Membrane separation bioreactors for wastewater treatment

With continuing depletion of fresh water resources, focus has shifted more toward water recovery, reuse, and recycling, which require an extension of conventional wastewater treatment technologies. Downstream external factors like stricter compliance requirements for wastewater discharge, rising tre atment costs, and spatial constraints necessitate renewed investigation of alternative technologies. Coupled with biological treatment processes, memb rane technology has gained considerable attention due to its wide range of applicability and the performance characteristics of membrane systems that have been established by various investigations and innovations during the last decade. This article summarizes research efforts and presents a review of the how and why of their development and applications. The focus is on appraising and comparing technologies on the basis of their relative merits and demerits. Additional facts and figures, especially regarding process p arameters and effluent quality, an used to evaluate primary findings on the se technologies. Key factors such as loadings rates, retention time, cross- flow velocities, membrane types, membrane fouling, and backwashing, etc. ar e some of the aspects covered. Membrane applications in various aerobic and anaerobic schemes are discussed at length. However, the emphasis is on the use of membranes as a solid/liquid separator, a key in achieving desired e ffluent quality. Further, technology development directions and possibiliti es are also explored. The review concludes with an economic assessment of t he technologies because one of the key technology selection criteria is fin ancial viability.