Influence of bacterial extracellular polymers on the membrane separation activated sludge process

The objective of this study is to elucidate influence of bacterial extracellular polymers (EPS) on the performance of the submerged membrane separation activated sludge process (SMAS). Hollow fiber membrane modules were submerged in laboratory-scale reactors and the permeate was pulled out from the modules by suction pumps. Acetic acid was used as a carbon source and peptone or ammonium nitrogen was used as a nitrogen source in the substrate. The change of EPS amount both in the mixed liquor and on the membrane was measured and its influence on the permeability of the membrane was studied. EPS was accumulated in the aeration tanks and also on the membrane, which caused an increase of viscosity of the mixed liquor and an increase in the filtration resistance. Specific resistance of EPS was calculated to be of the order of 10¹⁶ to 10¹⁷ m kg⁻¹. Change of the filtration resistance was explained as a function of viscosity of the mixed liquor, which is caused by rapid attachment of the suspended EPS and rapid detachment of the attached EPS. Detachment rate of the attached EPS was calculated to be nearly constant during the operation.