Wang YingDepartment of Environmental Hydrology and Microbiology
Dr. Meyer L. Rosoff and Rev. Benzion Bauer Prize for Excellence in Water Research, 2007
Description of research:
Extracellular Polymeric Substances (EPS) Characteristics and their Relation to Membrane Fouling in a Hybrid Growth Membrane Bioreactor (HG-MBR)
Supervisors: Prof. Gideon Oron, Dr. Moshe Herzberg
Membrane fouling is the most restricted and challenging factor for the widespread applications of membrane technology, including membrane bioreactor (MBR) systems. EPS, which are metabolic products accumulating on bacterial cell surface, are recognized as the most significant factor affecting biofouling in membrane bioreactors (MBRs). In this research study, quantitative, qualitative and spatial distribution analyses of EPS, which were obtained from an HG-MBR, were investigated under different operating conditions, in order to get a better insight and offer a possible approach of controlling biofouling process.
Membrane fouling in a hybrid-growth membrane bioreactor (HG-MBR) is a complex process affected by many factors. EPS, the metabolic products accumulating on bacterial cell’s surface, are recognized as the most significant factor regarding membrane biofouling. In this research study, we elucidated the role of sludge retention time (SRT) in fouling of ultrafiltration (UF) membrane in a HG-MBR system. Under constant organic loading rate, decrease in SRT caused a reduction in both mixed liquor suspended solids and sessile biomass. Even though biomass concentration in the reactor was lower, fouling rate was accelerated.
A highest EPS concentration adsorbed to the membrane was analyzed with significantly higher fraction of polysaccharides than proteins at the lowest SRT of 2.2 days, suggesting the direct inducement of fouling is due to the increase of production of either EPS or soluble microbial products (SMP) at higher organic loading rate per biomass unit.
To study the effect of water chemistry on EPS fouling potential, EPS adherence kinetics and viscoelastic properties were analyzed during adsorption to silica coated crystals in a quartz crystal microbalance with dissipation (QCM-D). Higher rate of EPS deposition was observed under higher ionic strength due to charge shielding of both negatively charged substances and the substratum suggesting that electrostatic interactions control EPS adsorption. Further study on the adsorption and structural changes of a relatively uncharacterized EPS layers is undertaken at various solution chemistries (pH and concentration of divalent cations).