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 [email protected] Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
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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
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
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