Long term effects of Pb2+ on the membrane fouling in a hydrolytic-anoxic-oxic-membrane bioreactor treating synthetic electroplating wastewater.

Long-term effects of Pb2+ on the operating performance and membrane fouling of two hydrolytic-anoxic-oxic-membrane bioreactors treating synthetic electroplating wastewater were investigated. The COD, NH4+-N and TN removal efficiencies decreased by 5.5%, 10.4% and 7.9% with long-term exposure of 2 mg L-1 Pb2+, while serious decreases achieved 25.4%, 35.0% and 26.2% with 6 mg L-1 Pb2+ exposure, respectively. 2 mg L-1 Pb2+ mitigated the cake layer fouling rate by 25.4% but increased the pore blocking rate by 69.1%, which was contributed by the increase of low and moderate molecular weight (MW) components in the soluble and colloidal foulants (SCFs). 6 mg L-1 Pb2+ accelerated the cake layer fouling rate by 101.1%, but mitigated the pore blocking rate by 6.4% due to the increase of high MW SCFs (especially polysaccharides). Thermodynamic analyses showed that Pb2+ regulated the concentration and protein/polysaccharide ratio of loosely bound extracellular polymeric substances, thus changing the flocs hydrophobicity and aggregation capacity, leading the cake layer fouling rate variation.