Recalcitrant industrial wastewater treatment by membrane bioreactor (MBR)

Membrane Bioreactor (MBR) process consists of a biological reactor integrated with membranes that combine clarification and filtration of an activated sludge process into a simplified, single step process. The membrane is an absolute barrier to suspended matter and microorganisms and it offers the possibility of operating the system at high mixed liquor suspended solids (MLSS) concentration. The implication of maintenance of high MLSS are— requirement of a smaller footprint and operation at high solids retention time (SRT) under low F/M ratio, hence, yielding reduced excess sludge. Operating as an MBR allows conventional activated sludge plants to become single step processes, which produce high quality effluent potentially suitable for reuse. Accordingly, over the past decade, submerged MBR processes have experienced unprecedented growth in domestic and municipal wastewater treatment/reuse. Application of MBR technology for industrial wastewater treatment has also gained attention because of the robustness of the process. Theoretically, maintenance of long SRT in MBR is in favor of the retention and development of special microorganisms, which may lead to better removal of refractory organic matter and make the system more robust to load variations and toxic shocks. Although in general MBR exhibits much improved overall treatment of concentrated industrial wastewater as compared to conventional activated sludge process, literature suggests that the conceptual expectation of enhanced biodegradation of hardly biodegradable compounds in MBR does not often come true. Very often the improved removal has been attributed to the adsorption of target compounds on sludge, which implies that further treatment of the periodically withdrawn, toxic compound-laden sludge would be required. Improved biodegradation to certain extent has been reported in a few studies; however the underlying factors leading to such improvement still remains to be elucidated. This chapter provides a comprehensive review of the studies dealing with recalcitrant industrial wastewater treatment by MBR, and casts light on the strategies to achieve enhanced biodegradation of hardly biodegradable industrial pollutants in MBR.