Anaerobic membrane bioreactors: Applications and research directions

Membranes provide exceptional suspended solids removal and complete biomass retention that can improve the biological treatment process, but their commercial application to anaerobic treatment has been limited. This review summarizes the state of the art with respect to anaerobic membrane bioreactors (AnMBRs), determines the types of wastewaters for which AnMBRs would be best suited, and identifies the research required to increase implementation. AnMBRs have been tested with synthetic, food processing, industrial, high solids content, and municipal wastewaters at laboratory, pilot, and full scale. Chemical oxygen demand removal ranges from 56% to 99%, while the reported design membrane fluxes range from 10 to 40 L/m(2)/h. AnMBRs should be immediately applicable to highly concentrated, particulate waste streams like municipal sludges where the membrane can decouple the solids and hydraulic retention times. Opportunity for application to dilute wastewaters also appears strong, while application to highly concentrated soluble wastewaters is likely limited. Greater assessment of vacuum-driven immersed membranes, combining external or immersed membranes with retained biomass reactor designs, control of membrane fouling, and economic feasibility are the key research areas to be addressed.