Evaluation of Membrane Bioreactors with Short Sludge Retention Times on Performance, Biomass Characteristics and Membrane Fouling

A recent paradigm shift is to view wastewater as a resource. Municipal wastewater contains more energy than what is required to treat it. Recovery of energy through anaerobic digestion of activated sludge can be enhanced through operation of activated sludge processes at short sludge retention times (SRT), thus reducing endogenous decay, increasing sludge production rates, and enhancing the diversion of energy to the sludge stream. There is currently little research on operation of short SRT systems. The objective of this paper was to investigate the treatment performance, sludge production, sludge settleability and membrane fouling of membrane bioreactors operated in parallel at SRTs of 2, 4, and 8 days, and HRTs of 3.4, 2.6 and 1.1 hours. Operation at 2 days SRT resulted in 59% higher diversion of energy to the sludge stream and 49% reduced oxygen utilization without significant detriment to treatment performance. However, higher membrane fouling was observed.