Adsorptive fouling of extracellular polymeric substances with polymeric ultrafiltration membranes

Extracellular polymeric substances (EPS) are currently considered as the major cause of membrane fouling in membrane bioreactors (MBR). Few works have dealt with the adsorptive interaction between EPS and different membrane types. The purpose of this study was to investigate the adsorptive fouling potential of the EPS extracted from an aerobic bioreactor. Three types of ultrafiltration membranes including polyethersulfone (PES), polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) were evaluated by directly interacting with six sludge samples. It is found that the adsorption capacities were almost saturated after 4 h interaction with EPS in each case. The adsorptive fouling degrees of the three membranes were orderly PAN < PVDF < PES by calculating FRPWF values from the pure water flux before and after adsorption. The microtopographical changes on membrane surfaces were observed by SEM and AFM images. In the case of fouled PAN membranes, most of the membrane surface pore could still be clearly observed in SEM images. This also suggested that the adsorptive fouling of PAN membranes was relatively lower. Synthetically, PES UF membranes were much more severely fouled due to its relatively high roughness and hydrophobicity.