Aerobic MBRs for domestic wastewater treatment: a review with cost considerations

Membrane bioreactors (MBRs) present a means of intensively biologically tre ating high COD or BOD wastewaters but, like other membrane processes, are c onstrained by their tendency to foul. Fouling is the general term given to those phenomena responsible for increasing membrane hydraulic resistance. I t can be reduced by maintaining turbulent conditions, operating at sub-crit ical flux and/or by the selection of a suitable fouling-resistant membrane material. The performance of various MBRs is appraised with reference to (i) fouling propensity, and (ii) removal of organics and microorganisms. Energy costs f or the two process configurations for MBRs, submerged and side-stream, are reported with particular attention paid to aeration and recycle pumping cos ts. A number of commercial plants treating domestic wastewater are describe d, with further details of the most recent full-scale MBR for sewage treatm ent tabulated. It is shown that the side-stream configuration has a higher total energy co st, by up to two orders of magnitude, compared with the submerged system du e to the recycle component. The submerged configuration operates more cost effectively than the side-stream configuration with respect to both energy consumption and cleaning requirements, with aeration providing the main ope rating cost component as it is required for both mixing and oxygen transfer . On the other hand, the lower flux under which the submerged system operat es implies a higher membrane area and thus a higher associated capital cost . It is concluded that the MBR is a highly effective treatment process for wastewater treatment in areas requiring a high quality effluent (such as di scharge to bathing waters or water reuse) or specialisation in the microbia l community (e.g, high strength liquors, effective nitrification). (C) 2000 Elsevier Science B.V. All rights reserved.