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2012
Sequential and simultaneous application ofactivated carbon with membrane bioreactor for anenhanced removal of trace organicsLuong NguyenUniversity of Wollongong
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Recommended CitationNguyen, Luong, Sequential and simultaneous application of activated carbon with membrane bioreactor for an enhanced removal oftrace organics, Master of Engineering thesis, School of Civil, Mining and Environmental Engineering, University of Wollongong, 2012.http://ro.uow.edu.au/theses/3586
School of Civil, Mining and Environmental Engineering
Faculty of Engineering
University of Wollongong, Australia
Sequential and simultaneous application of activated carbon with
membrane bioreactor for an enhanced removal of trace organics
Luong Nguyen
A thesis submitted in partial fulfilment of the
requirements for the award of the degree of
Master of Engineering
March, 2012
i
CERTIFICATION
I, Luong Nguyen, hereby declare that this thesis, submitted in partial fulfilment of the
requirements for the award of Master of Engineering by Research Degree, to the school
of Civil, Mining and Environmental Engineering, Faculty of Engineering, University of
Wollongong is wholly my own work unless otherwise referred or acknowledged. The
document has not been submitted for qualification at any other academic institution.
Luong Nguyen
ii
ABSTRACT
The occurrence of trace organics such as pesticides, pharmaceutically active
compounds, natural and synthetic hormones as well as various industrial compounds in
the aquatic environment is of great concern due to their potential adverse effects on
human health and those of other biota. Therefore, the removal of these compounds from
wastewater is an important consideration to ensure safe drinking water and better
protect the environment. In the literature, several techniques have been explored for
trace organics removal, namely, conventional activated sludge (CAS), membrane
bioreactors (MBRs), nanofiltration/reverse osmosis membrane filtration (NF/RO) and
adsorption; however a universal end-of-pipe treatment process is yet to be established.
Evidence from the literature indicates that neither MBR nor activated carbon on its own
can adequately remove all trace organics of concern. This thesis investigates sequential
and simultaneous application of activated carbon adsorption with MBR treatment for an
enhanced removal of trace organic contaminants. A set of 22 compounds representing
four major groups of trace organics including 11 pharmaceutical and personal care
products, 2 pesticides, 4 industrial chemicals and their metabolites and 5 steroid
hormones was selected for this investigation. Various investigations were conducted
during the continuous operation of a laboratory-scale MBR system for a total of 306
days. This thesis focuses on 93 days of operation of a combined MBR with granular
activated carbon (MBR - GAC system) followed by 100 days of operation of the MBR
after direct addition of powdered activated carbon (PAC) into it.
The MBR showed stable and high performance with respect to all key basic water
quality parameters (e.g., TOC, TN and turbidity) and operating parameters (e.g., pH,
and MLVSS/MLSS ratio). It was confirmed that MBR treatment can effectively remove
hydrophobic (i.e., compounds having a distribution coefficient, Log D >3.2) and readily
biodegradable trace organic compounds. The reported data also highlighted the
limitation of MBR in removing hydrophilic and persistent compounds such as
metronidazole, ketoprofen, carbamazepine, diclofenac, and fenoprop.
GAC post-treatment was observed to complement MBR treatment to obtain initially
high overall removal of less hydrophobic and biologically persistent trace organic
iii
compounds. Through long-term observation, breakthrough of 6 hydrophilic and
biologically persistent compounds (metronidazole, carbamazepine, diclofenac,
fenoprop, naproxen, and ketoprofen) was observed. Of these trace organic
contaminants, the neutral compounds (carbamazepine and metronidazole) exhibited
slower breakthrough than the rest of these compounds which were negatively charged
(diclofenac, fenoprop, naproxen and ketoprofen). The difference between the behaviour
of the neutral and the charged compounds was predicted by the single solute isotherm
parameters. The saturation of the GAC column indicated that strict monitoring should
be applied over the lifetime of the GAC column to detect the breakthrough point of
hydrophilic and persistent compounds which have low removal by MBR treatment.
The removal of the 22 selected trace organic contaminants by MBR treatment was
enhanced after direct addition of PAC into it. The high degree removal (95%) of the
hydrophobic and readily biodegradable compounds continued to be achieved in PAC –
MBR system. An immediate increase in removal efficiency of biologically persistent
hydrophilic compounds (metronidazole, fenoprop, naproxen, ketoprofen, diclofenac,
and carbamazepine), which showed low removal by MBR- only treatment, was
observed in the PAC – MBR system. However, within approximately three weeks the
removal efficiency dropped down to the level achieved before the addition of PAC. The
removal efficiency of these compounds could be recovered by adding a second dose of
PAC, raising the PAC concentration in the MBR to 0.5 g/L. The removal of the above
mentioned six persistent compounds did not drop below 60 % even after one month
(metronidazole 73 %, fenoprop 59 %, naproxen 93 %, ketoprofen 91 %, diclofenac 71
%, and carbamazepine 87%). However, except for ketoprofen and carbamazepine, the
removal efficiency of the other four problematic compounds further diminished
gradually, indicating that withdrawal of spent PAC and replenishment of fresh PAC
would be required to achieve more stable performance.
Overall, both simultaneous application of PAC within MBR and sequential application
of GAC adsorption following MBR treatment process are potential treatment processes
to enhance removal of trace organic contaminants. Based on a simple cost-benefit
analysis from the performance stability and activated carbon usage points of view, of
iv
the two processes, simultaneous application of PAC within MBR appears to be a better
option than sequential application of GAC following MBR treatment.
Keywords: Membrane bioreactor; powdered activated carbon; granular activated carbon;
adsorption; trace organic compounds and breakthrough
v
ACKNOWLEDGEMENTS
My Masters by Research study at the University of Wollongong has been an amazing
journey full of challenges, opportunities, and excitement. Things were shaky at the
beginning and without the support from many wonderful people it could have been
harder or even impossible to complete the journey. It is time for me to express my
sincere gratitude to people from whom I have received tremendous support. I would
like to express my sincere gratitude to my supervisors Dr Faisal Hai and Associate
Professor Long Nghiem for their comments and suggestions. Associate Professor Long
Nghiem is thanked for his arrangement of a postgraduate scholarship between the
University of Wollongong and the Thanh hoa provincial government, Vietnam.
I would like to thank the Thanh hoa provincial government and the University of
Wollongong for providing me scholarship to pursue my Master degree at the University
of Wollongong.
Professor William E. Price is thanked for his insightful comments and advice on
different aspects of my study. Dr Jinguo Kang is thanked for his assistance in doing
GC-MS analysis.
I would like to extend my thanks to Abdulhakeem Ali Alturki and Karin Tessmer for
their assistance in some laboratory analyses and in the operation of the MBR. Thanks
are also due to other students in membrane research group for their friendship and
companionship during my study.
Thanks are also due to Rebecca, an undergraduate student for her assistance in some of
the laboratory work.
The Mitsubishi Rayon Engineering, Japan, Activated Carbon Technologies Pty Ltd,
Australia and Australian Nuclear Science and Technology Organisation (ANSTO) are
thanked for the provision to membrane module, GAC samples, and analysis of GAC
properties, respectively. We are indebted to Professor Kazuo Yamamoto of the
University of Tokyo, Japan for introducing us to Mitsubishi Rayon Engineering.
Dad and Mum, thanks for having me.
vi
TABLE OF CONTENTS
ABSTRACT ................................................................................................................ ii
ACKNOWLEDGEMENTS ........................................................................................ v
TABLE OF CONTENTS ........................................................................................... vi
LIST OF FIGURES .................................................................................................... x
LIST OF TABLES .................................................................................................... xv
LIST OF ABBREVIATIONS .................................................................................. xvi
LIST OF SYMBOLS ............................................................................................. xviii
CHAPTER 1: INTRODUCTION .............................................................................. 1
1.1 Background of the study ................................................................................ 1
1.1.1 Trace organics in wastewater: sources and problems ................................ 1
1.1.2 Trace organic removal by membrane bioreactors ...................................... 2
1.1.3 Adsorption of trace organic on activated carbon ....................................... 3
1.2 Statement of the problem ............................................................................... 4
1.3 Objectives of the research .............................................................................. 5
1.4 Expected outcomes ........................................................................................ 5
1.5 Thesis outline ................................................................................................ 6
CHAPTER 2: LITERATURE REVIEW ................................................................... 7
2.1 Introduction ................................................................................................... 7
2.2 Trace organic contaminants .......................................................................... 7
2.2.1 Groups of trace organic contaminants ....................................................... 7
2.2.2 Sources of trace organic contaminants .................................................... 10
2.2.3 The effects of trace organic contaminants on human health and
environment ........................................................................................................... 12
2.2.4 Fate and behaviour of trace organic contaminants .................................. 16
2.2.5 Analysis of trace organic contaminants.................................................... 16
vii
2.3 Membrane bioreactor technology ................................................................ 17
2.3.1 Definition of MBR .................................................................................... 17
2.3.2 MBR application for trace organics removal ........................................... 19
2.4 Activated carbon adsorption ........................................................................ 25
2.4.1 Activated carbon ...................................................................................... 25
2.4.2 Application of activated carbon ............................................................... 25
2.4.3 Application of activated carbon with membrane bioreactor ..................... 27
CHAPTER 3: METHODOLOGY ........................................................................... 33
3.1 Introduction ................................................................................................. 33
3.2 Materials ..................................................................................................... 34
3.2.1 Selected trace organic compounds ........................................................... 34
3.2.2 Synthetic wastewater ............................................................................... 40
3.2.3 Activated carbon ...................................................................................... 40
3.3 Experimental set-up and operation protocol ................................................ 41
3.3.1 Laboratory–scale MBR set-up and operation protocol ............................. 41
3.3.2 Laboratory–scale MBR-GAC set-up and operation protocol .................... 44
3.3.3 Laboratory scale PAC - MBR set-up and operation protocol ................... 46
3.3.4 Adsorption isotherm ................................................................................ 46
3.4 Analytical techniques ................................................................................... 48
3.4.1 Total organic carbon and total nitrogen .................................................. 48
3.4.2 DO concentration, pH, turbidity, and sludge volume index ...................... 51
3.4.3 Mixed liquor suspended solids and mixed liquor volatile suspended solids ..
................................................................................................................ 52
3.4.4 Specific oxygen uptake rate (SOUR) ........................................................ 53
3.4.5 Nitrate and Ammonium ............................................................................ 53
3.4.6 Extracellular polymeric substances and soluble microbial products ........ 56
3.4.7 Trace organics analysis ........................................................................... 60
CHAPTER 4: PERFORMANCE OF MBR SYSTEM ............................................ 67
4.1 Introduction ................................................................................................. 67
4.2 Experimental set up and operation protocol ................................................ 67
4.3 Results and discussion ................................................................................. 67
viii
4.3.1 Mixed liquor suspended solids and mixed liquor volatile suspended solids ..
................................................................................................................ 67
4.3.2 Turbidity and sludge volume index ........................................................... 68
4.3.3 Dissolved oxygen concentration, pH and specific oxygen up take rate ..... 70
4.3.4 Nitrate and ammonium ............................................................................ 71
4.3.5 Total organic carbon and total nitrogen removal ..................................... 73
4.3.6 Removal of trace organic contaminants ................................................... 75
4.4 Conclusions ................................................................................................. 79
CHAPTER 5: REMOVAL OF TRACE ORGANIC CONTAMINATNS BY A
MEMBRANE BIOREACTOR (MBR) - GRANULAR ACTIVATED CARBON
(GAC) SYSTEM ....................................................................................................... 80
5.1 Introduction ................................................................................................. 80
5.2 Experimental set-up and operation protocol ................................................ 81
5.3 Results and discussion ................................................................................. 81
5.3.1 Performance stability and TOC/ TN removal by the MBR- GAC system ... 81
5.3.2 Complementary removal of trace organics by MBR – GAC system .......... 83
5.3.3 Adsorption of single compound on GAC .................................................. 85
5.3.4 Breakthrough of biologically persistent hydrophilic compounds .............. 86
5.4 Conclusions ................................................................................................. 94
CHAPTER 6: REMOVAL OF TRACE ORGANIC CONTAMINANTS BY PAC
- MBR HYBRID SYSTEM ....................................................................................... 95
6.1 Introduction ................................................................................................. 95
6.2 Experimental set-up and operation protocol ................................................ 95
6.3 Results and discussion ................................................................................. 96
6.3.1 Evaluation of the performance of the PAC - MBR hybrid system .............. 96
6.3.2 Removal of trace organics by PAC - MBR hybrid system ....................... 110
6.4 Conclusions ............................................................................................... 119
CHAPTER 7: CONCLUSIONS AND RECOMMENDATIONS.......................... 120
7.1 Conclusions ............................................................................................... 120
ix
7.2 Recommendations for further research ...................................................... 121
REFERENCES ....................................................................................................... 123
APPENDIX A.......................................................................................................... 144
APPENDIX B .......................................................................................................... 174
x
LIST OF FIGURES
Figure 1: Schematic description of the thesis structure. ................................................ 6
Figure 2: Configuration of MBR systems ................................................................... 19
Figure 3: Schematic diagram of the hybrid process..................................................... 29
Figure 4: Schematic illustrating the effects (a), causes (b) and mechanism (c) occurring
in an MBR after PAC addition [166]. .................................................................. 30
Figure 5: Experimental road map ............................................................................... 33
Figure 6: Membrane bioreactor (MBR) set-up (1 Feed tank, 2 Feed pump, 3 MBR , 4
Pressure gauge, 5 Permeate pump, 6 Permeate tank, 7 Computer). Dimensions of
the reactor were 360 mm (H) x 320 mm (L) x 45 mm (W)................................... 42
Figure 7: A schematic diagram of the MBR set up ..................................................... 43
Figure 8: PVDF hollow fiber membrane module used in this study (dimensions 29 cm
(L) x 17 cm (H) x 1 cm (W), Fiber length and outer diameter of 22 cm and 0.2 cm,
respectively. Membrane nominal pore size = 0.4 µm and total membrane surface
area = 0.074 m2) .................................................................................................. 43
Figure 9: Fixed bed GAC column. A borosilicate glass column (1cm diameter x 22 cm
L) filled with 7.5 g GAC was used. ..................................................................... 45
Figure 10: Combined MBR – GAC system ................................................................ 45
Figure 11: Total organics carbon and total nitrogen analyzer system (1 Auto sampler
and sample tray, 2 TOC analyzer, 3 TN analyzer unit, 4. Computer). .................. 49
Figure 12: A typical TOC calibration curve to determine TOC concentration in samples
............................................................................................................................ 50
Figure 13: A typical TN calibration curve to determine TN concentration in samples . 51
Figure 14: A typical calibration curve to determine nitrate concentration in samples .. 54
Figure 15: A typical calibration curve to determine ammonium concentration in
samples ............................................................................................................... 55
Figure 16: An Ion-chromatography system (1 Pump part, 2 Auto sampler, 3 Column
chamber, 4 Conductivity detectors, 5 System controller, 6 Computer). ................ 55
Figure 17: Schematic of sample preparation for EPS and SMP determination ............ 57
Figure 18: A typical calibration curve to determine carbohydrate concentration in
samples ............................................................................................................... 58
Figure 19: A typical calibration curve to determine protein concentration in samples . 59
xi
Figure 20: An UV-visible spectrophotometer ............................................................. 59
Figure 21: Schematic of sample preparation for GC-MS measurement of trace organics
(Reagent water is MBR feed without trace organics. MeOH - methanol, DCM –
dichloromethane, SPE – solid phase extraction, HLB -Hydrophilic-lipophilic-
balanced) ............................................................................................................. 62
Figure 22: The solid phase extraction manifold holding cartridges through which the
sample drips into the perforated chamber below, where tubes collect the effluent. A
vacuum port with gauge is used to control the vacuum applied to the chamber (1
Sample containers, 2 HLB cartridges, 3 Chamber, 4 Vacuum port). .................... 63
Figure 23: Gas chromatography-mass spectrometry system (1 Sample tray, 2 Sample
injector, 3 GCMS-QP 5000, 4 Computer) ............................................................ 63
Figure 24: High performance liquid chromatography system (1 Column, 2 Eluent
containers. 3. Auto sampler, sample tray and degasser, 4 Pump, 5 UV-VIS
Detector, 6 Controller, 7 Computer) .................................................................... 65
Figure 25: Liquid chromatography-mass spectrometry system (1, Computer, 2 Pump
and degasser, 3 Sample injector, 4 Eluent container, 5 Controller, 6 UV-PDA
detector, 7 Column chamber, 8 LCMS -2020) ..................................................... 66
Figure 26: Variation of MLSS and MLVSS concentration throughout the operation
period before adding PAC into MBR. ―S‖ and ―T‖ indicate the start-up period and
the point of trace organic contaminants addition, respectively. ............................ 68
Figure 27: Variation of MBR supernatant and permeate turbidity throughout the
operation period. The MBR supernatant was collected after centrifuging the mixed
liquor for 10 min at 1073 x g. ―S‖ and ―T‖ indicate the start-up period and the
point of trace organic contaminants addition, respectively. .................................. 69
Figure 28: Variation in SVI and MLSS concentration of the MBR throughout the
operation period. ―S‖ and ―T‖ indicate the start-up period and the point of trace
organic contaminants addition, respectively......................................................... 70
Figure 29: Variation of SOUR throughout operation period. ―S‖ and ―T‖ indicate the
start-up period and the point of trace organic contaminants addition, respectively.
............................................................................................................................ 71
Figure 30: Variation of ammonium concentration in MBR feed, supernatant and
permeate throughout the operation period. ―S‖ and ―T‖ indicate the start-up period
and the point of trace organic contaminants addition, respectively. ...................... 72
xii
Figure 31: Variation of nitrate (NO3-) concentration in MBR feed, supernatant and
permeate throughout the operation period. ―S‖ and ―T‖ indicate the start-up period
and the point of trace organic contaminants addition, respectively. ...................... 73
Figure 32: TOC concentration in MBR influent, effluent and the removal efficiency of
TOC throughout the operation period. ―I‖, ―S‖ and ―T‖ indicate the period when
the concentration of constituents in synthetic wastewater was kept at elevated
levels (double) temporarily, the start-up period and the point of trace organic
contaminants addition, respectively. .................................................................... 74
Figure 33: TN concentration in MBR influent, effluent and the removal efficiency
throughout the operation period. ―I‖, ―S‖ and ―T‖ indicate the period when the
concentration of constituents in synthetic wastewater was kept at elevated levels
(double) temporarily, the start-up period and the point of trace organic
contaminants addition, respectively. .................................................................... 75
Figure 34: Concentration of the trace organic contaminants in feed and MBR permeate.
Samples in duplicate were taken once a week. Error bars represent standard
deviation of 26 measurements regularly conducted over 13 weeks....................... 77
Figure 35: Removal efficiency of the selected trace organic contaminants and their
corresponding hydrophobicity (log D) by MBR treatment. Samples in duplicate
were taken once a week. Error bars represent standard deviation of 26
measurements regularly conducted over 13 weeks. .............................................. 78
Figure 36: TOC (a) and TN (b) concentrations in GAC effluent, MBR permeate and
feed throughout the operation period ................................................................... 82
Figure 37: Overall removal of trace organic contaminants by MBR-GAC system at 406
BV (a), 4472 BV (b), 9148 BV (c), 18093 BV (d) ............................................... 84
Figure 38: Breakthrough profiles of six biologically persistent and hydrophilic trace
organic compounds as a function of bed volume (BV) ......................................... 89
Figure 39: Relationship between breakthrough (%) and adsorption isotherm constants
(qm, Langmuir maximum adsorption capacity (a) ; Kf, Freundlich partitioning
coefficient (b)).(1.Metronidazole, 2.Fenoprop, 3.Ketoprofen, 4.Naproxen,
5.Diclofenac, 6.Carbamazepine). The breakthrough values are defined as
percentage of the effluent concentration over the influent concentration of the same
sampling event. ................................................................................................... 92
xiii
Figure 40: Relationship of adsorption isotherm constants (qm, Langmuir maximum
adsorption capacity; Kf, Freundlich partitioning coefficient) with various individual
parameters (governing adsorption of organics onto activated carbon) for
biologically persistent six hydrophilic trace organics. 1. Metronidazole,
2.Fenoprop, 3.Ketoprofen, 4.Naproxen, 5.Diclofenac, 6.Carbamazepine. Dipole
moment was calculated by molecular modelling Pro software using ―Modified Del
Re‖ method. Aromaticity ratio denotes the ratio of number of aromatic bonds to
total number of bonds in a molecule. ................................................................... 93
Figure 41: Variation of MLSS and MLVSS concentration in the reactor throughout the
operation period. ―T‖ indicates the point of trace organic contaminants addition,
and ―R‖ indicates the point of sludge withdrawal, while ―P1‖ and ―P2‖ indicate
points of PAC addition to achieve final PAC concentrations of 0.1 g/L and 0.5 g/L,
respectively. ........................................................................................................ 97
Figure 42: Variation of SVI and reactor supernatant turbidity throughout the operation
period. ―T‖ indicates the point of trace organic contaminants addition, while ―P1‖
and ―P2‖ indicate points of PAC addition to achieve final PAC concentrations of
0.1 g/L and 0.5 g/L, respectively. The MBR supernatant was collected in two
different ways i.e., by centrifuging (10 min at 1073 x g), and by gravity settling (30
min), respectively. ............................................................................................. 100
Figure 43: Variation of SOUR and DO concentration throughout the operation period.
―T‖ indicates the point of trace organic contaminants addition, while ―P1‖ and ―P2‖
indicate points of PAC addition to achieve final PAC concentrations of 0.1 g/L and
0.5 g/L, respectively. ......................................................................................... 101
Figure 44: TOC (a) and TN (b) removal efficiency in MBR and PAC - MBR system.
Error bars represent standard deviation of 46, 10, and 15 samples in MBR, MBR –
0.1 g/L PAC and MBR – 0.5 g/L PAC, respectively. ......................................... 104
Figure 45: Variation of (a) ammonium and (b) nitrate concentration in feed, supernatant
and permeate throughout the operation period. ―T‖ indicates the point of trace
organic contaminants addition while, ―P1‖ and ―P2‖ indicate points of PAC addition
achieve final PAC concentrations of 0.1 g/L and 0.5 g/L, respectively. .............. 106
Figure 46: Variation of transmembrane pressure (TMP) as a function of operation time.
―T‖ indicates the point of trace organic contaminants addition while ―P1‖ and ―P2‖
xiv
indicate the point of PAC addition to achieve final PAC concentrations of 0.1 g/L
and 0.5 g/L, respectively. .................................................................................. 109
Figure 47: Fouled membrane in both (a) MBR and (b) PAC – MBR systems. Pictures
were taken on day 186 and 306, respectively. .................................................... 110
Figure 48: Overall removal efficiency of trace organic compounds in PAC - MBR
hybrid system after addition of PAC at a concentration of 0.1 g/L. .................... 112
Figure 49: Removal of six biologically persistent hydrophilic trace organic compounds
as a function of operation time at 0.1 g PAC/L and 0.5 g PAC/L concentrations.115
Figure 50: Breakthrough profile of six biologically persistent hydrophilic trace organic
compounds as a function of operation time. The breakthrough values are defined as
percentage of the effluent concentration over the influent concentration of the same
sampling event. ................................................................................................. 116
xv
LIST OF TABLES
Table 1: Sources of PhACs (adapted from [61, 62]) .................................................... 11
Table 2: Information on the adverse effects of trace organics from recent studies
(adapted from [61]). ............................................................................................ 14
Table 3: Typical concentrations in various aquatic environment and information on the
removal efficiency of selected trace organic contaminants by MBR from recent
studies ................................................................................................................. 21
Table 4: Experimental timetable ................................................................................. 34
Table 5: Physicochemical properties of trace organics used in this study .................... 35
Table 6: Characteristic properties of PAC 1000 and GAC 1200 .................................. 41
Table 7: Gradient eluent profiles used in HPLC-UV analyses ..................................... 64
Table 8: GAC adsorption isotherm constants for six biologically persistent hydrophilic
trace organic compounds ..................................................................................... 85
Table 9: Information on some parameters in MBR and PAC – MBR systems (average ±
standard deviation) ............................................................................................ 102
Table 10: Comparison of the effectiveness between MBR - GAC and PAC - MBR
systems ............................................................................................................. 117
Table 11: Cost analysis for GAC and PAC usage. .................................................... 118
Table 12: TOC and TN concentration in MBR feed and permeate before adding trace
organics into the MBR. ..................................................................................... 144
Table 13: TOC and TN concentration in MBR feed and permeate after adding trace
organics............................................................................................................. 145
Table 14: Trace organics concentration and removal efficiency by MBR - GAC
treatment. .......................................................................................................... 147
Table 15: Trace organics concentration and removal efficiency by PAC - MBR
treatment with 0.1 g PAC /L concentration. ....................................................... 160
Table 16: Trace organics concentration and removal efficiency by PAC - MBR
treatment with 0.5 g PAC /L concentration. ....................................................... 165
xvi
LIST OF ABBREVIATIONS
AC Activated carbon
BAC Biologically activated carbon
BV Bed volume
CAS Conventional activated sludge
COD Chemical oxygen demand
DO Dissolved oxygen
GAC Granular activated carbon
GC-MS Gas chromatography- mass spectrometry
EBCT Empty bed contact time
EDCs Endocrine disrupting chemicals
EDG Electron donating group
EPS Extracellular polymeric substances
EWG Electron withdrawing group
HPLC High performance liquid chromatography
HRT Hydraulic retention time
LC-MS Liquid chromatography- mass spectrometry
MBR Membrane bioreactor
MLNVSS Mixed liquor non-volatile suspended solids
MLSS Mixed liquor suspended solids
MLVSS Mixed liquor volatile suspended solids
MWCO Molecular weight cut off
NF Nanofiltration
NPOC Non purgeable organic carbon
OUR Oxygen uptake rate
PAC Powdered activated carbon
PACT Powdered activated carbon treatment
PhACs Pharmaceutically active compounds
RO Reverse osmosis
SMP Soluble microbial products
SPE Solid phase extraction
SOUR Specific oxygen uptake rate
xvii
SRT Sludge retention time
SVI Sludge volume index
TMP Transmembrane pressure
TN Total nitrogen
TOC Total organic compounds
WWTPs Wastewater treatment plants
xviii
LIST OF SYMBOLS
1/n Freundlich exponential coefficient
b Langmuir’s constant (L/mg)
Ce Equilibrium concentration of compound in liquid (mg/L)
Kf Freundlich partitioning coefficient (mg/g)/(mg/L)1/n
H Height
L Length
qe Equilibrium mass of compound adsorbed on unit mass of adsorbent (mg/g)
qm Amount of adsorbate adsorbed per gram of adsorbent (mg/g)
qmb Adsorbent adsorbate relative affinity (L/g)
V Volume
W Width
Chapter 1 Introduction
1
CHAPTER 1: INTRODUCTION
1.1 Background of the study
1.1.1 Trace organics in wastewater: sources and problems
With recent development in analytical chemistry, a number of organic contaminants
have been reported at trace levels (from a few ng/L to several µg/L) in the aquatic
environment. Depending on their usage and characteristics, they can be divided into
several different groups such as pesticides, pharmaceutically active compounds
(PhACs) and endocrine disrupting chemicals (EDCs). Trace organics can be of both
natural and anthropogenic origin. Estrogenic hormones (e.g., estrone and 17β-estradiol
[1]) and phytoestrogens (e.g., isoflavones and lignans) are examples of natural trace
organics, which are released into the environment by humans, vertebrate animals and
certain plant species [2]. Examples of anthropogenic trace organics are synthetic
hormones, industrial chemicals, pharmaceutical and pesticides.
Trace organic contaminants can enter the environment via several different pathways.
For example, they can originate from chemicals directly applied to control waterborne
diseases and pest control (such as pesticides and antibiotics used in husbandry,
aquaculture and other agricultural activities) [3]. A major source of these trace organic
contaminants is sewage treatment plant effluent. Some trace organics can be highly
persistent, and thus they are likely to accumulate in the aquatic environment. With
continuous introduction of new consumer products in our modern days, an alarming
increase in the number of anthropogenic trace organics detected in natural water bodies
has been observed [4].
There is no doubt that various chemicals have contributed many benefits to human life
by increasing both industrial and agricultural activities, treating and preventing many
diseases. For example, atrazine, a well-know pesticide is used to stop pre- and post-
emergence broadleaf and grassy weeds in major crops [5]. The compound is both
effective and inexpensive. Atrazine is the most widely used herbicide in conservation
tillage systems, which are designed to prevent soil erosion. Another example is
bisphenol A, which is used primarily to make plastics, and products containing
bisphenol A-based plastics have been in commercial use since 1957 [6]. At least
4 million tons of bisphenol A are used by manufacturers yearly [6]. However, they also
Chapter 1 Introduction
2
present significant adverse effects to human health and the environment. For example,
bisphenol A is an EDC, which can mimic the hormones of vertebrates (including human
beings) and can lead to adverse health effects. Recent studies have shown that
compounds like estrone, 17β-estradiol and 17α-ethinylestradiol have high specific
biological estrogenic activity even at very low concentrations (several ng/L or less) [7].
Some hormones (e.g., natural hormones (estrone and 17β-estradiol), synthetic hormones
(ethinylestradiol), and phytoestrogens (isoflavoniods) have been also found to possess
endocrine disrupting effects [1, 8, 9]. These chemicals can interfere with the normal
function of the hormone system, for example, they can cause reduction of fish fertility
[3]. Some of these compounds (e.g., estriol and estrone) have been linked to human
cancers [9-11]. Accordingly the removal of these compounds during wastewater
treatment is of great importance to protect the environment and provide safe drinking
water.
1.1.2 Trace organic removal by membrane bioreactors
Trace organics have been detected in water supplies and wastewater effluents around
the world [12-16]. Several studies conducted on selected groups of trace organics have
indicated that coagulation, sedimentation, and conventional filtration achieve negligible
removal efficiency of these compounds [17-19]. The CAS process that is used for
treating sewage can remove bulk organic matter and suspended solids; however their
capacity for removing trace organic contaminants is limited. The removal capacity of
CAS depends significantly on the biological treatment stage where trace organics are
removed by adsorption on suspended solids and biodegradation. Removal of some
hydrophobic compounds has been reported to be positively correlated to sludge
retention time (SRT). Wick et al. [20] confirmed that no significant removal of
pharmaceuticals (i.e. carbamazepine and diclofenac) was observed in the CAS with an
hydraulic retention time (HRT) and SRT of one day and 0.5 day, respectively.
Incomplete removal of pharmaceuticals such as naproxen, ketoprofen and diclofenac
during CAS has also been reported by Kimura et al. [21].
Technical innovations and significant cost reductions of membranes have led to the
establishment of the MBR technology as an alternative to the CAS treatment process.
MBR can potentially achieve higher removal efficiency of some trace organics in
comparison to CAS (e.g., nonylphenol and nonylphenol ethoxylates [22] and several
Chapter 1 Introduction
3
acidic pharmaceuticals (naproxen and ketoprofen) [23, 24]). The membrane in an MBR
replaces the sedimentation tank in a CAS allowing for the uncoupling between HRT and
SRT. MBR systems can be operated at a long sludge age. In an MBR hydrophobic trace
organic compounds can adsorb to mixed liquor suspended solids (MLSS), which can
subsequently facilitate biodegradation of slowly biodegradable compounds such as
some pharmaceuticals under long SRT. Indeed, evidence from some studies has
demonstrated that MBR technology can offer enhanced removal efficiency for
moderately biodegradable compounds [24, 25]. The effect of SRT has been revealed in
a few studies. An MBR operated under an SRT of 65 days was reported to demonstrate
better removal of ketoprofen and diclofenac than an MBR operated under an SRT of 15
days [21]. However, previous studies have reported incomplete and low removal of
some compounds (i.e. carbamazepine, diclofenac and fenoprop) by MBRs which were
operated at an SRT of 70 days or more [26-28].
1.1.3 Adsorption of trace organic on activated carbon
Adsorption using either powdered activated carbon (PAC) or granular activated carbon
(GAC) is a well-know process for removing natural or synthetic organic compounds
such as pesticides in drinking water treatment [29-31]. Recently, several studies have
evaluated the adsorption of other emerging trace organics on activated carbon using
both laboratory and full-scale drinking water treatment systems [19, 32]. In comparison
to the investigations involving drinking water treatment, only a handful of studies have
investigated GAC adsorption as an option for tertiary treatment of conventional
biologically treated wastewater [10, 33, 34]. However, the adsorption of trace organics
on activated carbon decreases due to competition with bulk organic matter for
adsorptive sites [29, 35]. In fact, competition with bulk organic matter for adsorptive
sites has important implications to the lifetime and serviceability of GAC columns. For
efficient adsorption of trace organics, it is usually recommended that the feed to GAC
column be substantially free from bulk organics. Because MBR can produce suspended
solids-free permeate with low total organic carbon content [36], under less competition
from the bulk organic matter, GAC may specifically target the residual trace organics.
Therefore, subsequent GAC treatment of the MBR permeate may result in a better final
effluent quality. PAC can be directly added into MBR to form a hybrid process.
Simultaneous application of PAC within MBR has been mainly studied in relation to
Chapter 1 Introduction
4
membrane fouling mitigation [37, 38], performance improvement of MBR system [38-
40] and removal of some recalcitrant pollutant such as dyes [41]. The adsorption of
trace organics on to sludge facilitates their removal in the biological processes [42];
therefore, a solution to increase the biodegradation of slowly biodegradable compounds
may be the addition of adsorbent into bioreactor. As such, direct addition of PAC into
MBR may lead to significant increase in retention of soluble trace organics. Due to the
complete retention of sludge by membrane and application of longer SRT within MBR,
it is hypothesized here that the retained trace organics could be efficiently removed by
the PAC amended MBR.
1.2 Statement of the problem
The growing pressures from a recent trend towards indirect potable water reuse and the
increasingly stringent water quality regulations have challenged the conventional
wastewater treatment processes. MBR technologies have widely demonstrated superior
performance over CAS in term of basic effluent quality parameters. However, for the
removal of trace organic contaminants, previous studies on MBR have indicated
significant variation ranging from near complete removal for some compounds (e.g.
ibuprofen) to almost no removal for several others (e.g. carbamazepine and diclofenac)
[26, 27, 43]. The elimination of trace organics by MBR is only partially successful and
hence, trace organic contaminants are discharged and accumulated in the environment.
Therefore, post-treatment of MBR permeate or application of hybrid MBR processes
appears to be a logical means to prevent trace organics dispersion in the environment
via incompletely treated wastewater.
Sequential application of GAC adsorption following MBR treatment may result in
complementary advantages. Because MBR can produce high quality effluent with
virtually no suspended solids and with very low total organic carbon content [36], GAC
adsorption is expected to specifically target the residual trace organics in MBR
permeate without any significant interference from the bulk organics. However, to date,
there has been no extensive study on the efficiency of the sequential combination of
MBR and GAC processes for the removal of trace organic contaminants.
Chapter 1 Introduction
5
Simultaneous application of PAC within MBR has been explored in a few studies for
the removal of trace organic contaminants [44-46]. Zhang et al. [44] reported an
improved removal efficiency of carbamazepine in an PAC - MBR hybrid system. Li et
al. [45] observed an enhanced removal of two trace organic compounds, namely,
sulfamethoxazole and carbamazepine. However, a comprehensive understanding of the
involved phenomena is yet to be developed.
1.3 Objectives of the research
This project aims to investigate and demonstrate the complementarities between MBR
treatment and activated carbon (GAC and PAC) adsorption process for an enhanced
removal of trace organic contaminants.
The specific objectives are to
1. Evaluate the removal efficiency of a set of 22 trace organics by MBR
2. Evaluate and compare the removal of trace organics by sequential and
simultaneous applications of activated carbon and MBR.
3. Determine the break through profile of trace organics in a GAC column used for
the post-treatment of MBR permeate over an extended operation.
4. Elucidate the effect of PAC addition within MBR on removal of trace organics
and permeate flux.
1.4 Expected outcomes
Development of a hybrid activated carbon – MBR process achieving enhanced removal
of trace organic contaminants is the main expected outcome of this study. The
assessment of adsorption capacity of the trace organics on activated carbon will allow
for the evaluation of the treatment capacity of the hybrid activated carbon - MBR
systems. Moreover, systematic analysis of the dynamics of breakthrough of trace
organics through a fixed bed GAC column can be used to assess adsorption mechanism
and determine the period of replacement/regeneration and withdrawal/replenishment of
GAC inside the column and PAC in MBR, respectively. A comprehensive comparison
between MBR - GAC and PAC - MBR processes also can be used to select the
treatment process for treating trace organic contaminants.
Chapter 1 Introduction
6
1.5 Thesis outline
This thesis contains seven chapters as schematically presented in Figure 1. Chapter 1
introduces the background of this study. Chapter 2 provides a comprehensive literature
review. Chapter 3 describes the methodology used to achieve the aims and objectives
stated in introduction. The results of the experiment along with their detailed discussion
will be reported in chapters 4, 5, and 6. Finally, the conclusions and recommendations
for future research are provided in chapter 7.
Figure 1: Schematic description of the thesis structure.
Chapter 1: Introduction
Chapter 2: Literature review
Chapter 3: Methodology
Results and discussion
Chapter 4:
Performance of the
MBR
Chapter 5:
MBR followed by
GAC post - treatment
Chapter 6:
Combined PAC -
MBR
Chapter 7: Conclusions and Recommendations
Chapter 2 Literature review
7
CHAPTER 2: LITERATURE REVIEW
2.1 Introduction
The occurrence of trace organics such as pesticides, PhACs, natural and synthetic
hormones and various industrial compounds in the aquatic environment is of great
concern due to their potential adverse effects on human and ecological health [16]. This
chapter provides an overview of the current scientific research on the groups, sources,
occurrences and fate of emerging trace organic contaminants. A comprehensive
literature review on the basic principles of MBR technology, the performance of MBRs
in trace organics removal and associated governing factors, and the application of
activated carbon in removing emerging trace organic contaminants will be provided in
this chapter.
2.2 Trace organic contaminants
2.2.1 Groups of trace organic contaminants
Trace organic contaminants in wastewater can be divided into several different groups
depending on their intended uses such as pesticides, PhACs, surfactants and other
industrial chemicals, and steroid hormones. Most of them are of anthropogenic origin.
These trace organics also contain natural compounds which are excreted by humans,
animals and certain plant species. It is noteworthy that the categorisation here is not
complete. Compounds can be categorised based on the mode in which they may affect
human and aquatic biota. For example, endocrine disrupting chemicals were defined by
the US Environmental Protection Agency as ―an exogenous agent that interferes with
synthesis, secretion, transport metabolism, binding action or elimination of natural
blood-borne hormones that are present in the body and are responsible for homeostasis
reproduction and developmental process‖ [47]. EDCs consist of a vast number of
synthetic hormones (e.g., estrone and 17β-estradiol) and natural organics (e.g., 17 α-
estradiol) as well as inorganic chemicals (e.g., arsenic, cadmium, lead and mercury).
These compounds have a wide range of chemical structures but all of them have the
capacity of disrupting normal hormonal actions. In some cases they bind to steroid
hormone receptors and can have weak estrogenic or androgenic effects while others
disrupt thyroid hormones or other physiological functions [9]. Consequently, they may
Chapter 2 Literature review
8
disrupt reproductive or immune functions and can be carcinogenic. Detailed information
regarding various groups of trace organics is presented below.
2.2.1.1 Pharmaceutically activate compounds
Pharmaceuticals have been detected in water supplies and wastewater treatment plant
effluents around the world [12, 48]. The occurrence of pharmaceuticals and personal
care products (PPCPs) in the aquatic environment is an emerging concern because toxic
effects of these compounds may be observed even at very low concentrations [49-51].
PhACs are produced and used in very large volumes and their use and diversity is
increasing every year as new products are introduced. There are various
pharmaceuticals in different therapeutic groups and diverse physicochemical properties.
They are developed with the intention of performing a biological effect. Thus they have
many of the necessary properties to bio accumulate and provoke effects in the aquatic or
terrestrial ecosystems [52]. After having an internal curing effect in the human body,
pharmaceuticals will be excreted through urine or faeces as a mixture of metabolites, as
unchanged substance or conjugated with an inactivating compound attached to the
molecule mixture of metabolites depending on the pharmacology of the compounds
[52]. In this study, varieties of compounds representing a large group of PhACs were
selected. The selected compounds included analgesics and anti-inflammatory drugs such
as ibuprofen, ketoprofen, naproxen and diclofenac, cholesterol-lowering drugs
(gemfibrozil), and antiepileptic drug (carbamazepine). The physicochemical properties
of the selected compounds are shown in Table 5.
2.2.1.2 Pesticides
Pesticides are substances or mixture of substances intended for preventing, destroying,
repelling or mitigating any pest. Pesticides are categorised into four groups: pesticides,
fungicides, herbicides, and insecticides. The increased use of agricultural pesticides has
led to many benefits, for example, improved productivity and reduced maintenance
costs [5]. However, uncontrolled use of pesticides causes environmental contamination.
Because they can potentially accumulate in the food chain, pesticides constitute the
major source of potential environmental hazards to human and animal [5, 53]. The
usage and production of persistent pesticides have decreased in last two decades
because of extreme environmental hazards [5]. The current pesticides are less persistent
Chapter 2 Literature review
9
and harmful than before. However, harmful pesticides are still abundantly present in
polluted sites due to widespread and indiscriminate use in the past. In this study, two
pesticides namely, fenoprop and pentachlorophenol were used. Fenoprop is an herbicide
and a plant growth regulator while pentachlorophenol is an organochlorine compound
used as a pesticide and a disinfectant. Pentachlorophenol is used in preservation of
agricultural seeds (for non-food uses), leather, and wood. Its use has significantly
declined due to the high toxicity and persistence.
2.2.1.3 Surfactants and industrial compounds
Compounds selected in this study under this category include the well-known
industrial chemical bisphenol A, which is a monomer used in the production of epoxy
resins and of most common form of polycarbonate plastics which are used to make a
variety of common products including water bottles, sport equipments, medical and
dental devices, dental fillings, sealants, eyeglass lenses, CDs, DVDs, and household
electronics. However, bisphenol A is toxic for aquatic and terrestrial organisms
probably as a result of its interaction with proteins [54]. Accordingly bisphenol A has
been classified as an EDC by several organizations [55]. Three other organic
compounds of the alkyl-phenol group, namely, 4-tert-butyphenol, 4-n-nonylphenol and
4-tert-octylphenol were also selected in this study. These compounds have been
widely used as industrial surfactants and have been frequently detected in wastewater
and in some fresh water bodies.
2.2.1.4 Natural and synthetic hormones
Recently, a variety of natural and synthetic hormones, have been detected in the aquatic
environment. Although the full extent of the impact of natural and synthetic hormones
on human health is still a subject of intense scientific debate [56, 57], some of these
compounds have been shown to cause adverse effects on a range of aquatic organisms
in the concentration range of 0.1 to 0.5 ng/L [58]. For example, 17β-estradiol and 17α-
ethynylestradiol have been identified to cause adverse developmental and reproduction
issues in fish exposed to municipal wastewater effluent [59, 60]. These compounds act
as endocrine disruptors. Therefore, their occurrence, fate and effects are of heightened
interest. In the view of their presence in aquatic environment, several natural hormones
Chapter 2 Literature review
10
(i.e., estrone, estriol, 17-β-estradiol and 17-β-estradiol-acetate) and a synthetic hormone
(i.e., 17-α-ethinylestradiol) were selected in this study.
2.2.2 Sources of trace organic contaminants
As mentioned in previous section, trace organic contaminants can be categorised into
different groups based on their intended uses. As such, the sources of trace organic
contaminants may correlate to where they are applied. Several routes of trace organic
contamination of natural water bodies can be identified. The current and future amounts
of the micropollutants may be estimated based on the amount of chemical used, for
example, in agricultural and industrial practices and for treatment and prevention of
diseases.
A huge amount of active pharmaceutical ingredients are produced each year and applied
in human and veterinary medicine. The worldwide annual per capita consumption of
pharmaceuticals is 15 g [61]. The annual pharmaceutical consumption by individuals in
developed countries is three to ten times higher than the world average. After being
administered into the host body the pharmaceuticals undergo a metabolic transformation
process. Significant fractions of the compounds are excreted into raw sewage and
wastewater treatment systems. Conventional wastewater treatment plants (WWTPs) are
not designed to treat these compounds. Effluents are discharged to the water bodies or
reused for irrigation and biosolids produced are used in agriculture. Due to partial
metabolisation and excretion from human body followed by incomplete removal in
WWTPs, WWTPs effluents are considered to be the main source of trace organics into
the environment. In addition, improper disposal of unused or expired drugs and
pharmaceuticals residues from spill accidents are significant sources of trace organic
contaminants [62]. Furthermore, direct release of veterinary pharmaceuticals in the
environment may occur via application in aquaculture (fish farming). Pharmaceuticals
may also be indirectly released by way of topical treatment and mostly via run off and
leaching from agricultural fields and livestock wastes [62].
Chapter 2 Literature review
11
Table 1: Sources of PhACs (adapted from [61, 62])
Source Mode of exposure to environment
Hospital Discharge of wastes and expired drugs
Animal husbandries Hormones and drugs injected to poultry
and cattle
Aquacultures Hormones fed to fish, antibiotics are also
added to feed and water
Household discharge Discharge of expired and consumed drugs
from leaky sewers and septic systems
Companies manufacturing drugs Industrial waste containing drugs, storm
runoff carrying powdered drugs
Wastewater and sewage treatment plant Residuals from wastes and sewage
containing drugs and hormones
The widespread use and indiscriminate disposal of pesticides by farmers, institutions
and the general public provide many possible sources of pesticides in the environment
[5]. Following release into the environment, pesticides may have many different fates.
Pesticides which are sprayed in agricultural activities may move away from the target
sites and may end up in the air or other parts of the environment, such as in soil or
water. Pesticides which are applied directly to the soil may be washed off the soil into
nearby bodies of surface water or may percolate through the soil to lower soil layers and
groundwater. The application of pesticides directly to bodies of water for weed control,
or indirectly as a result of leaching from boat paint, runoff from soil or other routes,
may lead not only to build up of pesticides in water, but also may contribute to air levels
through evaporation.
Surfactants and industrial chemicals enter into the aquatic environment due to their
presence in wash water, as waste or by products of production processes or simply as a
Chapter 2 Literature review
12
result of normal use and disposal. After their application, they are usually discharged
into municipal sewer systems and afterwards treated in WWTPs, where they are
completely or partially removed by a combination of sorption and biodegradation [63,
64] and release into the environment via WWTPs effluent.
The main sources of steroid estrogens are the human population and livestock. Estrogen
excretion by humans and animals varies as a function of their sex, physiological and
developmental state [65]. Humans excrete a large quantity of estrone (E1), 17-β-
estradiol (E2), and estriol (E3) daily in their glucuronide and sulfate-conjugated forms,
mainly via urine (95%) [66]. For therapeutic purposes, the daily synthetic hormone
intake, for example, 17-α-ethinylestradiol (EE2) is around 20–60 μg for contraception
and about 10 μg to control menopausal disorders; from such ingested dosage, around 30
– 90% is excreted in urine and feces [67]. Hence, the total amount of excreted estrogens
discharged by humans into the environment has been estimated at some 4.4
kg/year/million inhabitants [68].
2.2.3 The effects of trace organic contaminants on human health and environment
The potential effects of trace organic contaminants have been well documented in
various studies since the last decade [69-71]. These compounds can disrupt endocrine
system by mimicking, blocking or also hampering functions of hormones, thereby
affecting health of human and animal species [70]. Schqaiger et at. [69] studied the
possible effects in rainbow trout after prolonged exposure to diclofenac. They reported
histopathological changes of kidney and liver when fishes were exposed to 5 µg/L of
diclofenac for 28 days. EDCs cause a wide range of adverse effects on aquatic organisms
e.g., feminisation of male fishes [72], demasculinisation of alligators [73], growth
inhibition, immobilisation, mutagenicity, increased mortality and changes in population
density [74, 75]. For example, bisphenol A has been proven to have estrogenic effects in
rats [76]. BPA has been shown to mimic estradiol in causing direct damage to the DNA
of cultured human breast cancer cells [77]. Some steroid hormones such as estrone, 17β -
estradiol, and 17 α - ethinylestradiol have a high specific biological estrogenic activity
even at extremely low concentrations [70] and may cause feminisation in male fish.
Table 2 summarises information regarding the adverse effects of trace organics from
recent studies. In the environment trace organics are present as a mixture of various
Chapter 2 Literature review
13
parent compounds and their transformation products. Mixture of trace organic
compounds may impose a more complicated effect when compared to that of single
compound [78-80] for example, ecotoxicity tests with antibiotics showed that combined
toxicity of two antibiotics can lead to either synergistic antagonistic or additive effects
[81]. In general, knowledge about the toxicity of compound mixtures is limited. This is a
new field of ecotoxicity and much remains to be studied.
Chapter 2 Literature review
14
Table 2: Information on the adverse effects of trace organics from recent studies (adapted from [61]).
No of
compounds
studied
Compounds causing risks:
concentration of exposure (range of
dose at which the risk was observed)
Type of risks involved Reference and
country
1 Diclofenac: 0.5 -50 µg/ L Affect tissues of gills and kidney of freshwater fish
brown trout
[82]
Germany
27
Ibuprofen, diclofenac, 17-β - estradiol and
17-β estradiol – 17 acetate:
0.01 µg/ L
Risk to aquatic environment with chronic toxic effect
(such as inhibited polyp regeneration and reduced
reproduction in hydra)
[71]
Sweden
13
Mixture of atenolol, bezafibrate,
carbamazepine, cyclophosphamide,
ciprofloxacin, ibuprofen, lincomycin,
ofloxacin, ranitidine, salbutamol and
sulfamethoxazole: 10 -1000 ng/L
Inhibit the growth of human embryonic kidney cells
HEK293 with the highest effect observed as a 30%
decrease in cell proliferation compared to control [83]
Italy
10
Diltiazem, acetaminophen and
sulfamethoxazole: 8.2 – 271.3 µg/L
Hazard quotient >1, diltiazem: most toxic ( lethal conc.
8.2 mg/L for freshwater invertebrate Daphnia magna
[84]
South Korea
Chapter 2 Literature review
15
4
Ethinylestradiol, zearalonol, 17 β
trenbolone and melengestrol acetate < 1-
68 ng
Freshwater fish fathead minnows experience different
levels of hepatic gene expression [85]
USA
1
17 α-ethinylestradiol (EE2): 5- 50 ng/L Brain and inter-renal steroidogenic acute regulatory
protein and cytochrome P-450 mediated cholesterol
side chain cleavage expressions of juvenile salmon
were modulated with time and concentration
[86]
Norway
3
Chloramphenicol, florfenicol, and
thiamphenicol (veterinary and
aquaculture): 1.3 – 158 mg/L
Inhibit the growth of Chlorella pyrenoidosa
(freshwater) Isochrysis galbana and Tetraselmis chui
(marine)
[87]
Taiwan
Chapter 2 Literature review
16
2.2.4 Fate and behaviour of trace organic contaminants
The removal of trace organic contaminants depend on the treatment process applied
(CAS, MBR and nanofiltration/reverse osmosis membrane filtration (NF/RO)) [7, 88].
In biological processes, the operating parameters that have profound influence on
removal of trace organics include operating temperature [43, 89, 90], HRT and SRT
[91, 92], mixed liquor pH and dissolved oxygen concentration [93, 94]. Detailed
information regarding trace organics removal by MBR can be found in section 2.3.2.2.
This section will focus on the extent of removal by CAS.
Elimination of trace organics in CAS treatment processes is often incomplete, and the
reported overall removal of trace organics in CAS varies [95, 96]. As a consequence, a
significant fraction of the trace organics is discharged with the final effluent into the
aquatic environment. Two major mechanisms of removal of trace organics during CAS
processes are sorption and biodegradation [97]. Higher removal efficiency of some
trace organic compounds has been attributed to their adsorption to the activated sludge
[98]. Trace organics which are relatively hydrophilic show limited sorption to sludge
[88]. However, some very hydrophilic compounds such as fluoroquinolone antibiotics
may mainly be eliminated by sorption to sludge by electrostatic interactions with the
cell membranes of the microorganisms [99, 100]. Therefore, the physical and chemical
properties of these compounds can greatly influence their fate and behaviour as well as
the removal efficiency of trace organic contaminants during CAS treatment. Most of the
studies report the removal of trace organics compound from the aqueous phase by
comparing influent and effluent concentrations, without distinguishing between the
three major fates of a substance in CAS; (i) degradation to low molecular weight
compounds, (ii) physical adsorption onto activated sludge and (iii) hydrolysis of
conjugates yielding the parent compound [101].
2.2.5 Analysis of trace organic contaminants
Trace organic contaminants represent structurally diverse classes of compounds and
different analytical methods have been applied for the identification and quantification
of these chemicals in water. The measurement of trace organics in water most
commonly consists of extraction of the chemicals from water, concentration of the
resulting extract, chromatographic separation and detection [102]. Most of trace
Chapter 2 Literature review
17
organics have been found in environment at sub - or µg/L concentrations [12]. An
extraction step is required to concentrate the target compounds to a detectable level.
After extraction, the extract is dried by passing nitrogen through a solid phase extraction
cartridge. In some cases the extract is concentrated further by evaporation with a gentle
stream of nitrogen. [103, 104].
Analytical procedures for the determination of trace organics in aqueous samples can
utilise either gas or liquid chromatography after extraction and clean up procedures. Gas
chromatography (GC) has high resolution, and sensitivity. However, GC needs the use
of volatile derivatives, which is labour intensive and can reduce analyte recovery [105].
On the other hand, high performance liquid chromatography (HPLC) is capable of the
analysis of non-volatile compounds. In addition, this technique provides a shorter
analysis time and less yield loss than the GC technique. The combination of GC and
mass spectrometry (MS) forms a powerful combination for simultaneous separation and
identification of many organic contaminants in environmental samples [106]. Analytical
methods by using GC-MS for the determination of acidic herbicides and polar
pharmaceutical residues in aqueous solutions have been used widely [106-108]. Several
studies have measured concentrations of residues of organic compounds, including
PhACs and/or EDCs in influents and the treated effluents by using various analytical
methods, e.g., HPLC, LC – MS/MS, GC-MS.
2.3 Membrane bioreactor technology
2.3.1 Definition of MBR
MBRs can be defined as a combination of two basic treatment processes - biological
degradation and membrane separation into a single process where suspended solids and
microorganisms responsible for biodegradation are separated from treated water by a
membrane filtration unit [51]. Although, it has been applied for the treatment of
domestic or industrial wastewater since the late 80s [109]. MBR processes have gained
great popularity in the water industry in recent years. By the turn of the 21st century,
more than 500 full scale MBR plants had been in operation worldwide [23]. In Japan,
over 150 MBRs were installed to different types of industrial wastewater such as food
processing and breweries. In the US, there were about 24 municipal wastewater
Chapter 2 Literature review
18
treatment plants using MBR processes. In Canada, nine MBR installations were in
operation [23]. Similarly, approximately 300 MBR plants for industrial applications and
about 100 municipal MBR wastewater treatment plants were in operation or being
constructed in Europe in 2005 [28]. The global MBR market in 2005 reached a market
value of $217 million in 2005 with a projection for the year 2010 of $360 million. The
application of MBR is expected to increase more dramatically due to more stringent
environmental regulations, growing water reuse and the emergence of low-cost
membrane with lower pressure requirement and higher permeate flux [109].
In comparison to the CAS processes, MBRs have several major advantages including a
smaller footprint, more flexibility for future expansion, scale-up and better effluent
quality in terms of removal of pathogens, suspended solids and nutrients [110-112]. In
addition, sludge separation is not dependent on the influent characteristics or the
flocculation state of the biological suspension as the flocs size is much larger than the
membrane pores [113]. The biomass concentration can also be higher than in CAS (up
to 10 times), resulting in a much more intensive treatment process in comparison to
CAS [114].
MBR is typically categorised into recirculated MBR (external circulation or side-stream
configuration) and submerged MBR based on relative positions of the membrane
module and bioreactor (Figure 2). In a recirculated MBR, the membrane module and the
bioreactor are separated. The mixed liquor is transferred to the membrane module
through a recirculation pump. After the separation process, the concentrated liquid is
recirculated back to the bioreactor. In a submerged membrane bioreactor the membrane
module is submerged inside the bioreactor and filtrated effluent is drawn by vacuum or
siphon. The submerged MBR is a more common configuration for municipal
wastewater treatment since it can significantly reduce power consumption [113]. The
membranes applied in submerged MBRs can be either hollow fiber or flat membrane
module design and multi–tube modules are used for side –stream MBR configuration
[109].
Chapter 2 Literature review
19
Figure 2: Configuration of MBR systems
(a) side-stream MBR configuration, (b) submerged MBR
2.3.2 MBR application for trace organics removal
2.3.2.1 Removal of trace organic contaminants by MBR
MBRs can operate at a biomass concentration of as high as 20 g/L and at a prolonged
SRT. The high sludge concentration in MBR is not only beneficial for biodegradation of
trace organic contaminants but it can also have a beneficial effect on the removal
efficiency of trace organics that can absorb to the sludge. This may promote the
degradation of persistent substances because of the improved adaptation of bacteria for
trace organics.
Considerable research efforts have been devoted to the assessment of trace organics
removal by MBR treatment. The reported data ranges from near complete removal for
some compounds to almost no removal for several others. Excellent MBR removal of
ibuprofen (up to 98%) was confirmed along with naproxen (84%) and erythromycin
(91%) by Reif et al. [115] in their pilot-scale MBR. In addition, sulfamethoxaole and
musk fragrances (galaxolide, tonalide, and celestolide) were moderately removed
(>50%) probably due to partial adsorption on the biomass. On the other hand,
carbamazepine, diazepam, diclofenac, and trimethoprim were poorly removed (<10%)
due to poorer biodegradation. Nghiem et al. [116] also confirmed the possibility of
achieving good treatment of bisphenol A (90%) due to both biodegradation and
adsorption. On the contrary, sulfamethoxazole removal was solely attributed to
Air
Influent
Air
Influent
Recirculated
Activated
sludge Sludge
Effluent
Effluent
Sludge
Activated
sludge
Membrane
(a) (b)
Chapter 2 Literature review
20
biodegradation, which can explain the poorer removal (50%) as this compound is rather
hydrophilic (log D = - 0.22 at pH 7) [116].
MBRs have been widely reported to achieve superior performance over that of CAS in
terms of basic water quality parameters. However, there have been several conflicting
reports on whether MBRs can offer enhanced removal of trace organic contaminants
compared to that achieved by CAS treatment. Cirja et al. [7] noted that the removal
rates differed from one compound to the another, however, no discernible difference
between CAS and MBR could be detected. Oppenheimer et al. [96] reported no
significant difference in removal efficiencies of ibuprofen, triclosan and caffeine by
both CAS and MBR process. Bernhard et al. [117] reported that treatment by MBR
resulted in significantly better removals compared to CAS for poorly biodegradable
compounds such as diclofenac, mecoprop, and sulfophenyl carboxylates which was
attributed to the long sludge retention time in MBR. Radijenovic et al. [118] reported
that the removal of pharmaceuticals in MBRs was superior for several compounds (e.g.,
naproxen, ketoprofen) and at least similar for others (e.g., carbamazepine and
diazepam). Kimura et al. [21] found that compounds with a complex chemical
structure, for example, ketoprofen and naproxen were not eliminated at all in CAS
treatment, but could be eliminated partially by MBRs.
Chapter 2 Literature review
21
Table 3: Typical concentrations in various aquatic environment and information on the
removal efficiency of selected trace organic contaminants by MBR from recent studies
Category Compound Concentration in
environment
(ng/L) References
Removal (%)
(min –
max)
References
Ph
arm
ace
uti
cal
an
d p
erso
nal
care
pro
du
cts
Ibuprofen SE: 780 – 48240
SW: 1300
[14, 15, 119,
120] 70 - 99 [115, 121, 122]
Acetaminophen PE: 80.000 [121] 85- 99 [16, 121, 123]
Naproxen SE: 24
SW: 2600 [14, 30] < 50 [26, 46, 123]
Ketoprofen SW: 180
GW: 611 [14, 124] 50 - 65 [23, 125]
Diclofenac SE: 424
SW: 370 - 990 [14, 15, 126] 0 - 80
[122, 127] [46,
128]
Primidone SE: 2-95
PE: 100 [121, 129] 12.4 – 90 [26] [43, 123]
Carbamazepine
SE: 1594
PE: 230 – 1850
SW: 950
[14, 95, 121] 12 - 68 [94] [46, 128,
130]
Salicylic acid SE: 220
GW: 418 [124, 131] > 90 [43]
Metronidazole Not available < 40 [43]
Gemfibrozil SE: 82 [30] 0 – 95 [30, 43, 98]
Triclosan
SE: 32
PE: 470
GW: 509
[30, 121, 124] 88 - 91 [27, 30]
Pes
tici
des
Fenoprop SW: 4 [132] < 60 [43]
Pentachlorophenol SW: 13000 [133] < 95 [134]
Chapter 2 Literature review
22
Ind
ust
ria
l ch
emic
als
an
d
thei
r m
eta
bo
lite
s
4-tert-butyphenol SW: 50 [135]
80 – 99 [43, 123] 4-tert-octylphenol SW: 18.0– 20.2 [136]
4-n-nonyphenol GW: 23088
SW: 10 - 1400 [18, 124, 137]
Bisphenol A SE:
SW: 1000 [137] > 90 [116] [122]
Ste
roid
ho
rmo
nes
Estrone GW: 9
SW: 2000 [124, 137] > 92 [122]
17-β-estradiol SW: 12000
GW : 31 [124, 137] > 98 [26, 43, 122]
17-β-estradiol-
acetate Not available 80 - 99 [26, 122]
17-α
ethinylestradiol
SW: 2000
PE: 140 [121, 137] 65 – 94 [122] [138]
Estriol SW: 23 - 660 [65] 90 - 99 [122] [43]
SW, PE, GW and SE refer to surface water, primary effluent, ground water and secondary
effluent, respectively.
2.3.2.2 Factors affecting the removal of trace organic contaminants by MBR
Physicochemical properties of trace organics have been reported to significantly govern
their removal efficiency by MBR treatment. Adsorption of trace contaminants on sludge
particles, driven primarily by hydrophobic interaction, appears to be one of the key
mechanisms controlling removal efficiency during MBR treatment. Hydrophobic
compounds (log D > 3.2) adsorbed on sludge can be retained by membrane and further
biodegradation by biomass in the reactor can occur. For instance, the removal efficiency
of the significantly hydrophobic compounds steroid hormones and alkyl phenolic
compounds have been consistently reported to be 95 – 99% [27]. Tadkaew et al. [26]
investigated the removal of 40 trace organics with different molecular weight ranging
from 151 g/mol to 455 g/mol by the MBR treatment. The results showed that
compounds with molecular weight of more than 300 g/mol were relatively well
removed, while the removal of those with molecular weight below 300 g/mol varied
from almost no removal to more than 95% removal. However, it was noted that the
Chapter 2 Literature review
23
compounds with molecular weight above 300 g/mol also possessed higher
hydrophobicity.
For hydrophilic compounds (log D < 3.2) sorption is no longer a dominating removal
mechanism and the removal of these compounds is much more strongly influenced by
their intrinsic biodegradability [26]. In this context, the presence of specific functional
groups in trace organic compound structures have been reported to influence the
removal efficiency by the MBR treatment [24, 26, 139]. Tadkaew et al. [26]
systematically demonstrated that compounds with strong electron withdrawing group
(EWG) (e.g., halogen, amide and carboxyl) are more resistant to MBR treatment, while
the removal of compounds possessing both electron donating group (EDG) (e.g.,
hydroxyl, amine, and methyl) and EWG can substantially vary depending on the
number and type of the functional groups. Cirja et al. [7] also reported that the removal
rates of xenobiotics by MBR are related to the physicochemical characteristics of the
compounds. Kimura et al. [24] reported that removal efficiencies of the studied PhACs
(clofibric acid, diclofenac, ibuprofen, mefenamic acid and naproxen) were found to be
dependent on their molecular structure such as number of aromatic rings or inclusion of
chlorine (i.e., chlorine group compounds (clofibric acid and diclofenac) were not
effectively removed by MBR). The functional group and hydrophobicity of compounds
may also have a combined effect on their removal efficiency; for example, Hai et al.
[140] demonstrated that there was a combined effect of halogen content (weight ratio)
and hydrophobicity on the removal of halogenated trace organic compounds in MBR.
Compounds with high halogen content (>0.3) were well removed (>85%) when they
possessed high hydrophobicity (Log D > 3.2), while those with lower Log D values
were also well removed if they had low halogen content (<0.1).
In addition to the physicochemical properties of trace organics, their removal also
depends on operating conditions such as operating temperature [43, 89, 90], HRT
[141] , SRT [91, 92, 142], mixed liquor pH [122], and dissolved oxygen concentration
[94, 128]. Hai et al. [43] studied the removal of trace organics by MBR under variation
of temperature and reported that while the removal of hydrophobic compounds was
stable at a temperature between 10 oC to 35
oC the removal of hydrophilic compounds
was lower at 10 oC than that at 20
oC. However, at 45
oC the removal of most trace
organics was deteriorated. Concerning SRT, increased SRT values have shown to
Chapter 2 Literature review
24
improve removal for most PPCPs [92], although beyond 25 – 30 days this parameter
appears not significant anymore [92]. Tadkaew et al. [122] investigated the removal of
ionisable and non-ionisable trace organics by MBR treatment under different mixed
liquor pH ranging from 5 to 9. High removal efficiency of the ionisable compounds was
observed at mixed liquor pH 5 while removal efficiency of two non-ionisable (bisphenol
A and carbamazepine) compounds was independent of the mixed liquor pH. Likewise,
Urase et al. [143] found that the higher removal rate of some acidic pharmaceuticals
such as ketoprofen, ibuprofen, clofibric acid, gemfibrozil, fenoprofen, ketoprofen,
naproxen, diclofenac and indomethacin by MBR treatment was observed at lower pH
(pH = 4.3 – 5) operation. On the other hand, the removal of neutral compounds 17-α
ethinylestradiol, carbamazepine, propyphenazone, and benzophenone was not
significantly affected by bioreactor pH.
Only a few studies specifically investigated the effect of different DO concentrations in
the reactor on the removal of trace organics. The reported results revealed not much
difference effect between aerobic and anoxic MBRs in terms of trace organics removal.
For example, Clara et al., [95] and Abegglen et al. [127] reported negligible level of
removal of carbamazepine in different configurations of MBR (sequential anoxic–
aerobic MBR and aerobic MBR, respectively). However, there are some studies, which
have reported better removal under anoxic environment, either in MBR or in batch tests.
Hai et al. [94] reported carbamazepine (a persistent trace organic) to be degraded only
under anoxic environment in their batch tests. In the MBR treatment the removal of
carbamazepine was 68 % and less than 20% under anoxic and aerobic conditions,
respectively [94]. Joss et al. [128], on the other hand, reported that the degradation of
estrone takes place under both anoxic and aerobic conditions, but achieves higher
degradation rate in aerobic conditions (DO = 2 -3 mg/L). Stasinakis et al. [93] reported
better removal of diuron during batch tests under anoxic environment (>95%) in
comparison to that in aerobic condition (60%). Zwiener et al. [144] also showed that
diclofenac was not degraded in short-term biodegradation test under aerobic conditions,
whereas it was degraded under anoxic conditions.
Chapter 2 Literature review
25
2.4 Activated carbon adsorption
2.4.1 Activated carbon
Activated carbon is a form of carbon that has been processed to make it extremely
porous, and thus, to have a very high surface area available for adsorption or chemical
reaction. Owing to its surface properties such as surface area, porosity and surface
chemistry, activated carbon is one of the most effective and widely used adsorbent for
the removal of organics from aqueous solutions. One major advantage of activated
carbon is its ability to efficiently remove a wide variety of toxic organic compounds
[145].
Adsorption is one of the most frequently applied methods for organics removal from
aqueous solution because of its efficiency, capacity and applicability on a large scale
[146]. Both PAC and GAC are commonly used for water and wastewater treatment
applications. A typical activated carbon particle, whether in powdered or granular form,
has a porous structure consisting of network of interconnected macrospores, mesopores
and micropores that provide a good capacity for the adsorption of organic molecules
due to its high surface area. This high surface permits the accumulation of a large
number of contaminant molecules [147]. The recent change in water discharge
standards regarding organic pollutants has placed additional emphasis on using
activated carbon. Adsorption is particularly effective in treating low concentration waste
streams and in meeting stringent treatment levels. Therefore, in the water and
wastewater treatment, activated carbon is expected to become an important tool for
trace organics removal.
2.4.2 Application of activated carbon
It is well known that activated carbon is one of the most effective adsorbents for the
removal of taste, color, and odor causing organic pollutants from aqueous or gaseous
phases. AC is widely applied as a commercial adsorbent in the purification of water and
air [94]. It is also widely used for treatment of taste and odor. Treatment with AC has
proved to be efficient for removal of geosmin and 2-MIB [78]. Zhang et al. [148]
demonstrated that GAC is an excellent adsorbent for two algal odorants dimethyl
trisulfide and β- cyclocitral. AC has been widely studied for treating landfill leachate
wastewater. Foo et al. [128] summarized lists of research on the landfill leachate
Chapter 2 Literature review
26
treatment via activated carbon adsorption process during the last 15 years and reported
that in most cases, activated carbon adsorption has revealed the prominence in removal
of an essential amount of organic compounds from the leachate samples. AC has been
also investigated intensively for treatment of dye wastewater [149-151]. The results
indicated that AC could be employed for efficient removal of dyes from wastewater [41,
149, 152].
PAC and GAC are frequently applied in drinking water treatment for removal of natural
or synthetic organic compounds (SOCs) e.g., pesticides [153]. Recently several studies
have evaluated adsorption of other trace organics (PhACs, EDCs) on activated carbon
both under laboratory conditions and surveys at full- scale drinking water treatment
plants [19, 32]. For example, Hernández-Leal et al. [34] reported complete adsorption of
all studied trace organics (bisphenol-A, benzophenone-3, hexylcinnamic aldehyde, 4-
methylbenzylidene-camphor (4MBC), triclosan, galaxolide, and ethylhexyl
methoxycinnamate) onto PAC in batch tests with milli-Q water spiked with 100 - 1600
µg/ L of trace organics at a PAC dosage of 1.25 g/ L and contact time of 5 minutes.
GAC has a relatively larger particle size compared to PAC and, consequently, presents a
relatively smaller surface area. Nevertheless, GAC has long been used in the removal of
traditional organic contaminants such as pesticides [153]. GAC has, therefore, been
proposed as a potential treatment method to aid in the effective removal of emerging
contaminants, particularly EDCs in wastewater treatment [154]. A significant reduction
in the concentration of steroidal estrogens (43-64%), mebeverine (84-99%) has been
achieved in a full-scale granular activated carbon plant [10]. In a study by Hernández-
Leal et al. [34] , three GAC columns were operated to treat aerobically treated grey
water which was spiked with the above micropollutants in the range of 0.1 - 10 µg/ L at
a flow rate of 0.5 bed volumes (BV)/h. They observed more than 72% removal of all
compounds (bisphenol-A, hexylcinnamic aldehyde, 4-methylbenzylidene-camphor
(4MBC), benzophenone-3 (BP3), triclosan, galaxolide, and ethylhexyl
methoxycinnamate). Tanghe et al. [155] reported that at least 100 mg/ g of nonyphenol
adsorbed on GAC in an adsorption test. A few studies have investigated GAC
adsorption as an option for tertiary treatment of conventional biologically treated
wastewater [10, 156], for example, Grover et al., [10] reported that a full scale GAC
plant could reduce above 60% of steroidal estrogens in sewage effluent.
Chapter 2 Literature review
27
Even though GAC columns demonstrate high initial adsorption capacity, the GAC
media can gradually become exhausted with adsorbed organic pollutants. Choi et al.
[157] reported that the initial high removal efficiency of nonylphenol gradually
decreased with operation time. This is a typical pattern observed with adsorption
systems. Adsorption efficiency steadily decreases as adsorption sites are gradually filled
up over operation time. However, it has been reported that AC can provide support for
microbial growth [144, 158], thus offering the potential of achieving the so called
biologically activated carbon (BAC), where organic contaminants can be removed by
simultaneous adsorption and biosorption. The BAC process can enhance the adsorption
of AC for non- or slowly biodegradable compounds by eliminating these compounds
that would otherwise compete for adsorptive sites. This concept has been demonstrated
in the literature [157, 159, 160]. Choi et al. [157] reported that used GAC, which had
already been used to adsorb amitrol, showed better performance of amitrol removal
than that of virgin GAC. The results suggested that perhaps biological degradation was
involved in amitrol removal and the microbes accustomed to amitrol was present in the
used GAC, which led to enhanced removal of the compound during the subsequent
application of that GAC .
2.4.3 Application of activated carbon with membrane bioreactor
Over the last decade, the tightening of water quality regulations and the increased
attention given to trace organic contaminants has been favouring the emergence of
alternative treatment technologies in order to completely eliminate trace organic
contaminants. In this connection, the concept of combined processes such as coupling of
MBR with NF/RO, MBR with ozonation, MBR with UV irradiation and MBR with
PAC/GAC has been tested. The idea of application of activated carbon adsorption in
conjunction with an MBR has given rise to two modes of its application: i) direct
addition of activated carbon (mainly PAC) into MBR, and ii) post-treatment of MBR
permeate by passing it through a GAC column or by dosing of PAC.
2.4.3.1 PAC-MBR systems
PAC is generally added directly into other process units [161]. The application of PAC
into biological treatment systems is usually called powdered activated carbon treatment
(PACT) process [162]. PACT process is based on the concept of simultaneous
Chapter 2 Literature review
28
adsorption and biodegradation, and has been reported to be effective for treating organic
toxic pollutants such as dyes [163]. Orshasky et al. [164] compared the removal
efficiency of three processes for the removal of phenol and aniline: biological treatment,
adsorption on powdered activated carbon and simultaneous adsorption and
biodegradation. The results revealed that simultaneous adsorption and biodegradation
processes achieved the best removal. Shaul et al. [165] reported an enhanced removal of
organics and colour in CAS to which PAC had been added. However, due to short
sludge retention time in CAS, a portion of carbon is wasted frequently along with the
withdrawn sludge. As compared to that in CAS, the use of PAC in MBR may be more
effective.
A PAC- added MBR combines three individual processes, namely physical adsorption
on PAC, biological degradation and membrane filtration in a single unit where all of the
processes occur simultaneously. In the PAC-MBR, membranes provide a physical
barrier preventing the passage of PAC, thus ensuring retention of the organic
compounds adsorbed on the PAC that otherwise would not be rejected by the membrane
alone. High biological activity may also be achieved when PAC is added into MBR
because PAC helps microbial growth in surface [166]. The hybrid process is shown in
Figure 3. The PAC absorbs organic compounds on its surface and extends contact time
between the biomass and adsorbed organic compounds, increases oxygen concentration
at the PAC surface and absorbs compounds that are toxic to the biomass. Hybrid
sorption-membrane bioreactors equipped with either microfiltration or ultrafiltration
modules have been reported for the treatment of landfill leachate and refinery
wastewater as well as for the removal of refractory organic matter from secondary
sewage effluent [159]. Excellent stable decoloration of the waste water containing two
dyes (Poly S 119 and Orange II) was achieved with simultaneous PAC
Chapter 2 Literature review
29
Figure 3: Schematic diagram of the hybrid process
The use of PAC as a support material for organics accumulation and biological
degradation also has the advantage that the effects of shock loads or toxic
concentrations of pollutants can be buffered as a result of their adsorption onto and
diffusion into the activated particles. This results in physical separation of the toxic
materials from the biological catalyst and ensures that the bacteria are able to continue
their metabolic activities [32]. Munz et al. [167] reported the synergistic effect of PAC
addition in an MBR treating tannery wastewater. In their study, PAC was shown to
reduce the negative effects of natural and synthetic tannins that impose toxicity to
tannery wastewater. PAC dosage of 10 g/L improved significantly the leachate
treatment in a PAC – MBR hybrid system [168]. In one study on biodegradation of
trace compounds in an aerobic MBR, it was found that PAC dosage of 500 mg/L
reduced trihalomethane (THM) precursor by over 98% [169]. Addition of PAC in to
MBR also improved effluent quality and provided stability against shock loading [40,
166].
Figure 4 illustrates the effects of PAC addition in an MBR and the underlying reasons
for the associated benefits. Recently, PAC has been widely investigated to mitigate the
fouling problem in membrane hybrid system. The addition of PAC increased the
rejection of low molecular weight organics by adsorption and thus reduced membrane
fouling. Vigneswaran et al. [170] showed that the direct addition of PAC into the
submerged MBR minimized the bio-fouling of the membranes and no chemically
cleaning of the membrane was required for a long time.
Biodegradation
Membrane
separation
Adsorption
Pollutants
Chapter 2 Literature review
30
Figure 4: Schematic illustrating the effects (a), causes (b) and mechanism (c) occurring
in an MBR after PAC addition [166].
The removal of certain trace organics by MBR treatment is unstable (see Section 2.3.2).
As mentioned earlier, two main mechanisms may account for removal of trace organics
in MBRs namely, adsorption on sludge and biodegradation [116]. Obviously, adsorption
mechanisms play an important role in the total removal efficiency of hydrophobic trace
organics in MBRs [7]. For instance, Tadkaew et al. [26] investigated the removal of
two model compounds bisphenol A and sulfamethoxazole and reported that the removal
(c)
(b)
(a) Enhanced biodegradation
involving the breakdown of
refractory compounds
PAC addition in MBR
Capability to tolerate
shock loads of
inhibitory compounds
Slow flux
decline
Improved sludge
dewaterability
Simultaneous adsorption
and biodegradation
Change in particle size, floc
formation, incompressible cake
formation and scouring effect
Synergistic
effects
Additive
effects
Simple combination of
adsorption and
biodegradation
Biofilm formation of PAC, growth of specific
microbial population, increased enzymatic activity,
bio regeneration of PAC
Chapter 2 Literature review
31
efficiency was 90% and 50%, respectively. In contrast to sulfamethoxazole, which is
rather hydrophilic, bisphenol A is a hydrophobic compound, therefore, both
biodegradation and adsorption may be responsible for its removal. Compounds
containing complex structure and toxic groups (such as halogens, nitro groups)
however, can show higher resistance to biodegradation and tend to have very low
removal [26]. Because the adsorption of trace organics onto sludge facilitates their
removal in the biological process, it is envisaged that addition of adsorbents such as
PAC directly into the MBR reactor can lead to significant retention of soluble trace
organics. Due to the complete retention of sludge by the membrane and application of
long SRT, the retained trace organics may be efficiently removed in an MBR to which
PAC has been added.
In recent years, a few studies on the performance of trace organics removal by MBR
coupled with PAC have been published [45, 46]. Results have shown that PAC addition
has positive effects on MBR performance in removal of trace organic contaminants. For
example, Li et al.[45] demonstrated an improved removal of two different PhACs,
namely, sulfamethoxazole and carbamazepine in a PAC-amended MBR system. Serrano
et al.[46] investigated the removal of several recalcitrant PhACs, namely,
carbamazepine, diazepam, diclofenac and trimethoprim by adding PAC into the aeration
tank. The results demonstrated that this approach was a successful tool to improve the
removal of the more recalcitrant compounds (carbamazepine, diazepam, diclofenac and
trimethoprim) up to 85 %.
2.4.3.2 GAC system coupled with MBR systems
While PAC is added directly into the MBR reactor, GAC is used in a packed bed
reactor. In comparison to investigations involving drinking water treatment, only a
handful of studies have investigated GAC adsorption as an option for tertiary treatment
of conventional biologically treated wastewater [10, 34, 156]. It has been noted in those
studies that the adsorption of trace organics on activated carbon decreased due to
competition with bulk organic matter for adsorptive sites. In fact, competition with bulk
organic matter for adsorptive sites has important implications to the lifetime and
serviceability of GAC columns. For efficient adsorption of trace organics, it is
recommended that the feed to GAC column has a low bulk organic content. Because
Chapter 2 Literature review
32
MBR can produce suspended solids-free permeate with low total organic carbon
content, GAC may be a suitable post treatment option for MBR permeate. In such a
system, GAC can specifically target the residual trace organics in MBR permeate
without any significant interference from the bulk organics.
Chapter 3 Methodology
33
CHAPTER 3: METHODOLOGY
3.1 Introduction
This chapter describes the research methodology, experimental setups and analytical
techniques used in this study. The physicochemical properties of the selected trace
organics are also presented in this section. The operation of the lab-scale MBR was
initiated on 7 Feb, 2011. The start–up period continued for 51 days until 29 Mar, 2011
to ensure the stability of operating conditions in the MBR system and build up of
biomass in the reactor. A synthetic wastewater was continuously fed into the MBR. At
the end of the start-up period, mixed liquor suspended solids concentration was 5 g/L.
Following the start-up period, selected trace organic compounds were spiked
continuously into synthetic wastewater that was fed to the MBR. The experimental
scheme has been systematically presented in
Figure 5. Table 4 outlines the timeline of different steps of MBR operation. Further
details will be given throughout this chapter.
Figure 5: Experimental road map
MBR start – up period
MBR combined with activated carbon
Simultaneous PAC adsorption
in MBR (PAC - MBR)
Sequential application of
MBR and GAC adsorption
(MBR - GAC)
Chapter 3 Methodology
34
Table 4: Experimental timetable
Experiment Time (Day)
MBR start- up period (without trace organics in feed) 51
MBR 15
MBR – GAC experiment 93
MBR 38
MBR (after sludge withdrawal) 9
PAC – MBR (0.1 g/L PAC) 36
PAC – MBR (0.5 g/L PAC) 64
3.2 Materials
3.2.1 Selected trace organic compounds
A set of 22 compounds representing four major groups of trace organic contaminants,
namely, (1) pharmaceutically active compounds, (2) pesticides, (3) surfactants and
industrial chemicals, and (4) steroid hormones, were selected in this study. The
selection of these model compounds was also based on their widespread occurrence in
domestic sewage and their diverse physicochemical properties (e.g. hydrophobicity,
molecular weight, charge). The effective hydrophobicity of these compounds varies
significantly as reflected by their Log D at pH 7. A combined stock solution was
prepared in methanol, kept in a freezer and used within a month.
Their physicochemical properties are shown in Table 5.
Chapter 3 Methodology
35
Table 5: Physicochemical properties of trace organics used in this study
Category Compound CAS
number
Molecular
weight
(g/mol)
Log KOWa
Log D at
pH 7 a
Dissociation
constant
( pKa)a
Water
solubility
(mg/L)b
Charge Structure of compounds
Ph
arm
ace
uti
call
y a
cti
ve
com
po
un
ds
Ibuprofen
(C13H18O2)
15687-27-1 206.28 3.50 ± 0.23 0.94 4.41 ± 0.10 21 Negative
Acetaminophen
(C8H9NO2)
103-90-2 151.16 0.48 ± 0.21 0.47
9.86 ± 0.13
1.72 ± 0.50
14000 Neutral
Naproxen
(C14H14O3)
22204-53-1 230.26 2.88 ± 0.24 0.73 4.84 ± 0.30 16 Negative
Ketoprofen
(C16H14O3)
22071-15-4 254.28 2.91 ± 0.33 0.19 4.23 ± 0.10 16 Negative
Chapter 3 Methodology
36
Diclofenac
(C14H11Cl2NO2)
15307-86-5 296.15 4.55 ± 0.57 1.77
4.18 ± 0.10
-2.26 ± 0.50
2.4 Negative
Primidone
(C12H14N2O2)
125-33-7 218.25 0.83 ± 0.50 0.83
12.26 ± 0.40
-1.07 ± 0.40
500 Negative
Carbamazepine
(C15H12N2O)
298-46-4 236.27 1.89 ± 0.59 1.89
13.94 ± 0.20
-0.49 ± 0.20
18 Neutral
Salicylic acid
(C7H6O3)
69-72-7 138.12 2.01 ± 0.25 -1.13 3.01 ± 0.10 2240 Negative
Metronidazole
(C6H9N3O3) 443-48-1 171.15 -0.14 ± 0.30 -0.14
14.44 ± 0.10
2.58 ± 0.34
9500 Neutral
Chapter 3 Methodology
37
Gemifibrozil
(C15H22O3)
25812-30-0 250.33 4.30 ± 0.32 2.07 4.75 19 Negative
Triclosan
(C12H7Cl3O2)
3380-34-5 289.54 5.34 ± 0.79 5.28 7.80 ± 0.35 10 Neutral
Pest
icid
es
Fenoprop
(C9H7Cl3O3)
93-72-1 269.51 3.45 ± 0.37 - 0.13 2.93 71 Negative
Pentachlorophenol
(C6HCl5O)
87-86-5 266.34 5.12 ± 0.36 2.58 4.68 ± 0.33 14 Negative
4-tert-butyphenol
(C10H14O)
98-54-4 150.22 3.39 ± 0.21 3.40 10.13 ± 0.13 580 Neutral
Chapter 3 Methodology
38
Su
rfa
cta
nts
an
d i
nd
ust
ria
l ch
em
icals
4-tert-octylphenol
(C14H22O)
140-66-9 206.32 5.18 ± 0.20 5.18 10.15 ± 0.15 5 Neutral
4-n-nonylphenol
(C15H24O)
104-40-5 220.35 6.14 ± 0.19 6.14 10.15 6.35 Neutral
Bisphenol A
(C15H16O2)
80-05-7 228.29 3.64 ± 0.23 3.64 10.29 ± 0.10 120 Neutral
Ste
roid
horm
on
es
Estrone
(C18H22O2)
53-16-7 270.37 3.62 ± 0.37 3.62 10.25 ± 0.40 677 Neutral
17-β-estradiol
(C18H24O2)
50-28-2 272.38 4.15 ± 0.26 4.15 10.27 3.9 Neutral
HO
(CH2)8 CH3
Chapter 3 Methodology
39
17-β-estradiol –
acetate
(C20H26O3)
1743-60-8 314.42 5.11 ± 0.28 5.11 10.26 ± 0.60
Neutral
17-α
ethinylestradiol
(C20H24O2)
57-63-6 269.40 4.10 ± 0.31 4.11 10.24 ± 0.60 11.3 Neutral
Estriol (E3)
(C18H24O3)
50-27-1 288.38 2.53 ± 0.28 2.53 10.25 ± 0.70 441 Neutral
a Log Kow and pKa are obtained from Sci Finder (ACS) database
b water solubility are obtained from http://chem.sis.nlm.nih.gov/chemidplus/
Chapter 3 Methodology
40
3.2.2 Synthetic wastewater
A synthetic wastewater that was utilized in a previous study [26] was modified as
mentioned below to simulate medium strength municipal wastewater. A concentrated
stock solution was prepared and stored in a refrigerator at 40C. Then it was diluted with
Milli-Q water on a daily basis to make up a feed solution containing glucose (100
mg/L), peptone (100 mg/L), KH2PO4 (17.5 mg/L), MgSO4 (17.5 mg/L), FeSO4 (10
mg/L), CH3COONa (225 mg/L) and (NH2)2CO (35 mg/L Because the wastewater was
made with Milli-Q water, its turbidity was very low (<1 NTU). The chemical oxygen
demand (COD), total organic carbon (TOC) and total nitrogen (TN) was 600, 180 and
25 mg/L, respectively.
3.2.3 Activated carbon
In this study, two types of activated carbon namely GAC 1200 and PAC 1000
(Activated Carbon, Technologies Pty Ltd, Victoria, Australia), were used. The
characteristics of each type of activated carbon are listed in the Table 6.
Chapter 3 Methodology
41
Table 6: Characteristic properties of PAC 1000 and GAC 1200
Parameters Values
PAC GAC
Apparent density (g/mL) a 0.35-0.45
0.42-0.50
Surface area (MultiPoint BET
m2/g)
b 1355
1121
Ash content (%) a 14
3
Iodine number (mg of I2/g) a > 1000
>1200
Particle size a 15-30 µm
6 x 12 mesh (1.6-2.0
mm)
Pore volume (cc/g) b 0.228
0.043
Pore diameter (nm) b 3.139
3.132
a Data from Activated Carbon Pty Ltd, Australia.
b Data obtained from a nitrogen adsorption/desorption measurement using an
Autosorb iQ. The measurement was conducted at the Australian Nuclear Science
and Technology Organisation. Pore volume and pore diameter were calculated
based on the Barret-Joyner-Halenda method.
3.3 Experimental set-up and operation protocol
3.3.1 Laboratory–scale MBR set-up and operation protocol
A laboratory scale MBR system was employed in this study. A schematic diagram of
the MBR is shown in Figure 7. The MBR system consisted of a glass reactor with an
active volume of 4.5 L, one air pump, a pressure sensor, feed and permeate tanks,
influent and effluent peristaltic pumps. A PVDF hollow fiber membrane module
supplied by Mitsubishi Rayon Engineering, Japan was submerged in the reactor (Figure
8). The membrane had a nominal pore size 0.4 µm and total surface area of 0.074 m2.
Transmembrane pressure (TMP) was continuously monitored using a high-resolution
pressure sensor (± 0.1 kPa) (SPER scientific 840064, Extech equipment Pty Ltd,
Victoria, Australia) to detect probable onset of fouling. During continuous operation
without any routine cleaning, ex-situ chemical cleaning had to be performed only twice
(on day 186 and 306) over the whole operation period (306 days). During ex-situ
chemical cleaning, the membrane was soaked into sodium hypochlorite solution (0.5 g
Cl/L) for 60 min and then backwashed with a freshly prepared sodium hypochlorite
Chapter 3 Methodology
42
solution ((0.5 g Cl/L) at a flux of 0.21 m/d for 30 min. The permeate pump (Masterflex
L/S, Cole-Parmer Instrument Company) was operated on a 14 min suction and 1 min
rest cycle to provide relaxation time to the membrane module. The membrane was
operated under an average flux of 2.6 L/m2h. The average flow rate of the influent pump
was adjusted to match with that of the effluent pump to maintain a constant reactor
volume.
Figure 6: Membrane bioreactor (MBR) set-up (1 Feed tank, 2 Feed pump, 3 MBR , 4
Pressure gauge, 5 Permeate pump, 6 Permeate tank, 7 Computer). Dimensions of the
reactor were 360 mm (H) x 320 mm (L) x 45 mm (W).
(6)
(7) (5)
(4)
(2)
(1)
(3)
Chapter 3 Methodology
43
Figure 7: A schematic diagram of the MBR set up
Figure 8: PVDF hollow fiber membrane module used in this study (dimensions 29 cm
(L) x 17 cm (H) x 1 cm (W), Fiber length and outer diameter of 22 cm and 0.2 cm,
respectively. Membrane nominal pore size = 0.4 µm and total membrane surface area =
0.074 m2)
Feed pump
Suction pump
PC
Permeate tank
Pressure gauge
Membrane reactor
Hollow fiber
membrane
Feed tank
Air pump
Diffuser
Chapter 3 Methodology
44
The reactor was seeded with activated sludge from another lab scale MBR system [26].
The hydraulic retention time was set at 24 hours. Air was supplied via a diffuser located
at the bottom of the aeration tank. Temperature and the dissolved oxygen concentration
of the mixed liquor were maintained at 20 ± 0.1 oC and 3 ± 1 mg/L, respectively. The
pH of the mixed liquor remained stable within the range of 7.2 – 7.5. After an initial
start up period of 51 days, stable operation of the MBR in terms of TOC and TN
removal had been achieved. At this point, the selected trace organic compounds were
added to the synthetic wastewater. The performance of the MBR system was
investigated in terms of trace organic contaminants removal efficiency, TOC/TN
removal and ammonium/ nitrate removal. Operating parameters, namely,
MLSS/MLVSS concentration, turbidity, EPS and SMP concentration, SVI and SOUR
were also monitored. Duplicate samples of both influent and effluent were taken once a
week for trace organic contaminants analysis throughout the operation period.
3.3.2 Laboratory–scale MBR-GAC set-up and operation protocol
A borosilicate glass column (Omnifit, Danbury, CT, USA) filled with 7.5 g of GAC was
used as a post-treatment unit for the MBR permeate. The column had an internal
diameter and an active length of 1 cm and 22 cm, respectively resulting in a bed volume
(BV) of 17 mL. GAC-1200, obtained from Activated Carbon, Technologies Pty Ltd,
Victoria, Australia, was utilized in this study. The characteristics of the utilized GAC
have been outlined in Table 6. The GAC set-up also contained a pump, and influent and
effluent tanks. The GAC set-up has been presented in
Figure 10.
Chapter 3 Methodology
45
Figure 9: Fixed bed GAC column. A borosilicate glass column (1cm diameter x 22 cm
L) filled with 7.5 g GAC was used.
Figure 10: Combined MBR – GAC system
GAC
effluent
tank
Feed pump
GAC fixed
bed column
Suction
pump
Permeate
tank
Pressure gauge
Membrane
Bioreactor
Feed tank
Air
pump
Diffuser
GAC post-treatment unit
Hollow fiber
membrane
Chapter 3 Methodology
46
The MBR permeate was pumped through the GAC column in an up-flow mode at a
flow rate 2.4 mL/min (8.5 BV/h), resulting in an empty bed contact time (EBCT) of 7
min. The GAC post treatment column was attached to the MBR setup at two weeks
after the start of spiking the synthetic wastewater with trace organics, and it was
operated for thirteen weeks (equivalent to 18093 BV).
The performance of the MBR – GAC system was investigated in terms of trace organic
contaminants removal efficiency, and TOC/TN removal. Independent batch tests were
conducted to explain the breakthrough profiles observed in the GAC column (see
Section 3.3.4).
3.3.3 Laboratory scale PAC - MBR set-up and operation protocol
During this part of experiment, the MBR set-up and operation were exactly the same as
before (see Section 3.3.2). In the course of 196 days of continuous operation, the MLSS
concentration in the MBR rose up to 11.5 g/L. MLSS concentrations were reduced to 5
g/L by withdrawing sludge on day 197. Nine days after the withdrawal of the sludge,
PAC (Table 6) was added into the reactor on day 206 and subsequently on day 243 of
continuous operation to obtain a PAC concentration of 0.1 and 0.5 g/L, respectively.
PAC (0.45 and 1.8 g, respectively) was mixed with 200 mL feed media which was then
poured into the MBR. Operating conditions (temperature, HRT, pH and DO
concentration) were kept the same as that during MBR operation without PAC.
All analyses including that of trace organics were performed in the same fashion as in
MBR only or MBR – GAC experiment.
3.3.4 Adsorption isotherm
Adsorption is a natural process by which molecules of a dissolved compound adhere to
the surface of an adsorbent. The process involves concentration changes in both phases
[171]. In case of the activated carbon application for the removal of trace organics from
wastewater, concentration of the trace organics in liquid phase decreases while
concentration in the activated carbon surface increases. The specific capacity of
activated carbon to adsorb organic compounds is related to: molecular surface
attraction, the total surface area available per unit weight of carbon, and the
concentration of contaminants in the wastewater [172]. Adsorption isotherms are widely
used as a tool to evaluate activated carbon adsorption capacity. The isotherm represents
Chapter 3 Methodology
47
an empirical relationship between the amount of contaminant adsorbed per unit weight
of carbon and its equilibrium water concentration.
3.3.4.1 Kinetic experiments
Kinetic experiments were designed to determine the time necessary for the adsorption
process to reach equilibrium. 30 mg of fresh GAC was added in each of 6 breakers
separately; then 100 mL of 20 mg/L trace organic solution was added. All the beakers
were covered with aluminium foil and placed in a shaker (BL 4500 Bioline incubator,
Edward Instrument Company, NSW, Australia) at a speed of 150 rpm and under a
temperature of 22°C. Then 2 mL sample was taken at 0, 6, 12, 18, 24, 36 and 48 hrs,
respectively. The concentration of trace organic in sample was measured by Shimadzu
HPLC systems (see Section 3.4.7.2).
3.3.4.2 Isotherm experiment
Fresh GAC was added in amounts ranging from 15 to 50 mg in glass beakers separately.
Then 100 mL of single trace organic solution with a concentration of 20 mg/L was
added into each beaker. All the beakers were covered with aluminium foil and incubated
for 24 h under 22 oC and 150 rpm in a temperature controlled rotary shaker (BL 4500,
Bioline, Edward Instrument Company, NSW, Australia). Samples were taken after 24 h
(previously established point of equilibrium adsorption). The concentration of trace
organic in sample was measured by Shimadzu HPLC systems (see Section 3.4.7.2).
The experimental data was evaluated by fitting to the Freundlich and Langmuir
isotherms. The equation that describes the Freundlich isotherm is given below.
nefe Ckq
1
(1)
The equation can be rewritten in a linear form as follows:
efe Logcn
LogkLogq1
(2)
The Langmuir isotherm can be expressed in the following form:
Chapter 3 Methodology
48
m
e
me
e
q
c
c
b
1
(3)
Where:
qe equilibrium mass of compound adsorbed on unit mass of adsorbent (mg/g)
Ce equilibrium concentration of compound in liquid (mg/L)
Kf Freundlich partitioning coefficient (mg/g)/(mg/L)1/n
1/n Freundlich exponential coefficient
qm amount of adsorbate adsorbed per gram of adsorbent (mg/g)
b Langmuir’s constant (L/mg)
qmb adsorbent adsorbate relative affinity (L/g)
3.4 Analytical techniques
3.4.1 Total organic carbon and total nitrogen
All samples were kept at 4oC and analysed within two weeks. TOC and TN
concentrations were determined using Shimadzu TOC/TN-VCSH analyser (Figure 11).
The combination of the TOC-VCSH and the TNM-1 can simultaneously measure TOC
and TN. TOC analysis was conducted in non-purgeable organic carbon (NPOC) mode
in order to reduce a large error in TOC value due to high amount of inorganic carbon
(IC) in the samples. The sample was acidified and sparged with ultra purity (zero grade)
air to drive off the inorganic carbon in the form of CO2 gas. For total nitrogen
determination, the sample is combusted to nitrogen monoxide and nitrogen dioxide.
Calibrations were performed using reagent grade potassium hydrogen phthalate and
reagent grade potassium nitrate in the range from 0 to 1,000 mg/L for TOC and from 0
to 100 mg/L for TN, respectively. Calibrations were performed using reagent grade
potassium hydrogen phthalate and reagent grade potassium nitrate for TOC (0 to 100
mg/L) and TN (0 to 100 mg/L) measurement, respectively.
Chapter 3 Methodology
49
Figure 11: Total organics carbon and total nitrogen analyzer system (1 Auto sampler
and sample tray, 2 TOC analyzer, 3 TN analyzer unit, 4. Computer).
TC standard solutions were prepared by adding 2.125 g of pre-dried (105 oC, 1 h)
reagent grade potassium hydrogen phthalate into 1L of Milli Q water. This solution was
used as the standard stock solution with the concentration of 1,000 mg C/L. The
standard stock solution was diluted with Milli Q water to prepare standard solutions at
0, 5, 10, 25, 50 and 100 mg C/L (Figure 12).
(1) (2)
(3)
(4)
Chapter 3 Methodology
50
0 100 200 300 400 500
0
20
40
60
80
100 TOC concentration (mg/L) = 4.7 x average peak area
R2
= 0.99
TO
C c
once
ntr
atio
n (
mg C
/L)
Average peak area (mV)
Figure 12: A typical TOC calibration curve to determine TOC concentration in samples
Chapter 3 Methodology
51
TN standard solutions were prepared by adding 7.219 g of pre-dried (105 oC, 3 h)
reagent grade potassium nitrate into 1L with Milli-Q water. This solution was used as
the standard stock solution with the concentration of 1,000 mg N/L. The standard stock
solution was diluted with Milli-Q water to prepare standard solution at 0, 5, 10, 25, 50
and 100 mg N/L (Figure 13).
0 200 400 600 800 1000 1200 1400 1600 1800
0
20
40
60
80
100
Average peak area (mV)
TN
co
nce
ntr
atio
n (
mg
N/L
)
TN concentration (mg/L) = 16.59 x average peak area
R2 = 1
Figure 13: A typical TN calibration curve to determine TN concentration in samples
3.4.2 DO concentration, pH, turbidity, and sludge volume index
The pH and dissolved oxygen (DO) of mixed liquor in the MBR was measured by a
Metrohm Advanced pH/Ion Meter and DO meter (YSI model 59, USA), respectively.
Turbidity of influent, supernatant and effluent samples were measured by a turbidity
meter (HACH 2100A). It is an optical method, which measures the amount of scattering
when light passes through the sample. The turbidity meter was calibrated by using
standard solution each time before measuring.
The sludge volume index (SVI) is the volume in mL occupied by 1 g of sludge after 30
min settling. SVI typically is used to monitor settling characteristics of activated sludge
and other biological suspensions. Although SVI is not supported theoretically,
experience has shown it to be useful in routine process control. The SVI is calculated
by following equation:
Chapter 3 Methodology
52
)( 0 MLSSV
VSVI
(4)
Where:
SVI is the sludge volume index (mL/g).
V is the volume of the sludge that has been allowed to settle for half an hour (mL).
Vo is the initial volume of the sludge before being allowed to settle (L).
MLSS represents the mixed liquor suspended solids concentration (g/L).
3.4.3 Mixed liquor suspended solids and mixed liquor volatile suspended solids
Mixed liquor suspended solids (MLSS) represents the concentration of non- soluble
solids in the mixed liquor in the bioreactor. The solids are comprised of biomass (dead
and living bacteria as well as debris) and organic and inorganic compounds either
introduced from raw wastewater or produced during biomass growth and decay. MLSS
gives an estimation of the biomass concentration. A mixed liquor sample of 25 mL was
taken from the bioreactor once a week. The sample was centrifuged for 10 min with
1073 x g; the supernatant was discarded and the sludge was transferred to a pre-weighed
crucible. The sample was kept in a water bath for 1 h at 100 oC to dewater the sample
and then over night in an oven at 100 oC. The sample was weighed after the temperature
of the crucible cooled down to the room temperature. For mixed liquor volatile
suspended solids (MLVSS) measurement, the samples were put in the furnace at 550 oC
for 15 min, during which the organic fraction evaporated leaving behind the inorganic
portion. The MLSS and MLVSS are expressed by g/L.
Calculations:
MLSS = mdried sample – m empty crucible (5)
MLNVSS = m evaporated sample – m empty crucible (6)
MLVSS = MLSS – MLNVSS (7)
Where:
MLSS is mixed liquor suspended solids (g/L)
MLVSS is mixed liquor volatile suspended solids (g/L)
MLNVSS is mixed liquor non-volatile suspended solids (g/L)
Chapter 3 Methodology
53
3.4.4 Specific oxygen uptake rate (SOUR)
Microorganisms in sludge use oxygen as they consume available organic matter. The
level of microbial activity in sludge is indicated by the microorganism oxygen uptake
rate. Some conclusions about the situation in the reactor e.g. organic load, presence of
toxins in feed and changes in metabolism can be made by periodically monitoring
SOUR [173]. Lower oxygen uptake rates than usual may indicate a reduced microbial
activity due to any form of stress.
Spiked and un-spiked SOUR were measured throughout the study. For the un-spiked
SOUR, on the day of measurement, 400 mL sludge was taken out of the reactor and the
concentration of DO was increased by aeration for 30 min to reach air saturation. Then a
part of the sample was transferred to a 300 mL borosilicate bottle and kept well mixed
by a stirrer attached to the DO probe. DO was recorded for 15 min in 30-second
intervals using a DO meter (YSI model 59, USA). In the spiked SOUR, the MBR feed
was mixed with mixed liquor (1:1 V/V).
The oxygen consumption rate was calculated as following and represented in mg O2 /
L* hr.
)/(60 2 hrLmgOslopeOUR (8)
Where:
Slope = Slope of the linear portion of the DO profile versus time
The SOUR was obtained by dividing the oxygen uptake rate by the mixed liquor
volatile suspended solids (MLVSS) concentration.
)/( 2 gMLVSShmgOMLVSS
OURSOUR
(9)
3.4.5 Nitrate and Ammonium
Nitrate concentration was measured by an ion chromatography system (Figure 16)
(Shimadzu, Japan). MBR feed, supernatant, MBR permeate, and GAC effluent samples
were measured twice a week. The mixed liquor sample was centrifuged for 10 min at
1073 x g and the supernatant was used to measure nitrate. Standard solutions of
potassium nitrate (KNO3) having a concentration of 5, 10, 15, 20, 30, 40 and 50 mg/L of
Chapter 3 Methodology
54
NO3-.were prepared The concentration of nitrate in sample was calculated based on the
calibration curve established from the standard solutions.
0
500000
1000000
1500000
2000000
25000000
10
20
30
40
50
Nit
rate
co
nce
ntr
atio
n (
mg
/L)
Peak area (µS)
NO3
- = 0.0002 x peak area + 2.91
R2 = 0.99
Figure 14: A typical calibration curve to determine nitrate concentration in samples
Ammonium concentration was measured using phenate method [174]. The analytical
reagents were hypochlorous acid, manganous sulphate solution and phenate reagent.
The reaction of ammonia, hypochlorite and phenol catalyzed by a manganous salt
produces a bluish color corresponding to a wave length of 630 nm. The sample
preparation was same as that of nitrate samples. Ammonium chloride (NH4Cl) was used
to prepare standard solutions having a concentration of 0.1, 0.5, 1.0, 2.0, 2.5 and 5 mg/L
of NH4+. An UV- visible spectrophotometer (Shimadzu UV-1700, Japan, Figure 20)
was used to measure the absorbance at a wavelength of 630 nm. The concentration of
ammonium in samples was calculated based on the calibration curve established from
the standard solutions.
Chapter 3 Methodology
55
0.0 0.2 0.4 0.6 0.8 1.0 1.2
0
1
2
3
4
5
Co
nce
ntr
atio
n N
H3-N
(m
g/L
)
Absorption at 630 nm (1/cm)
NH3-N concentration = 4.22 x Abs - 0.25
R2 = 0.98
Figure 15: A typical calibration curve to determine ammonium concentration in
samples
Figure 16: An Ion-chromatography system (1 Pump part, 2 Auto sampler, 3 Column
chamber, 4 Conductivity detectors, 5 System controller, 6 Computer).
(1)
(2) (3)
(4)
(5)
(6)
Chapter 3 Methodology
56
3.4.6 Extracellular polymeric substances and soluble microbial products
Extracellular polymeric substances (EPS) are a complex mixture of polymers excreted
by microorganisms. They are mainly made up of humic and fulvic acids,
polysaccharides, proteins, amino acids and exocellular enzymes [175]. Many authors
have defined two types of EPS: soluble and bound EPS. The soluble part appears in the
supernatant, and it is also referred to as soluble microbial product (SMP). The bound
EPS exists as a capsule surrounding the bacteria cell wall [176]. SMP and EPS have
been found to influence various properties of activated sludge such as floc strength and
size distribution, dewaterability, settleability and compressibility, non-settleable solids
fraction and hydrophobicity. Although controversies exist, EPS and SMP have been
reported as important parameters governing membrane fouling [177].
The mixed liquor and permeate sample were collected in this experiment for EPS and
SMP measurements. The samples were stored in the fridge at below 4oC for 2 weeks
until measurement. The process of sample preparation has been illustrated in Figure 17.
The mixed liquor samples were centrifuged for 20 min at 3270 x g to separate the SMP
and EPS. After centrifugation, the supernatant, which contains SMP, was transferred to
20 mL amber bottles. The rest of the samples were subjected to EPS extraction. EPS
was extracted by adding 50 mL of sodium chloride (0.9%) into the samples and then
placing it in a water bath at 80 oC for one hour. After that the samples were centrifuged
for 20 min at 3270 x g. Finally, the supernatant was used to detect EPS.
Chapter 3 Methodology
57
Figure 17: Schematic of sample preparation for EPS and SMP determination
For determination of concentration of polysaccharides, a standard calibration curve was
established by using glucose solutions covering a concentration range of 0 to 100 mg/L.
The determination was based on reaction of glucose with phenol and sulphuric acid. An
UV-visible spectrophotometer (Shimadzu UV-1700, Japan, Figure 20) was used to
measure the absorbance at a wavelength of 490 nm. The concentration of samples was
calculated based on the calibration curve shown in Figure 18.
Heat in water bath at 80 0C
for 1 h and cool to room
temperature
25 mL of mixed liquor
sample
Soluble EPS (SMP)
Polysaccharides & Protein
determination on
supernatant
Add 50-100 mL
of NaCl 0.9 %
Bound EPS
Centrifuged at
3270 x g, 20 min
Centrifuged at
3270 x g, 20 min
Chapter 3 Methodology
58
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
0
20
40
60
80
100 Carbonhydrate concentration (mg/L) = 0.013 x Abs + 0.03
R2 = 0.99
Absorption at 490 nm (1/cm)
Co
nce
ntr
atio
n o
f ca
rbo
nh
yd
rate
(m
g/L
)
Figure 18: A typical calibration curve to determine carbohydrate concentration in
samples
For protein determination, a BSA (Bovine Serum Albumin) solution was used to
develop a calibration curve. The calibration curve covered a range of 0 to 100 mg/L.
The analytical reagents were copper (II) sulphate, sodium carbonate, sodium hydroxide,
and Folin-Ciocalteu reagent. An UV- visible spectrophotometer (Figure 20) (Shimadzu
UV-1700, Japan) was used to measure the absorbance at a wavelength of 750 nm [178].
The concentration of samples was calculated based on the calibration curve shown in
(Figure 19).
Chapter 3 Methodology
59
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0
20
40
60
80
100
Absorption at 750 nm (1/cm)
Co
nce
ntr
atio
n o
f p
rote
in (
mg
/L)
Protein concentration (mg/L) = 0.003 x Abs +0.03
R2 = 0.98
Figure 19: A typical calibration curve to determine protein concentration in samples
Figure 20: An UV-visible spectrophotometer
Chapter 3 Methodology
60
3.4.7 Trace organics analysis
In this study, trace organic analysis was conducted using different methods namely gas
chromatography – mass spectrometry (GC-MS), high - performance liquid
chromatography (HPLC) - UV and liquid chromatography – mass spectrometry (LC-
MS).
3.4.7.1 Gas chromatography – mass spectrometry
The trace organic compounds in feed and permeate samples were extracted using 6 mL
200 mg Oasis HLB cartridges (Waters, Milford, MA, USA). The cartridges were pre-
conditioned with 7 mL dichloromethane and methanol (1:1, v/v), 7 mL methanol, and 7
mL reagent water, respectively. The feed and permeate samples (500 mL each) were
adjusted with H2SO4 0.4 M to pH 2 – 3, then loaded onto the cartridges at a flow rate of
15 mL/min, after which the cartridges were rinsed with 20 mL Milli-Q water and dried
with a stream of nitrogen for 30 min (see Figure 21). The trace organic compounds were
eluted from the cartridges with 7 mL methanol followed by 7 mL dichloromethane and
methanol (1:1, v/v) at a flow rate of 1 – 5 mL/min, and the eluents were evaporated to
dryness under a gentle stream of nitrogen in a water bath at 40 °C. The extracted
residues were then dissolved with 200 µL methanol solution which contained 5 µg
bisphenol A-d16 and transferred into 1.5 mL vials, and further evaporated to dryness
under a gentle nitrogen stream. Finally, the dry residues in the vials were derivatized by
addition of 100 µL of BSTFA (1% TMCS) plus 100 µL of pyridine (dried with KOH
solid), which were then heated in a heating block at 60 – 70°C for 30min. The
derivatives were cooled to room temperature and subjected to GC-MS analysis [179].
Analyses of the trace organic compounds were conducted using a Shimadzu GCMS-
QP5000 system (Figure 23), equipped with a Shimadzu AOC 20i autosampler. A
Phenomenex Zebron ZB-5 (5% diphenyl – 95% dimethylpolysiloxane) capillary column
(30 m × 0.25 mm ID, df = 0.25 µm) was used. Helium carrier gas was maintained at a
constant flow rate of 1.3 mL/min. The GC column temperature was programmed from
100 °C (initial equilibrium time 1 min) to 175 °C via a ramp of 10 °C/min and
maintained 3 min, 175 – 210 °C via a ramp of 30 °C, 210 – 228 °C via a ramp of 2
°C/min, 228 – 260 °C via a ramp of 30 °C, 260 – 290 °C via a ramp of 3 °C/min and
maintained 3 min. The injector port and the interface temperature were maintained at
280 °C. Sample injection (1 µL) was in splitless mode.
Chapter 3 Methodology
61
For the qualitative analysis, the MS full-scan mode from m/z, 50 – 600 was used, apart
from the mass spectrum, the relative retention times of each compound was used for
confirmation of the compound. Quantitative analysis was carried out using selected ion
monitoring (SIM) mode. For each compound, the most abundant and characteristic ions
were selected for quantization. The selected ions of the analysed compounds after silyl
derivatization are in agreement with those reported elsewhere [180-182].
Standard solutions of the analytes were prepared at 1, 10, 50, 100, 500 and 1000 ng/mL,
and an internal instrument calibration was carried out with bisphenol A- d16 as internal
standard. The calibration curves for all the analytes had a correlation coefficient of 0.99
or better. Detection limits were defined as the concentration of an analyte giving a
signal to noise (s/n) ratio greater than 3. The limit of reporting was determined using an
s/n ratio of greater than 10.
Chapter 3 Methodology
62
Figure 21: Schematic of sample preparation for GC-MS measurement of trace organics
(Reagent water is MBR feed without trace organics. MeOH - methanol, DCM –
dichloromethane, SPE – solid phase extraction, HLB -Hydrophilic-lipophilic-balanced)
Sample preparation
600 mL beakers are
rinsed
Filter samples and
adjust pH to 2-3
Take 500 mL sample
SPE equipment requirement
Rinse the lines and valves
1. Methanol
2. Milli-Q water
Wash Oasis HLB cartridge with
1. 7 mL of MeOH-DCM (1:1)
2. 7 mL of Methanol
3. 7 mL of reagent water
Filter the sample through HLB cartridge
(Approximately one individual drop/sec)
Rinse cartridges with 6 x 7mL Milli-Q
water
Dry samples with gentle stream of Nitrogen
(30 min)
Keep the cartridges in freezer
Chapter 3 Methodology
63
Figure 22: The solid phase extraction manifold holding cartridges through which the
sample drips into the perforated chamber below, where tubes collect the effluent. A
vacuum port with gauge is used to control the vacuum applied to the chamber (1 Sample
containers, 2 HLB cartridges, 3 Chamber, 4 Vacuum port).
Figure 23: Gas chromatography-mass spectrometry system (1 Sample tray, 2 Sample
injector, 3 GCMS-QP 5000, 4 Computer)
(1)
(2)
(4) (3)
(1)
(2) (3)
(4)
(1)
Chapter 3 Methodology
64
3.4.7.2 High performance liquid chromatography
The concentration of trace organic in adsorption test samples was measured by a
Shimadzu HPLC system (Shimadzu, Kyoto, Japan, Figure 24) equipped with a Supelco
Drug Discovery C-18 column (with diameter, length and pore size of 4.6 mm, 150 mm,
and 5µm, respectively) and a UV-Vis detector. The detection wavelength was set at 280
nm for carbamazepine and diclofenac and 225 nm for ketoprofen, naproxen and
fenoprop, respectively. The column temperature was set at 20oC. A sample injection
volume of 50 μL was used. The mobile phase composed of acetonitrile and Milli-Q
grade deionized water buffered with 25 mM KH2PO4. Two eluents, namely, eluent A
(80 % acetonitrile + 20% buffer, v/v) and eluent B (20 % acetonitrile + 80 % buffer,
v/v) were delivered at 1.0 mL/min through the column in time-dependent gradient
proportions for 33 minutes. The proportion of eluent B remained at 85 % for the first
five minutes, then gradually dropped to 40 % within the subsequent eight minutes,
remained at 40 % for the next ten minutes, sharply returned to 85 % within the
following one minute, and remained constant for the rest of the period this method was
used to detect carbamazepine and diclofenac. In detection of ketoprofen, naproxen and
fenoprop, the proportion of eluent B remained at 50 % for the first seven minutes, then
gradually dropped to 20 % within the subsequent 12 minutes, and sharply returned to 50
% and remained for 15 minutes. Calibration always yielded standard curves with
coefficients of determination (R2) greater than 0.98 within the range of experimental
concentrations used. The quantification limit for the analytes under investigation using
these conditions was approximated at 10 μg/L.
Table 7: Gradient eluent profiles used in HPLC-UV analyses
For carbamazepine and diclofenac
Time (min) 0 5 13 23 24 33
Eluent B, % 85 85 40 40 85 85
For ketoprofen, naproxen and fenoprop
Time (min) 0 7 19 20 35
Eluent B, % 50 50 20 50 50
Chapter 3 Methodology
65
Figure 24: High performance liquid chromatography system (1 Column, 2 Eluent
containers. 3. Auto sampler, sample tray and degasser, 4 Pump, 5 UV-VIS Detector, 6
Controller, 7 Computer)
3.4.7.3 Liquid chromatography – mass spectrometry
A Shimadzu LC-MS 2020 system (Shimadzu, Kyoto, Japan, Figure 25) was used to
detect metronidazole in the adsorption test. The mobile phase (Milli-Q water with 0.1%
formic acid) – acetonitrile (98:2, V/V) was delivered at a flow rate of 0.5 mL/min. The
injection volume was 5 µL. The data acquisition time was set at 12.5 min. Ionization of
the analyte was obtained by electrospray in the positive ion mode (ESI+), Nitrogen was
used as nebulizer and drying gas, which was set at 1.5 L/ min and 5.0 L/ min,
respectively. Calibration standards were 10, 50, 250, 500, 750, 1000 ng/ mL, calibration
curve yielded with coefficient of determination (R2) greater than 0.98 within the range
of experimental concentrations used.
(1) (2)
(3)
(4) (5)
(6)
(7)
Chapter 3 Methodology
66
Figure 25: Liquid chromatography-mass spectrometry system (1, Computer, 2 Pump
and degasser, 3 Sample injector, 4 Eluent container, 5 Controller, 6 UV-PDA detector, 7
Column chamber, 8 LCMS -2020)
(2)
(3) (1)
(5)
(6) (4)
(7) (8)
Chapter 4 Performance of MBR system
67
CHAPTER 4: PERFORMANCE OF MBR SYSTEM
4.1 Introduction
This study aims to investigate and demonstrate the complementarities between MBR
treatment and application of activated carbon for an enhanced removal of trace organic
contaminants. This chapter provides an overview of the long term performance of the
MBR with respect to the basic water quality parameters such as total organic carbon
(TOC), total nitrogen (TN) removal, Transmembrane pressure (TMP), turbidity, SVI,
MLSS/MLVSS, SOUR, ammonium/nitrate, and the removal of trace organic
contaminants.
4.2 Experimental set up and operation protocol
Detailed descriptions of the MBR system, its operation protocol, and analytical
techniques have been provided in chapter 3. The obtained data is systematically
analysed to depict the overall performance of the MBR throughout the operation period.
4.3 Results and discussion
4.3.1 Mixed liquor suspended solids and mixed liquor volatile suspended solids
The MBR operation was initiated with a MLSS concentration of 3.2 g/L. The MBR was
fed daily with synthetic wastewater without trace organic contaminants during the start-
up period of 51 days. At the end of start-up period the MLSS concentration was 5 g/L.
The profiles of MLSS and MLVSS have been illustrated in Figure 26. Apart from the
samples for MLSS /MLVSS and EPS/ SMP measurement, no sludge was withdrawn
from the MBR during this operation period. As a result, the concentration of MLSS
increased from 5 g/L to 9.8 g/L over a period of 110 days (Figure 26). Nevertheless, the
ratio of MLVSS to MLSS was stable at around 0.9, which indicates that the
accumulation of inorganic compounds did not occur during the experiment. The
increase in MLSS concentration did not lead to any significant variation in TOC and TN
removal (see Section 4.3.5). The observation made in this study is in line with that of
Nghiem et al. [116] who reported that the MBR performance appeared to be
independent of the MLSS concentration. TMP across the membrane module increased
slowly and after 157 days of operation, the TMP was only 10.6 kPa. In absence of any
periodic in situ or ex situ cleaning, the membrane did eventually get fouled. Chemical
Chapter 4 Performance of MBR system
68
cleaning of the membrane was performed on day 186, when the TMP of 70.7 kPa was
recorded.
0 20 40 60 80 100 120 140 160
0
1
2
3
4
5
6
7
8
9
10
MLSS (g/L) = 0.04x Time (Day) + 3.29
R2= 0.94
MLSS (g/L) MLVSS (g/L)
ML
SS
/ML
VS
S c
on
cen
trati
on
(g
/L)
Time (day)
S T
Figure 26: Variation of MLSS and MLVSS concentration throughout the operation
period before adding PAC into MBR. ―S‖ and ―T‖ indicate the start-up period and the
point of trace organic contaminants addition, respectively.
4.3.2 Turbidity and sludge volume index
It is generally accepted that MBR provides excellent treated water turbidity [36, 183]. In
this study, the turbidity of MBR permeate was generally below 0.2 NTU and all
recorded data were below 0.4 NTU (Figure 27). Turbidity in water is caused by
suspended and colloidal matter such as organic and inorganic matter including
microorganisms. The MBR process involves a suspended growth-activated sludge
system that utilizes microporous membrane for solid/liquid separation instead of
secondary clarifiers in CAS. Only particles significantly smaller than the maximum
membrane nominal pore size (around 0.4 µm) can pass through the membrane. Thus, it
has been widely reported that MBR can produce suspended solids-free permeate [36,
183, 184].
Chapter 4 Performance of MBR system
69
0 20 40 60 80 100 120 140 160
0.0
0.5
1.0
1.5
2.0
2.5
10
15
20
25 Supernatant Permeate
Tu
rbid
ity
(N
TU
)
Time (Day)
TS
Figure 27: Variation of MBR supernatant and permeate turbidity throughout the
operation period. The MBR supernatant was collected after centrifuging the mixed
liquor for 10 min at 1073 x g. ―S‖ and ―T‖ indicate the start-up period and the point of
trace organic contaminants addition, respectively.
Besides the turbidity of MBR permeate, that of the supernatant (obtained by
centrifuging the mixed liquor for 10 min at 1073 x g) was also measured. As can be
seen in Figure 27, supernatant turbidity decreased gradually and remained below 5
NTU. The supernatant turbidity may indicate sludge settleability [140]. At the start-up
period, the supernatant turbidity was 11.2 ± 4.0 (n = 16) and the SVI was significantly
high (see Section 6.3.1.2).
Sludge volume index is widely used to characterize sludge settleability and floc
formation [185, 186]. Figure 28 shows the variation of SVI and MLSS in the MBR.
The SVI varied between 126 and 208 mL/g. The SVI decreased slightly, indicating an
improvement of sludge settleability, with the increase in MLSS concentration.
However, the SVI became stable after 100 days of operation. This indicates the
dependence of SVI on MLSS in the initial phase only. Pollice et al. [187] reported
limited dependence of SVI on the biomass concentration in complete sludge retention
MBR.
Chapter 4 Performance of MBR system
70
0 20 40 60 80 100 120 140 1602
3
4
5
6
7
8
9
10
11 MLSS SVI
Time (Day)
ML
SS
(g
/L)
S T
MLSS (g/L) = 0.04x Time (Day) + 3.29
R2= 0.94
0
50
100
150
200
250
SV
I (m
L/g
)
SVI= - 0.62x Time (Day) + 211
R2 = 0.88
Figure 28: Variation in SVI and MLSS concentration of the MBR throughout the
operation period. ―S‖ and ―T‖ indicate the start-up period and the point of trace organic
contaminants addition, respectively.
4.3.3 Dissolved oxygen concentration, pH and specific oxygen up take rate
The MBR was operated under aerobic conditions. Oxygen was supplied via a diffuser
located at the bottom of the aeration tank. DO concentration and sludge pH was
measured on a daily basis throughout the operation period and the values fluctuated in a
range of 6 - 8 mg/L and 7.2 – 7.5, respectively. The optimum pH for biological
performance of MBR appears to be near neutral pH [122]. Therefore, in this study, the
MBR was operated within the recommended range of pH.
The oxygen consumption rate can be used as an indicator of metabolic activity of sludge
in the MBR at different periods of operation [188]. In this study both spiked and un-
spiked SOUR were measured for comparison purpose. The recorded data has been
Chapter 4 Performance of MBR system
71
presented in Figure 29. As can be seen in Figure 29, the un-spiked SOUR values were
low and fluctuated in a range of 0.76 to 1.42 (mg O2/h*g MLVSS) only during the
continuous operation. As expected, the spiked SOUR appeared more sensitive towards
biological changes in the MBR. However, the values varied within a range of only 14 ±
3 (n=9), and it apparently did not impose any impact on the removal performance (see
Section 4.3.5).
0 20 40 60 80 100 120 140 1600
2
4
6
8
10
12
14
16
18
20
unspiked SOUR spiked SOUR
SO
UR
(m
g O
2/h
*g
ML
VS
S)
Time (Day)
ML
VS
S (
g/L
)
0
1
2
3
4
5
6
7
8
9
10
MLVSS
S T
Figure 29: Variation of SOUR throughout operation period. ―S‖ and ―T‖ indicate the
start-up period and the point of trace organic contaminants addition, respectively.
4.3.4 Nitrate and ammonium
Biological treatment processes use nitrifiers and denitrifiers to achieve the removal of
nitrogenous compounds from wastewater. Normally, nitrate and nitrite produced by
nitrifiers under aerobic condition would be cycled to an anoxic condition to achieve
denitrification [189]. Nitrogen removal requires both aerobic and anoxic stages. In an
aerobic MBR, nitrification occurs because of a high SRT that can create a suitable
condition for the growth of nitrifying microorganisms [190]. A strategy to increase the
removal of nitrogenous compounds may be to configure the system so that aerobic and
anoxic regimes occur sequentially (e.g., intermittent aeration) [191]. Alternately anoxic
zones, separated by baffles from the aerobic part, can be established within the same
tank [189]. In this study, the MBR was operated under aerobic conditions (DO
concentration > 3 mg/L). As such, significant denitrification was not expected to occur
Chapter 4 Performance of MBR system
72
in the MBR. This is evident by the low removal of total nitrogen (see Section 4.3.5) and
detection of nitrate in MBR permeate (Figure 31). The nitrate and ammonium
concentration in MBR feed, supernatant and permeate has been illustrated in Figure 30
and Figure 31. The detection of ammonium in MBR permeate (Figure 30) suggests that
complete nitrification did not occur within the reactor. In full scale wastewater
treatment plants, the nitrogenous organics are converted to ammonia during their
transport from the source to the treatment plants in the sewer. In this study, synthetic
wastewater was prepared by adding nitrogen as bound in organics (e.g., urea and
peptone) and was directly fed to the MBR. Accordingly, partial nitrification occurred
following the hydrolysis of the organic-bound nitrogen to ammonia.
0 20 40 60 80 100 120 140 1600
2
4
6
8
10
12
14
16
18
20
22 Feed Supernantant Permeate
Am
mo
niu
m c
on
cen
trat
ion
(m
g/L
)
Time (Day)
S T
Figure 30: Variation of ammonium concentration in MBR feed, supernatant and
permeate throughout the operation period. ―S‖ and ―T‖ indicate the start-up period and
the point of trace organic contaminants addition, respectively.
Chapter 4 Performance of MBR system
73
0 20 40 60 80 100 120 140 160
0
1
2
3
4
5
6
7
8
9
10
11 Supernantant Permeate
Nit
rate
co
ncen
trati
on
(m
g/L
)
Time (Day)
TS
Figure 31: Variation of nitrate (NO3-) concentration in MBR feed, supernatant and
permeate throughout the operation period. ―S‖ and ―T‖ indicate the start-up period and
the point of trace organic contaminants addition, respectively.
4.3.5 Total organic carbon and total nitrogen removal
In this study, a synthetic wastewater was used to ensure a consistent influent
composition and to simulate medium strength municipal wastewater in term of TOC
and TN concentration. TOC and TN concentration in both influent and effluent were
measured on a regular basis to assess the basic biological performance of the MBR.
Despite considerable variation in the MLSS concentration in the reactor as shown in
Figure 26, the removal efficiencies of both TOC and TN remained relatively constant
(Figure 32, Figure 33). As such, the performance of the MBR in term of TOC and TN
removal appears to be independent with the MLSS concentration in the reactor [116].
The removal of TOC varied between 90% and 99% with an average of above 95%, and
the TOC concentration in permeate was typically less than 7 mg/L. The MBR achieved
above 98 % removal of TOC even though the TOC concentration in influent was kept at
elevated levels (double) from day 18 to day 27 in order to accelerate sludge growth.
The high removal of TOC was in good agreement with previous literature [122]. It is
also worth noting that the removal of TOC did not change after the start of adding trace
organic contaminants (dissolved in methanol) in the synthetic wastewater although the
concentration of TOC in the feed increased from 135 mg/L to 180 mg/L. A similar
Chapter 4 Performance of MBR system
74
observation was made by Li et al. [45]. They noticed that the continuous high dosing
(750 µg/L) of micropollutants (carbamazepine and sulfamethoxazole) to the feed for
extended period did not exert any discernible adverse effect on TOC and TN removal.
0 20 40 60 80 100 120 140 1600
2
4
6
8
100
150
200
250
T Influent Effulent
TO
C (
mg
/L)
Time (Day)
Rem
ov
al (
%)
IS
0
20
40
60
80
100
Removal
Figure 32: TOC concentration in MBR influent, effluent and the removal efficiency of
TOC throughout the operation period. ―I‖, ―S‖ and ―T‖ indicate the period when the
concentration of constituents in synthetic wastewater was kept at elevated levels
(double) temporarily, the start-up period and the point of trace organic contaminants
addition, respectively.
As noted earlier, the MBR system was operated under aerobic conditions (DO > 3
mg/L) and, therefore, was not expected to have high nitrogen removal via
denitrification. Accordingly, the TN removal in our study ranged from 31 to 68%
(Figure 33). Notably, nitrogen in the synthetic feed solution was supplied mostly in
organic-bound form (from peptone and urea). The ratio of influent COD, total nitrogen
and total phosphorous (CODin:TN:TP) in the synthetic feed solution was 150:6.5:1, and
Chapter 4 Performance of MBR system
75
residual ammonia at a concentration of 6 mg/L was detected in the MBR permeate. This
suggests that partial nitrification occurred following the hydrolysis of the organic-bound
nitrogen to ammonia.
0 20 40 60 80 100 120 140 160
10
20
30
40
50
Infulent Effulent
TN
(m
g/L
)
Time (Day)
Rem
ov
al
(%)
0
20
40
60
80
100
Removal STI
Figure 33: TN concentration in MBR influent, effluent and the removal efficiency
throughout the operation period. ―I‖, ―S‖ and ―T‖ indicate the period when the
concentration of constituents in synthetic wastewater was kept at elevated levels
(double) temporarily, the start-up period and the point of trace organic contaminants
addition, respectively.
4.3.6 Removal of trace organic contaminants
Given the diverse physicochemical properties of the 22 compounds selected in this
study, it is not surprising that their removal efficiency by MBR varied quite
significantly.
Chapter 4 Performance of MBR system
76
Figure 35 illustrates the removal efficiency of trace organics by MBR. Little or no
removal was observed for carbamazepine, diclofenac and fenoprop, while 80 – 99%
removal of all five steroid hormones and four alkyl phenolic trace organics could be
observed. The significant removal of hydrophobic compounds (Log D > 3.2) such as
the hormones and alkyl phenolic compounds used in this study is probably dominated
by sorption to the activated sludge facilitating enhanced biological degradation in some
cases [26, 192]. On the other hand Tadkaew et al., [26], proposed that functional groups
play an important role in determining the extent of biodegradation of compounds
possessing lower hydrophobicity (Log D < 3.2). They systematically demonstrated that
compounds with strong electron withdrawing groups (EWG) are more resistant to MBR
treatment, while the removal of compounds possessing both electron donating group
(EDG) and EWG can substantially vary depending on the number and type of the
functional groups. The low to moderate removal of six significantly hydrophilic
compounds (i.e., carbamazepine, diclofenac, fenoprop, naproxen, ketoprofen and
metronidazole) in this study, therefore, can be attributed to the presence of one or more
strong EWG (such as chlorine atom, amide group and nitro group) or absence of strong
EDG in their structures (see Table 5). Our results regarding the removal efficiency of
these biologically persistent compounds are in line with previous reports [26, 95, 98,
193, 194]. One anomalous result obtained was the high removal of primidone, despite
containing a strong EWG (amide) [26]. A possible explanation may be that the presence
of methyl groups (weak EDG) led to conversion of the methyl group to alcohol [195],
bypassing the problematic amide conversion. On the other hand, in good agreement
with the literature reports [134], among the less hydrophobic compounds (Log D < 3.2)
those containing the strong EDG hydroxyl group (i.e., acetaminophen, salicylic acid,
pentachlorophenol) were consistently removed to a high degree in our study. It is
noteworthy that in line with the observations reported by Hai et al. [140], the removal of
the halogenated organics correlated better with the ratio of halogen content to Log D
rather than Log D only. This substantiates that the former is a better indicator for the
prediction of halogenated trace organics removal by MBR treatment.
In addition to adsorption and biodegradation, volatilization may also contribute toward
the removal of highly volatile trace organics from an aqueous solution. The removal of
a trace organic due to aeration during wastewater treatment depends on its vapour
Chapter 4 Performance of MBR system
77
pressure (Henry’s constant) and hydrophobicity [7]. However, given the very low
Henry’s constant (H) and low H/Log D ratio of all compounds selected in this study,
their removal by volatilization is expected to be negligible. Except for MLSS sampling,
no sludge was withdrawn from MBR in this study. The removal via sludge wastage,
therefore, can also be considered to be insignificant.
One may wonder whether the gradual increase in MLSS concentration (Section 3.4.3)
influenced the removal of the significantly hydrophobic compounds (Log D >3.2), for
which biosorption may precede biodegradation. However, the removal of those
compounds in this study was highly stable right from the beginning, nullifying any
apparent effect of MLSS concentration under the tested range.
-2
-1
0
1
2
3
4
5
6
7
Salic
ylic
aci
d
Met
roni
dazo
le
Fenop
rop
Ket
opro
fen
Ace
tam
inop
hen
Nap
roxe
n
Primid
one
Ibup
rofe
n
Dic
lofe
nac
Car
bam
azep
ine
Gem
fibro
zil
Estrio
l
Penta
chlo
roph
enol
4-te
rt-bu
tylp
heno
l
Estro
ne
Bisph
enol
A
17-a
-eth
ynyl
estra
diol
17-b
-estra
diol
17-b
-estro
diol
-17-
acet
ate
4-te
rt-oc
tylp
heno
l
Triclo
san
4-n-
nony
lphe
nol
0
1000
2000
3000
4000
5000
6000
7000
8000
Co
ncen
trati
on
(n
g/L
)
Feed MBR permeate
Log D > 3.2Log D < 3.2
Log D at pH 7
Lo
g D
at
pH
7
Figure 34: Concentration of the trace organic contaminants in feed and MBR permeate.
Samples in duplicate were taken once a week. Error bars represent standard deviation of
26 measurements regularly conducted over 13 weeks.
Chapter 4 Performance of MBR system
78
Salicylic acid
Metro
nida
zole
Feno
prop
Ketop
rofe
n
Ace
tam
inop
hen
Nap
roxe
n
Primid
one
Ibup
rofe
n
Diclo
fena
c
Car
bam
azep
ine
Gem
fibro
zil
Estrio
l
Pentach
loro
phen
ol
4-tert-
butylp
heno
l
Estro
ne
Bisph
enol
A
17-a
-eth
ynyles
tradi
ol
17-b
-estra
diol
17-b
-estro
diol
-17-
acetate
4-tert-
octylp
heno
l
Triclo
san
4-n-
nony
lphe
nol
0
10
20
30
40
50
60
70
80
90
100
MBR Log D at pH 7
Rem
ov
al
eff
icie
ncy
(%
)Log D < 3.2 Log D > 3.2
-2
-1
0
1
2
3
4
5
6
7
Lo
g D
at
pH
7
Figure 35: Removal efficiency of the selected trace organic contaminants and their
corresponding hydrophobicity (log D) by MBR treatment. Samples in duplicate were
taken once a week. Error bars represent standard deviation of 26 measurements
regularly conducted over 13 weeks.
Chapter 4 Performance of MBR system
79
4.4 Conclusions
This chapter reported the basic biological performance of the submerged MBR system
during continuous operation over a period of over 160 days. The overall biological
performance of the MBR system was quite stable as reflected by the considerably stable
values of the basic water quality parameters.
The reported results in this chapter also confirm that MBR treatment can effectively
remove hydrophobic (Log D > 3.2) and readily biodegradable trace organic compounds,
but is less effective for the removal of hydrophilic (log D < 3.2) and biologically
persistent compounds. The limitation of the MBR treatment in removing hydrophilic
trace organic contaminants requires a complementary post-treatment processes to polish
the MBR permeate prior to water reuse.
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
80
CHAPTER 5: REMOVAL OF TRACE ORGANIC CONTAMINATNS BY A
MEMBRANE BIOREACTOR (MBR) - GRANULAR ACTIVATED CARBON
(GAC) SYSTEM
5.1 Introduction
GAC adsorption has routinely been used as a tertiary treatment process in the water
industry. The potential of activated carbon for the removal of pesticides and other
emerging trace organics in drinking water treatment has been widely demonstrated [19,
30-32]. However, much of the available literature focused on the removal of trace
organics by activated carbon from surface water [34] and only a few have investigated
the use of GAC adsorption for the removal of trace organics from biologically treated
effluent [10, 33, 34]. An aggravated competition with bulk organics for adsorptive sites
is usually a common phenomenon associated with such applications, and this has
important implications to the life and serviceability of GAC columns. Because MBR
can produce high quality effluent with virtually no suspended solids and with very low
total organic carbon content [36], GAC adsorption is expected to specifically target the
residual trace organics in MBR permeate without any significant interference from the
bulk organics.
Adsorption on GAC may lead to high initial removal of trace organics; however, over
time, the adsorption capacity of the GAC column will eventually become exhausted
[34]. A system, therefore, needs to be in place to appropriately design a specific GAC
system and determine the point of regeneration of the spent carbon. Quantitative
structure activity relationship (QSAR) models have been developed to predict activated
carbon adsorption capacity for herbicides, pesticides, and other low-molecular-weight,
neutral compounds on the basis of molar volumes and hydrogen bonding affinity as the
key predictive parameters [4, 33, 202]. However, several specific trace organic classes
could not be accurately predicted using such models [4]. Furthermore, QSAR models
require parameters (e.g., hydrogen bonding affinity) that are difficult to obtain for many
deprotonated/protonated acid and base compounds [202]. To date, experimental studies
of the equilibrium and breakthrough dynamics of trace organics in activated carbon
systems remain very limited [32, 34].
In this chapter, the removal of trace organics via sequential applications of GAC
adsorption following MBR treatment was presented. The extent of overall removal of a
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
81
set of selected compounds possessing varieties of chemical structures was assessed. The
breakthrough behavior of biologically persistent and hydrophilic compounds was
systematically investigated through long-term operation of the GAC column and a
series of batch tests. Discussion was furnished on the use of log D (hydrophobicity),
charge, and adsorption isotherm parameters to generally identify the set of compounds
likely to experience rapid breakthrough and about possible indicators of the initiation of
trace organic breakthrough (e.g., saturation of the GAC column with total nitrogen).
5.2 Experimental set-up and operation protocol
Detailed descriptions of the MBR-GAC system, its operation protocol, and analytical
techniques have been provided in chapter 3. The obtained data is systematically
analysed to depict the overall performance of the MBR - GAC over more than three
months of continuous operation. Based on the long-term overall removal performance
of the MBR - GAC systems, six problematic trace organics (carbamazepine, diclofenac,
ketoprofen, naproxen, fenoprop and metronidazole) were selected for single solute batch
adsorption isotherm tests (see Section 3.3.4).
5.3 Results and discussion
5.3.1 Performance stability and TOC/ TN removal by the MBR- GAC system
The same operating condition of the MBR was maintained throughout this operation
period. Sludge withdrawal was not conducted except for the MLSS and EPS/SMP
sampling, thus allowing for a gradual build up of the MLSS concentration in the reactor
from 5 to 9.8 g/L. Performance of the MBR with respect to the removal of TOC and TN
was stable during the entire study. Turbidity of the MBR permeate was always below
0.2 NTU. The addition of trace organic contaminants to the influent did not result in any
discernible disturbance on the MBR performance regarding the basic water parameters
described above.
The background carbonaceous organic content of the MBR permeate was low. The
TOC concentration in the MBR permeate was mostly between 1 and 3 mg/L and was
always below 5 mg/L (Figure 36). GAC post-treatment only resulted in a marginal
reduction in the concentration of TOC. In the absence of a denitrification zone, the TN
removal by the MBR was approximately 50% and up to 15 mg/L of TN could be
detected in the permeate (Figure 36). GAC post-treatment did not result in any
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
82
discernible reduction in the concentration of TN (Figure 36). GAC was reported to
show negligible removal of ammoniacal compounds through physical adsorption, which
was attributed to their high polarity and solubility in water [203]. Results reported here
(Figure 36) suggest that adsorption of background organic matter in the MBR permeate
to the GAC was negligible and the background organic matter did not compete
significantly for the adsorptive sites of the GAC.
0 2000 4000 6000 8000 10000 12000 14000 160000
1
2
3
4
5
6
7
8
0
50
100
150
200
0 2000 4000 6000 8000 10000 12000 14000 160000
5
10
15
20
25
30
0
5
10
15
20
25
30
Number of bed volume
TO
C c
on
cen
trati
on
(m
g/L
)
(F
eed
)
MBR permeate GAC effluent
TO
C c
on
cen
trati
on
(m
g/L
)
(MB
R p
erm
eate
, G
AC
eff
luen
t)
100 % saturation(a)
Feed
TN
co
ncen
trati
on
(m
g/L
)
(
Feed
)
Feed MBR permeate GAC effluent 100 % saturation
TN
co
ncen
trati
on
(m
g/L
)
(MB
R p
erm
eate
, G
AC
eff
luen
t)
(b)
Number of bed volume
Figure 36: TOC (a) and TN (b) concentrations in GAC effluent, MBR permeate and
feed throughout the operation period
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
83
5.3.2 Complementary removal of trace organics by MBR – GAC system
The low removal of hydrophilic and biologically persistent trace organic compounds by
MBR treatment (see Section 4.3.6) may necessitate a post-treatment process. Several
previous studies have proposed the use of GAC filtration for the removal of trace
organics from surface water or biologically treated wastewater [10, 19, 32-34]. Our
results (Figure 37) confirm that initially GAC post-treatment could significantly
improve the removal of the compounds which demonstrated low to moderate removal
by MBR treatment (i.e., metronidazole, carbamazepine, diclofenac, ketoprofen,
fenoprop, and naproxen). In this study, because all significantly hydrophobic
compounds had already been well removed by MBR treatment (see Section 4.3.6) and
competition of the background organic matter for the adsorptive sites was low, the GAC
post treatment process was particularly effective for the removal of hydrophilic trace
organic compounds from the MBR permeate. However, results presented in Figure 38
also show that the performance of the GAC column gradually deteriorated, and at
approximately 18,000 BV no additional removal of fenoprop and diclofenac by the
GAC column could be observed. Results reported here suggest that strict monitoring
should be applied over the life of the GAC column to detect the breakthrough point of
hydrophilic and persistent compounds which have low removal by MBR treatment.
Whether there was any biological activity in the GAC column was not specifically
monitored in this study. However, based on the gradual breakthrough of TOC (The
TOC concentration in GAC effluent was higher than that in MBR permeate (Figure 36))
as well as the trace organic contaminants, it can be stated that biodegradation within
GAC media may not have occurred.
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
84
0
20
40
60
80
100R
emo
val
eff
icie
ncy
(%
)
MBR GAC 406 BV
0
20
40
60
80
100
Rem
ov
al e
ffic
ien
cy (
%)
MBR GAC 4472 BV
0
20
40
60
80
100
Rem
ov
al e
ffic
ien
cy (
%)
MBR GAC 9148 BV
Salic
ylic
aci
d
Met
roni
dazo
le
Fenop
rop
Ket
opro
fen
Ace
tam
inop
hen
Nap
roxe
n
Primid
one
Ibup
rofe
n
Dic
lofe
nac
Car
bam
azep
ine
Gem
fibro
zil
Estrio
l
Penta
chlo
roph
enol
4-te
rt-bu
tylp
heno
l
Estro
ne
Bisph
enol
A
17-a
-eth
ynyl
estra
diol
17-b
-estra
diol
17-b
-estro
diol
-17-
acet
ate
4-te
rt-oc
tylp
heno
l
Triclo
san
4-n-
nony
lphe
nol
0
20
40
60
80
100
Rem
ov
al e
ffic
ien
cy (
%)
MBR GAC 18093 BV
(a)
(b)
(c)
(d)
Log D < 3.2 Log D > 3.2
Figure 37: Overall removal of trace organic contaminants by MBR-GAC system at 406
BV (a), 4472 BV (b), 9148 BV (c), 18093 BV (d)
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
85
5.3.3 Adsorption of single compound on GAC
The adsorption isotherms give useful information on the adsorption capacity of a given
adsorbate on a given adsorbent for a particular range of concentration. Therefore, they
play a crucial role in the choice and in the utilization of adsorbents. In this study, the
parameters of Freundlich (F) and Langmuir (L) models were evaluated by fitting the
theoretical isotherm to experimental data. Six problematic trace organics
(carbamazepine, diclofenac, ketoprofen, naproxen, fenoprop and metronidazole) were
selected based on the long-term overall removal performance of the MBR-GAC systems
for conducting the adsorption isotherm. Table 8 summaries the results obtained for
Freundlich and Langmuir isotherm parameters of selected trace organic compounds.
The adsorption data for GAC fitted the Langmuir isotherm relatively better.
The results showed that GAC has a good adsorption capacity for all selected trace
organic compounds, with the calculated qm (Langmuir maximum adsorption capacity)
ranging from 41.2 to 250.0 mg/g. Therefore, it can be expected that a full scale GAC
filter unit will efficiently remove these compounds.
Table 8: GAC adsorption isotherm constants for six biologically persistent hydrophilic
trace organic compounds
Compound
Freundlich isotherm constants Langmuir isotherm constants
Kf
(mg/g)/(mg/L)1/n
1/n R
2 qm
(mg/g)
b
(L/mg) R
2
Metronidazole 29.3 0.36 0.92 84.3 1.3 0.99
Fenoprop 53.2 0.23 0.96 49.3 1.80 0.99
Ketoprofen 48.3 0.33 0.99 62.11 1.35 0.97
Naproxen 19.6 0.60 0.86 41.2 1.16 0.98
Diclofenac 29.2 0.42 0.93 94.3 0.76 0.96
Carbamazepine 54.2 0.56 0.95 250.0 0.76 0.99
Freundlich isotherm: qe = Kf Ce1/n
Langmuir isotherm:
qe, equilibrium mass of compound sorbed on unit mass of adsorbent; Ce, equilibrium
concentration of compound in liquid; qm, Langmuir maximum adsorption capacity; Kf,
Freundlich partitioning coefficient; 1/n, Freundlich exponential coefficient; b,
Langmuir’s constant; qmb, adsorbent-adsorbate relative affinity
m
e
me
e
q
C
bqq
C 1
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
86
5.3.4 Breakthrough of biologically persistent hydrophilic compounds
5.3.4.1 Analysis of breakthrough profiles
The breakthrough profiles of six hydrophilic trace organics (metronidazole,
carbamazepine, diclofenac, fenoprop, naproxen, and ketoprofen) exhibiting low removal
efficiency by MBR treatment were examined to provide further insight to their
adsorption to GAC. Percentage of the ratio of GAC effluent concentration and influent
concentration (MBR permeate) during the same sampling event has been presented as
breakthrough values in Figure 38. Significant differences in the breakthrough profiles
amongst these hydrophilic trace organic compounds are evident in Figure 38. While a
20 % breakthrough of diclofenac, ketoprofen, fenoprop, and naproxen occurred within
1000-3000 BV, the same did not happen in case of metronidazole and carbamazepine
before 11000 BV. Breakthrough profiles are influenced by the characteristics of the
target trace organics, properties of the activated carbon, the influent water quality, and
operational conditions [204]. In the current study, apart from the experimental variation
of the influent loading, all other parameters remained unchanged. Therefore discussion
regarding the removal efficiency or breakthrough can be focused on the characteristics
of the target trace organics. In the literature, several solute properties that influence the
adsorption of organic compounds onto activated carbon have been identified. These
properties include, among others, solute hydrophobicity, aromaticity, charge, size, and
presence of specific functional groups [4, 19, 33, 34, 202, 204, 205]. The adsorption
mechanisms related to these properties occur simultaneously, and their respective
dominance can vary from compound to compound [4, 33].
It has been reported that hydrophobic partitioning is more relevant at higher log D
values, while non-hydrophobic interactions govern in case of compounds with low log
D [4, 31, 33]. All six compounds (metronidazole, carbamazepine, diclofenac, fenoprop,
naproxen, and ketoprofen) presented in Figure 38 were of low hydrophobicity and, as
expected, no particular correlation between their log D and extent of breakthrough could
be ascertained (Figure 38). Notably, although the two neutral compounds
(metronidazole and carbamazepine) possess significantly different log D values (-0.14
and 1.89, respectively), they demonstrated similar removal efficiency. In addition, their
removal efficiency was higher than that of all four negatively charged compounds of
concern in Figure 38. This observation is in line with that of Vieno et al., [204] who
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
87
reported higher affinity of the neutral pharmaceutical carbamazepine when compared to
an ionic compound — naproxen. Yu et al. [31] also observed severer reduction in
adsorption capacity for the acidic compound naproxen, compared to the neutral
compound carbamazepine.
In addition to hydrophobic partitioning, various other mechanisms such as hydrogen
bonding, - -interaction between aromatic rings, and van der Waals forces (e.g., dipole-
dipole interaction, London dispersion force) can contribute towards the adsorption of a
compound onto a specific adsorbent [4, 19, 33, 34, 202, 204, 205]. However, as noted
earlier, their relative dominance will depend on the specific compound. For instance, it
has been reported that larger number of hydrogen bond donor groups implies stronger
hydrogen bonding between the solute and adsorbent than between the solute and water
[33]. For solutes possessing no hydrogen-bond donor/acceptor groups, however, the
main bonding mechanisms are van der Waals dispersion forces and/or - -interaction.
On the other hand, an aliphatic solute without any hydrogen bond donor/acceptor
groups can form neither - bonds nor hydrogen-bonds, and the weaker van der Waals
forces may then become more dominant for its removal [4]. Furthermore, the presence
of specific functional groups in the structure of compounds can also influence their
adsorption onto adsorbent. For instance, Radovic et al. [206] reported that the presence
of electron-withdrawing functional groups will influence the -electron distribution by
removing electrons and creating positive holes in the conduction band of the -electron
system, thus decreasing the adsorption potential on the carbon surface.
All six compounds under consideration in Figure 38 are aromatic and possess one or
more strong electron withdrawing groups, and except for carbamazepine and
metronidazole, all are negatively charged. Therefore, - -interaction and/or other
specific polar interactions can be considered relevant mechanisms, although their
relative importance may be different for each compound. For instance, dispersion
interactions of -electrons of their aromatic rings with -electrons of the carbon
graphene planes was reported to govern the adsorption of metronidazole [207], while
hydrogen bonding with adsorbent was reported to be the predominant mechanism in
case of diclofenac and naproxen, which are strong hydrogen bond donor solutes [33]. A
detailed quantitative assessment of structure-activity relationship [4, 33, 202], and
confirmation of the specific dominating mechanism for each compound fall beyond the
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
88
scope of this study. In the context of this study, it is more important to note that the
neutral compounds (carbamazepine and metronidazole) showed slower breakthrough
than the negatively charged compounds (Figure 38).
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
89
02000
40006000
800010000
1200014000
1600018000
0
1000
2000
3000
4000
5000
6000
7000
0
20
40
60
80
100
02000
40006000
800010000
1200014000
1600018000
0
1000
2000
3000
4000
5000
6000
7000
0
20
40
60
80
100
02000
40006000
800010000
1200014000
1600018000
0
1000
2000
3000
4000
5000
6000
7000
02000
40006000
800010000
1200014000
1600018000
0
1000
2000
3000
4000
5000
6000
7000
02000
40006000
800010000
1200014000
1600018000
0
1000
2000
3000
4000
5000
6000
7000
0
20
40
60
80
100
02000
40006000
800010000
1200014000
1600018000
0
1000
2000
3000
4000
5000
6000
7000
0
20
40
60
80
100B
reak
thro
ug
h (
%)
Co
ncen
trati
on
(n
g/L
)
MBR effluent GAC effluentC
on
cen
trati
on
(n
g/L
)
Metronidazole (Log D = -0.14)
Neutral
Bre
ak
thro
ug
h (
%)
Breakthrough
Ketoprofen (Log D = 0.19)
Negatively charged
Number of bed volume
Bre
ak
thro
ug
h (
%)
Co
ncen
trati
on
(n
g/L
)
Number of bed volume
Diclofenac (Log D = 1.77)
Negatively charged
0
20
40
60
80
100
Bre
ak
thro
ug
h (
%)
Co
ncen
trati
on
(n
g/L
)
0
20
40
60
80
100Carbamazepine (Log D = 1.89)
Neutral
Bre
ak
thro
ug
h (
%)
Co
ncen
trati
on
(n
g/L
)
Fenoprop (Log D = -0.13)
Negatively charged
Bre
ak
thro
ug
h (
%)
Co
ncen
trati
on
(n
g/L
)Naproxen (Log D = 0.73)
Negatively charged
Figure 38: Breakthrough profiles of six biologically persistent and hydrophilic trace
organic compounds as a function of bed volume (BV)
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
90
5.3.4.2 Prediction of breakthrough
For a full scale installation, monitoring the breakthrough of a large set of compounds
may not be always feasible. Adsorption isotherms give useful information on the
adsorption capacity of a given adsorbate on a given adsorbent for a particular range of
concentration. In order to generally assess the applicability of isotherms in predicting
the order of breakthrough of the compounds, the breakthrough data were contrasted
with the adsorption isotherm parameters obtained from a series of batch tests. Table 8
shows the Langmuir and Freundlich isotherm parameters (qm and Kf, respectively) for
the compounds that demonstrated relatively rapid breakthrough from the GAC column.
Our isotherm data conform to the general trends found in the literature, such as
relatively higher adsorption capacity of the neutral compounds carbamazepine [19, 205,
208] and metronidazole [207] in comparison to that of the ionized compounds, namely,
diclofenac [19, 205, 208] and naproxen [19, 205, 208]. However, as shown in Figure 40,
the isotherm parameters did not demonstrate any discernible correlation individually
with any of the governing parameters such as log D, number of hydrogen-bond
donor/acceptor groups, dipole moment or aromaticity ratio of the compounds. This
observation is also in line with that of De Ridder et al. [4] and reaffirms the point
discussed earlier (Section 5.3.4.1) regarding the simultaneous roles of various governing
mechanisms on net adsorption.
Because reasonably linear breakthrough profiles for the compounds (except
metronidazole) were obtained (Figure 38), percentage breakthrough (BT) at the end of
operation (18093 BV) was plotted against the Langmuir (qm) and Freundlich (Kf)
isotherm parameters (Figure 39). qm was observed to fit BT data relatively better. The
inverse relationship between qm and BT was evident from the plot; however, the
coefficient of determination (R2) of the fitting line was only 0.38. Such deviation is not
surprising, given the fact that the single-solute isotherms were obtained in ultrapure
water (Milli-Q), and for analytical reasons the isotherms were obtained at equilibrium
concentrations higher than that applied to the GAC column. In fact, inaccuracies arising
from mismatch between equilibrium concentration and actual loading [31] and due to
the effect of competition with bulk organics [19, 148] have been previously
documented. The fact that the MBR permeate concentration (i.e., feed to the GAC
column) was not completely stable for individual compounds, and varied within a few
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
91
thousands of ng/L between the compounds (Figure 38), may have been also responsible
for such deviation. Nevertheless, the isotherm data can be useful to predict a general
trend regarding the set of compounds likely to experience rapid breakthrough. It is also
worth noting that the difference between the behaviour of the neutral (carbamazepine
and metronidazole) and the ionized compounds was predicted by the isotherm
parameters.
It is noteworthy that the GAC column became completely saturated with TN and TOC
within 1000 and 11000 BV, respectively (Figure 36), while the complete breakthrough
of diclofenac occurred after 18000 BV. Hernández-Leal et al. [34] also observed
significant removal of micropollutants following the saturation of a GAC column by
background TOC. However, from the practical point of view, the detection of a defined
level of breakthrough, not complete breakthrough, is important. In this context, it is
interesting to note that the point of TN saturation (1000 BV) coincides with the
initiation of appreciable level (e.g., 20%) of trace organic breakthrough. Under the
tested level of TN concentration (10-15 mg/L) in the influent to the GAC column, it
appears that TN saturation can be a useful indicator of the initiation of trace organics
breakthrough.
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
92
0 20 40 60 80 1000
50
100
150
200
250
0 20 40 60 80 1000
10
20
30
40
50
60
50 % breakthrough
Charged compoundsNeutral compounds
qm
q m(m
g/g)
Breakthrough (%) at 18903 BV
(a)
1
6
3
4
5
2
Breakthrough (%) at 18903 BV
Charged compoundsNeutral compounds
Kf
Kf(m
g/g)
/(m
g/L
)1/n
1
6
4
3
5
2
(b)
50 % breakthrough
Figure 39: Relationship between breakthrough (%) and adsorption isotherm constants
(qm, Langmuir maximum adsorption capacity (a) ; Kf, Freundlich partitioning coefficient
(b)).(1.Metronidazole, 2.Fenoprop, 3.Ketoprofen, 4.Naproxen, 5.Diclofenac,
6.Carbamazepine). The breakthrough values are defined as percentage of the effluent
concentration over the influent concentration of the same sampling event.
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
93
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.00
50
100
150
200
250
q m(m
g/g)
Log D at pH 7
1
23
4
5
6
1
23
4
5
6
0
10
20
30
40
50
60
Kf(m
g/g)
/(m
g/L
)1/n
4.0 4.5 5.0 5.5 6.0 6.5 7.00
50
100
150
200
250
Hydrogen bonding affinity
Kf(m
g/g)
/(m
g/L
)1/n
q m(m
g/g)
623
4
42
3
1
1
5
5
0
10
20
30
40
50
60
0.12 0.14 0.16 0.18 0.20 0.22 0.240
50
100
150
200
250
qm K
f
Kf(m
g/g)
/(m
g/L
)1/n
q m(m
g/g)
Aromaticity ratio
1
1
2
2
4
4
3
3
5
5
6
0
10
20
30
40
50
60
0.0 0.5 1.0 1.5 2.0 2.5 3.00
50
100
150
200
250
Dipole moment (debyes)
0
10
20
30
40
50
60
Kf(m
g/g)
/(m
g/L
)1/n
q m(m
g/g)
1
1
5
5
4
4
2
23
3
6
Figure 40: Relationship of adsorption isotherm constants (qm, Langmuir maximum
adsorption capacity; Kf, Freundlich partitioning coefficient) with various individual
parameters (governing adsorption of organics onto activated carbon) for biologically
persistent six hydrophilic trace organics. 1. Metronidazole, 2.Fenoprop, 3.Ketoprofen,
4.Naproxen, 5.Diclofenac, 6.Carbamazepine. Dipole moment was calculated by
Chapter 5 Removal of trace organic contaminants by MBR –GAC system
94
molecular modelling Pro software using ―Modified Del Re‖ method. Aromaticity ratio
denotes the ratio of number of aromatic bonds to total number of bonds in a molecule.
5.4 Conclusions
High ( 98%) removal of trace organics by a GAC column following the MBR
treatment was demonstrated. However, through long-term observation, significant
breakthrough of six hydrophilic and biologically persistent compounds (carbamazepine,
diclofenac, fenoprop, naproxen, ketoprofen and metronidazole) was detected. Of the six
problematic compounds, the neutral compounds (carbamazepine and metronidazole)
demonstrated slower breakthrough than the rest of the compounds which were
negatively charged. The difference between the behaviour of the neutral and the charged
compounds was accurately predicted by the single solute isotherm parameters. Under
the tested level of TN concentration (10-15 mg/L) in the influent to the GAC column, it
appears that TN saturation can be a useful indicator of the initiation of trace organics
breakthrough.
Chapter 6 Removal of trace organic contaminants by PAC - MBR hybrid system
95
CHAPTER 6: REMOVAL OF TRACE ORGANIC CONTAMINANTS BY
PAC - MBR HYBRID SYSTEM
6.1 Introduction
The incomplete removal of biologically persistent trace organic contaminants by MBR
treatment has been reported in the literature. The results presented in chapter 4 reaffirm
the problem. Therefore, it is necessary to formulate modified treatment processes to
adequately address this problem. Chapter 5 describes GAC adsorption post-treatment
process for MBR permeate. The reported data demonstrate that GAC adsorption can
effectively serve the purpose of post-treatment of MBR permeate. The application of
PAC within MBR has been studied in relation to membrane fouling mitigation [37, 40].
Despite the conceptual expectation of enhanced biodegradation of biologically
persistent organic compounds in a PAC - enhanced MBR, a few studies have in fact
assessed this aspect in relation to different types of wastewater, namely, textile
wastewater [41], distillery wastewater [166], tannery wastewater [167], oily wastewater
[38], and leachate [209]. To date, only a few studies have specifically explored PAC -
MBR for the removal of trace organics [44-46]. Previously reported data confirmed the
improved removal efficiency of some trace organics by PAC - MBR; however, a
comprehensive understanding of the involved phenomena has not been developed.
The aim of this chapter was to assess the removal efficiency of the selected trace
organic contaminants in synthetic municipal wastewater by simultaneous application of
PAC in MBR. The addition of PAC into the MBR was assessed as a tool to provide an
additional removal of persistent trace organic compounds. The data pertaining to the
overall removal efficiency of trace organics by the PAC - MBR system was compared
with that relating to the performance of sequential application of GAC adsorption
following MBR treatment. The performance of the PAC – MBR system in regards to
basic water quality parameters is also systematically discussed.
6.2 Experimental set-up and operation protocol
Detailed descriptions of the PAC - MBR set-up, operation protocol, and analytical
techniques have been provided in chapter 3. Before the addition of PAC into the MBR
on day 206, chemical cleaning of the membrane and sludge withdrawal were conducted
on day 186 and 197, respectively. 9 days after the sludge withdrawal, the MLSS
Chapter 6 Removal of trace organic contaminants by PAC - MBR hybrid system
96
concentration in the MBR was at 6 g/L. PAC was added into MBR at this point to
obtain a concentration of 0.1 g PAC /L. Following this, the MBR was operated for 36
days, and on day 243 PAC was added again to obtain a concentration of 0.5 g PAC/L.
In this chapter, the obtained data is systematically analysed to assess the overall
performance of the hybrid PAC - MBR system.
6.3 Results and discussion
6.3.1 Evaluation of the performance of the PAC - MBR hybrid system
To confirm that the trace organics removal efficiency was obtained under stable
biological activity in the PAC – MBR system, the basic water quality parameters (TOC,
TN, and turbidity removal) and the key operating parameters (pH, temperature, DO
concentration, and MLSS concentration) were periodically monitored. The performance
of the MBR with and without addition of PAC was compared in terms of the basic
water quality parameters and trace organics removal.
6.3.1.1 Mixed liquor suspended solids and mixed liquor volatile suspended solids
The MLSS/MLVSS profile over the entire operation period has been illustrated in
Figure 41. Before PAC addition the MLSS concentration in the MBR increased
gradually; however, no significant change in MLSS concentration was seen after PAC
addition. In fact, the MLSS concentration decreased slightly. Contradictory reports on
the effect of PAC addition on sludge growth have been reported. Lesage et al. [38]
reported that PAC addition may reduce the MLSS concentration increase while
Satyawali et al. [210] mentioned that the MLSS build up was faster as compared to
operation without PAC supplementation. In their study, it took almost 140 days to reach
a MLSS concentration of 8 g/L without PAC supplementation [210] while the same
MLSS concentration was achieved in 65 days with PAC supplementation.[166].
However, the authors [166] did not clarify the underlying reasons of their respective
observations. The slight decrease in the MLSS concentration toward the end in this
study may be attributed to the withdrawal of sludge for MLSS/MLVSS and EPS/SMP
sampling events. During the period of PAC – MBR experiment, approximately 5 g
MLSS was withdrawn for sampling. This is equivalent to an MLSS concentration drop
of 1.1 g/L in the MBR. Assuming that net sludge growth was zero, the amount of sludge
withdrawal can explain the observed drop in MLSS concentration.
Chapter 6 Removal of trace organic contaminants by PAC - MBR hybrid system
97
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 3200
1
2
3
4
5
6
7
8
9
10
11P
2
MLSS (g/L) MLVSS (g/L)
ML
SS
/ML
VS
S (
g/L
)
Time (Day)
P1R
T
Figure 41: Variation of MLSS and MLVSS concentration in the reactor throughout the
operation period. ―T‖ indicates the point of trace organic contaminants addition, and
―R‖ indicates the point of sludge withdrawal, while ―P1‖ and ―P2‖ indicate points of
PAC addition to achieve final PAC concentrations of 0.1 g/L and 0.5 g/L, respectively.
Chapter 6 Removal of trace organic contaminants by PAC - MBR hybrid system
98
6.3.1.2 Turbidity, Sludge volume index, and SOUR
Turbidity of both MBR and PAC – MBR permeate was consistently observed to be
below 0.2 NTU (Table 9). As discussed earlier in section 4.3.2, owing to complete
removal of suspended solids by membrane filtration, usually MBR permeate is
characterized with very low turbidity [27, 183, 184]. Turbidity in water is caused by
suspended and colloidal matter such as organic and inorganic matter including
microorganism. The MBR process involves a suspended growth-activated sludge
system that utilizes microporous membrane for solid/liquid separation instead of
secondary clarifiers in CAS. Only particles significantly smaller size than the maximum
membrane nominal pore size (around 0.4 µm) can pass through the membrane. Thus, it
is usually reported that MBR can produce suspended solids-free permeate [36, 183,
184].
In a CAS process, to predict the outcome of effluent turbidity, operators usually test the
supernatant turbidity from sludge settling tests as a useful indication of what will
happen in secondary clarifier. The supernatant turbidity results are used to evaluate the
state of biomass dispersion and how well sludge flocculates [211, 212]. High turbidity is
associated with a relatively small fraction of the MLSS, which tends to remain in
supernatant and/or detach easily from sludge flocs [213]. In an MBR, an increase in
supernatant turbidity may be associated with the occurrence of sludge deflocculation
and increase in concentration of soluble matter in the sludge supernatant [213]. A study
by Rosenberger et al. [214] showed that the non-settleable sludge fraction was found to
impact membrane fouling. Other study also found that the solutes in sludge supernatant
played significant role in membrane fouling [215]. The properties of sludge supernatant
may have impacts on membrane performance. Therefore, supernatant turbidity data can
be used to assess the properties of sludge supernatant and as an indicator for evaluating
membrane fouling. In this study, the turbidity of supernatant obtained by centrifuging
and gravity settling, respectively was measured throughout the operation period. The
data has been presented in Figure 42. Except for the initial period, the supernatant
turbidity was already very low even before the addition of PAC, and no significant
change in the supernatant turbidity, irrespective of the method used to obtain the
supernatant, was observed.
Chapter 6 Removal of trace organic contaminants by PAC - MBR hybrid system
99
The sludge volume index (SVI) values decreased significantly after 100 days of
operation and remained stable through to the end of the operation period (Figure 42).
The SVI profile correlated well with that of supernatant turbidity (Figure 42). A
decrease in supernatant turbidity was accompanied by a decrease in SVI value. Previous
studies have reported that the addition of PAC into MBR can enhance floc formation.
For example, a significant enhancement in the biomass settling after an addition of 1
g/L PAC into MBR was observed in a study by Serrano et al.[46]. This was revealed by
an SVI value less than 100 mL/g as compared to the value of 580 mL/g before addition
of PAC. A few other studies have reported that activated sludge shows better settling
properties after PAC addition, due to lower compressibility of sludge flocs [38, 216,
217]. Nevertheless in this study no significant change in SVI value was observed after
PAC addition, suggesting that the sludge originally had good settleability. On the other
hand, the SVI was in fact notably high at the initial period. The results are consistent
with several previous studies where the poor settling properties of sludge were observed
at the beginning of an MBR [46]. This may be attributed to the highly dispersed nature
of the flocs at the beginning of MBR operation. Poor sludge settling and high SVI
values at the start-up period of MBR have been reported in other studies [46]. However,
as the membrane acts as a barrier between liquid/solid phases, poor sludge settling and
high SVI did not affect effluent quality such as turbidity and TOC/TN removal (see
Section 6.3.1.3).
Chapter 6 Removal of trace organic contaminants by PAC - MBR hybrid system
100
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0
10
20
30
40
50
60
Supernatant (centrifuge) Supernatant (gravity settling)
Tu
rbid
ity
(N
TU
)
Time (Day)
SV
I (m
L/g
)
P1
P2T
0
20
40
60
80
100
120
140
160
180
200
220
SVI
Figure 42: Variation of SVI and reactor supernatant turbidity throughout the operation
period. ―T‖ indicates the point of trace organic contaminants addition, while ―P1‖ and
―P2‖ indicate points of PAC addition to achieve final PAC concentrations of 0.1 g/L and
0.5 g/L, respectively. The MBR supernatant was collected in two different ways i.e., by
centrifuging (10 min at 1073 x g), and by gravity settling (30 min), respectively.
In this study both spiked and unspiked SOUR were measured for comparison purpose.
SOUR is often useful to assess microbial activities at different periods of operation of a
biological reactor [188]. The dynamic variation of spiked and unspiked SOUR of both
MBR and PAC - MBR sludge has been illustrated in Figure 43. As can be seen in
Figure 43 virtually no change in unspiked SOUR in both MBR and PAC - MBR was
observed.
The spiked SOUR value gradually improved as the experiment progressed (Figure 43).
Due to the lack of data points during the initial period of this experimental component
(day 132 to day 198), it is difficult to identify the point when the improvement occurred,
but it appears to have happened before addition of PAC probably simply due to gradual
acclimatization. Interestingly, the spiked SOUR value dropped significantly towards the
end of operation period. It has been previously reported that SOUR decreases with
operation time [218, 219]. Under a long sludge age, the accumulation of inert matter in
Chapter 6 Removal of trace organic contaminants by PAC - MBR hybrid system
101
MBR occurs. The reduction of SOUR during prolonged operation of PAC – MBR has
been reported in other studies [38, 216]. Nevertheless, in this study, even after the drop
in SOUR toward the end of operation, the SOUR values were comparable to the values
at the initiation of operation, and such drop apparently did not affect the TOC and TN
removal performance (see Section 6.3.1.4)
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8
10
12
14
16
18
20
22
24
26
28
30
0
1
2
3
4
5
6
7
8
9
10
Spiked (1:1) Unspiked
SO
UR
(m
g O
2/h
*g
ML
VS
S)
Time (Day)
P1
P2
Dis
solv
ed o
xy
gen
(m
g/L
)
T DO
Figure 43: Variation of SOUR and DO concentration throughout the operation period.
―T‖ indicates the point of trace organic contaminants addition, while ―P1‖ and ―P2‖
indicate points of PAC addition to achieve final PAC concentrations of 0.1 g/L and 0.5
g/L, respectively.
Chapter 6 Removal of trace organic contaminants by PAC - MBR hybrid system
102
Table 9: Information on some parameters in MBR and PAC – MBR systems (average ± standard deviation) 1
2
Parameters TOC feed
(mg/L)
TN feed
(mg/L)
TOC
permeate
(mg/L)
TN
permeate
(mg/L)
Turbidity
permeate
(NTU)
EPS (mg/g VSS) in
supernatant
SMP (mg/L) in
supernatant
Protein Polysaccharide Protein Polysaccharide
MBR 179 ± 8
(n = 46)
24 ± 2
(n = 46)
3.5 ± 3.2
(n = 46)
12.6 ± 3.3
(n = 46)
< 0.2 67 ± 20
(n = 4)
9.5 ± 2.0
(n = 4)
1.5 ± 1
(n = 4)
2.5 ± 0.4
(n = 4)
MBR + 0.1
g/L PAC
171 ± 10
(n = 10)
23 ± 1
(n = 10)
2.5 ± 1.1
(n = 10)
15.8 ± 2.1
(n = 10) < 0.2
51.0 ± 4
(n = 3)
91.5 ± 12
(n = 3)
11 ± 9.7
(n = 3)
13 ± 11
(n = 3)
MBR + 0.5
g/L PAC
178 ± 6
(n = 15)
26 ± 2
(n = 15)
3.3 ± 2.8
(n = 15)
11.9 ± 3.8
(n = 15)
< 0.2 113 ± 57
(n = 12)
34 ± 24
(n = 12)
18 ± 11
(n = 12)
16 ± 13
(n = 12)
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
103
6.3.1.3 Comparison of TOC/TN removal by MBR and PAC – MBR systems 3
The average percentage removal of TOC and TN by the MBR and PAC – MBR at two 4
different concentration of PAC addition has been illustrated in Figure 44. It can be seen 5
that the TOC removal was already 98 ± 2 % before the addition of PAC, and an 6
insignificant change in TOC removal was observed in the PAC - MBR system. The high 7
TOC removal efficiency observed in this study can possibly be contributed to the 8
conversion of soluble organics into insoluble biomass rather than their complete 9
mineralisation into carbon dioxide. As expected, a high degree of removal of TOC 10
continued to be achieved in the PAC – MBR system. A similar observation was made 11
by Li et al. [45]. They noticed that TOC removal remained around 97 % even after 12
adding PAC into MBR at a concentration of 1 g/L. 13
On the other hand, as expected, in the absence of a denitrification zone within the MBR, 14
the removal of TN in this study was fairly low (Figure 44). In this study, there was no 15
discernible increase in removal of TN after addition of PAC at a concentration of 0.1 16
g/L. However, a slight increase in TN removal in MBR with a PAC concentration of 0.5 17
g/L was observed. 18
19
20
21
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
104
MBR MBR+0.1 g/L PAC MBR + 0.5g/L PAC
0
20
40
60
80
100
TO
C r
emo
val
eff
icie
ncy
(%
)
(a)
(b)
MBR MBR+0.1 g/L PAC MBR+ 0.5 g/L PAC
0
10
20
30
40
50
60
70
TN
rem
ov
al e
ffic
ien
cy (
%)
22
Figure 44: TOC (a) and TN (b) removal efficiency in MBR and PAC - MBR system. 23
Error bars represent standard deviation of 46, 10, and 15 samples in MBR, MBR – 0.1 24
g/L PAC and MBR – 0.5 g/L PAC, respectively. 25
In this study, the occurrence of NH3-N in MBR permeate suggests that complete 26
nitrification did not occur. The NH3-N concentrations in MBR permeate fluctuated in 27
the range of 2.5 - 8.4 mg/L (Figure 45). In a submerged MBR at a HRT 24 h an almost 28
complete conversion of NH4+ - N to NO3
- N was achieved with influent NH4
+ - N 29
concentration ranging from 180 mg/L to 1300 mg/L [220]. Li et al. [221] reported that 30
98 % conversion of NH4+ - N to NO3
- - N was achieved in a submerged MBR treating 31
ammonia-bearing inorganic wastewater without sludge withdrawal during 260 days of 32
operation. The high nitrification rate in MBR under a long SRT is attributed to the 33
prevention of washout of the slow-growing nitrifiers, which are responsible for the 34
nitrification process [222, 223]. However, controversies exist regarding the efficiency 35
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
105
of nitrification process within MBR. Incomplete nitrification of ammonia nitrogen in 36
MBR has been reported in other studies [224, 225]. In full scale wastewater treatment 37
plants, the nitrogenous organics are converted to ammonia during their transport from 38
the source to the treatment plants in the sewer. In this study, synthetic wastewater was 39
prepared by adding nitrogen as bound in organics (e.g., urea and peptone) and was 40
directly fed to the MBR. Accordingly, partial nitrification occurred following the 41
hydrolysis of the organic-bound nitrogen to ammonia. PAC has previously been 42
reported to show negligible removal of ammonium through physical adsorption due to 43
their high polarity and solubility in water [226]. In this study too there was no 44
discernible difference between the levels of ammonium in permeate before and after 45
addition of PAC into MBR. 46
As discussed earlier, (see Section 4.3.4) sequential anoxic – aerobic tanks [227] or 47
separate aerobic and anoxic zones within the same tank [189] or special designs 48
facilitating alternate aerobic and anoxic regimes, such as application of intermittent 49
aeration [191], are required for biological nitrogen removal However, in this study the 50
MBR was operated under aerobic conditions (DO concentration 3 – 7 mg/L) (see 51
Section 4.3.4). In the absence of a denitrification zone or any other means to promote 52
denitrification, complete denitrification was not expected in this study. The nitrate 53
concentration in the MBR permeate remained stable around a value of 2 mg/L during 54
the whole period of operation with PAC. The concentration of nitrate in supernatant and 55
MBR permeate was not much different. 56
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
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4
6
8
10
Feed Supernatant Permeate
Am
mo
niu
m (
mg
/L)
Time (Day)
P1
P2
T
Supernatant Permeate
Nit
rate
(m
g/L
)
Time (Day)
P1
P2T
(a)
(b)
57
Figure 45: Variation of (a) ammonium and (b) nitrate concentration in feed, supernatant 58
and permeate throughout the operation period. ―T‖ indicates the point of trace organic 59
contaminants addition while, ―P1‖ and ―P2‖ indicate points of PAC addition achieve 60
final PAC concentrations of 0.1 g/L and 0.5 g/L, respectively. 61
62
63
64
65
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
107
6.3.1.4 Transmembrane pressure 66
Membrane fouling is an unavoidable consequence of interactions between mixed liquor 67
and the membrane within an MBR. In absence of periodic cleaning, TMP generally 68
increases with the operating time. The focus of this study was on the removal 69
performance of the MBR. Therefore the reactor was designed as such that frequent 70
membrane fouling, requiring periodic cleaning, could be avoided by maintaining a low 71
average membrane flux. The average membrane flux as applied in this study (0.07 m/d) 72
was significantly lower than the maximum allowable flux (0.8 m/d) reported by the 73
manufacturer for similar but larger modules practically used in MBRs. Therefore the 74
membrane was operated with periodic relaxation (operation in a 14 min on and 1 min 75
off mode) without any periodic cleaning. Nevertheless, TMP was recorded throughout 76
this work. During continuous operation without any routine cleaning, ex-situ chemical 77
cleaning was performed only twice (on day 186 and 306) over the whole operation 78
period (306 days). As can be seen in Figure 46, TMP remained stable during the 51-day 79
start-up period. No abnormal transmembrane pressure increase was observed following 80
the introduction of the trace organic contaminants in the feed solution. The TMP started 81
to gradually increase approximately after 80 days of continuous operation. On day 186, 82
a high TMP value of 70.7 kPa was observed, which necessitated immediate cleaning. 83
Following this, PAC was added directly into the MBR to obtain a PAC concentration of 84
0.1 g/L. Direct addition of PAC into MBR has been widely reported to mitigate 85
membrane fouling [40, 161, 228] via several mechanisms including the adsorption of 86
membrane foulants on PAC, scouring action of PAC, changing the composition and 87
permeability of the cake layer and improved flocculation of MLSS [37, 40, 161, 228, 88
229]. In contrary, A few studies have reported that addition of PAC directly into MBR 89
did not improve the membrane permeability [227, 230]. The data presented in Figure 90
46, at the first instance indicate that TMP in the MBR increased slightly faster after the 91
addition of PAC. However, the MLSS concentration was 6 g/L at the point of initiation 92
of the operation with PAC, while at the very beginning the MLSS concentration was 93
only 3 g/L. Considering the TMP data from day 100 (MLSS concentration at around 6 94
g/L) to day 186 (operation without PAC, MLSS concentration ≥ 6 g/L) and that for day 95
206 to day 306 (operation with PAC, MLSS concentration ≈6 g/L), the rate of TMP 96
increase would in fact seem a bit slower for the operation with PAC. 97
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
108
EPS and SMP levels in the mixed liquor may have significant implication on floc 98
structure and sludge settleability and consequently on membrane fouling [231-233], 99
although controversies exist [234]. Yamato et al. [234] reported that no clear 100
relationship between the amount of EPS or carbohydrate on membrane fouling in pilot 101
MBR was established. It is worth mentioning that in this study EPS and SMP 102
components have been detected at higher concentration during operation with PAC 103
(Table 9). The contradictory effect of PAC addition on EPS concentration has been 104
reported in the literature. Kim et al. [217] reported that PAC addition decreases the EPS 105
content. In a study by Lesage et al. [38], a decrease in protein and carbonhydrate in 106
MBR supernatant was observed after PAC addition, while Thuy et al. [235] observed an 107
increase in soluble EPS concentration (SMP) after GAC addition into MBR. In addition, 108
variation of EPS content with different PAC dosage has also been reported. A decrease 109
in EPS content was observed at a PAC concentration of 0.75 g/L while an increase in 110
EPS concentration happened when the PAC concentration was doubled [228]. Although 111
the exact reason of elevated SMP during operation with PAC could not be explained, it 112
is interesting to note that despite significantly higher concentration of SMP in the MBR 113
after PAC addition, the rate of TMP increase was not significantly different from that 114
during operation without PAC, indicating that EPS and SMP concentrations did not 115
have any direct effect on fouling. 116
In this study, vigorous aeration was applied to maintain adequate level of DO within the 117
reactor and avoid settling of sludge at the corners of the reactor. However, as the reactor 118
design was not hydraulically optimized, mixing was not found to be adequate enough to 119
avoid settling of sludge at certain locations of the reactor and also to avoid accumulation 120
of sludge onto membrane surface. One may notice from Figure 47 that cake layer 121
appeared to cover more membrane area during the operation with PAC. The coverage 122
and characteristics of cake layer may be another factor responsible for the increase in 123
TMP in PAC – MBR. A comparison on the TMP between two MBRs operated in 124
parallel with 0.75 and 1.5 g/L PAC revealed that the TMP increased faster in the MBR 125
with higher dosage of PAC [228]. The authors explained that in the condition of high 126
PAC concentration, there was more chance of PAC particles to deposit on the 127
membrane surface. A similar observation has been also reported by Aurangzeb et al., 128
[39]. Because the MBR system in this study was not hydraulically optimized, a precise 129
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
109
comment about the role of PAC on mitigation of membrane fouling cannot be made 130
based on the observations made in this study. 131
132
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20
30
40
50
60
70
0
1
2
3
4
5
6
7
8
9
10
11
P2
P1
TMP
Tra
nsm
em
bra
ne p
ress
ure
(k
Pa)
Time (Day)
T
Chemical cleaning
ML
SS
(g
/L)
MLSS
133
Figure 46: Variation of transmembrane pressure (TMP) as a function of operation time. 134
―T‖ indicates the point of trace organic contaminants addition while ―P1‖ and ―P2‖ 135
indicate the point of PAC addition to achieve final PAC concentrations of 0.1 g/L and 136
0.5 g/L, respectively. 137
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
110
(a) Cake layer build up on the membrane
surface in MBR system
(b) Cake layer build up on the membrane
surface in PAC – MBR system
138
Figure 47: Fouled membrane in both (a) MBR and (b) PAC – MBR systems. Pictures 139
were taken on day 186 and 306, respectively. 140
141
6.3.2 Removal of trace organics by PAC - MBR hybrid system 142
As mentioned earlier in Section 4.3.6, low and variable removal efficiency was 143
observed for six biologically persistent and hydrophilic trace organic compounds 144
(metronidazole, fenoprop, ketoprofen, naproxen, diclofenac and carbamazepine) by 145
MBR before the PAC addition. The average removal efficiency of metronidazole, 146
fenoprop, ketoprofen, naproxen, diclofenac and carbamazepine was 39 ± 25 %, 20 ± 15 147
%, 67 ± 12 %, 45 ± 14 %, 15 ± 11 %, and 32 ± 17 %, respectively. Immediately after 148
adding PAC directly into the MBR, a sharp increase in removal efficiency was observed 149
for six biologically persistent and hydrophilic trace organic compounds (metronidazole, 150
fenoprop, ketoprofen, naproxen, diclofenac and carbamazepine), which showed low 151
removal by MBR- only treatment. On the other hand, as discussed earlier in (Section 152
4.3.6), a significant removal of hydrophobic compounds (Log D > 3.2) was observed in 153
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
111
MBR even before the addition of PAC. The dominant mechanism accounting for the 154
removal of hydrophobic compounds is sorption to activated sludge facilitating enhanced 155
biological degradation in some cases [236], [237]. As expected, a high degree of 156
removal of the hydrophobic compounds continued to be achieved by the MBR after 157
PAC addition. In addition, efficient removal of seven hydrophilic compounds (salicylic 158
acid, acetaminophen, primidone, ibuprofen, gemfibrozil, estriol and pentachlorophenol) 159
(log D < 3.2), which were consistently removed to higher than 60 (pentachlorophenol) 160
to higher than 80 % (the rest six) removal by MBR-only treatment, (see Section 4.3.6) 161
continued in PAC-MBR (Figure 48). 162
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
112
Salicylic
acid
Metronidazole
Fenoprop
Ketoprofen
Acetaminophen
Naproxen
Primidone
Ibuprofen
Diclofenac
Carbamazepine
Gemifibrozil
Pentachlorophenol
Estriol
4-tert-
butylphenol
Estrone
Bisphenol A
17-a-ethynylestradiol
17-b-estradiol
17-b-estrodiol-1
7-acetate
4-tert-
occtylphenol
Triclosan
4-n-nonylphenol0
20
40
60
80
100Log D < 3.2
Rem
ov
al e
ffic
ien
cy (
%)
A
MBR only Day 2 Day 5 Day 12 Day 18 Day 31
Log D < 3.2
Lo
g D
at
pH
7
-2
0
2
4
6
8
Log D at pH 7
163
Figure 48: Overall removal efficiency of trace organic compounds in PAC - MBR hybrid system after addition of PAC at a concentration of 0.1 164
g/L. 165
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
113
The removal efficiency for biologically persistent trace organics by the PAC - MBR
system was observed to improve in comparison to that by MBR- only treatment. PAC is
a well-known adsorbent for a wide range of organics (Section 2.4.1). Addition of PAC
into MBR supplies additional adsorptive sites for trace organic compounds in the PAC –
MBR system. Moreover, the growth of microorganisms on PAC surface can constitute a
process called biologically activated carbon. Therefore, conceptually, adsorption,
biodegradation and PAC regeneration can occur simultaneously within the PAC –
MBR. This process can enhance the removal of non- or slowly biodegradable
compounds. Similar observation has been reported in previous studies, for instance, in
case of treating dye wastewater [238] or high strength municipal synthetic wastewater
[45]. In this study, however, the increase in removal efficiency of the biologically and
persistent hydrophilic compounds under a PAC concentration of 0.1 g/L was only
temporary. As can be seen in
Figure 49, the removal efficiency dropped significantly after twelve days of operation
with a PAC concentration of 0.1 g/L. Observation of trace organics removal by the PAC
– MBR system for further twenty days revealed no increase in the removal efficiency of
the biologically persistent hydrophilic trace organic compounds. The possible
explanation is, in the presence of competition with other organics and inorganics in the
synthetic wastewater, PAC addition at a concentration of 0.1 g/L may not have been
sufficient enough to provide adequate additional adsorptive sites for the enhancement of
trace organics. According to Zhang et al., [44] under the competition with other
organics in the synthetic wastewater, only 30 % of the added PAC into MBR was
effectively utilized for carbamazepine adsorption. Other studies also pointed out that
competition for adsorptive sites and pore blockage are two mechanisms involved in the
reduction of adsorption capacity of target compounds on PAC [30, 239].
The instantaneous increase in removal efficiency of six biologically persistent
hydrophilic compounds (metronidazole, fenoprop, ketoprofen, naproxen, diclofenac and
carbamazepine) (log D < 3.2) suggests greater adsorption of trace organics onto PAC
than onto sludge. This observation is in line with available studies which report that
other mechanisms apart from hydrophobic interaction plays role in adsorption of target
compounds onto activated carbon [4, 19, 33, 34, 202, 204, 205]. Therefore, the
application of PAC can be a potential technique to enhance MBR performance.
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
114
However, as opposed to only temporary improvement in removal, achievement of
relatively more stable performance is important. For further understanding of the
phenomenon, 36 days after the first addition of PAC, PAC was added again to obtain a
PAC concentration of 0.5 g/L in the MBR. Following this, the PAC - MBR was
operated for further 64 days. Under the higher PAC concentration (0.5 g/L), an
improved removal of the hydrophilic and persistent compounds (metronidazole,
fenoprop, naproxen, ketoprofen, diclofenac and carbamazepine) was sustained for a
longer period, beyond which, however, the deterioration in removal efficiency did start
to occur for certain compounds. Although an instantaneous improvement in removal of
all six biologically persistent and hydrophilic trace organic compounds was observed
after addition of PAC, their profiles of removal efficiency followed different trends
afterwards (
Figure 49).
Significant variation in the breakthrough profiles amongst six biologically persistent
and hydrophilic trace organic compounds is evident from Figure 50. During operation
under a PAC concentration of 0.1 g/L, except for ketoprofen, the breakthrough of the
compounds gradually increased over time. Under an elevated concentration of 0.5 g
PAC/L, however, the breakthrough of ketoprofen, carbamazepine and naproxen
remained stable within 20%. Notably, during sequential operation of MBR-GAC, the
order of compounds in terms of decreasing severity of breakthrough was:
fenoprop=diclofenac>ketoprofen>naproxen>carbamazepine>metronidazole, indicating
some differences in breakthrough profiles of the compounds in the two distinct systems.
In the MBR – GAC, fixed bed GAC column treated MBR permeate. Breakthrough from
a GAC column will increase with operation time (number of bed volume) unless there is
biodegradation (like in biologically activated carbon, BAC) or regeneration of GAC
surface. The development of BAC within a GAC column depends on attainment of
several conditions which necessitate special design considerations [240, 241] .However,
in a PAC – MBR system, the bio-regeneration of PAC surface may occur immediately
to increase the adsorptive sites. The differences in breakthrough profiles of the
compounds in MBR - GAC and PAC - MBR may be attributed to the occurrence of bio-
regeneration in PAC - MBR. Nevertheless, the MBR - GAC and the PAC - MBR were
operated in two different configurations. The GAC column treated MBR permeate
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
115
under less competition for adsorptive sites between trace organics and the bulk organics.
Therefore, a direct comparison between two systems is not possible.
0 10 20 30 40 50 60 70 80 90 100 1100
10
20
30
40
50
60
70
80
90
100
Metronidazole Fenoprop Naproxen
Ketoprofen Diclofenac Carbamazepine
Rem
ov
al
eff
icie
ncy
(%
)
Time (Day)
0.5 g PAC/L
0.1 g PAC/L
Figure 49: Removal of six biologically persistent hydrophilic trace organic compounds
as a function of operation time at 0.1 g PAC/L and 0.5 g PAC/L concentrations.
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
116
0 10 20 30 40 50 60 70 80 90 100 110
0
10
20
30
40
50
60
70
80
90
100
0.5 g PAC/L0.1 g PAC/L
Metronidazole Fenoprop Naproxen
Ketoprofen Diclofenac Carbamazepine
Bre
ak
thro
ug
h (
%)
Time (Day)
50
% b
reak
thro
ug
h l
ine
Figure 50: Breakthrough profile of six biologically persistent hydrophilic trace organic
compounds as a function of operation time. The breakthrough values are defined as
percentage of the effluent concentration over the influent concentration of the same
sampling event.
Table 10 furnishes a preliminary estimate for the purpose of comparison between
simultaneous application of PAC within MBR and sequential application of GAC
adsorption following MBR treatment in terms of activated carbon usage and
effectiveness of the processes. The PAC-MBR was operated for 100 days with a total
addition of 2.25 g of PAC in two stages. A total of 450 L of permeate was produced
during the operation in the PAC - MBR configuration. On the other hand 7.5 g of GAC
in the fixed bed column produced 321 L of permeate over 93 days. When the above data
relating to volume treated per unit weight of GAC (Table 10) is considered in
conjunction with the difference in the extent of breakthrough from each configuration, it
can be said that the PAC-MBR performed relatively better. For instance, a complete
breakthrough of fenoprop and diclofenac occurred in the course of operation of the
GAC column at a GAC usage rate of 42.8 L (effluent) /g (GAC), while in the course of
production of 450 L of permeate from the PAC-MBR, the breakthrough of fenoprop and
diclofenac were 70 and 45 %, respectively although a PAC usage rate of 200 L
(effluent)/ g (PAC) was applied. The comparison of performance between MBR – GAC
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
117
and PAC – MBR systems in terms of trace organics removal has not been reported in
the literature. However, the performance of PAC—MBR and GAC—MBR in terms of
oily wastewater removal was compared in a study by William et al., [242].The results
highlighted that PAC - MBR was better than GAC – MBR system in terms of economy
(lower capital and operation cost in PAC – MBR system), effluent quality, less frequent
cleaning, tolerance to upsets and immediate acclimation [242]. Based on the current
study, activated carbon, either through sequential operation or through direct addition
into MBR can be used to achieve better removal over MBR-only treatment, however,
dosage and periodic replenishment of activated carbon will be critical for maintaining
excellent removal. In this study, the removal of fenoprop, which demonstrated the worst
removal by PAC – MBR system, was significantly decreased to below 80 % after 17
days of operation with 0.5 g/L PAC addition. If fenoprop is taken as a tracer for the
determination of the frequency of replenishment of PAC for maintaining above 80 %
removal, a 5.8 % of sludge wastage per day (0.26 L/day) and 5.8 % new PAC addition
per day (0.13 g/day).
Table 10: Comparison of the effectiveness between MBR - GAC and PAC - MBR
systems
Parameters MBR – GAC PAC – MBR *
Activated carbon usage during experiment (g) 7.5 2.25
Operation time (Day) 93 100
Treated water volume (L/day) 3.45 4.5
Total treated water volume (L) 321 450
Treated volume per unit weight of activated
carbon (L/g) 42.8 200
Breakthrough of fenoprop (%) **
100 70
Breakthrough of diclofenac (%) **
100 45
* PAC was added at day 206 and 243 to obtain a concentration of 0.1 g PAC/L and 0.5 g
PAC/L, respectively.
**The breakthrough values are defined as percentage of the effluent concentration over
the influent concentration of the same sampling event.
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
118
Table 11 presents estimated costs of GAC and PAC for operation of MBR – GAC and
PAC – MBR systems, respectively with a typical capacity of 1 m3/day based on the lab-
scale system data. As noted above, for maintaining an SRT of 17 days, 0.26 L of sludge
will need to be withdrawn and 0.13 g of PAC will need to be added daily to maintain a
PAC concentration of 0.5 g/L in MBR. The total corresponding cost for PAC usage is
24.5 AU $ per year. Consequently, the addition of PAC within the MBR treatment
process cost an extra 0.07 AU$/ m3 of treated water. On the other hand, in the MBR –
GAC configuration, 2.2 kg of GAC would need to be replaced every 14 days. The cost
required for GAC usage is 241 AU $ per year, which amounts to a cost of 0.7 AU$/ m3
treated water. Therefore, it can be concluded that simultaneous application of PAC
within MBR is a better configuration compared to sequential application of GAC
adsorption following MBR treatment.
Table 11: Cost analysis for GAC and PAC usage.
Parameters MBR – GAC PAC – MBR
System capacity (m3/day) 1 1
Cost for activated carbon
(AU $/kg) a
4.20 2.15
Activated carbon usage (kg) 2.2 0.5
Total activated carbon usage (kg/year) 57.4
11.4
Activated carbon replenishment period
(Day) b 14
17
Cost for activated carbon usage
(AU$/year) 241 24.5
Cost per unit volume of treated water
(AU$/m3.day)
0.7 0.07
a Typical industrial costs provided by Activated Carbon Technologies Pty Ltd, Victoria,
Australia.
b The activated carbon replacement period was selected to maintain above 80 % removal
of fenoprop in both MBR – GAC and PAC – MBR systems.
Chapter 6 Removal of trace organic contaminants by PAC- MBR hybrid system
119
6.4 Conclusions
The addition of PAC directly into MBR resulted in a sharp increase in removal
efficiency of six biologically persistent and hydrophilic trace organic compounds,
which showed low removal by MBR- only treatment. The high degree removal (>95%)
of the hydrophobic compounds continued to be achieved, while the high removal
efficiency of the biologically persistent hydrophilic compounds did not last for long.
Significant drops in removal efficiencies of all six persistent compounds except
ketoprofen were observed within twelve days of the start of operation with a PAC
concentration of 0.1 g/L. The removal efficiency could be recovered by adding a second
dose of PAC, raising the PAC concentration in the MBR to 0.5 g/L. Good removal
(>70%) of ketoprofen, carbamazepine and naproxen sustained for 64 days (until the
end of operation). Overall, activated carbon, either through sequential operation or
through direct addition into MBR can be used to achieve better removal over MBR-only
treatment, however, dosage and periodic replenishment of activated carbon will be
critical for maintaining excellent removal.
Chapter 7 Conclusions and Recommendations
120
CHAPTER 7: CONCLUSIONS AND RECOMMENDATIONS
7.1 Conclusions
Laboratory scale experiments were conducted to investigate the removal efficiency of
trace organic contaminants by sequential and simultaneous application of activated
carbon adsorption with a submerged MBR system. The MBR system was equipped with
a microfiltration membrane module. Results obtained from this study demonstrate an
excellent performance of MBR regarding basic water quality parameters such as
turbidity, TOC and TN. However, removal efficiency of specific trace organic
contaminants was found strongly dependent on their physicochemical properties. Both
adsorption to the sludge and biodegradation were thought to be responsible for the
removal of hydrophobic compounds. In contrast, the former mechanism was absent for
hydrophilic and biologically persistent trace organic compounds. Accordingly,
approximately 90% removal efficiency or above of hydrophobic trace organic
compounds (log D > 3.2) was recorded, while under the same conditions, the removal
efficiency of less or moderately hydrophobic and biologically persistent trace organic
compounds was significantly variable.
Given the limitations of MBR treatment for the removal of hydrophilic and biologically
persistent trace organic compounds, a GAC post-treatment column was applied to
polish the MBR permeate. Our results confirm that initially GAC post-treatment could
significantly improve the removal of the compounds which experienced low to
moderate removal by MBR treatment (carbamazepine, diclofenac, fenoprop, naproxen,
ketoprofen and metronidazole). Because MBR produces suspended solids free permeate
and all significantly hydrophobic compounds had been already significantly removed by
the MBR, in presence of a reduced competition for the adsorptive sites, the GAC post-
treatment helped removing extensively the hydrophilic compounds from MBR
permeate. However, the adsorption capacity of GAC column gradually diminished, and
within a BV of 18093, there was no further additional removal of six hydrophilic and
biologically persistent compounds (carbamazepine, diclofenac, fenoprop, naproxen,
ketoprofen and metronidazole), especially for fenoprop and diclofenac. Of the six
problematic compounds, the neutral compounds (carbamazepine and metronidazole)
demonstrated slower breakthrough than the rest of the compounds which were
negatively charged. Single solute isotherm data appeared to be a good indicator to
Chapter 7 Conclusions and Recommendations
121
predict the set of compounds likely to experience rapid breakthrough and especially can
differentiate the breakthrough behavior of negatively charged and neutral trace organic
contaminants.
Finally, PAC was directly added into the MBR in two steps to achieve a PAC
concentration of 0.1 and 0.5 g/L PAC, respectively. An improved removal of trace
organic contaminants by the hybrid PAC - MBR was demonstrated. Especially,
simultaneous application of PAC within MBR improved the removal performance of
the hydrophilic and biologically persistent trace organic compounds. The removal
performance of certain compounds for example, fenoprop, metronidazole, ketoprofen,
naproxen, diclofenac and carbamazepine was 80 %, 88 %, 92 % , 86 %, 85 %, and 96
%, respectively, after five days of 0.1 g/L PAC addition. However, gradual deterioration
in removal efficiency was observed, where the time taken for a certain level of
deterioration depended on the PAC concentration in the MBR. For example, during
operation under a PAC concentration of 0.1 g/L, except for ketoprofen, the
breakthrough of the compounds gradually increased over time (e.g., above 50 and 80 %
breakthrough was observed for fenoprop and diclofenac after 12 and 16 days of
operation, respectively). Under an elevated concentration of 0.5 g PAC/L, however, the
breakthrough of ketoprofen, carbamazepine and naproxen remained stable within 20%to
the end of the operation period. Periodic sludge withdrawal from MBR was not
practised in this study. Judging from the operation time and PAC concentration-
dependent performance of the PAC – MBR system, periodic withdrawal of sludge and
addition of fresh PAC are recommended. From the performance stability and activated
carbon usage points of view, simultaneous application of PAC within MBR could be a
better choice compared to sequential application of GAC adsorption following MBR
treatment. Overall, application of activated carbon can be used as post-treatment options
for MBR permeate.
7.2 Recommendations for further research
During the process of conducting this research work, new ideas emerged:
(i) Metabolites arising from degradation of the parent compounds need to be monitored
to understand the degradation pathway and the fate of the compounds following MBR
treatment. Data on the degradation pathway and the fate of the compounds would
facilitate the assessment of the potential risks of trace organics.
Chapter 7 Conclusions and Recommendations
122
(ii) A comprehensive understanding of the performance of GAC column in removal of
trace organic contaminants will be a useful tool for the water industry in dealing with
these contaminants. As discussed particularly in chapter 5, the GAC column
demonstrated a good capacity of adsorption of a wide spectrum of trace organic
compounds. However, in this study, the GAC column was used to treat suspended
solids free permeate which resulted in an extended lifetime of the GAC column. The
performance of GAC column treating trace organic contaminants spiked in raw
wastewater and in Milli-Q water, respectively will need to be tested to study the effect
of suspended solids and background organics concentration on adsorption process.
(iii) Factors influencing the adsorption process for example, pH and EBCT need also to
be investigated. The results of these experiments will allow us to better understand the
performance of GAC column in the field.
(iv) The PAC dosage in parallel MBRs running under distinct SRTs and MLSS can be
varied to ascertain the effect of PAC dosage, SRT and MLSS on performance of PAC-
MBR. This will directly help to precisely estimate the required dosage and frequency of
withdrawal of spent PAC and replenishment. The effects of different HRTs on trace
organics removal also need to be studied.
(v) The disposal of PAC-mixed sludge from MBR and also the spent GAC from GAC
column can potentially cause secondary pollution by the residual trace organic
contaminants on PAC and GAC. The issue of sludge handling has not been dealt with in
this study. This can be an important point to explore in the future studies.
References
123
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Appendix
144
APPENDIX A
RECORDING DATA THROUGHOUT EXPERIMENT
Table 12: TOC and TN concentration in MBR feed and permeate before adding trace
organics into the MBR.
Days TOC (mg/L) TN (mg/L)
Days TOC (mg/L) TN (mg/L)
Feed Permeate Feed Permeate Feed Permeate Feed Permeate
1 25
2 26 252 3.3 48.20 37.02
3 139.90 4.29 27.04 10.34 27
4 28
5 136.9 3.56 27.23 9.04 29 136.3 4.523 24.9 41.75
6 30
7 31
8 132.90 2.67 25.95 11.60 32 145 4.534 27.44 39.92
9 33
10 140.60 2.21 26.53 12.87 34
11 35
12 136.10 2.00 24.98 13.02 36
13 37 128.00 7.273 28.45 39.07
14 38
15 136.90 2.17 25.29 13.92 39
16 40
17 140.00 3.32 26.65 19.83 41
18 42
19 272.50 1.97 48.75 18.04 43 132.60 4.07 26.63 22.57
20 44
21 45
22 268.90 2.61 51.33 28.37 46 136.20 3.193 26.79 19.66
23 47
24 48 124.80 3.428 25.44 21.56
Appendix
145
Table 13: TOC and TN concentration in MBR feed and permeate after adding trace
organics.
Days
TOC (mg/L) TN (mg/L)
Days
TOC (mg/L) TN (mg/L)
Feed Permeate Feed Permeate Feed Permeate Feed Permeate
49 85
50 86 185.5 2.222 26.05 12.12
51 87
52 189.6 2.62 23.16 14.95 88 186.1 1.918 25.63 13.29
53 89
54 190.2 2.37 26.56 13.47 90
55 91 178.1 1.855 24.66 15.06
56 92
57 184.1 5.12 22.01 15.25 93 185.5 2.326 23.77 15.74
58 94
59 184.6 2.00 26.42 16.68 95 184.5 1.553 21.84 12.03
60 96
61 97 183.6 1.54 25.65 8.785
62 98
63 99 170.5 2.484 23.58 10.16
64 184.3 4.11 25.69 12.77 100
65 101
66 164.2 2.27 23.73 13.52 102
67 103
68 178.5 1.45 26.39 12.43 104
69 105
70 106 160.5 5.61 26.04 13.26
71 161.5 1.68 23.79 10.11 107
72 108 173.5 7.72 23.34 13.49
73 189.5 1.639 24.56 9.789 109
74 110 175.8 6.005 22.25 13.58
75 187.3 1.364 26.82 8.578 111
76 112
77 177.8 1.297 25.68 8.834 113 173.2 3.87 23.4 12.79
78 114
79 115 177.2 2.617 24.58 14.21
80 183.4 2.442 25.76 12.45 116
81 117
82 195.5 1.711 24.55 11.47 118
83 119
84 189.1 1.714 24.92 11.66 120 171.3 1.479 19.4 13.08
Appendix
146
TOC (mg/L) TN (mg/L) TOC (mg/L) TN (mg/L)
Day Feed Permeate Feed Permeate Day Feed Permeate Feed Permeate
121 157
122 184.8 6.07 17.87 13.42 158
123 159 174.2 1.845 24.04 13.46
124 160
125 161
126 162
127 178.5 2.761 21.07 10.21 163
128 164 178.1 1.855 23.66 15.06
129 177.2 2.652 23.53 7.609 165
130 166
131 180.6 2.515 25.58 6.572 167
132 168
133 169
134 170.3 2.302 24.56 6.72 170 173.5 7.72 23.34 13.49
135 171
136 173.3 2.132 26.25 13.73 172
137 173
138 174
139 175 184.10 5.12 22.01 15.25
140 176
141 177
142 178
143 173.6 3.2 18.99 13.04 179 178.1 6.22 23.16 17.22
144 180
145 181
146 182
147 183 186 5.45 26.9 20.59
148 184
149 185 189.5 1.901 26.83 21.88
150 170.1 1.758 23.97 9.236 186
151 187
152 188
153 189
154 188.9 2.575 26.65 8.107 190
155 191
156 192
(Table 13, continued)
Appendix
147
Table 14: Trace organics concentration and removal efficiency by MBR - GAC
treatment.
Day 67 Feed After treated by MBR After further treated by GAC
Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
%
Concentration
(ng/L)
Removal
%
Salicylic acid 5946 24 99.6 181 97
Metronidazole 1561 533 65.8 37 97.6
Fenoprop 3760 2559 31.9 29 99.2
Ketoprofen 4919 3076 37.5 57 98.9
Acetaminophen 2104 442 79.0 272 87.1
Naproxen 5153 3735 27.5 50 99
Primidone 1067 69 93.5 33 96.9
Ibuprofen 3039 357 88.2 0 100
Diclofenac 5102 3781 25.9 55 98.9
Carbamazepine 5365 4271 20.4 107 98
Gemfibrozil 7117 332 95.3 10 99.9
Estriol (E3) 2310 44 98.1 35 98.5
Pentachlorophenol 5388 1801 66.6 9 99.8
4-tert-butylphenol 5908 408 93.1 13 99.8
Estone (E1) 4236 15 99.6 13 99.7
Bisphenol A 5810 837 85.6 169 97.1
17-α-
ethinylestradiol
(EE2) 4097 458 88.8 27 99.3
17-β estradiol (E2) 5382 15 99.7 0 100
17-β-estradiol-17-
acetate (E2Ac) 3225 30 99.1 25 99.2
4-tert-octylphenol 7248 75 99.0 19 99.7
Triclosan 6617 56 99.1 20 99.7
4-n-nonylphenol 4516 72 98.4 55 98.8
(Table 14, continued)
Appendix
148
Day 74 Feed After treated by MBR After further treated by GAC
Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 5974 127 97.9 43 99.3
Metronidazole 1331 449 66.3 2 99.8
Fenoprop 3308 1411 57.3 429 87
Ketoprofen 4501 2345 47.9 273 93.9
Acetaminophen 2466 586 76.2 211 91.4
Naproxen 3845 1510 60.7 22 99.4
Primidone 2706 64 97.6 100 96.3
Ibuprofen 2040 265 87.0 187 90.8
Diclofenac 3914 2510 35.9 280 92.8
Carbamazepine 3774 3597 4.7 90 97.6
Gemfibrozil 4443 142 96.8 23 99.5
Estriol (E3) 1624 2 99.9 1 99.9
Pentachlorophenol 4416 2215 49.8 62 98.6
4-tert-butylphenol 5210 389 92.5 25 99.5
Estone (E1) 2082 52 97.5 36 98.2
Bisphenol A 5638 491 91.3 59 99
17-α-ethinylestradiol
(EE2) 3522 340 90.3 25 99.3
17-β estradiol (E2) 3722 16 99.6 3 99.9
17-β-estradiol-17-
acetate (E2Ac) 3715 58 98.4 27 99.3
4-tert-octylphenol 5239 159 97.0 6 99.9
Triclosan 5294 99 98.1 33 99.4
4-n-nonylphenol 2875 151 94.8 65 97.7
(Table 14, continued)
Appendix
149
Day 80 Feed After treated by MBR After further treated by GAC
Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 6085 94 98.5 103 98.3
Metronidazole 752 341 54.7 76 89.8
Fenoprop 4172 3866 7.3 915 78.1
Ketoprofen 3481 1113 68.0 342 90.2
Acetaminophen 1806 189 89.5 94 94.8
Naproxen 5884 5387 8.4 796 86.5
Primidone 4390 545 87.6 0 100
Ibuprofen 4496 278 93.8 78 98.3
Diclofenac 5464 5036 7.8 1383 74.7
Carbamazepine 3392 2666 21.4 71 97.9
Gemfibrozil 4098 145 96.5 56 98.6
Estriol (E3) 2030 100 95.1 17 99.2
Pentachlorophenol 4887 2138 56.2 47 99
4-tert-butylphenol 4108 218 94.7 19 99.5
Estone (E1) 2400 660 72.5 290 87.9
Bisphenol A 4759 289 93.9 32 99.3
17-α-
ethinylestradiol
(EE2) 3354 374 88.9 22 99.3
17-β estradiol (E2) 3039 19 99.4 14 99.5
17-β-estradiol-17-
acetate (E2Ac) 3941 56 98.6 18 99.5
4-tert-octylphenol 4430 126 97.2 19 99.6
Triclosan 6215 51 99.2 12 99.8
4-n-nonylphenol 2393 100 95.8 54 97.7
(Table 14, continued)
Appendix
150
Day 87 Feed After treated by MBR After further treated by GAC
Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 5380 89 98.3 286 94.7
Metronidazole 644 437 32.2 94 85.4
Fenoprop 4206 3745 11.0 1231 70.7
Ketoprofen 3429 912 73.4 443 87.1
Acetaminophen 2051 165 91.9 75 96.3
Naproxen 7144 3844 46.2 1187 83.4
Primidone 1911 8 99.6 0 100
Ibuprofen 5411 170 96.9 94 98.3
Diclofenac 6608 5127 22.4 1552 76.5
Carbamazepine 3048 2617 14.1 168 94.5
Gemfibrozil 4493 106 97.6 54 98.8
Estriol (E3) 1446 2 99.8 4 99.7
Pentachlorophenol 4396 2191 50.2 117 97.3
4-tert-butylphenol 5251 286 94.5 28 99.5
Estone (E1) 3825 141 96.3 106 97.2
Bisphenol A 5547 180 96.8 51 99.1
17-α-ethinylestradiol
(EE2) 3152 260 91.8 46 98.5
17-β estradiol (E2) 3201 12 99.6 5 99.8
17-β-estradiol-17-
acetate (E2Ac) 3789 12 99.7 10 99.7
4-tert-octylphenol 4968 132 97.3 24 99.5
Triclosan 5610 33 99.4 13 99.8
4-n-nonylphenol 2441 105 95.7 28 98.9
(Table 14, continued)
Appendix
151
Day 94 Feed After treated by MBR After further treated by GAC
Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 5589 96 98.3 73 98.7
Metronidazole 541 532 1.7 71 86.9
Fenoprop 4570 3666 19.8 2252 50.7
Ketoprofen 3432 917 73.3 404 88.2
Acetaminophen 1246 228 81.7 69 94.5
Naproxen 8279 3971 52 1684 79.7
Primidone 7883 0 100 0 100
Ibuprofen 5478 275 95 16 99.7
Diclofenac 6593 5187 21.3 3652 44.6
Carbamazepine 3142 2631 16.3 316 90
Gemfibrozil 4615 57 98.8 34 99.3
Estriol (E3) 2311 50 97.8 22 99
Pentachlorophenol 4351 1952 55.1 224 94.8
4-tert-butylphenol 5530 145 97.4 34 99.4
Estone (E1) 2827 19 99.3 190 93.3
Bisphenol A 5417 104 98.1 26 99.5
17-α-ethinylestradiol (EE2)
3831 162 95.8 38 99
17-β estradiol (E2) 3438 0 100 22 99.4
17-β-estradiol-17-
acetate (E2Ac) 4343 33 99.2 11 99.7
4-tert-octylphenol 5512 118 97.9 31 99.4
Triclosan 5130 68 98.7 44 99.1
4-n-nonylphenol 2149 171 92.1 94 95.6
(Table 14, continued)
Appendix
152
Day 101 Feed After treated by MBR After further treated by GAC
Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 5022 70 98.6 162 96.8
Metronidazole 482 462 4.2 16 96.7
Fenoprop 3817 3982 -4.3 2895 24.2
Ketoprofen 3226 1081 66.5 719 77.7
Acetaminophen 1780 143 92 25 98.6
Naproxen 7061 4113 41.8 2135 69.8
Primidone 3839 3 99.9 44 98.8
Ibuprofen 5767 77 98.7 62 98.9
Diclofenac 6273 6589 -5 5057 19.4
Carbamazepine 3140 2486 20.8 549 82.5
Gemfibrozil 4072 44 98.9 35 99.2
Estriol (E3) 1578 33 97.9 25 98.4
Pentachlorophenol 3825 1525 60.1 329 91.4
4-tert-butylphenol 3756 94 97.5 34 99.1
Estone (E1) 2404 159 93.4 140 94.2
Bisphenol A 4796 172 96.4 62 98.7
17-α-ethinylestradiol (EE2)
3111 221 92.9 77 97.5
17-β estradiol (E2) 3070 44 98.6 9 99.7
17-β-estradiol-17-
acetate (E2Ac) 3764 53 98.6 10 99.7
4-tert-octylphenol 4452 92 97.9 35 99.2
Triclosan 4606 19 99.6 38 99.2
4-n-nonylphenol 3142 83 97.4 132 95.8
(Table 14, continued)
Appendix
153
Day 110 Feed After treated by MBR After further treated by GAC
Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 4420 90 98 149 96.6
Metronidazole 982 630 35.8 0 100
Fenoprop 4418 3620 18.1 2452 44.5
Ketoprofen 3374 875 74.1 510 84.9
Acetaminophen 3861 835 78.4 603 84.4
Naproxen 5827 2703 53.6 1417 75.7
Primidone 5692 496 91.3 56 99
Ibuprofen 5366 72 98.7 34 99.4
Diclofenac 3569 3437 3.7 2884 19.2
Carbamazepine 5486 2846 48.1 453 91.7
Gemfibrozil 4092 22 99.5 24 99.4
Estriol (E3) 2830 33 96.2 46 98.4
Pentachlorophenol 3626 1305 64 238 93.4
4-tert-butylphenol 4339 232 94.6 60 98.6
Estone (E1) 2708 9 99.7 6 99.8
Bisphenol A 4587 311 93.2 36 99.2
17-α-ethinylestradiol (EE2) 4121 233 94.4 162 96.1
17-β estradiol (E2) 3534 4 99.9 0 100
17-β-estradiol-17-
acetate (E2Ac) 5104 12 99.8 0 100
4-tert-octylphenol 4269 114 97.3 5 99.9
Triclosan 4486 23 99.5 12 99.7
4-n-nonylphenol 2034 49 97.6 18 99.1
(Table 14, continued)
Appendix
154
Day 117 Feed After treated by MBR After further treated by GAC
Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 4853 129 97.3 180 96.3
Metronidazole 1553 988 36.4 0 100
Fenoprop 4713 3836 18.6 2635 44.1
Ketoprofen 3869 563 85.5 472 87.8
Acetaminophen 4013 500 87.6 987 75.4
Naproxen 6190 2856 53.9 1278 79.4
Primidone 4811 593 87.7 0 100
Ibuprofen 5955 285 95.2 79 98.7
Diclofenac 3798 3875 -2 2666 29.8
Carbamazepine 5324 2703 49.2 453 91.5
Gemfibrozil 4427 23 99.5 27 99.4
Estriol (E3) 3071 72 97.7 51 98.3
Pentachlorophenol 3823 1564 59.1 237 93.8
4-tert-butylphenol 4836 435 91 94 98.1
Estone (E1) 2826 19 99.3 0 100
Bisphenol A 5177 555 89.3 43 99.2
17-α-ethinylestradiol
(EE2) 4663 280 94 132 97.2
17-β estradiol (E2) 3880 15 99.6 0 100
17-β-estradiol-17-
acetate (E2Ac) 5599 38 99.3 12 99.8
4-tert-octylphenol 5096 218 95.7 28 99.4
Triclosan 4918 63 98.7 45 99.1
4-n-nonylphenol 2279 78 96.6 73 96.8
(Table 14, continued)
Appendix
155
Day 124 Feed After treated by MBR
After further treated by
GAC Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 4124 190 95.4 128 96.9
Metronidazole 995 683 31.4 40 96
Fenoprop 5091 4191 17.7 3480 31.6
Ketoprofen 3530 874 75.2 735 79.2
Acetaminophen 1880 226 88 162 91.4
Naproxen 5424 3210 40.8 2108 61.1
Primidone 4407 577 86.9 0 100
Ibuprofen 4630 114 97.5 77 98.3
Diclofenac 4166 3784 9.2 3236 22.3
Carbamazepine 5267 3156 40.1 699 86.7
Gemfibrozil 3919 34 99.1 38 99
Estriol (E3) 3086 120 96.1 105 96.6
Pentachlorophenol 3888 1913 50.8 420 89.2
4-tert-butylphenol 3802 628 83.5 97 97.5
Estone (E1) 3017 11 99.6 39 98.7
Bisphenol A 4954 470 90.5 69 98.6
17-α-ethinylestradiol
(EE2) 4989 319 93.6 109 97.8
17-β estradiol (E2) 4083 25 99.4 29 99.3
17-β-estradiol-17-
acetate (E2Ac) 4672 0 100 6 99.9
4-tert-octylphenol 3936 244 93.8 52 98.7
Triclosan 4854 41 99.2 0 100
4-n-nonylphenol 1719 0 100 9 99.5
(Table 14, continued)
Appendix
156
Day 132 Feed After treated by MBR
After further treated by
GAC Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 3810 325 91.5 233 93.9
Metronidazole 918 852 7.2 77 91.6
Fenoprop 3985 3813 4.3 3118 21.8
Ketoprofen 3507 1060 69.8 723 79.4
Acetaminophen 2000 377 81.2 56 97.2
Naproxen 5538 3082 44.3 1707 69.2
Primidone 3953 292 92.6 226 94.3
Ibuprofen 4535 101 97.8 69 98.5
Diclofenac 4899 3870 21 2946 39.9
Carbamazepine 5094 2614 48.7 750 85.3
Gemfibrozil 3925 27 99.3 26 99.3
Estriol (E3) 2768 123 95.6 31 98.9
Pentachlorophenol 3834 1102 71.3 247 93.6
4-tert-butylphenol 3300 182 94.5 45 98.6
Estone (E1) 2689 0 100 15 99.4
Bisphenol A 4314 206 95.2 38 99.1
17-α-ethinylestradiol
(EE2) 3882 300 92.3 68 98.2
17-β estradiol (E2) 3515 33 99.1 15 99.6
17-β-estradiol-17-
acetate (E2Ac) 4303 37 99.1 38 99.1
4-tert-octylphenol 3390 158 95.3 41 98.8
Triclosan 3933 28 99.3 31 99.2
4-n-nonylphenol 1112 12 98.9 23 97.9
(Table 14, continued)
Appendix
157
Day 140 Feed After treated by MBR
After further treated by
GAC Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 3049 14 99.5 32 98.9
Metronidazole 863 453 47.5 53 93.9
Fenoprop 4239 4039 4.7 3119 26.4
Ketoprofen 3085 1118 63.7 836 72.9
Acetaminophen 2706 175 93.5 298 89
Naproxen 4937 2757 44.2 1812 63.3
Primidone 4126 1562 62.1 413 90
Ibuprofen 3972 14 99.6 94 97.6
Diclofenac 4418 3796 14.1 3074 30.4
Carbamazepine 3612 2596 28.1 891 75.3
Gemfibrozil 3287 26 99.2 20 99.4
Estriol (E3) 2449 0 100 45 98.2
Pentachlorophenol 3318 1373 58.6 365 89
4-tert-butylphenol 2671 387 85.5 70 97.4
Estone (E1) 2400 6 99.7 8 99.7
Bisphenol A 4141 92 97.8 24 99.4
17-α-ethinylestradiol
(EE2) 3885 260 93.3 107 97.2
17-β estradiol (E2) 3591 27 99.2 0 100
17-β-estradiol-17-
acetate (E2Ac) 5325 75 98.6 24 99.6
4-tert-octylphenol 3349 228 93.2 53 98.4
Triclosan 4055 29 99.3 19 99.5
4-n-nonylphenol 2109 56 97.3 50 97.6
(Table 14, continued)
Appendix
158
Day 148 Feed After treated by MBR After further treated by GAC
Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 3896 25 99.4 47 98.8
Metronidazole 1241 385 69 0 100
Fenoprop 4793 3620 24.5 2784 41.9
Ketoprofen 3133 948 69.7 766 75.6
Acetaminophen 3178 59 98.2 55 98.3
Naproxen 5696 2571 54.9 1435 74.8
Primidone 5373 1310 75.6 340 93.7
Ibuprofen 4152 0 100 27 99.4
Diclofenac 3659 3215 12.1 2536 30.7
Carbamazepine 5047 2520 50.1 648 87.2
Gemfibrozil 3591 30 99.2 29 99.2
Estriol (E3) 2597 110 95.8 0 100
Pentachlorophenol 3729 970 74 176 95.3
4-tert-butylphenol 3889 248 93.6 87 97.8
Estone (E1) 2506 2 99.9 17 99.3
Bisphenol A 4180 76 98.2 18 99.6
17-α-ethinylestradiol
(EE2) 3896 174 95.5 63 98.4
17-β estradiol (E2) 3434 4 99.9 12 99.6
17-β-estradiol-17-
acetate (E2Ac) 5382 25 99.5 7 99.9
4-tert-octylphenol 4510 194 95.7 55 98.8
Triclosan 4399 46 99 13 99.7
4-n-nonylphenol 2538 30 98.8 32 97.9
(Table 14, continued)
Appendix
159
Day 154 Feed After treated by MBR After further treated by GAC
Compounds
Concentration
(ng/L)
Concentration
(ng/L)
Removal
(%)
Concentration
(ng/L)
Removal
(%)
Salicylic acid 3296 19 99.4 29 99.1
Metronidazole 1149 323 71.9 140 87.8
Fenoprop 4482 3044 32.1 3136 30
Ketoprofen 2790 1011 63.7 818 70.7
Acetaminophen 3606 160 95.6 195 94.6
Naproxen 5454 2344 57 1936 64.5
Primidone 4971 1257 74.7 646 87
Ibuprofen 3936 16 99.6 24 99.4
Diclofenac 3520 2605 26 2517 28.5
Carbamazepine 4326 2096 51.5 995 77
Gemfibrozil 3436 45 98.7 33 99
Estriol (E3) 2486 43 98.3 0 100
Pentachlorophenol 3254 824 74.7 293 91
4-tert-butylphenol 2949 191 93.5 42 98.6
Estone (E1) 2230 42 98.1 31 98.6
Bisphenol A 3957 60 98.5 30 99.2
17-α-ethinylestradiol
(EE2) 3694 169 95.4 91 97.6
17-β estradiol (E2) 3344 16 99.5 1 100
17-β-estradiol-17-
acetate (E2Ac) 5165 84 98.4 30 99.4
4-tert-octylphenol 3816 108 97.2 36 99.1
Triclosan 4060 37 99.1 11 99.7
4-n-nonylphenol 2556 0 100 0 100
(Table 14, continued)
Appendix
160
Table 15: Trace organics concentration and removal efficiency by PAC - MBR treatment
with 0.1 g PAC /L concentration.
Day 205 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 2674 122 95.4
Metronidazole 1860 19 99
Fenoprop 2784 145 94.8
Ketoprofen 1844 6 99.7
Acetaminophen 1834 192 89.5
Naproxen 3752 102 97.3
Primidone 3553 17 99.5
Ibuprofen 2995 137 95.4
Diclofenac 3098 139 95.5
Carbamazepine 3793 118 96.9
Gemfibrozil 2534 21 99.2
Estriol 1985 40 98
Pentachlorophenol 2071 114 94.5
4-tert-butylphenol 2726 48 98.2
Estrone 2026 13 99.4
Bisphenol A 2786 24 99.1
17-α ethinylestradiol 3219 53 98.4
17-β- estradiol 2927 8 99.7
17-β- estradiol-17 acetate 3665 14 99.6
4-tert-octylphenol 2867 66 97.7
Triclosan 2532 82 96.8
4-n-nonylphenol 1229 90 92.7
(Table 15, continued)
Appendix
161
Day 209 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 2683 14 99.5
Metronidazole 1873 225 88
Fenoprop 2889 575 80.1
Ketoprofen 1995 170 91.5
Acetaminophen 2088 188 91
Naproxen 3708 531 85.7
Primidone 3406 71 97.9
Ibuprofen 2763 21 99.3
Diclofenac 3485 539 84.5
Carbamazepine 3753 149 96
Gemfibrozil 2671 17 99.4
Estriol 1956 35 98.2
Pentachlorophenol 2210 137 93.8
4-tert-butylphenol 2884 98 96.6
Estrone 2030 14 99.3
Bisphenol A 2923 37 98.7
17-α ethinylestradiol 3515 45 98.7
17-β- estradiol 3093 25 99.2
17-β- estradiol-17 acetate 4761 30 99.4
4-tert-octylphenol 3578 32 99.1
Triclosan 3033 30 99
4-n-nonylphenol 2058 41 98
(Table 15, continued)
Appendix
162
Day 216 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 3484 31 99.1
Metronidazole 1644 330 79.9
Fenoprop 3200 1662 48
Ketoprofen 1936 80 95.9
Acetaminophen 1712 133 92.2
Naproxen 3889 1003 74.2
Primidone 2003 6 99.7
Ibuprofen 3489 237 93.2
Diclofenac 3053 1124 63.2
Carbamazepine 2854 404 85.8
Gemfibrozil 3088 15 99.5
Estriol 1602 2 99.9
Pentachlorophenol 2757 275 90
4-tert-butylphenol 2980 50 98.3
Estrone 1722 48 97.2
Bisphenol A 2606 53 98
17-α ethinylestradiol 2608 62 97.6
17-β- estradiol 2394 33 98.6
17-β- estradiol-17 acetate 2778 62 97.8
4-tert-octylphenol 3121 43 98.6
Triclosan 2679 17 99.4
4-n-nonylphenol 1341 29 97.8
(Table 15, continued)
Appendix
163
Day 222 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 2355 52 97.8
Metronidazole 1123 335 70.2
Fenoprop 2485 2381 4.2
Ketoprofen 1940 188 90.3
Acetaminophen 1318 100 92.4
Naproxen 3618 1919 47
Primidone 2460 221 91
Ibuprofen 2564 50 98
Diclofenac 2345 2098 10.5
Carbamazepine 3295 1674 49.2
Gemfibrozil 2418 45 98.1
Estriol 1951 61 96.9
Pentachlorophenol 1912 557 70.9
4-tert-butylphenol 1800 31 98.3
Estrone 1966 27 98.6
Bisphenol A 2713 55 98
17-α ethinylestradiol 3318 117 96.5
17-β- estradiol 2966 3 99.9
17-β- estradiol-17 acetate 3708 40 98.9
4-tert-octylphenol 2044 88 95.7
Triclosan 2481 77 96.9
4-n-nonylphenol 901 88 90.2
(Table 15, continued)
Appendix
164
Day 235 Concentration (ng/L) PAC - MBR
Compound Feed Permeate Removal (%)
Salicylic acid 1881 173 90.8
Metronidazole 1310 534 59.3
Fenoprop 2041 1974 3.3
Ketoprofen 1451 219 84.9
Acetaminophen 1490 130 91.3
Naproxen 2976 1142 61.6
Primidone 1612 62 96.2
Ibuprofen 1979 58 97.1
Diclofenac 2155 1840 14.6
Carbamazepine 2450 453 81.5
Gemfibrozil 2053 3 99.9
Estriol 1564 116 92.6
Pentachlorophenol 1707 267 84.4
4-tert-butylphenol 1849 23 98.8
Estrone 1515 11 99.3
Bisphenol A 2099 38 98.2
17-α ethinylestradiol 2547 104 95.9
17-β- estradiol 2234 4 99.8
17-β- estradiol-17 acetate 3194 65 98
4-tert-octylphenol 2032 64 96.8
Triclosan 2083 100 95.2
4-n-nonylphenol 838 80 90.5
Appendix
165
Table 16: Trace organics concentration and removal efficiency by PAC - MBR treatment
with 0.5 g PAC /L concentration.
Day 247 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 2532 248 90.2
Metronidazole 1997 172 91.4
Fenoprop 2970 216 92.7
Ketoprofen 1774 64 96.4
Acetaminophen 1004 40 96
Naproxen 3692 44 98.8
Primidone 785 5 99.3
Ibuprofen 2638 0 100
Diclofenac 2560 147 94.2
Carbamazepine 3422 80 97.7
Gemfibrozil 2835 32 98.9
Estriol 1436 121 91.6
Pentachlorophenol 2184 64 97
4-tert-butylphenol 2397 17 99.3
Estrone 1694 17 99
Bisphenol A 2512 10 99.6
17-α ethinylestradiol 2413 47 98.1
17-β- estradiol 2160 0 100
17-β- estradiol-17 acetate 3096 0 100
4-tert-octylphenol 2635 16 99.4
Triclosan 2722 18 99.4
4-n-nonylphenol 1431 2 99.9
(Table 16, continued)
Appendix
166
Day 253 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 2497 226 90.9
Metronidazole 2031 259 87.3
Fenoprop 3006 413 86.3
Ketoprofen 1800 143 92
Acetaminophen 1797 143 92
Naproxen 2934 349 88.1
Primidone 795 4 99.5
Ibuprofen 2116 86 96
Diclofenac 2757 286 89.6
Carbamazepine 2690 156 94.2
Gemfibrozil 2031 41 98
Estriol 1707 24 98.6
Pentachlorophenol 2340 179 92.4
4-tert-butylphenol 2283 84 96.3
Estrone 2124 21 99
Bisphenol A 2879 26 99.1
17-α ethinylestradiol 3078 67 97.8
17-β- estradiol 2767 7 99.8
17-β- estradiol-17 acetate 4095 53 98.7
4-tert-octylphenol 3007 27 99.1
Triclosan 2797 71 97.5
4-n-nonylphenol 1664 57 96.6
(Table 16, continued)
Appendix
167
Day 260 Concentration (ng/L) PAC - MBR
Compound Feed Permeate Removal (%)
Salicylic acid 3288 256 92.2
Metronidazole 2729 397 85.4
Fenoprop 3263 750 77
Ketoprofen 1945 158 91.9
Acetaminophen 1031 141 86.3
Naproxen 3742 535 85.7
Primidone 1045 4 99.6
Ibuprofen 3413 32 99.1
Diclofenac 2383 487 79.6
Carbamazepine 3035 169 94.4
Gemfibrozil 2891 33 98.9
Estriol 1420 30 97.9
Pentachlorophenol 2518 158 93.7
4-tert-butylphenol 3003 33 98.9
Estrone 1679 19 98.8
Bisphenol A 2823 177 93.7
17-α ethinylestradiol 2385 99 95.8
17-β- estradiol 2231 2 99.9
17-β- estradiol-17 acetate 3143 59 98.1
4-tert-octylphenol 2929 17 99.4
Triclosan 2920 31 99
4-n-nonylphenol 1455 39 97.3
(Table 16, continued)
Appendix
168
Day 267 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 2302 120 94.8
Metronidazole 2340 416 82.2
Fenoprop 2648 669 74.7
Ketoprofen 1817 50 97.2
Acetaminophen 1728 214 87.6
Naproxen 3426 485 85.8
Primidone 885 0 100
Ibuprofen 2432 86 96.4
Diclofenac 1365 537 60.6
Carbamazepine 2953 168 94.3
Gemfibrozil 2435 40 98.3
Estriol 1495 16 98.9
Pentachlorophenol 2059 150 92.7
4-tert-butylphenol 2203 40 98.2
Estrone 1701 45 97.3
Bisphenol A 2688 199 92.6
17-α ethinylestradiol 2616 40 98.5
17-β- estradiol 2454 3 99.9
17-β- estradiol-17 acetate 3145 38 98.8
4-tert-octylphenol 2314 21 99.1
Triclosan 2526 19 99.3
4-n-nonylphenol 1146 28 97.5
(Table 16, continued)
Appendix
169
Day 275 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 3098 266 91.4
Metronidazole 2503 658 73.7
Fenoprop 3687 1500 59.3
Ketoprofen 2656 230 91.3
Acetaminophen 1161 216 81.4
Naproxen 4573 280 93.9
Primidone 1364 25 98.2
Ibuprofen 3649 157 95.7
Diclofenac 2807 825 70.6
Carbamazepine 3589 458 87.2
Gemfibrozil 3380 53 98.4
Estriol 2196 315 85.6
Pentachlorophenol 2878 279 90.3
4-tert-butylphenol 2689 60 97.8
Estrone 2393 41 98.3
Bisphenol A 3572 71 98
17-α ethinylestradiol 3798 75 98
17-β- estradiol 3632 13 99.6
17-β- estradiol-17 acetate 4731 73 98.5
4-tert-octylphenol 3026 60 98
Triclosan 3574 53 98.5
4-n-nonylphenol 1476 73 95
(Table 16, continued)
Appendix
170
Day 285 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 3037 280 90.8
Metronidazole 1769 560 68.3
Fenoprop 3668 2484 32.3
Ketoprofen 2642 267 89.9
Acetaminophen 845 208 75.4
Naproxen 4787 98 97.9
Primidone 1570 0 100
Ibuprofen 4130 150 96.4
Diclofenac 2479 740 70.1
Carbamazepine 3364 268 92
Gemfibrozil 3519 47 98.7
Estriol 2373 48 98
Pentachlorophenol 2944 409 86.1
4-tert-butylphenol 2606 24 99.1
Estrone 2455 16 99.3
Bisphenol A 3686 84 97.7
17-α ethinylestradiol 3842 108 97.2
17-β- estradiol 3559 35 99
17-β- estradiol-17 acetate 4934 22 99.6
4-tert-octylphenol 3364 44 98.7
Triclosan 3651 98 97.3
4-n-nonylphenol 1625 20 98.8
(Table 16, continued)
Appendix
171
Day 292 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 2468 163 93.4
Metronidazole 2307 743 67.8
Fenoprop 2645 1420 46.3
Ketoprofen 1834 135 92.6
Acetaminophen 942 108 88.5
Naproxen 3412 46 98.7
Primidone 1003 0 100
Ibuprofen 2821 46 98.4
Diclofenac 1131 393 65.2
Carbamazepine 2266 193 91.5
Gemfibrozil 2578 27 98.9
Estriol 1368 28 97.9
Pentachlorophenol 2189 230 89.5
4-tert-butylphenol 1815 25 98.6
Estrone 1740 221 87.3
Bisphenol A 2418 33 98.6
17-α ethinylestradiol 2227 48 97.9
17-β- estradiol 2213 88 96
17-β- estradiol-17 acetate 3207 37 98.8
4-tert-octylphenol 2124 26 98.8
Triclosan 2551 32 98.8
4-n-nonylphenol 1094 7 99.3
(Table 16, continued)
Appendix
172
Day 299 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 2374 179 92.4
Metronidazole 1791 1185 33.8
Fenoprop 2635 1866 29.2
Ketoprofen 1884 234 87.6
Acetaminophen 2085 123 94.1
Naproxen 3529 56 98.4
Primidone 1204 0 100
Ibuprofen 2684 0 100
Diclofenac 1326 528 60.2
Carbamazepine 2319 638 72.5
Gemfibrozil 2512 53 97.9
Estriol 1594 31 98
Pentachlorophenol 2217 354 84
4-tert-butylphenol 1848 45 97.6
Estrone 1995 3 99.9
Bisphenol A 2709 113 95.8
17-α ethinylestradiol 2697 66 97.5
17-β- estradiol 2640 7 99.7
17-β- estradiol-17 acetate 3488 42 98.8
4-tert-octylphenol 2323 26 98.9
Triclosan 2746 44 98.4
4-n-nonylphenol 1115 7 99.4
(Table 16, continued)
Appendix
173
Day 306 Concentration (ng/L) PAC - MBR
Compounds Feed Permeate Removal (%)
Salicylic acid 2548 99 96.1
Metronidazole 1942 884 54.5
Fenoprop 2723 1930 29.1
Ketoprofen 2103 291 86.2
Acetaminophen 2202 248 88.7
Naproxen 3549 80 97.8
Primidone 1074 0 100
Ibuprofen 2899 0 100
Diclofenac 1473 664 54.9
Carbamazepine 2349 577 75.5
Gemfibrozil 2756 26 99.1
Estriol 1693 52 96.9
Pentachlorophenol 2315 488 78.9
4-tert-butylphenol 1899 51 97.3
Estrone 2327 56 97.6
Bisphenol A 2928 109 96.3
17-α ethinylestradiol 2962 101 96.6
17-β- estradiol 2799 7 99.7
17-β- estradiol-17 acetate 3433 63 98.2
4-tert-octylphenol 2165 53 97.6
Triclosan 2758 133 95.2
4-n-nonylphenol 1055 20 98.1
(Table 16, continued)
Appendix
174
APPENDIX B
PUBLICATION RESULTED FROM THIS RESEARCH
Accepted
1. NGUYEN, L. N., HAI, F. I., KANG, J., PRICE, W. E. & NGHIEM, L. D.
Removal of trace organic contaminants by a membrane bioreactor – granular
activated carbon (MBR-GAC) system, Bioresource Technology, 2012. 113: p.
169-173.
In preparation
1. NGUYEN, L. N., HAI, F. I., KANG, J., PRICE, W. E. & NGHIEM, L. D.
Coupling granular activated carbon adsorption with membrane bioreactor
treatment for the removal of trace organic contaminants: breakthrough behavior
of persistent and hydrophilic compounds, CHEMOSPHERE.
2. NGUYEN, L. N., HAI, F. I., KANG, J., PRICE, W. E. & NGHIEM, L. D.
Removal of emerging trace organic contaminants by MBR-based hybrid
treatment processes, Bioresource Technology.
3. NGUYEN, L. N., HAI, F. I., NGHIEM, L. D., KANG, J., PRICE, W. E., &
Yamamoto, K. Enhancing removal of trace organic contaminants by powdered
activated carbon dosing into membrane bioreactors— can long term stable
performance be achieved?, Journal of Membrane Science.
4. NGUYEN, L. N., HAI, F. I., NGHIEM, L. D., KANG, J., PRICE, W. E., NGO,
H. H., & Guo, W. Comparison between sequential and simultaneous
applications of activated carbon with membrane bioreactor for micropollutant
removal, Desalination.
Conference presentation
1. NGUYEN, L. N., HAI, F. I., KANG, J., PRICE, W. E. & NGHIEM, L. D. (oral
presentation) Removal of trace organic contaminants by a membrane bioreactor
– granular activated carbon (MBR-GAC) hybrid system. The 4th
Challenges in
Environmental Sciences and Engineering conference in Tainan City, Taiwan
(25 - 30 September 2011).
2. NGUYEN, L. N., HAI, F. I., KANG, J., PRICE, W. E. & NGHIEM, L. D. (oral
presentation) Removal of trace organic contaminants by membrane filtration
Appendix
175
technology. Micropol & Ecohazard conference, Sydney, Australia (11 - 13 July
2011).
3. NGUYEN, L. N., HAI, F. I., KANG, J., PRICE, W. E. & NGHIEM, L. D.
Removal of emerging trace organic contaminants by MBR-based hybrid
treatment processes. The 5th
Challenges in Environmental Sciences and
Engineering conference in Melbourne, Australia (9 - 13 September 2012)
(accepted).
4. NGUYEN, L. N., HAI, F. I., KANG, J., PRICE, W. E. & NGHIEM, L. D.
Coupling powdered activated carbon (PAC) adsorption with membrane
bioreactor (MBR) treatment for enhanced removal of trace organics.
Euromembrane 2012, London, UK, (23 - 27 September 2012) (accepted).