Sludge characteristics and their contribution to microfiltration in submerged membrane bioreactors

Abstract

This study focused on the physicochemical and biological characteristics of sludge in submerge membrane bioreactors (MBRs), and their roles in microfiltration behavior: cake formation and membrane fouling. Since membrane filtration has a complete separation of microorganism, a long sludge retention time (SRT) can be maintained in MBR. In this work, hence, three lab-scale submerge MBRs with SRTs of 20, 40 and 60 days were performed at a constant permeate flux of 9L/㎡/h to accomplish objectives of this study. Better permeability was achieved at longer SRTs (40 and 60 days) having higher sludge concentrations because of the formation of more dynamic cake layer. There was a larger tendency for the pore blocking and pore narrowing at SRT 20 days having lower sludge concentration. The size of particulates and colloids appeared key parameters to estimate the formation of dynamic membrane and fouling resistance in microfiltration of sludge. Membrane fouling was categorized into microbial-floc-cause and supernatant-cause fouling, which were performed with a batch set with the same membrane used in the lab-scale MBRs. Hydrophobicity, surface charge and microbial activity, which were related to composition and properties of extracellular polymeric substances (EPS), appeared key factors to evaluate microbial-floc-cause fouling, while no remarkable factor appeared for supernatant-cause fouling.