Influence of Loading Patterns on Sludge Properties and Membrane Fouling in Membrane Bioreactors Treating Synthetic Early Planetary Base Wastewater

This research studied the influence of membrane bioreactor (MBR) loading/decanting patterns on sludge properties and membrane fouling. Two MBRs, one with continuous loading/decanting (cMBR) and the other with batch loading/decanting (bMBR), were setup and operated in parallel treating synthetic Early Planetary Base Wastewater (EPBW) and generate sludge mixed liquor that was used in batch filtration tests to characterize membrane fouling. During the MBR operation, the concentration of extracellular polymeric substances (EPS), floc size distribution, viscosity, and zeta potential of the sludge mixed liquor in the two MBRs were compared. The results showed that the bMBR generated sludge with lower EPS concentrations, larger flocs, lower viscosity, and lower zeta potential as compared to the cMBR, suggesting bMBR sludge could result in reduced membrane fouling. The sludge mixed liquor in the two MBRs were used for both cross flow filtration with constant transmembrane pressure and submerged filtration with constant transmembrane flux. Microfiltration (MF) membranes and ultrafiltration (UF) membranes were used in all the filtration tests. Consistent with the sludge property results, both cross flow and submerged filtrations suggested that sludge mixed liquor in the bMBR resulted in lesser membrane fouling. Analysis of the microbial communities in the planktonic and the corresponding sessile biomass on the MF membranes after cross flow filtrations suggested that the microbial community of the planktonic biomass was significantly different from that of the sessile biomass. This study showed that membrane fouling could be reduced by designing MBRs with more appropriate loading/decanting patterns. Future research on biofouling mechanisms should include the function of particular bacterial population in biofilm initiation.