Anaerobic membrane bioreactors for municipal wastewater treatment

Abstract

Anaerobic treatment has historically been considered unsuitable for the treatment of domestic wastewaters. The work presented in this thesis focuses on the incorporation of membranes into the anaerobic bioreactor to uncouple solid retention time and hydraulic retention time. This in turn prevents biomass washout and allows sufficient acclimatisation periods for anaerobes. However, the exposure of membranes to anaerobic biomass comes with its own inherent problems namely fouling. Fouling was found to take place in two stages; a rapid phase characterised by solid and bacterial cell deposition and a slow phase characterised by the travel of colloidal matter to the membrane surface. Gas sparging was also found to attenuate fouling to a considerable extent despite the fact that biomass characteristics were critical factors in the fouling of the system. In addition, side stream membranes showed differing characteristics to submerged membranes. A comparison of anaerobic membrane bioreactors to conventional anaerobic systems and aerobic membrane bioreactors highlighted the advantage of this system over other comparable technologies. The anaerobic membrane bioreactor is less energy intensive than the aerobic membrane bioreactor, fouls differently to this system and achieves much better performance than would be seen if conventional anaerobic systems were used in the treatment of domestic or municipal wastewaters.