Temporal Changes in Extracellular Polymeric Substances on Hydrophobic and Hydrophilic Membrane Surfaces in a Submerged Membrane Bioreactor (original) (raw)
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Biofouling, 2017
Laboratory-scale reverse osmosis (RO) flat-sheet systems were used with two parallel flow cells, one treated with cleaning agents and a control (ie undisturbed). The cleaning efforts increased the affinity of extracellular polymeric substances (EPS) to the RO membrane and altered the biofilm surface structure. Analysis of the membrane biofilm community composition revealed the dominance of Proteobacteria. However, within the phylum Proteobacteria, γ-Proteobacteria dominated the cleaned membrane biofilm, while β-Proteobacteria dominated the control biofilm. The composition of the fungal phyla was also altered by cleaning, with enhancement of Ascomycota and suppression of Basidiomycota. The results suggest that repeated cleaning cycles select for microbial groups that strongly attach to the RO membrane surface by producing rigid and adhesive EPS that hampers membrane performance.
Mini-review: novel non-destructive in situ biofilm characterization techniques in membrane systems
Membrane systems are commonly used in the water industry to produce potable water and for advanced wastewater treatment. One of the major drawbacks of membrane systems is biofilm formation (biofouling), which results in an unacceptable decline in membrane performance. Three novel in situ biofouling characterization techniques were assessed: (i) optical coherence tomography (OCT), (ii) planar optodes, and (iii) nuclear magnetic resonance (NMR). The first two techniques were assessed using a biofilm grown on the surface of nanofiltration (NF) membranes using a transparent membrane fouling simulator that accurately simulates spiral wound modules, modified for in situ biofilm imaging. For the NMR study, a spiral wound reverse osmosis membrane module was used. Results show that these techniques can provide information to reconstruct the biofilm accurately, either with 2-D (OCT, planar optodes and NMR), or 3-D (OCT and NMR) scans. These non-destructive tools can elucidate the interaction of hydrodynamics and mass transport on biofilm accumulation in membrane systems. Oxygen distribution in the biofilm can be mapped and linked to water flow and substrate characteristics; insights on the effect of crossflow velocity, flow stagnation, and feed spacer presence can be obtained, and in situ information on biofilm structure, thickness, and spatial distribution can be quantitatively assessed. The combination of these novel non-destructive in situ biofilm characterization techniques can provide realtime observation of biofilm formation at the mesoscale. The information obtained with these tools could potentially be used for further improvement in the design of membrane systems and operational parameters to reduce impact of biofouling on membrane performance.
Kinetic development of biofilm on NF membranes at the Méry-sur-Oise plant, France
Biofouling, 2013
The kinetic formation of biofilms developing on nanofiltration (NF) membranes was studied for 2 years in the water production unit of Méry-sur-Oise, France. New membranes were set up in a pilot train integrated to the plant and autopsied after operation for 7, 80, 475 and 717 days. The biofouling layer was studied by confocal laser scanning microscope after 4′,6-diamidino-2-phenyindole dihydrochloride and lectin staining, and by attenuated total reflectance-Fourier transform infrared spectroscopy and rheology experiments. Three stages of biofilm growth were discriminated: (1) the presence of sessile microcolonies embedded in an exopolymeric matrix (after filtration for seven days); (2) membrane coverage expansion through microcolony development and biofilm growth in three dimensions (up to 80 days filtration); and (3) biofilm maturation by densification (after filtration for 80-717 days). Biofilm maturation resulted in total coverage of the membrane surface and matrix residue diversification, development of the polysaccharide network, and the strengthening of matrix cohesion through viscosity and elasticity increases. The wettability and permeability of the fouled NF membranes decreased quickly and continuously throughout the biofilm development process. The longitudinal pressure drop (LPD) increased only after the biofilm reached a quantitative threshold. The decline in membrane permeability may be the result of contributions from many fouling mechanisms but the LPD was more substantially influenced by biofilm development.
Water Research, 2007
Biofilm DGGE AFM a b s t r a c t The structure and microbial communities of biofilms developing on cross-flow nanofiltration (NF) membranes at different temperatures (20, 25 or 34 1C) and operation lengths (8 h-24 days) were studied. Feedwater comprised tertiary quality wastewater effluent or synthetic media mimicking effluents of intermediate quality. After each run, the membranes were autopsied for bacterial enumeration, bacterial community composition and microscopy visualization (SEM, CLSM and AFM/NSOM). Community composition was analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) coupled with sequence analysis of 16S rRNA gene fragments from dominant bands.
An in-situ technique for the direct structural characterization of biofouling in membrane filtration
Journal of Membrane Science, 2019
In the present work, a convenient and direct technique which enables to characterize the intrinsic structure and the mechanical properties of the biofilm without altering its chemical and physical properties is proposed. By utilizing the Optical Coherence Tomography (OCT) as a structural imaging tool coupled with an advance mathematical framework, thickness, micro-porosity, normal stress-strain curve, bulk modulus and total permeability of the biofilm structures are determined. The accuracy of this mathematical technique for the in situ characterization is validated by analyzing two different membrane structures for porosity and permeability values against the mercury intrusion porosimetry method. Three-dimensional images of biofouling were obtained with high resolution aided to numerically analyze the intrinsic biofilm structure at microscale. Growth of biofilm in a dead-end filtration experimental setup was investigated by varying the feed flow rate which allowed uniform compression and decompression to compute normal stress-strain relation of the evolving biofilm structure. At early development of biofilm (day 3), the thickness and normal stress/strain curve showed that the biofilm structure behave similar to elastic material. However, hysteresis-like trend starts to appear with the growth of biofilm suggesting the deviation of biofilm properties to viscoelastic nature at day 8. The microstructure porosity increased from 0.214 (day 3) to 0.482 (day 8) at a feed flow rate of 15 mL/min. The total membrane/biofilm permeability decreased with biofilm age to reach 5.19x10-15 m 2 at day 8 at the same flow rate, leading to a reduction of permeate flux over time. All the structural properties were found to be time dependent as the biofilm continuously evolved.
2011
Membrane biofouling is a complicated process and can include both abiotic and biotic fouling. The objective of this research was to determine the contribution of conditioning layer in the presence of active cells to early stage membrane biofouling. Membranes were operated for 4, 11, and 24 h using buffered synthetic water composed of a conditioning layer (130.14 ppm sodium acetate trihydrate) and either inactive (fixed) or active cells (10 3 cells/mL). This study was performed using cross flow filtration through cellulose acetate (CA) ultrafiltration (UF) membranes. Flux decline, biofilm activity, biofilm surface area coverage, and biofilm morphology (surface roughness and skewness) were monitored over time. While biofilm surface area coverage could not effectively distinguish membranes being filtered with active and inactive cells, permeate flux data indicated that the presence of active cells resulted in significantly more flux decline. Feature height analyses (TM-AFM) combined with biofilm metabolic activity assessment allowed the consideration of abiotic and biotic fouling. The membrane resistance increased in the presence of active bacterial cells, regardless of the level of abiotic fouling. However, abiotic fouling and bacterial cell activity are not independent since abiotic fouling serves as a food source that helps activate cells. Desalination j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / d e s a l 3.4. Assessment of biofilm development in terms of cell metabolic activity and membrane surface morphology In this section, the cell activity of the biofilm formed on the membrane is also considered. Since active cells and inactive cells were introduced in separate experiments in the presence of a conditioning J f /J o (4 hr) = 0.993 ± 0.004 J f /J o (11 hr) = 0.973 ± 0.003 J f /J o (24 hr) = 0.972 ± 0.005 J f /J o (24 hr) = 0.912 ± 0.010 J f /J o (11 hr) = 0.946 ± 0.005 J f /J o (4 hr) = 0.987 ± 0.005
Desalination, 2013
One significant challenge to membrane filtration technologies is membrane fouling causing pressure drop, flux decline and eventually significant cost of membrane replacement. The objective of this research was to determine the impact of metabolic activity as measured in adenosine triphosphate (ATP) concentration of the pure culture of biofoulants on the membrane biofilm metabolic activity, biofilm formation rate, and operational flux decline. Our results showed that after 10-12 h of filtration, the biofilm ATP levels reach an equilibrium concentration (avg. 8 amol/cell) and do not appear to be related to biofoulant ATP levels from cells harvested in the late exponential growth phase regardless of initial ATP level. However, the bacterial growth phase affected the ATP activity of cells and membrane biofilms formed from biofoulants in the lag and stationary phases of growth contained similar levels of activity, and the exponential phase cells resulted in significant higher activity. Flux decline does not appear to be related to metabolic activity of the biofoulant or biofilm following 24 h of filtration but notably, there was much less flux decline when the biofoulant cells were inactive.
Journal of Membrane Science, 2006
Extracellular polymeric substances (EPS) play a significant role in modifying surface characteristics, eventually creating conditions suitable for bacterial attachment. The purpose of this study was to investigate the fouling potential of the EPS present in the effluent of an aerobic membrane bioreactor during intermittent filtration conditions. The aerobic rotational membrane system (ARMS) is a novel compact reactor which is designed to convert ammonia nitrogen in concentrated wastewater to nitrates with high conversion rates. The effluent from the reactor contains significant amounts of dissolved substrates which include EPS produced by the biofilm and salts. A series of cross-flow filtration tests were conducted with intermittent once a day short filtration periods using SEPA CFII membrane test cell and an RO membrane. The intermittent tests runs were conducted for overall filter use times of 1, 2, 4, and 6 days. Progression of the microtopographical changes, amount of EPS accumulation, and flux characteristics were evaluated. The images taken by atomic force microscopy (AFM) showed a layer of soft deposits forming over a strong sublayer firmly covering the membrane surface within a short time. The sublayer consisted of distinct modular units which were firmly attached to each other and to the membrane surface. The amount of EPS deposited on the membranes increased with use time and the membranes became significantly hydrophilic. The membrane flux declined gradually after each daily intermission until the 5th ± 1 day, then a small increase in flux was observed. The flux increase may be due to dislodging of some of the deposited material from the membrane surface due to shearing during cross-flow filtration conditions.
Characterization of biofouling in a lab-scale forward osmosis membrane bioreactor (FOMBR)
Water Research, 2014
Forward osmosis membrane bioreactor Biofouling Biofilm Community analysis Wastewater treatment Membrane fouling a b s t r a c t Forward osmosis membrane bioreactors (FOMBR) provide high quality permeate, however the propensity for membrane biofouling in FOMBRs is unknown. Here, FOMBRs were operated under high and low aeration and the membrane-associated biofilms were characterized by confocal laser scanning microscopy (CLSM) and rRNA gene-tagged pyrosequencing. CLSM images revealed that there was little biofilm formed under high aeration, while thick biofilms were observed on the membranes operated under low aeration. The diversity and richness of bacterial and archaeal communities as assessed by pyrosequencing varied under high and low aeration. The composition of the bacterial suspended sludge communities and the sessile biomass on the membrane surface, as assessed by non-metric multidimensional scaling, was significantly different under high aeration, but was more similar under low aeration. SIMPER analysis indicated that Pseudomonas, Aeromonas and Fluviicola preferentially attached to the membrane. The results presented here provide a comprehensive understanding of membrane biofouling in FOMBRs, which is essential for the development of effective control strategies. ª w a t e r r e s e a r c h 5 8 ( 2 0 1 4 ) 1 4 1 e1 5 1 http://dx.