effect of hydraulic retention time on the extracellular polymeric substances and membrane fouling in a high loaded membrane bioreactor

In the present study, the effect of hydraulic retention time (hrt) at two levels (namely 6 and 2.5 h) on the performance of a high loaded membrane bioreactor (hl-mbr) operated at an srt of 1 day for the treatment of synthetic municipal wastewater was studied. the hrt variation did not have any effect on cod removal, as the system's cod removal efficiency was 92% and 94% at hrt of 6 h and 2.5 h, respectively. the trans-membrane pressure variation indicated that the membrane fouling was more severe at a hrt of 2.5 h compared to that of 6 h. the overall filtration resistance analysis showed that cake layer formation was the dominant fouling mechanism during both operating conditions, contributing to 63.47% and 79.46% of the total resistance for hrts of 6 h and 2.5 h, respectively. the concentrations of total extracellular polymeric substances (eps), the protein content of eps (epsp), and extracellular polymers (ecp) increased with decreasing hrt. in contrast, loosely bound extra-microcolony polymers content (lb-emp) and lb to tightly bound emp content (tb-emp) (lb/tb) decreased. furthermore, the main composition of the eps shifted from protein toward polysaccharide dominance in the cake layer.