL [134] for purchasing the racking and

mounting hardware required to set up the solar panels in a structurally sound manner.

The capital cost of the battery storage (Cbatt) required for the system design was calculated

as follows:

𝐶𝑏𝑎𝑡𝑡 = (𝐶𝑐𝑎𝑝,𝑏𝑎𝑡𝑡)(𝐹𝑒𝑞𝑢𝑖𝑣,𝑎𝑛𝑛𝑢𝑎𝑙) 𝐶𝑟𝑒𝑝𝑙𝑎𝑐𝑒,𝑏𝑎𝑡𝑡 (7-15)

where Ccap,batt is the capital cost of the batteries, Fequiv,annual is the equivalent annual cost factor

given by Equation (7-7) and Creplace,batt is the replacement costs for the batteries. The capital

cost of the batteries (Ccap,batt) was given by:

𝐶𝑐𝑎𝑝,𝑏𝑎𝑡𝑡 = 𝐶𝑠𝑡𝑜𝑟𝑎𝑔𝑒(𝐸𝑠𝑡𝑜𝑟𝑎𝑔𝑒,𝑟𝑒𝑞 ) (7-16)

114

where Cstorage is the cost per kWh of lead-acid battery storage ($80 USD/kWh in 2015) [135] and

Estorage,reqd is the amount of battery storage required to ensure steady operation of the reverse

osmosis system during daylight hours as computed based on the simulation model.

The cost to replace the batteries (Creplace,batt) was given by:

𝐶𝑟𝑒𝑝𝑙𝑎𝑐𝑒,𝑏𝑎𝑡𝑡 = 𝐶𝑐𝑎𝑝,𝑏𝑎𝑡𝑡𝑅𝑏𝑎𝑡𝑡𝐹𝑒𝑞𝑢𝑖𝑣,𝑎𝑛𝑛𝑢𝑎𝑙 (7-17)

where Ccap,batt is the capital cost of the batteries, Rbatt is the replacement rate of the batteries,

Fequiv,annual is the equivalent annual cost factor. The only battery operating and maintenance cost

considered was the cost of battery replacement because it is the main operating and maintenance

cost for a lead-acid battery system [38]. The batteries are assumed to require replacing about

every 5 years for a system life of 25 years [38] based on 40,000 hrs between the mean time

between failure [146].

7.3.3.2 Water Treatment System Cost Model

The costs of the water system can be broken down into the capital and operating costs. The

capital costs of the reverse osmosis system were included for the optimization of the solar

powered water treatment system design. The capital costs of the reverse osmosis water treatment

system (CRO) were given by:

𝐶𝑅𝑂 = 𝐶𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡𝑠 𝐶𝑡𝑎𝑛𝑘 𝐶𝑝𝑖𝑝𝑖𝑛𝑔 (7-18)

where Ccomponents is the cost of the components of the reverse osmosis system, Ctank is the cost of

the tank for water storage, and Cpiping is the cost of the piping required to install the reverse

osmosis system. The Ccomponents was given by:

𝐶𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡𝑠 = 𝐶𝑚𝑒𝑚𝑏 𝐶𝑃𝑟𝑒𝑠𝑉𝑒𝑠 𝐶𝑝𝑢𝑚𝑝 𝐶𝑚𝑜𝑡𝑜𝑟 𝐶𝑝𝑟𝑒−𝑡𝑟𝑒𝑎𝑡 (7-19)

115

where Cmemb is the capital cost of the membrane selected in the design, CPresVes is the capital cost

of the pressure vessel, Cpump is the cost of the pump, Cmotor is the cost of the motor, Cpre-treat is

the cost of the pre-treatment system. The cost of the pre-treatment system (Cpre-treat) was given

by:

𝐶𝑝𝑟𝑒−𝑡𝑟𝑒𝑎𝑡 = 𝐶𝑓𝑖𝑙𝑡𝑒𝑟 𝑜𝑢𝑠𝑖𝑛𝑔 𝐶𝑓𝑖𝑙𝑡𝑒𝑟 𝐶𝐴𝑆,𝑝𝑢𝑚𝑝 𝐶𝐴𝑆,𝑡𝑎𝑛𝑘 (7-20)

where Cfilterhousing is the capital cost of the filter cartridge housing, Cfilter is the capital cost of the

filter cartridge, CAS,pump is the capital cost of the anti-scalant dosing peristaltic pump and CAS,tank

is the capital cost of the a small tank for holding the anti-scalant. The cost of the piping (Cpiping)

was given by [11]:

𝐶𝑝𝑖𝑝𝑖𝑛𝑔 = 0. (𝐶𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡𝑠) (7-21)

The annual operating costs for the reverse osmosis system were given by:

𝐴𝑅𝑂,𝑅𝑒𝑝𝑙 = 𝐶𝑚𝑒𝑚𝑏(𝑅𝑚𝑒𝑚) 𝐶𝑓𝑖𝑙𝑡𝑒𝑟(𝑅𝑓𝑖𝑙𝑡) 𝐶𝑝𝑢𝑚𝑝(𝑅𝑝𝑢𝑚) 𝐶𝑚𝑜𝑡𝑜𝑟(𝑅𝑚𝑜𝑡) 𝐶𝑝−𝑐 𝑒𝑚 𝐶𝐴𝑆−𝑐 𝑒𝑚 (7-22)

where Rmem is the replacement rate of the reverse osmosis membrane selected in the design

optimization, Rfilt is the annual replacement rate of the cartridge filter pre-treatment, Rpum is the

replacement rate of the pump, Rmot is the replacement rate of the motor, Cp-chem is the cost of the

post-treatment chemicals for re-mineralizing the water to a drinkable standard, Rpc is the

replacement rate of the post-chemicals and CAS-chem is the annual cost of the anti-scalant

chemicals.

The cost of chemicals (Cp-chem) for re-mineralizing the water post-treatment was given

by:

𝐶𝑝−𝑐 𝑒𝑚 = 𝑚𝑟𝑒−𝑚𝑖𝑛 (𝐶𝑟𝑒−𝑚𝑖𝑛) (7-23)

116

where mre-min is the mass of re-mineralizing chemicals used per year in kg as calculated by the

simulation model and Cre-min is the cost of the re-mineralizing chemicals in USD/kg [147].

The cost of anti-scalant chemicals (CAS-chem) was given by:

𝐶𝐴𝑆−𝑐 𝑒𝑚 = 𝑚𝑎𝑛𝑡𝑖−𝑠𝑐𝑎𝑙(𝐶𝐴𝑆) (7-24)

where manti-scal is the mass of anti-scalant used per year in kg as calculated by the simulation

model and CAS is the cost of the anti-scalant in USD/kg. The total annualized cost of the reverse

osmosis water treatment system (ARO) was given by Equation (7-10). The water cost (Cwater) of

the reverse osmosis water treatment system in USD/m3 was given by:

𝐶𝑤𝑎𝑡𝑒𝑟 = 𝐴𝑅𝑂 ÷ 𝑉𝑦𝑒𝑎𝑟 (7-25)

where ARO is the total annualized reverse osmosis system cost from Equation (7-10) and Vyear is

the total volume of drinking water in m3 that was produced per year by the system.

7.4 Optimization Results and Discussion

The design optimization was performed for La Mancalona, Mexico for water production

between one to ten m3/day to show the application of the design optimization for a broad range

of water system sizes. In addition, sensitivity to the fouling models were analyzed for La

Mancalona, Mexico. Finally, the influence of system location on the design was analyzed using

three additional geographic locations.

7.4.1 Effect of System Size on Optimal System Cost

The sensitivity of the system configuration to the system size for three sizes (1 m3/day,

5 m3/day, 10 m3/day) was analyzed for La Mancalona, Mexico. For all system sizes, the variation

in system configuration was determined for a range of LOWP. It was found that the annualized

system cost decreased with increased loss of water probability for all system sizes (Figure 7-9a).

The larger system size (10 m3/day) showed the most reduction in annualized system cost for

117

higher LOWP. This was because for the smaller system size (1 m3/day), the system design was

slightly over-sized. For the 1 m3/day system, there is a limitation in place due to the module

availability and any smaller system would not meet the reliability constraints.

The change in system cost is a piece-wise linear function, due to the modular nature of

the design problem and the same system configuration meets a wide-range of reliability

constraints. The actual LOWP of the optimal configurations were less than the design goal

LOWP (Figure 7-9b). The system configuration is the same for the design goal LOWP 1%-3%

for all three system sizes (1 m3/day, 5 m3/day, 10 m3/day), and it was not until the system design

goal LOWP constraint was 4% that the system configuration changed, resulting in a decreased

annualized system cost.

Figure 7-9: a) Annualized system cost vs. design goal LOWP for variable system size (m3/day)

and b) the actual LOWP compared to the design goal LOWP for a 10 year simulation period

for La Mancalona, Mexico.

The water cost (Cwater in USD/m3) was also determined for La Mancalona, Mexico for

systems ranging from 1 m3/day to 10 m3/day (Figure 7-10). The water cost decreased slightly for

increased loss of water probabilities, however, the cost savings from lower reliability systems

are very small and overlap in Figure 7-10. The water cost vs. system size follows an exponential

1800

2300

2800

3300

3800

4300

0% 2% 4% 6% 8% 10%

An

nu

aliz

ed C

ost

(USD

)

Design Goal LOWP

1m³/day

5m³/day

10m³/day

a)

0%

2%

4%

6%

8%

10%

0% 2% 4% 6% 8% 10%

Act

ual

LO

WP

Design Goal LOWP

1m3/day

5m3/day

10m3/day

1800

2300

2800

3300

3800

4300

0% 2% 4% 6% 8% 10%

An

nu

ali

zed

Co

st (

USD

)

Design Goal LOWP

1m³/day

5m³/day

10m³/day

b)

118

decay, where the smaller system size (1 m3/day) is significantly more expensive than the larger

systems (5 m3/day and 10 m3/day) (Figure 7-10 and Table 7-5). This is due to economies of

scale, since the larger pressure vessels and larger RO modules are cheaper per volume treated

than the smaller RO components (Table 7-4). Therefore, even if a community requires only

1 m3/day during the design process, it would be better for the community to increase their system

size within their budgetary range to ensure they can benefit from these economies of scale. These

larger systems would also facilitate meeting future demand growth over the system lifetime of

25 years.

Figure 7-10: Water cost ($/m3) vs. the system size (m3/day) for La Mancalona, Mexico at

various design goal loss of water probabilities (1%, 5%, 10%).

0.5

1.5

2.5

3.5

4.5

5.5

0 2 4 6 8 10

Wat

er C

ost

(Cwater

in $

/m3 )

System Size (m3/day)

1% LOWP

5% LOWP

10% LOWP

119

Table 7-5: Water cost (USD/m3) for various system sizes (1, 5, 10 m3/day) and LOWP (1%,

5%, 10%). Shows decreasing water costs for reduced system reliability (increasing LOWP).

Design Goal LOWP

System Size

(m3/day) 1% 5% 10%

1 $5.53/m3 $5.42/m3 $5.42/m3

5 $1.56/m3 $1.54/m3 $1.45/m3

10 $1.05/m3 $1.00/m3 $0.93/m3

7.4.2 Effect of System Size on System Configuration

The cost-optimal system configurations for several system sizes (1 m3/day, 5 m3/day, and

10 m3/day) for the community in La Mancalona, Mexico at a 5% loss of water probability

constraint are shown in Figure 7-11. The 5% design goal LOWP was selected as a mid-point in

the analysis range. The larger system design for 10 m3/day required a larger tank size, more solar

panels, and larger energy storage than the smaller system designs (1 m3/day and 5 m3/day). In

all cases, the system configuration uses a tank size that is approximately two to three times the

daily water requirement. Storing the end-product, clean drinking water, is much cheaper than

energy storage, which requires expensive battery replacement costs. The most economical choice

for the membrane modules is the 2.5”x40” module for 1 m3/day and 5 m3/day. The membrane

module is 4”x40” for 10 m3/day. The number of solar panels increased drastically from one solar

panel for 1 m3/day to ten solar panels for 5 m3/day and increased slightly to fourteen solar panels

for 10 m3/day. The system design had increased power requirements to provide larger volumes

of water. For all system sizes, the cost-optimal operating condition was to use anti-scalant and

daily rinsing of the membranes. As well, for all system sizes, the membranes required

replacement at the maximum replacement time (five years).

120

Figure 7-11: System configuration varies with size of the system for a 10 year simulation

period and at 5% LOWP with experimental fouling and anti-scalant usage with daily rinsing.

7.4.3 Effect of System Reliability on Optimal System Configuration

Changing the reliability design goal (LOWP) for a 10 m3/day system for the community

of La Mancalona, Mexico changed the system configuration (Table 7-6). The system was

oversized for a design goal LOWP of 2% and 3% as well as for 5%-8%, 9%, 10%. This

emphasizes the effect discrete design choices have on the overall system configuration. If a

community can withstand a system LOWP of 4% (which translates to approximately 14 days per

year, typically not consecutively, without sufficient water) the annualized system cost can be

decreased by about 150 USD. As well, since the solar panels and the battery storage are the main

components that change to increase the system reliability, a community could purchase the water

components of the system and the solar panels and battery storage for the lower reliability

system, and then upgrade to a higher reliability system by purchasing the solar panels and extra

batteries at a later point in time.

1m3/day 5m3/day 10m3/day

# RO Membranes

Size of RO Membranes

# Solar PV Panels

Battery Storage

Tank Size

2.5”x40” 2.5”x40” 4”x40”

3.0 m3 9.8 m3 18.9 m3

9.5 kWh3.9 kWh1.3 kWh

121

Table 7-6: Effect of changing the design goal LOWP for a 10 m3/day system for La Mancalona,

Mexico.

Replace

Membranes

(Days)

# RO

Memb-

ranes

RO

Dimen-

sions

Tank

Size

(m3)

# Solar

PV

Panels

LOWP Design

LOWP

Goal

Annual

Cost

(USD)

Battery

Storage

(kWh)

1825 6 4" x 40” 18.9

17 0 1%-3% 3827 9.361

14 0.0391 4%-8% 3657 9.499

10 0.0823 9%-10% 3396 8.025

7.4.4 Effect of Membrane Permeability Decline on System Reliability

To evaluate the need to consider membrane fouling in the design of PVRO systems, a

system was optimized for La Mancalona, Mexico without considering fouling and then simulated

for ten years under different fouling cases. A pair-wise comparison of the optimal system

configuration when optimized considering fouling and without considering fouling is shown in

Table 7-7. The number of solar panels selected for the optimal configuration was much smaller

when no fouling was considered. As well, for larger system sizes (5 m3/day and 10 m3/day) the

annualized system cost was significantly higher when fouling was considered.

The annualized system cost for the 5 m3/day system optimized considering fouling was

19% more expensive than the system optimized without considering fouling. The annualized

system cost for the 10 m3/day system optimized considering fouling was 31% more expensive

than the system optimized without considering fouling. By contrast, the 1 m3/day system

optimized considering fouling was only 8% more expensive than the system optimized without

considering fouling.

122

Table 7-7: Effect of considering membrane fouling on the optimal system configuration for a

design goal loss of water probability of 1%.

System Size of

1 m3/day

System Size of

5 m3/day

System Size of

10 m3/day

Optimized

considering:

No

Fouling Fouling

No

Fouling Fouling

No

Fouling Fouling

# RO

Membranes 3 3 5 6 5 6

Size of RO

Membranes 2.5"x40" 2.5"x40" 2.5"x40" 2.5"x40" 2.5"x40" 4"x40"

# Solar PV

Panels 1 3 5 11 12 17

Tank Size

(m3) 3 3 9.8 9.8 18.9 18.9

Battery Size

(kWh) 1.3 2.8 3.4 2.9 3.3 9.4

Annualized

Cost (USD) 1862 2019 2402 2850 2918 3827

To investigate the sensitivity of the LOWP to the membrane fouling model, a set of

fouling cases were tested. The optimal system configuration determined without considering

fouling was then simulated with the experimental fouling model of Case 3 from Table 7-3

(labeled as ‘Exp. Fouling’ in Figure 7-12) and the fouling model from literature developed by

Abbas et. al. [110] which had similar water characteristics, Case 4 from Table 7-3 (labeled as

‘Abbas et. al. [20]’ in Figure 7-12). The difference in the system’s actual loss of water probability

can be seen in Figure 7-12 for 1 m3/day, 5 m3/day, and 10 m3/day systems.

The results show that for larger systems (5 m3/day and 10 m3/day) the effect of not

considering fouling is more important. A solar powered reverse osmosis system that is designed

considering no membrane fouling will severely underperform when membrane fouling occurs.

123

For the 5 m3/day system, the actual LOWP increases to 33% for the Abbas fouling model at a

design goal of 6%-8%, the actual LOWP increases to 20% at a design goal of 9%-10%. This was

because the system configuration at 6%-8% LOWP had more solar panels than RO membranes

compared to the system configuration for 8%-10% LOWP and as a result, the membrane fouling

had a smaller influence on performance.

Figure 7-12: Actual loss of water probability (LOWP) when simulated vs. the Designed goal

LOWP for several system sizes ( a) 1 m3/day, b) 5 m3/day, c) 10 m3/day). The optimal system

design was determined considering no fouling then simulated for a 10 year period with

experimental fouling (with anti-scalant and rinsing) and Abbas et. al. [110] fouling.

For a lower system size (1 m3/day), the difference in system reliability caused by fouling

is smaller. This is due to the oversizing of the system at the lower solar powered reverse osmosis

system size due to the modular components of the system design. These results demonstrate it is

crucial to consider fouling when performing the cost-optimized design of these systems.

Otherwise, the system would be unable to meet the demands of a community once membrane

fouling occurs and the community would be confronted with higher membrane replacement

operating costs than originally anticipated.

0%

10%

20%

30%

40%

0% 5% 10%

Act

ual

LO

WP

Design Goal LOWP

1m3/day

No Fouling

Abbas(AS,NoRinse)

Exp(AS,Rinse)

0%

10%

20%

30%

40%

0% 5% 10%

Design Goal LOWP

5m3/day

No Fouling

Abbas(AS,NoRinse)

Exp(AS,Rinse)

b)a)

0%

10%

20%

30%

40%

0% 5% 10%

Design Goal LOWP

10m3/day

No Fouling

Abbas et. al. [20]

Exp. Fouling

c)

124

7.4.5 Effect of Geographic Location on Optimal System Configuration

To evaluate the impact of variable solar radiation and required net driving pressure,

optimal system designs were configured for several distinct geographic locations (Figure 7-13).

The fouling models described in Table 7-3 were used in these analyses as all communities were

reported to have similar scaling compounds. Nelhal Village in the state of Karnataka, India was

selected because the village has a high total dissolved solids (TDS) in the range of 3000 μS/cm

[148]. As well, in the sub-district where Nelhal is located, 25% of the rural population only has

access to untreated water [149]. Tarkwa Bremang Village in the Prestea-Huni Valley District,

Ghana was selected because the Birimian formation in the region has a high TDS of greater than

2000 μS/cm [150–152]. As well, in the Prestea-Huni Valley District over 30% of rural

households use drinking water from groundwater [153]. The experimental fouling model, Case

3, was used in these geographic case studies.

Figure 7-13: Several communities were selected for evaluating the optimization algorithm in

four countries (Mexico, Ghana, India and Bangladesh).

In Bangladesh, coastal regions are experiencing increased groundwater salinity during

the dry season and this problem is only expected to increase due to climate change and sea-level

125

rise [154]. About 20 million people in the coastal communities of Bangladesh are affected by

saline water sources and these communities also rely heavily on rivers, groundwater (tube wells)

and rain-fed ponds [155]. This over-reliance on saline intruded water sources is degrading

maternal health. There is a 12% increase in hypertension during the dry-season for pregnant

mothers in these coastal communities [154]. The Tala community in the Khulna district of

Bangladesh’s southwest coastal region was selected because during the dry season, on average,

the groundwater reaches a high TDS of about 2600 μS/cm [154].

The variation in system cost versus LOWP for 1 m3/day, 5 m3/day, and 10 m3/day

systems are shown in Figure 7-14. The system configuration did not change significantly for the

three geographic locations for the 1 m3/day system size (Table 7-8). For the 1 m3/day system

size, between the three locations, only the battery storage required a slightly different size. The

battery storage for all three system configurations for 1 m3/day were within ±11% of the median

battery storage (2.7 kWh).

Figure 7-14: Annualized system cost (USD) vs. variable LOWP for three communities in

India, Ghana, and Bangladesh) for variable system sizes (m3/day) a) 1 m3/day, b) 5 m3/day, c)

10 m3/day and a 10 year simulation period.

It is interesting to note that in Figure 7-14 the annualized cost for India was the most

expensive for the 1 m3/day system, but the least expensive for the 5 m3/day and 10 m3/day. This

was because there was a trade-off between the energy availability versus the energy requirements

a) b) c)

1910

1920

1930

1940

1950

1960

1970

0% 5% 10%

An

nu

aliz

ed C

ost

(USD

)

Design Goal LOWP

2500

2550

2600

2650

2700

2750

0% 5% 10%

Design Goal LOWP

3100

3200

3300

3400

3500

3600

3700

0% 5% 10%

Design Goal LOWP

India

Ghana

Bangladesh

126

for the higher driving pressure. India had the highest solar insolation and also the highest TDS

of the three locations. For the 1 m3/day, the number of solar panels could not be reduced while

meeting the water demand, as it could be only done in discrete steps. However, for the larger

systems, the total number of solar panels was higher and there was more flexibility to reduce the

number of solar panels enabling reduction of the solar array size and the corresponding cost

savings.

Table 7-8: Effect of geographic location on the optimal system configuration for a design goal

loss of water probability (LOWP) of 1%. For all the shown design configurations the optimal

operating condition was Case 3 (with anti-scalant and with rinsing) and the optimization found

the optimal system cost at the maximum membrane life of five years.

1 m3/day 5 m3/day 10 m3/day

Location India Ghana Bangladesh India Ghana Bangladesh India Ghana Bangladesh

# RO

Membranes 3 6 6 5 6

Size of RO

Membranes 2.5" x 40" 2.5" x 40" 4” x 40”

# Solar PV

Panels 2 7 8 9 12 15 14

Tank Size

(m3) 3 9.8 18.9

Battery Size

(kWh) 2.9 2.7 2.4 2.5 2.9 2.6 9.6 8.9 8.7

These results show that for widespread adoption of this technology, for the smaller

system size, it would be possible to mass produce a system configuration for a wide range of

locations. For the 5 m3/day and 10 m3/day system sizes, the number of solar panels and the

battery storage varied for the three locations. As a result, for the larger system sizes, the water

system components could be ordered in bulk for widespread implementation of the technology

in various locations. This geographic comparative analysis provides useful comparisons of the

system configurations for consideration prior to widespread adoption of the technology.

127

7.5 Conclusions

In summary, the cost-optimal system configurations for solar powered reverse osmosis

water treatment systems for several geographic locations (Mexico, Ghana, India and

Bangladesh) were compared. It was shown that for lower reliability systems, the annualized

system cost was lower. As well, it was shown that despite variations in solar insolation and water

quality between these geographic locations, a similar system configuration meets the water

demands. Indicating that for widespread adoption, large-scale manufacturing of the systems may

be possible.

The optimization results show that considering membrane fouling during the design is

essential. Not considering membrane fouling during the system design would result in an under-

sized system that would not be able to produce the daily water requirements for the community.

Intermittent operation of solar powered water treatment systems is a useful method to decrease

the energy storage requirements and reduce the system costs to an achievable range

(one USD/m3). Decreased reliability systems can reduce the annualized system costs of solar

powered water treatment systems, however, the savings gained are not significant enough to

justify low quality system performance. The optimal system configuration used tank sizes

between two to three times the daily water requirements of the system to ensure water availability

even during low solar insolation periods. The time to replace the membranes did not seem to

have a significant effect. All optimization study results showed the membrane should be replaced

at the maximum allowable 5-year life. This is likely because the fouling model reached a steady

state membrane permeability after an initial rapid decrease. In practice, community members

should be trained to observe system performance parameters (e.g. pressure fluctuations, salt

rejection) and replace the RO membranes as required.

128

Chapter 8

Summary and Conclusions

8.1 Summary

This thesis presented the experimental characterization of reverse osmosis (RO)

membrane fouling caused by intermittent operation commonly experienced by solar powered

water treatment systems. These solar powered reverse osmosis (PVRO) water treatment systems

are frequently designed with minimal battery storage to decrease the system costs. Instead of

continuous operation, these systems are often operated at a constant pressure only when there is

sufficient solar insolation. This thesis involved the design, building, commissioning and

operation of an experimental system fully equipped for autonomous control and continuous data

collection to characterize the membrane permeability throughout various operating conditions.

Simple operational conditions appropriate for remote areas, including rinsing of the membranes

prior to shut down and pre-treatment with anti-scalant were investigated and shown to help

maintain membrane permeability. The membrane permeability decline seen in the intermittently

operated experiments was modeled mathematically for inclusion in a design optimization

framework.

A novel design optimization framework for solar powered reverse osmosis systems was

developed that considers the membrane permeability decline and selects the system components

(reverse osmosis modules, pumps, solar panels, tank capacity). It was shown that for small

system sizes 1 m3/day to 5 m3/day, systems can be configured to minimize component variation

for mass production. Several case studies were also presented, demonstrating that location to

location solar availability had minimal effect on the cost-optimal system configuration.

129

The details of the individual investigations presented in this thesis are summarized below.

In addition, this thesis resulted in several contributions to the field, detailed in Section 8.2.

Furthermore, recommended avenues for future research are presented in Section 8.3.

8.1.1 Initial Experimental Characterization of Intermittent Operation

The initial experiments on membrane fouling for intermittent operation were performed

on an experimental setup designed to collect data continuously and to have autonomous control

for rinsing with permeate water at the end of each day. The initial experimental results showed

that intermittent operation alone did not have a significant effect on the decline of the membrane

permeability when the experimental system was operated without anti-scalant. This was the first

report in literature of the effect of intermittent operation for extended shutdown periods.

8.1.2 Improved Experimental Characterization of Intermittent Operation at the Lab-scale

The experimental system was improved prior to further experimentation by increasing

the footprint and using a new flow manifold with stainless steel tubing to allow for equal division

of the flow rates. Other experimental system improvements included improved signal processing

to maintain the recovery ratio and replacement of the flow meters with improved pressure-based

flow measurements. The experimental characterization of membrane permeability studied the

effects of intermittent operation, anti-scalant F135 addition, and permeate rinsing. The

comparison of intermittent operation and continuous operation, as well as anti-scalant usage and

membrane rinsing with permeate water showed that a simple permeate rinse prior to shut down

can minimize membrane permeability decline.

The experimental results showed that intermittent operation alone did not have a

significant negative impact on the membrane performance in the short-term (several days of

130

operation in the cross-flow unit). Anti-scalants were observed to improve the membrane

performance when used in isolation for intermittent operation. Rinsing the membranes with 8 L

of permeate water prior to shut down when anti-scalant was used had a significant improvement

on the membrane performance during intermittent operation. On the sixth day of operation, the

average normalized permeability declined only slightly to (87±9) % for intermittent operation

with anti-scalant and with rinse; while all the other operating conditions declined to nearly zero

except continuous operation with anti-scalant (30±4) %.

8.1.3 Experimental Characterization of Intermittent Operation using Groundwater

Chapter 6 presented an experimental study on the effects of intermittent operation, anti-

scalant addition and permeate rinsing had on membrane permeability when the improved

experimental system was operated with the experimental groundwater-based matrix. The

comparison of intermittent operation and continuous operation, as well as anti-scalant usage and

membrane rinsing with permeate water showed the results were consistent with the experimental

MilliQ-based matrix results from Chapter 5, the membrane permeability decline was minimized

by rinsing with permeate water prior to the extended shut down period. The membrane

performance was not significantly impacted by intermittent operation over several days of

operation in the cross-flow unit.

The pilot-scale system results compared to the improved experimental system showed

that the lab-scale system adequately represented the normalized membrane permeability decline

of a full-scale spiral wound reverse osmosis membrane module. The fouling mechanisms

discussed provide a set of potential mechanisms that occur during the extended shutdown periods

towards an improved understanding of membrane fouling under intermittent operation.

131

8.1.4 Design Optimization of Solar Powered Water Treatment Systems Considering Membrane Fouling

A new design optimization framework was developed that considers the unique features

of the community (geographic location, water demand and water salinity) to design the cost-

optimal system considering membrane fouling. The cost-optimal design is configured from an

inventory of off-the-shelf components that are commercially available for the power and water

treatment system components. The cost-optimal system configurations for solar powered reverse

osmosis treatment systems for several geographic locations (Mexico, Ghana, India and

Bangladesh) were compared. It was shown that for lower reliability systems, the annualized

system cost was lower than higher reliability systems. It was demonstrated that considering

membrane fouling was crucial for designing reliable systems. As well, it was shown that despite

variations in solar insolation and water quality between these geographic locations, a similar

system configuration could meet the water demands. Indicating that for widespread adoption,

large-scale manufacturing of the systems would be possible.

8.2 Conclusions

This thesis provides several significant conclusions and contributions towards resolving

the challenge of supplying clean drinking water to off-grid, resource-constrained communities.

This was accomplished through the experimental characterization of membrane permeability

decline in intermittently operated systems and the development of a design optimization tool that

considers this membrane fouling. The research objectives outlined in Section 1.3 were addressed

in this thesis and resulted in the following conclusions:

1. Development of a new experimental system equipped with autonomous control, pre-

treatment, rinsing and continuous data collection to characterize the effect of

intermittent operation on membrane fouling. Prior to this thesis, it was widely

132

acknowledged in the literature, without experimental validation, that intermittent

operation with a daily extended shut down period, common of solar powered reverse

osmosis systems, increased membrane fouling. To address the lack of evidence for

increased membrane fouling caused by intermittent operation, this thesis contributed

the first-in-literature experimental characterization of membrane permeability

decline observed during intermittent operation compared to continuous operation.

The experimental system was designed, built, commissioned and operated as a part

of this thesis. The preliminary experimental results showed that there was minimal

difference in the membrane permeability decline of continuously operated systems

and intermittently operated systems when no anti-scalant was used.

2. Membrane fouling caused by intermittent operation can be minimized by using anti-

scalant pre-treatment and rinsing with permeate water prior to shut down for

experimental lab-scale systems operated with the experimental MilliQ-based matrix.

The experimental characterization of membrane fouling from intermittent operation

was performed on the improved experimental system for longer duration experiments

(up to six days of operation). The improved experimental system was also operated

under more realistic conditions of a real operating desalination system, consistent

operating pressure (20.7 bar) and consistent recovery ratio (75%). This was the first-

report in literature of the detailed experimental characterization of the effects of anti-

scalant and rinsing of the membranes prior to shut down for intermittent operation

compared to continuous operation. These experimental results highlighted the

importance of using anti-scalant pre-treatment for these solar powered reverse

osmosis systems since they are typically operated at high recovery ratios to minimize

the brine which needs to be discharged to the environment. As well, the results

133

demonstrated the efficacy of using a permeate water rinse prior to shut down to

maintain high membrane permeability. An analytical model of the membrane

permeability decline was derived for use in the design optimization framework to

ensure the systems could adequately consider the membrane permeability.

3. Membrane fouling caused by intermittent operation can be minimized by using anti-

scalant pre-treatment and rinsing with permeate water prior to shut down for the

experimental lab-scale and pilot-scale systems operated with the experimental

groundwater-based matrix composed of a local groundwater augmented with lab-

grade chemicals. The results showed that intermittent operation did not have a

significant negative impact on the membrane permeability in the short-term (seven

days of operation in the cross-flow unit) when using the experimental groundwater-

based matrix with organic content. The membrane permeability decline was the least

when the system was operated intermittently with anti-scalant and a daily permeate

water rinse prior to the extended shutdown period. The pilot-scale experimental

system results were consistent with the improved experimental lab-scale system

results. Therefore, the lab-scale system adequately represented the normalized

membrane permeability decline of a full-scale spiral wound reverse osmosis

membrane module.

4. A novel design optimization framework considering membrane fouling was

developed to address the need for a computer-based design tool for configuring solar

powered reverse osmosis systems for resource-constrained communities. The design

optimization considers membrane permeability decline common of intermittently

operated solar reverse osmosis systems and consisted of a simulation model coupled

with a genetic algorithm. It was shown that higher reliability systems have a higher

134

water cost. The case studies for Mexico, Ghana, India and Bangladesh showed that

despite variations in solar insolation and water salinity, a similar system

configuration could meet the community’s water demands. This indicates for

widespread adoption of these systems, large-scale manufacturing would be possible.

The optimization demonstrated that considering membrane fouling during the design

is essential. Without considering membrane fouling in the system design, the system

would be under-sized system and unable to produce the daily drinking water

requirements for the community. It was concluded that intermittent operation of solar

powered water treatment systems effectively decreases the energy storage

requirements and reduces the system cost to an achievable range (one USD/m3) for

resource-constrained communities.

8.3 Recommendations for Future Work

The experimental investigations presented in this thesis can be extended to further

understand the mechanisms of fouling seen by PVRO systems under intermittent operation. This

could involve studying the behavior of membrane fouling for a wider range of water sources to

see the impact of different scaling compounds and organic foulant concentrations. A database of

fouling models for this wide range of water sources could be developed to create a set of models

for use in the design optimization framework. As well, the effect of the recovery ratio could also

be studied. There could be interesting trade-offs between membrane fouling and brine volume.

Furthermore, detailed experimental studies on the various steps during intermittent operation

could be studied to visually quantify the rate of scale growth, biological growth, scale dissolution

and foulant removal. These studies could inform the development of continuous on-line

monitoring for the early identification of membrane fouling and autonomous implementation of

remedial actions during operation.

135

The most immediate extension of this thesis would be to use the design optimization tool

to configure a real system for a new community. This would involve working with project

partners PVPure to find community partners and funding organizations to deploy the custom-

configured water treatment system. Lab-scale analyses could be conducted on the community’s

water using the experimental system and the results could be inputted into the design

optimization framework and subsequently built in the community.

As well, the design optimization framework could be expanded to include multiple

sources of renewable energy for example, wind, tidal or hydropower resources to expand the

application of the water treatment systems to communities with low solar insolation. For

example, Canada’s Northern communities are facing drinking water crises with the end-of-life

of water infrastructure. Adapting the design optimization tool for a broader range of power

sources and a broader range of water treatment technologies could help address the growing need

for small-scale water treatment in resource-constrained communities.

Future work could entail taking this optimization algorithm and adding uncertainty into

the design algorithm for the design of water treatment systems that are robust to increases in

community water demands, annual fluctuations in local groundwater quality, and resilient to

extreme weather events. Further studies are required to identify the dominating fouling

mechanisms for a wide range of water qualities to elucidate methods to effectively minimize

membrane fouling. For example, membrane fouling could be reduced by investigating multiple

forms of pre-treatment, and potentially coupling multiple stages of water treatment technologies

(e.g. Ultrafiltration and RO, Microfiltration and RO).

136

8.4 List of Published Papers from this Thesis

This thesis resulted in one journal article in-preparation and three peer-reviewed journal articles:

Freire-Gormaly, M., Bilton, A., (2017) An Experimental System for Characterization of

Membrane Fouling of Solar Photovoltaic Reverse Osmosis Systems under Intermittent

Operation, Desalination and Water Treatment, Volume 73, pp.54-63.

Freire-Gormaly, M., Bilton, A., (2018) Experimental Quantification of the Effect of

Intermittent Operation on Membrane Performance of Solar Powered Reverse Osmosis

Desalination Systems, Desalination, Volume 435, pp.188-197.

Freire-Gormaly, M., Bilton, A., (In-Preparation) Experimental Lab-scale and Pilot-scale

Characterization of the Effect of Intermittent Operation on Membrane Fouling for Solar

Powered Reverse Osmosis Desalination Systems, Desalination.

Freire-Gormaly, M., Bilton, A., (Under review, 2018) Design of Solar Powered Reverse

Osmosis Desalination Systems Considering Membrane Fouling Caused by Intermittent

Operation, Desalination, DES_2018_301.

8.5 List of Conference Proceedings from this Thesis

The work in this thesis resulted in several conference papers, oral presentations and posters:

Freire-Gormaly, M., Bilton, A., (2017) Optimization of Solar Powered Reverse Osmosis

Water Treatment Systems, CSCE 15th International Conference on Environmental

Engineering, May 31-June 3, Vancouver, BC. (Oral Presentation and Paper)

Freire-Gormaly, M., Bilton, A., (2016) Degradation of Photovoltaic Reverse Osmosis

Systems under Intermittent Operation, EDS Desalination for the Environment: Clean

Water and Energy, May 22-26, Rome, Italy. (Oral Presentation and Paper)

Freire-Gormaly, M., Bilton, A., (2015) Multi-Objective Optimization of Renewable

Power Systems for Remote Communities, ASME 2015 International Design Engineering

Technology Conf., August 2-5, Boston, MA. (Oral Presentation and Paper)

Freire-Gormaly, M., Bilton, A., (2015) Multi-Objective Design of PV-Wind-Battery

Power Systems for Remote Communities, 6th Annual Mechanical and Industrial

Engineering Research Symposium, June 4, University of Toronto, Toronto, ON. (Oral

Presentation)

Freire-Gormaly, M., Bilton, A., (2017) Optimization of Solar Powered Reverse Osmosis

Systems Design Considering Membrane Fouling, 8th Ann. Mech. & Ind. Eng. Research

Symposium, June 9, Toronto, ON. (Poster Presentation)

137

Freire-Gormaly, M., Bilton, A., (2016) Development of Experimental System for

Characterization of Membrane Degradation in Photovoltaic Reverse Osmosis Systems,

7th Ann. Mech. & Ind. Eng. Research Symposium, June 9, Toronto, ON. Awarded Best

Poster Prize. (Poster Presentation)

Freire-Gormaly, M., Bilton, A., (2016) Experimental Characterization of Degradation in

Photovoltaic Reverse Osmosis Systems for Remote Communities, University of

Toronto’s Inst. of Sustainable Energy Symposium, March 22, Toronto, ON. Awarded

Best Poster Prize. (Poster Presentation)

Freire-Gormaly, M., Mahmoud, A., Bilton, A., (2015) Water and Energy Systems for

Remote Communities, University of Toronto CEIE Building Ground Breaking Research,

June 24, Toronto, ON. (Poster Presentation)

Freire-Gormaly, M., Bilton, A., (2014) Optimization of a Renewable Power System for

a Remote Off-Grid Community in Marsabit, Kenya, 5th Ann. MIE Research Symposium,

June 2, Toronto, ON. (Poster Presentation)

138

References

[1] World Health Organization (WHO) and Unicef Joint Monitoring Program (JMP), Progress

on Sanitation and Drinking Water: 2014 Update, Geneva, Switzerland, 2014. doi:ISBN

9789 24 150724 0.

[2] G. Legros, I. Havet, N. Bruce, S. Bonjour, The energy access situation in developing

countries, New York, 2009. http://www.undp.org/content/dam/undp/library/Environment

and Energy/Sustainable Energy/energy-access-situation-in-developing-countries.pdf.

[3] H. Morais, P. Kádár, P. Faria, Z.A. Vale, H.M. Khodr, Optimal scheduling of a renewable

micro-grid in an isolated load area using mixed-integer linear programming, Renew.

Energy. 35 (2010) 151–156. doi:10.1016/j.renene.2009.02.031.

[4] A.A. Setiawan, Y. Zhao, C. V. Nayar, Design, economic analysis and environmental

considerations of mini-grid hybrid power system with reverse osmosis desalination plant

for remote areas, Renew. Energy. 34 (2009) 374–383. doi:10.1016/j.renene.2008.05.014.

[5] B. Peñate, L. García-Rodríguez, Current trends and future prospects in the design of

seawater reverse osmosis desalination technology, Desalination. 284 (2012) 1–8.

doi:10.1016/j.desal.2011.09.010.

[6] K. Khanafer, K. Vafai, Applications of Nanomaterials in Solar Energy and Desalination

Sectors, in: Adv. Heat Transf., 1st ed., Elsevier Inc., 2013: pp. 303–329.

doi:10.1016/B978-0-12-407819-2.00005-0.

[7] L. Henthorne, B. Boysen, State-of-the-art of reverse osmosis desalination pretreatment,

Desalination. 356 (2015) 129–139. doi:10.1016/j.desal.2014.10.039.

139

[8] J.L. Lienhard, M.A. Antar, A. Bilton, A. Blanco, G. Zaragoza, Solar Desalination, Annu.

Rev. Heat Transf. 15 (2012) 277–347.

[9] F. Vince, F. Marechal, E. Aoustin, P. Bréant, Multi-objective optimization of RO

desalination plants, Desalination. 222 (2008) 96–118. doi:10.1016/j.desal.2007.02.064.

[10] M.M. El-Halwagi, Synthesis of reverse-osmosis networks for waste reduction, AIChE J.

38 (1992) 1185–1198. doi:10.1002/aic.690380806.

[11] A. Bilton, A modular design architecture for application to community-scale photovoltaic-

powered reverse osmosis systems, PhD, Massachusetts Institute of Technology, 2013.

http://dspace.mit.edu/bitstream/handle/1721.1/79337/845073888.pdf?sequence=1.

[12] I. de la Nuez Pestana, F.J.G. Latorre, C.A. Espinoza, A.G. Gotor, Optimization of RO

desalination systems powered by renewable energies. Part I: Wind energy, Desalination.

160 (2004) 293–299. doi:10.1016/S0011-9164(04)90031-8.

[13] A. Bilton, L. Kelley, F. Mazzini, Design Optimization of Sustainable Off-Grid Power

Systems for the Developing World, in: ASME 2011 5th Int. Conf. Energy Sustain., 2011:

pp. 1531–1540. doi:10.1115/ES2011-54815.

[14] P. Poovanaesvaran, M.A. Alghoul, K. Sopian, N. Amin, M.I. Fadhel, M. Yahya, Design

aspects of small-scale photovoltaic brackish water reverse osmosis (PV-BWRO) system,

Desalin. Water Treat. 27 (2011) 210–223. doi:10.5004/dwt.2011.1824.

[15] L.F. Greenlee, D.F. Lawler, B.D. Freeman, B. Marrot, P. Moulin, P. Ce, Reverse osmosis

desalination: Water sources, technology, and today’s challenges, Water Res. 43 (2009)

2317–2348. doi:10.1016/j.watres.2009.03.010.

140

[16] B. Peñate, V.J. Subiela, F. Vega, F. Castellano, F.J. Domínguez, V. Millán, Uninterrupted

eight-year operation of the autonomous solar photovoltaic reverse osmosis system in Ksar

Ghilène (Tunisia), Desalin. Water Treat. (2014) 1–8. doi:10.1080/19443994.2014.940643.

[17] B.G. Keefer, R.D. Hembree, F.C. Schrack, Optimized matching of solar photovoltaic

power with reverse osmosis desalination, Desalination. 54 (1985) 89–103.

doi:10.1016/0011-9164(85)80008-4.

[18] L. Kelley, H. Elasaad, S. Dubowsky, Autonomous operation and maintenance of small-

scale PVRO systems for remote communities, Desalin. Water Treat. (2014) 1–13.

doi:10.1080/19443994.2014.940650.

[19] A. Al-Karaghouli, D. Renne, L.L. Kazmerski, Technical and economic assessment of

photovoltaic-driven desalination systems, Renew. Energy. 35 (2010) 323–328.

doi:10.1016/j.renene.2009.05.018.

[20] S. Dallas, N. Sumiyoshi, J. Kirk, K. Mathew, N. Wilmot, Efficiency analysis of the

Solarflow - An innovative solar-powered desalination unit for treating brackish water,

Renew. Energy. 34 (2009) 397–400. doi:10.1016/j.renene.2008.05.016.

[21] A.I. Schafer, C. Remy, B.S. Richards, Performance of a small solar-powered hybrid

membrane system for remote communities under varying feedwater salinities, Water Sci.

Technol. Water Supply. 4 (2004) 233–243.

[22] B. Durham, A. Walton, Membrane pretreatment of reverse osmosis: Long-term experience

on difficult waters, Desalination. 122 (1999) 157–170. doi:10.1016/S0011-

9164(99)00037-5.

141

[23] S.P. Chesters, Innovations in the inhibition and cleaning of reverse osmosis membrane

scaling and fouling, Desalination. 238 (2009) 22–29. doi:10.1016/j.desal.2008.01.031.

[24] NREL, National Solar Radiation Data Base (NSRDB), (2017). http://maps.nrel.gov/nsrdb-

viewer/.

[25] K. Bourouni, T. Ben M’Barek, a. Al Taee, Design and optimization of desalination

reverse osmosis plants driven by renewable energies using genetic algorithms, Renew.

Energy. 36 (2011) 936–950. doi:10.1016/j.renene.2010.08.039.

[26] S. Lee, S. Myung, J. Hong, D. Har, Reverse osmosis desalination process optimized for

maximum permeate production with renewable energy, Desalination. 398 (2016) 133–

143. doi:10.1016/j.desal.2016.07.018.

[27] D.G. Harrison, G.E. Ho, K. Mathew, Desalination using renewable energy in Australia,

Renew. Energy. 8 (1996) 509–513. doi:10.1016/0960-1481(96)88909-9.

[28] A. Serna, F. Tadeo, D. Torrijos, Rule-Based Control of Off-Grid Desalination Powered by

Renewable Energies, J. Renew. Energy Sustain. Dev. (2015) 205–213. http://apc.aast.edu.

[29] N. Ghaffour, J. Bundschuh, H. Mahmoudi, M.F. a. Goosen, Renewable energy-driven

desalination technologies: A comprehensive review on challenges and potential

applications of integrated systems, Desalination. 356 (2015) 94–114.

doi:10.1016/j.desal.2014.10.024.

[30] F. Calise, A. Cipollina, M. Dentice d’Accadia, A. Piacentino, A novel renewable

polygeneration system for a small Mediterranean volcanic island for the combined

production of energy and water: Dynamic simulation and economic assessment, Appl.

142

Energy. 135 (2014) 675–693. doi:10.1016/j.apenergy.2014.03.064.

[31] F.J. García Latorre, S.O. Pérez Báez, A. Gómez Gotor, Energy performance of a reverse

osmosis desalination plant operating with variable pressure and flow, Desalination. 366

(2015) 146–153. doi:10.1016/j.desal.2015.02.039.

[32] H. Sharon, K.S. Reddy, A review of solar energy driven desalination technologies,

Renew. Sustain. Energy Rev. 41 (2015) 1080–1118. doi:10.1016/j.rser.2014.09.002.

[33] H. Elasaad, A. Bilton, L. Kelley, O. Duayhe, S. Dubowsky, Field evaluation of a

community scale solar powered water puri fi cation technology: A case study of a remote

Mexican community application, Desalination. 375 (2015) 71–80.

doi:10.1016/j.desal.2015.08.001.

[34] A. Bilton, S. Dubowsky, Modular Design of Community-Scale Photovoltaic Reverse

Osmosis Systems Under Uncertainty, in: ASME 2014 Int. Des. Eng. Tech. Conf. Comput.

Inf. Eng. Conf., ASME, Buffalo, New York, 2014: p. 10.

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2090522.

[35] M. Thomson, D. Infield, Laboratory demonstration of a photovoltaic-powered seawater

reverse-osmosis system without batteries, Desalination. 183 (2005) 105–111.

doi:10.1016/j.desal.2005.03.031.

[36] M. Thomson, D. Infield, A photovoltaic-powered seawater reverse-osmosis without

batteries, Desalination. 153 (2002) 1–8.

http://www.sciencedirect.com/science/article/pii/S0011916403800048.

[37] G. Xia, Q. Sun, X. Cao, J. Wang, Y. Yu, L. Wang, Thermodynamic analysis and

143

optimization of a solar-powered transcritical CO2 (carbon dioxide) power cycle for

reverse osmosis desalination based on the recovery of cryogenic energy of LNG (liquefied

natural gas), Energy. 66 (2014) 643–653. doi:10.1016/j.energy.2013.12.029.

[38] E. Koutroulis, D. Kolokotsa, A. Potirakis, K. Kalaitzakis, Methodology for optimal sizing

of stand-alone photovoltaic/wind-generator systems using genetic algorithms, Sol. Energy.

80 (2006) 1072–1088. doi:10.1016/j.solener.2005.11.002.

[39] F. Majali, H. Ettouney, N. Abdel-Jabbar, H. Qiblawey, Design and operating

characteristics of pilot scale reverse osmosis plants, Desalination. 222 (2008) 441–450.

doi:10.1016/j.desal.2007.01.169.

[40] M.D. Afonso, J.O. Jaber, M.S. Mohsen, Brackish groundwater treatment by reverse

osmosis in Jordan, Desalination. 164 (2004) 157–171. doi:10.1016/S0011-

9164(04)00175-4.

[41] H.E.S. Fath, F.M. El-Shall, G. Vogt, U. Seibert, A stand alone complex for the production

of water, food, electrical power and salts for the sustainable development of small

communities in remote areas, Desalination. 183 (2005) 13–22.

doi:10.1016/j.desal.2005.03.028.

[42] D.E. Moudjeber, H. Mahmoudi, M. Djennad, D.C. Sioutopoulos, S.T. Mitrouli, A.J.

Karabelas, Brackish water desalination in the Algerian Sahara—Plant design

considerations for optimal resource exploitation, Desalin. Water Treat. 52 (2014) 4040–

4052. doi:10.1080/19443994.2013.875947.

[43] A.M. Bilton, S. Dubowsky, A Computer Architecture for the Automatic Design of

144

Modular Systems With Application to Photovoltaic Reverse Osmosis, J. Mech. Des. 136

(2014) 101401. doi:10.1115/1.4027879.

[44] A.M. Gilau, M.J. Small, Designing cost-effective seawater reverse osmosis system under

optimal energy options, Renew. Energy. 33 (2008) 617–630.

doi:10.1016/j.renene.2007.03.019.

[45] Y.Y. Lu, Y.D. Hu, D.M. Xu, L.Y. Wu, Optimum design of reverse osmosis seawater

desalination system considering membrane cleaning and replacing, J. Memb. Sci. 282

(2006) 7–13. doi:10.1016/j.memsci.2006.04.019.

[46] K.M. Sassi, I.M. Mujtaba, Effective design of reverse osmosis based desalination process

considering wide range of salinity and seawater temperature, Desalination. 306 (2012) 8–

16. doi:10.1016/j.desal.2012.08.007.

[47] W. He, Y. Wang, M.H. Shaheed, Stand-alone seawater RO (reverse osmosis) desalination

powered by PV (photovoltaic) and PRO (pressure retarded osmosis), Energy. 86 (2015)

423–435. doi:10.1016/j.energy.2015.04.046.

[48] M. Elshafei, A.K. Sheikh, N. Ahmad, Directly Driven RO System by PV Solar Panel

Arrays, Open J. Appl. Sci. 3 (2013) 35–40. doi:10.4236/ojapps.2013.32B007.

[49] C. Tzotzi, T. Pahiadaki, S.G. Yiantsios, a. J. Karabelas, N. Andritsos, A study of CaCO3

scale formation and inhibition in RO and NF membrane processes, J. Memb. Sci. 296

(2007) 171–184. doi:10.1016/j.memsci.2007.03.031.

[50] A. Cipollina, E. Tzen, V. Subiela, M. Papapetrou, J. Koschikowski, R. Schwantes,

Renewable energy desalination: performance analysis and operating data of existing RES

145

desalination plants, Desalin. Water Treat. 55 (2015) 3126–3146.

doi:10.1080/19443994.2014.959734.

[51] C. Fritzmann, J. Löwenberg, T. Wintgens, T. Melin, State-of-the-art of reverse osmosis

desalination, Desalination. 216 (2007) 1–76.

[52] S.R. Suwarno, X. Chen, T.H. Chong, V.L. Puspitasari, D. McDougald, Y. Cohen, S.A.

Rice, A.G. Fane, The impact of flux and spacers on biofilm development on reverse

osmosis membranes, J. Memb. Sci. 405–406 (2012) 219–232.

doi:10.1016/j.memsci.2012.03.012.

[53] E. El-Zanati, S. Eissa, Development of a locally designed and manufactured small-scale

reverse osmosis desalination system, Desalination. 165 (2004) 133–139.

doi:10.1016/j.desal.2004.06.015.

[54] K.M. Sassi, I.M. Mujtaba, Optimal operation of RO system with daily variation of

freshwater demand and seawater temperature, Comput. Chem. Eng. 59 (2013) 101–110.

doi:10.1016/j.compchemeng.2013.03.020.

[55] M.G. Marcovecchio, P.A. Aguirre, N.J. Scenna, Global optimal design of reverse osmosis

networks for seawater desalination: Modeling and algorithm, Desalination. 184 (2005)

259–271. doi:10.1016/j.desal.2005.03.056.

[56] A. Alkhatib, Reverse-Osmosis Desalination of Water Powered by Photo-Voltaic Modules,

Comput. Water, Energy, Environ. Eng. 3 (2014) 22–29. doi:10.4236/cweee.2014.31003.

[57] A.G. Pervov, Scale formation prognosis and cleaning procedure schedules in reverse

osmosis systems operation, Desalination. 83 (1991) 77–118. doi:10.1016/0011-

146

9164(91)85087-B.

[58] E. Lyster, M.M. Kim, J. Au, Y. Cohen, A method for evaluating antiscalant retardation of

crystal nucleation and growth on RO membranes, J. Memb. Sci. 364 (2010) 122–131.

doi:10.1016/j.memsci.2010.08.020.

[59] S. Sobana, R.C. Panda, Modeling and control of reverse osmosis desalination process

using centralized and decentralized techniques, Desalination. 344 (2014) 243–251.

doi:10.1016/j.desal.2014.03.014.

[60] G. Greenberg, D. Hasson, R. Semiat, Limits of RO recovery imposed by calcium

phosphate precipitation, Desalination. 183 (2005) 273–288.

doi:10.1016/j.desal.2005.04.026.

[61] T. Nguyen, F.A. Roddick, L. Fan, Biofouling of water treatment membranes: a review of

the underlying causes, monitoring techniques and control measures., Membranes (Basel).

2 (2012) 804–40. doi:10.3390/membranes2040804.

[62] A.A. Alawadhi, Pretreatment plant design — Key to a successful reverse osmosis

desalination plant, Desalination. 110 (1997) 1–10. doi:10.1016/S0011-9164(97)00079-9.

[63] Z. Hu, A. Antony, G. Leslie, P. Le-Clech, Real-time monitoring of scale formation in

reverse osmosis using electrical impedance spectroscopy, J. Memb. Sci. 453 (2014) 320–

327. doi:10.1016/j.memsci.2013.11.014.

[64] A.I. Radu, J.S. Vrouwenvelder, M.C.M. van Loosdrecht, C. Picioreanu, Modeling the

effect of biofilm formation on reverse osmosis performance: Flux, feed channel pressure

drop and solute passage, J. Memb. Sci. 365 (2010) 1–15.

147

doi:10.1016/j.memsci.2010.07.036.

[65] R.A. Al-Juboori, T. Yusaf, Biofouling in RO system: Mechanisms, monitoring and

controlling, Desalination. 302 (2012) 1–23. doi:10.1016/j.desal.2012.06.016.

[66] K.P. Lee, T.C. Arnot, D. Mattia, A review of reverse osmosis membrane materials for

desalination—Development to date and future potential, J. Memb. Sci. 370 (2011) 1–22.

doi:10.1016/j.memsci.2010.12.036.

[67] M. Herzberg, M. Elimelech, Biofouling of reverse osmosis membranes: Role of biofilm-

enhanced osmotic pressure, J. Memb. Sci. 295 (2007) 11–20.

doi:10.1016/j.memsci.2007.02.024.

[68] P. Bacchin, P. Aimar, R.W. Field, Critical and sustainable fluxes: Theory, experiments

and applications, J. Memb. Sci. 281 (2006) 42–69. doi:10.1016/j.memsci.2006.04.014.

[69] F. a. Abd El Aleem, K. a. Al-Sugair, M.I. Alahmad, Biofouling problems in membrane

processes for water desalination and reuse in Saudi Arabia, Int. Biodeterior.

Biodegradation. 41 (1998) 19–23. doi:10.1016/S0964-8305(98)80004-8.

[70] A. Matin, Z. Khan, S.M.J. Zaidi, M.C. Boyce, Biofouling in reverse osmosis membranes

for seawater desalination: Phenomena and prevention, Desalination. 281 (2011) 1–16.

doi:10.1016/j.desal.2011.06.063.

[71] V. Kochkodan, N. Hilal, A comprehensive review on surface modified polymer

membranes for biofouling mitigation, Desalination. 356 (2015) 187–207.

doi:10.1016/j.desal.2014.09.015.

148

[72] A.I. Radu, J.S. Vrouwenvelder, M.C.M. van Loosdrecht, C. Picioreanu, Effect of flow

velocity, substrate concentration and hydraulic cleaning on biofouling of reverse osmosis

feed channels, Chem. Eng. J. 188 (2012) 30–39. doi:10.1016/j.cej.2012.01.133.

[73] O. Gibert, B. Lefèvre, M. Fernández, X. Bernat, M. Paraira, M. Calderer, X. Martínez-

Lladó, Characterising biofilm development on granular activated carbon used for drinking

water production., Water Res. 47 (2013) 1101–10. doi:10.1016/j.watres.2012.11.026.

[74] J.S. Vrouwenvelder, C. Picioreanu, J.C. Kruithof, M.C.M. van Loosdrecht, Biofouling in

spiral wound membrane systems: Three-dimensional CFD model based evaluation of

experimental data, J. Memb. Sci. 346 (2010) 71–85. doi:10.1016/j.memsci.2009.09.025.

[75] S.H. Joo, B. Tansel, Novel technologies for reverse osmosis concentrate treatment: A

review, J. Environ. Manage. 150 (2015) 322–335. doi:10.1016/j.jenvman.2014.10.027.

[76] T. Chen, A. Neville, M. Yuan, Calcium carbonate scale formation - Assessing the initial

stages of precipitation and deposition, J. Pet. Sci. Eng. 46 (2005) 185–194.

doi:10.1016/j.petrol.2004.12.004.

[77] L.F. Greenlee, F. Testa, D.F. Lawler, B.D. Freeman, P. Moulin, The effect of antiscalant

addition on calcium carbonate precipitation for a simplified synthetic brackish water

reverse osmosis concentrate, Water Res. 44 (2010) 2957–2969.

doi:10.1016/j.watres.2010.02.024.

[78] Z. Amjad, Applications of antiscalants to control calcium sulfate scaling in reverse

osmosis systems, Desalination. 54 (1985) 263–276. doi:10.1016/0011-9164(85)80022-9.

[79] E. Lyster, J. Au, R. Rallo, F. Giralt, Y. Cohen, Coupled 3-D hydrodynamics and mass

149

transfer analysis of mineral scaling-induced flux decline in a laboratory plate-and-frame

reverse osmosis membrane module, J. Memb. Sci. 339 (2009) 39–48.

doi:10.1016/j.memsci.2009.04.024.

[80] S. Salvador Cob, C. Beaupin, B. Hofs, M.M. Nederlof, D.J.H. Harmsen, E.R. Cornelissen,

a. Zwijnenburg, F.E. Genceli Güner, G.J. Witkamp, Silica and silicate precipitation as

limiting factors in high-recovery reverse osmosis operations, J. Memb. Sci. 423–424

(2012) 1–10. doi:10.1016/j.memsci.2012.07.016.

[81] G. Braun, W. Hater, C. Zum Kolk, C. Dupoiron, T. Harrer, T. Götz, Investigations of

silica scaling on reverse osmosis membranes, Desalination. 250 (2010) 982–984.

doi:10.1016/j.desal.2009.09.086.

[82] M. Badruzzaman, A. Subramani, J. DeCarolis, W. Pearce, J.G. Jacangelo, Impacts of

silica on the sustainable productivity of reverse osmosis membranes treating low-salinity

brackish groundwater, Desalination. 279 (2011) 210–218.

doi:10.1016/j.desal.2011.06.013.

[83] S.P. Chesters, M.W. Armstrong, M. Fazel, R. Wilson, D.A. Golding, RO Membrane

Cleaning, Past, Present, Future – Innovations for Improving Ro Plant Operating

Efficiency, Int. Desalin. Assoc. World Congr. Desalin. Water Reuse. (2013).

[84] N. Prihasto, Q.F. Liu, S.H. Kim, Pre-treatment strategies for seawater desalination by

reverse osmosis system, Desalination. 249 (2009) 308–316.

doi:10.1016/j.desal.2008.09.010.

[85] E.E.A. Ghafour, Enhancing RO system performance utilizing antiscalants, Desalination.

150

153 (2003) 149–153. doi:10.1016/S0011-9164(02)01117-7.

[86] C. Gabelich, T. Yun, J. Green, I. Suffet, W. Chen, Evaluation of precipitative fouling for

Colorado River Water desalination using reverse osmosis, Los Angeles, California, 2002.

http://scholar.google.com/scholar?hl=en&btnG=Search&q=intitle:EVALUATION+OF+P

RECIPITATIVE+FOULING+FOR+COLORADO+RIVER+WATER+DESALINATION

#0.

[87] J.S. Vrouwenvelder, J.W.N.M. Kappelhof, S.G.J. Heijman, J.C. Schippers, D. van der

Kooij, Tools for fouling diagnosis of NF and RO membranes and assessment of the

fouling potential of feed water, Desalination. 157 (2003) 361–365. doi:10.1016/S0011-

9164(03)00417-X.

[88] A.C.M. Franken, Prevention and control of membrane fouling : practical implications and

examining recent innovations, 2009. http://www.ispt.eu/media/CS-01-02-Final-report-

Prevention-and-reduction-of-membrane-fouling.pdf.

[89] C. Liu, S. Caothien, J. Hayes, T. Caothuy, T. Otoyo, T. Ogawa, Membrane Chemical

Cleaning: From Art to Science, Am. Water Work. Assoc. (2001) 25.

[90] Koch Membrane Systems Inc., Anti-scalants reduce membrane cleaning, Membr.

Technol. (2005) 2–3.

[91] I. Zaslavschi, H. Shemer, D. Hasson, R. Semiat, Rotating cylinder technique for assessing

the effectiveness of anti-scalants, Water Res. 47 (2013) 3716–3722.

doi:10.1016/j.watres.2013.04.022.

[92] H. Wang, G. Liu, J. Huang, Y. Zhou, Q. Yao, S. Ma, K. Cao, Y. Liu, W. Wu, W. Sun, Z.

151

Hu, Performance of an environmentally friendly anti-scalant in CaSO4 scale inhibition,

Desalin. Water Treat. 53 (2015) 8–14. doi:10.1080/19443994.2013.837007.

[93] S.P. Chesters, F. Del Vigo, E.G. Darton, Theoretical and practical experience of calcium

phosphate inhibition in RO waters, IDA World Congr. Canar. (2007) 1–14.

[94] E.G. Darton, S. Gallego, Simple laboratory techniques improve the operation of RO pre-

treatment systems., in: IDA World Congr. Canar., 2007: pp. 1–11.

http://www.genesysro.com/Distributors_docs/5.Genesys Research

Papers07/Simple_laboratory_techniques.pdf%5Cnpapers://54d15a03-26bc-4494-9a1b-

dac933b164ea/Paper/p5866.

[95] B.K. Pramanik, Y. Gao, L. Fan, F.A. Roddick, Z. Liu, Antiscaling effect of polyaspartic

acid and its derivative for RO membranes used for saline wastewater and brackish water

desalination, Desalination. 404 (2017) 224–229. doi:10.1016/j.desal.2016.11.019.

[96] D. Lisitsin, Q. Yang, D. Hasson, R. Semiat, Inhibition of CaCO3 scaling on RO

membranes by trace amounts of zinc ions, Desalination. 183 (2005) 289–300.

doi:10.1016/j.desal.2005.10.002.

[97] A. Antony, J.H. Low, S. Gray, A.E. Childress, P. Le-Clech, G. Leslie, Scale formation and

control in high pressure membrane water treatment systems: A review, J. Memb. Sci. 383

(2011) 1–16. doi:10.1016/j.memsci.2011.08.054.

[98] Y.O. Rosenberg, I.J. Reznik, S. Zmora-Nahum, J. Ganor, The effect of pH on the

formation of a gypsum scale in the presence of a phosphonate antiscalant, Desalination.

284 (2012) 207–220. doi:10.1016/j.desal.2011.08.061.

152

[99] B. Peñate, F. Castellano, P. Ramírez, PV-RO desalination stand-alone system in the

village of Ksar Ghilène (Tunisia), in: IDA World Congr., Maspalomas, Gran Canaria -

Spain, 2007: pp. 1–12.

[100] D.J. London, Reverse Osmosis Membrane Fouling Control for an Integrated membrane

water reclamation system, MASc, University of Toronto, 2005.

http://search.library.utoronto.ca/details?5739771&uuid=1baf8de5-6b5d-4689-af8f-

3c5223fac62d.

[101] E.R. Cornelissen, J. Vrouwenvelder, S. Heijman, X. Viallefont, D. Vanderkooij, L.

Wessels, Periodic air/water cleaning for control of biofouling in spiral wound membrane

elements, J. Memb. Sci. 287 (2007) 94–101. doi:10.1016/j.memsci.2006.10.023.

[102] M.A. Saad, Early discovery of RO membrane fouling and real-time monitoring of plant

performance for optimizing cost of water, Desalination. 165 (2004) 183–191.

doi:10.1016/j.desal.2004.06.021.

[103] M.A. Saad, Silent Alarm software optimizes membrane plants, Int. Desalin. Water Reuse

Q. 13 (2003) 45–49.

[104] M. Uchymiak, A. Rahardianto, E. Lyster, J. Glater, Y. Cohen, A novel RO ex situ scale

observation detector (EXSOD) for mineral scale characterization and early detection, J.

Memb. Sci. 291 (2007) 86–95. doi:10.1016/j.memsci.2006.12.038.

[105] R.K. McGovern, G.P. Thiel, G. Prakash Narayan, S.M. Zubair, J.H. Lienhard V,

Performance limits of zero and single extraction humidification-dehumidification

desalination systems, Appl. Energy. 102 (2013) 1081–1090.

153

doi:10.1016/j.apenergy.2012.06.025.

[106] E.M. V Hoek, J. Allred, T. Knoell, B.H. Jeong, Modeling the effects of fouling on full-

scale reverse osmosis processes, J. Memb. Sci. 314 (2008) 33–49.

doi:10.1016/j.memsci.2008.01.025.

[107] A.S. Kahdim, S. Ismail, A. Abdulrazaq, Modeling of reverse osmosis systems, Water. 158

(2003) 323–329.

[108] H.-J. Oh, Y.-K. Choung, S. Lee, J.-S. Choi, T.-M. Hwang, J.H. Kim, Scale formation in

reverse osmosis desalination: model development, Desalination. 238 (2009) 333–346.

doi:10.1016/j.desal.2008.10.005.

[109] J. Thompson, N. Lin, E. Lyster, R. Arbel, T. Knoell, J. Gilron, Y. Cohen, RO membrane

mineral scaling in the presence of a biofilm, J. Memb. Sci. 415–416 (2012) 181–191.

doi:10.1016/j.memsci.2012.04.051.

[110] A. Abbas, N. Al-Bastaki, Performance decline in brackish water Film Tec spiral wound

RO membranes, Desalination. 136 (2001) 281–286. doi:10.1016/S0011-9164(01)00191-6.

[111] Y.G. Lee, Y.S. Lee, J.J. Jeon, S. Lee, D.R. Yang, I.S. Kim, J.H. Kim, Artificial neural

network model for optimizing operation of a seawater reverse osmosis desalination plant,


[112] S.S. Madaeni, M. Shiri, A.R. Kurdian, Modeling, Optimization, and Control of Reverse

Osmosis Water Treatment in Kazeroon Power Plant Using Neural Network, Chem. Eng.

Commun. 202 (2014) 6–14. doi:10.1080/00986445.2013.828606.

154

[113] A.M. Aish, H.A. Zaqoot, S.M. Abdeljawad, Artificial neural network approach for

predicting reverse osmosis desalination plants performance in the Gaza Strip,


[114] M.A. Alghoul, P. Poovanaesvaran, M.H. Mohammed, A.M. Fadhil, A.F. Muftah, M.M.

Alkilani, K. Sopian, Design and experimental performance of brackish water reverse

osmosis desalination unit powered by 2 kW photovoltaic system, Renew. Energy. 93

(2016) 101–114. doi:10.1016/j.renene.2016.02.015.

[115] A.M. Helal, S.A. Al-Malek, E.S. Al-Katheeri, Economic feasibility of alternative designs

of a PV-RO desalination unit for remote areas in the United Arab Emirates, Desalination.

221 (2008) 1–16. doi:10.1016/j.desal.2007.01.064.

[116] B.A. Qureshi, S.M. Zubair, A.K. Sheikh, A. Bhujle, S. Dubowsky, Design and

performance evaluation of reverse osmosis desalination systems: An emphasis on fouling

modeling, Appl. Therm. Eng. 60 (2013) 208–217.

doi:10.1016/j.applthermaleng.2013.06.058.

[117] A. Antony, T. Chilcott, H. Coster, G. Leslie, In situ structural and functional

characterization of reverse osmosis membranes using electrical impedance spectroscopy,

J. Memb. Sci. 425–426 (2013) 89–97. doi:10.1016/j.memsci.2012.09.028.

[118] K. Ishida, R. Bold, D. Phipps, Identification and evaluation of unique chemicals for

optimum membrane compatibility and improved cleaning eficiency, 2005.

[119] A.H. Taheri, L.N. Sim, T.H. Chong, W.B. Krantz, A.G. Fane, Prediction of reverse

osmosis fouling using the feed fouling monitor and salt tracer response technique, J.

155

Memb. Sci. 475 (2015) 433–444. doi:10.1016/j.memsci.2014.10.043.

[120] L. Seminario-vidal, E.R. Lazarowski, S.F. Okada, Assessment of Extracellular ATP

Concentrations, in: P.B. Rich, C. Douillet (Eds.), Biolumin. Methods Mol. Biol., 2009: pp.

25–36. doi:10.1007/978-1-60327-321-3.

[121] A. Sweity, T. Rezene, I. David, S. Bason, Y. Oren, Z. Ronen, M. Herzberg, T.R. Zere, I.

David, S. Bason, Y. Oren, Z. Ronen, M. Herzberg, Side effects of antiscalants on

biofouling of reverse osmosis membranes in brackish water desalination, J. Memb. Sci.

481 (2015) 172–187. doi:10.1016/j.memsci.2015.02.003.

[122] S.M. Hunt, E.M. Werner, B. Huang, M.A. Hamilton, P.S. Stewart, Hypothesis for the

Role of Nutrient Starvation in Bio lm Detachment, Appl. Environ. Microbiol. 70 (2004)

7418–7425. doi:10.1128/AEM.70.12.7418.

[123] . BWA Water Additives UK, Product Information Flocon 885 - Biodegradable and

Phosophorous Free Antiscalant for Reverse Osmosis, (2014) 2.

http://www.wateradditives.com/images/Updated_WF/Flocon_885_GP_WF.pdf (accessed

April 14, 2015).

[124] A.M. Bilton, L.C. Kelley, S. Dubowsky, Photovoltaic Reverse Osmosis – Feasibility and a

Pathway to Develop Technology, Desalin. Water Treat. 31 (2011) 24–36.

[125] P. Belotti, C. Kirches, S. Leyffer, J. Linderoth, J. Luedtke, A. Mahajan, Mixed-integer

nonlinear optimization, Acta Numer. 22 (2013) 1–131. doi:10.1017/S0962492913000032.

[126] D.E. Goldberg, Genetic Algorithms in Search, Optimization and Machine Learning, 1st

ed., Addison-Wesley Longman Publishing Co., Inc., Boston, MA, USA, 1989.

156

https://dl.acm.org/citation.cfm?id=534133.

[127] B.S. Richards, D.P.S. Capão, W.G. Früh, A.I. Schäfer, Renewable energy powered

membrane technology: Impact of solar irradiance fluctuations on performance of a

brackish water reverse osmosis system, Sep. Purif. Technol. 156 (2015) 379–390.

doi:10.1016/j.seppur.2015.10.025.

[128] V.J. Subiela, B. Penate, Autonomous Desalination and Cooperation. The Experience in

Morocco Within the ADIRA Project, in: Water Secur. Mediterr. Reg., 2011: pp. 319–337.

doi:10.1007/978-94-007-1623-0.

[129] A. Habte, M. Sengupta, A. Lopez, Evaluation of the National Solar Radiation Database

(NSRDB): 1998-2015, NREL (National Renew. Energy Lab. (2017) 1998–2015.

http://www.nrel.gov/docs/fy17osti/67722.pdf.

[130] P. Yang, A. Nehorai, Joint Optimization of Hybrid Energy Storage and Generation

Capacity with Renewable Energy, IEEE Trans. Smart Grid. 5 (2014) 1566–1574.

http://arxiv.org/abs/1309.5832 (accessed October 3, 2014).

[131] M. Freire-Gormaly, A.M. Bilton, Experimental quantification of the effect of intermittent

operation on membrane performance of solar powered reverse osmosis desalination

systems, Desalination. (2017).

doi:http://www.sciencedirect.com/science/article/pii/S0011916417311104.

[132] M. Freire-Gormaly, A.M. Bilton, An experimental system for characterization of

membrane fouling of solar photovoltaic reverse osmosis systems under intermittent

operation, Desalin. Water Treat. 73 (2017) 54–63. doi:10.5004/dwt.2017.20391.

157

[133] CS, Civic Solar, (2017). https://www.civicsolar.com/product/solarworld-plus-sw-280-

mono-280w-mono-slvwht-1000v-us-solar-panel (accessed July 13, 2017).

[134] R. Fu, D. Chung, T. Lowder, D. Feldman, K. Ardani, R. Fu, D. Chung, T. Lowder, D.

Feldman, K. Ardani, U.S. Solar Photovoltaic System Cost Benchmark: Q1 2016, Golden,

CO, 2016. http://www.nrel.gov/docs/fy16osti/66532.pdf.

[135] P.T. Moseley, D.A.J. Rand, J. Garche, Lead-acid batteries for future automobiles: Status

and prospects. Status and prospects., Elsevier B.V., 2017. doi:10.1016/B978-0-444-

63700-0.00021-0.

[136] Water Anywhere, (2017). http://www.wateranywhere.com (accessed August 20, 2017).

[137] FWS, Fresh Water Systems, (2017). https://www.freshwatersystems.com/ (accessed

August 23, 2017).

[138] EA, Evoqua Advantage, (2017). https://www.evoquaadvantage.com/ (accessed August 23,

2017).

[139] A, Aquatell, (2017). https://www.aquatell.ca/products/standard-water-filter-housing-kit-

20-blue (accessed August 15, 2017).

[140] WP, Williamson Pumps, (2017). http://www.williamson-shop.co.uk/100-series-with-dc-

powered-motors-3586-p.asp (accessed July 21, 2017).

[141] Canadian Tire, (2017). http://www.canadiantire.ca/en/pdp/reliance-rectangular-aqua-pak-

water-container-0854035p.html (accessed August 31, 2017).

[142] BWA Water Additives UK, BWA Water Additives, (2017).

158

http://www.wateradditives.com/ (accessed August 12, 2017).

[143] R. Meeks, Water works: The economic impact of water infrastructure, 2012.

http://heep.hks.harvard.edu/files/heep/files/dp35_meeks.pdf.

[144] PM, Plastic Mart, (2017). http://www.plastic-mart.com/category/9/plastic-water-tanks

(accessed September 5, 2017).

[145] AltEsource, Solar Panels, (2017). http://www.altestore.com/store/Solar-Panels/c541/.

[146] SunXtenderInc, AGM Deep Cycle Solar Battery Datasheet, West Covina, CA, 2014.

https://s3.amazonaws.com/ecodirect_docs/CONCORDE/Sun_Xtender.pdf.

[147] M. Sarai Atab, A.J. Smallbone, A.P. Roskilly, An operational and economic study of a

reverse osmosis desalination system for potable water and land irrigation, Desalination.

397 (2016) 174–184. doi:10.1016/j.desal.2016.06.020.

[148] B.M. Jha, Ground water quality in shallow aquifers of India, 2010.

http://www.cgwb.gov.in/documents/Waterquality/GW_Quality_in_shallow_aquifers.pdf.

[149] C. Chandramouli, District Census Handbook of Raichur, Raichur, Karnataka, 2011.

http://www.censusindia.gov.in/2011census/dchb/2905_PART_B_DCHB_RAICHUR.pdf.

[150] S.M. Yidana, A. Yidana, An assessment of the origin and variation of groundwater

salinity in southeastern Ghana, Environ. Earth Sci. 61 (2010) 1259–1273.

doi:10.1007/s12665-010-0449-y.

[151] B.Y. Bruce, S.M. Yidana, Y. Anku, T. Akabzaa, D. Asiedu, Water quality characterization

in some birimian aquifers of the Birim Basin, Ghana, KSCE J. Civ. Eng. 13 (2009) 179–

159

187. doi:10.1007/s12205-009-0179-4.

[152] J.P. Milési, P. Ledru, P. Ankrah, V. Johan, E. Marcoux, C. Vinchon, The metallogenic

relationship between Birimian and Tarkwaian gold deposits in Ghana, Miner. Depos. 26

(1991) 228–238. doi:10.1007/BF00209263.

[153] P. Nyarko, 2010 Population and Housing Census, District Analytical Report - Prestea-

Huni Valley District, 2014.

http://www.statsghana.gov.gh/docfiles/2010_District_Report/Western/Prestea Huni-

Valley.pdf.

[154] A.E. Khan, A. Ireson, S. Kovats, S.K. Mojumder, A. Khusru, A. Rahman, P. Vineis,

Drinking water salinity and maternal health in coastal Bangladesh: Implications of climate

change, Environ. Health Perspect. 119 (2011) 1328–1332. doi:10.1289/ehp.1002804.

[155] L. Hossain, M. Kamal Hossain, Impact of Sea-Level Rise on Land Use Suitability and

Adaptation Options: Coastal Land Zoning in the Southwest, Dhaka, Bangladesh, 2006.

http://www.academia.edu/1224958/CLIMATE_CHANGE_SEA_LEVEL_RISE_AND_C

OASTAL_VULNERABILITIES_OF_BANGLADESH_WITH_ADAPTATION_OPTIO

NS.

Experimental Characterization of Membrane Fouling under ... · This research work on reverse osmosis water treatment systems is divided into two main parts: (1) the experimental characterization

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