Biofouling of an Aerated Membrane Reactor: Four Distinct Microbial Communities

Abstract

Membrane fouling is a significant operational challenge in the application of membranes in drinking and wastewater treatment. Microbial association with the surfaces of membranes and the extracellular polymeric substances (EPS) associated with biofilms contribute to fouling. Within the microbial community, there are polysaccharide producers and consumers. A better understanding of the microbial community at the interfaces of the membrane material will be important in supporting next-generation cleaning strategies. A laboratory-scale mesophilic-aerated membrane bioreactor using sheet polyvinylidene fluoride microfiltration membrane was used as a model system. The microbial community was characterized from four distinct compartments: mixed liquor suspended biomass (MLSB); the membrane cake (i.e., extramembrane loosely bound [EMLB]); the foulant layer (i.e., extramembrane tightly bound [EMTB]), and the intracore membrane biofilm (ICMB). Electron microscope images revealed an established biofilm in the ICMB. Microbial structures were observed in the macrovoids of the asymmetric membrane and the open architecture of the support web. This is the first study to acknowledge the presence of ICMB. The community structure of all four compartments (i.e., MLSB, EMLB, EMTB, and ICMB) was characterized at the genus level and results indicate four distinct microbial communities exist. Composition of the ICMB compartment most closely aligns with MLSB and is distinct from the community found in the contiguous EMTB compartment. Results identify the need to characterize the microbial community, and conditions for growth and EPS production, in both the EMTB and ICMB compartments to understand irreversible fouling. Biofilm characterization in the EMLB compartment is insufficient.