Heterogeneous biofilms can help to stabilize long-term ... · protozoa Stable flux without grazing 71421 2835 42 Days of operation. 71421 2835 42 Days of operation No membrane biofouling

Heterogeneous biofilms can help to stabilize long-term flux in gravity-driven ultra-low

pressure ultrafiltration systems

N.Derlon, M. Peter-Varbanets, W.Pronk and E.Morgenroth

Nicolas.derlon@eawag.ch

Eawag: Das Wasserforschungs-Institut des ETH-Bereichs

Context

900 M people using unprotected water sources (Data: MDG 2008)

500 million people: health problems due to the lack of safe drinking water

5.3 billion people (83%) recontamination of water(Data: WHO, HWTS Network, 2006)

Solution Decentralized membrane systems reduced risk of water related diseases (Montgomery, M.A., Elimelech, M Environ. Sci. Technol. 41, 17-24 (2007).

Effective, low-cost, robust and less chemical- and energy- intensivethan other technologiesShannon M.A. et al. Nature 452, 301-310 (2008).

Gravity-driven ultra-low pressure ultrafiltration system

No energy requirement

No backwashing

No cleaning

No cross-flow

No energy requirement

No backwashing

No cleaning

No cross-flow

Storage tanks

Filtration modules

Hyd

rost

atic

pre

ssur

e65

mB

ar

Picture from Butler R., 2009

Gravity-driven ultra-low pressure ultrafiltration

Flux stabilization due to the bacterial activity in the BFL

What is the process governing the

development of different BFL

structure?Filtration time (days)

0 5 10 15 20 25 30

Flux

(L h

m )

0

10

20

30

40River water, TOC 2.5 mg L-1

Lake water, TOC 3.7 mg L-1

Diluted wastewater, TOC 12.5 mg L-1

Diluted wastewater, TOC 4.8 mg L-1

Flux

(L m

-2 h

-1)

Peter-Varbanet et al. (2010). Water Research 43 (2).

SHEAR STRESSSHEAR STRESS

CONCENTRATION GRADIENTSCONCENTRATION GRADIENTS

Objectives of this study

#1: How does protozoan grazing influence the biofouling layer structure?

#2: How does the development of an open structure help to maintain high flux?

PROTOZOAN GRAZINGPROTOZOAN GRAZING

Experimental Approach

Surface water…

Storage tank

Membrane Module(Ultrafiltration)

permeateClean water storage tank

No cleaning

0.5 m hydrostatic pressure 65 mBar

to the tap

Intermittentoperation

Low-PG: inhibition using cycloheximide

Nat.-PG: no control

High-PG: inoculation of the system using Tetrahymena Pyriformis

#1: How does protozoan grazing influence the biofouling layer

structure?

Dynamic structure of the biofouling layer “Nat.-PG”

Homogeneous, flat basal layer open and heterogeneous

#1: How does protozoan grazing influence the biofouling layer structure at the mesoscale?

#1: How does protozoan grazing influence the biofouling layer structure at the mesoscale?

Nat.PG

High-PG

21d 29d 36d 42d

21d 29d 36d 42d

#1: How does protozoan grazing influence the biofouling layer structure at the mesoscale?

Nat.PG

Low-PG

21d 29d 36d 42d

21d 29d 36d 42d

100μm Optical Coherence Tomography

Protozoan grazing favors the growth in z-direction at the meso-scale

OCT images without treatment

low

Nat

High

#2 How does the development of an open structure help to maintain high

flux?

#2: How does the development of an open structure help to maintain high flux?

No membrane biofouling

Dynamic flux evolution with

protozoa

Stable flux without grazing

7 14 21 28 35 42

Days of operation

7 14 21 28 35 42

Days of operation

No membrane biofouling

Dynamic flux evolution with

protozoa

Stable flux without grazing

#2: How does the development of an open structure help to maintain high flux?

7 14 21 28 35 42

Days of operation

No membrane biofouling

Dynamic flux evolution with

protozoa

Stable flux without grazing

#2: How does the development of an open structure help to maintain high flux?

#2: How does the development of an open structure help to maintain high flux?

7 14 21 28 35 42

Days of operation

Prot

ozoa

n G

razi

ng

How are structural heterogeneities and system performances linked?

1 week 2 weeks 4 weeks

Image analysis to measure the “uncovered” membrane fraction (ImageJ : http://rsbweb.nih.gov/ij/)

× with protozoan grazing ☐ without protozoan grazing

How are structural heterogeneities and system performances linked?

1 week 2 weeks 4 weeks

Small variation of coverage induces a significant increase of the flux, why?

× with protozoan grazing ☐ without protozoan grazing

Low

PG

Membrane coverage – after one month

50μm

50μm

Nat

. PG

- All bacterial cells (SYBR® Gold) - Particles and the membrane (Reflection)

Low

PG

Membrane coverage – after one month

50μm

50μm

Nat

. PG

Thinner local thickness induces smaller local hydraulic resistance

Conclusions and perspectives

Protozoan shapes the BFLstructure. The change in the filtration performances is explained by the reduction of the surface coverage associated with a thinner basal layer

System is suitable to provide drinking/cooking water: 60 - 15 people per day with 1 m2 of membrane considering 2-8 L/person/day for drinking/cooking

System is stable: stable flux observed over 1.5 year

Significant impact of protozoan grazing is more and more observed

•Biofilm structure (Böhme et al., 2009; Garny et al., 2009)•Granulation (Weber et al., 2007)•Reactor stability (Aspergen et al., 2010; Duque and Morgenroth, submitted)•Pathogen removal (Bomo et al., 2009)

Thanks for your attention