Anaerobic membrane bioreactors for wastewater treatment: A review

This review provides an overview of the present situation, from 2006 to date, of the anaerobic membrane bioreactor technology with special emphasis on performance and bottlenecks in terms of its application at industrial scale. Most of the studies considered in this review were performed at bench scale: there is no description of real industrial applications in the literature and almost no pilot cases have been described. Anaerobic membrane bioreactors were fitted with flat sheet, hollow fibre or tubular membranes operating either in the microfiltration or in the ultrafiltration region, but the use of ceramic membranes has not been widely reported. Even though, under normal conditions, there should not be any difference in transmembrane pressure between hollow fibre and flat sheet membranes, hollow fibre membranes may lead to higher transmembrane pressures due to insufficient hydraulic shear on each of their fibres. Bioreactors were mainly tested under mesophilic or thermophilic conditions. The application of thermophilic conditions allowed treating higher organic loading rates. Chemical oxygen demand removal efficiencies up to 99%, total suspended solids removal efficiencies up to 100%, and complete removal of pathogens were reported. Therefore, treated waters may be directly discharged into water bodies or re-used for unrestricted crop irrigation if they meet the effluent discharge or irrigation standard of the area. The renewable energy produced within the plants (i.e. from methane production) was reported to cover the energy required for membrane filtration and the excess energy could be further used. Anaerobic membrane bioreactors are an attractive technology that needs further research efforts and industrialisation. However, membrane fouling, which still remains a major problem for all membrane bioreactors, seems much more severe under anaerobic conditions than aerobic ones. (C) 2012 Elsevier B.V. All rights reserved.