Ultrafiltration of activated sludge with ceramic membranes in a cross-flow membrane bioreactor process

A cross-flow membrane bioreactor (MBR) for raw municipal wastewater treatment, consisting of a suspended growth bioreactor and a ceramic membrane ultrafiltration unit, was run over a period of more than 300 days in a wastewater treatment plant (WWTP). Sludge Retention Times (SRT) of 20, 10 and 5 days, respectively, and Hydraulic Retention Times (HRT) of 15 and 7.5 hours were tested. Membrane fouling was found to be a function of SRT and permeate flux. Under an SRT of 20 days and flux of 71 l/m(2.)h at 30 degrees C, the MBR was successfully run over 70 days without the need for chemical cleaning. However chemical cleaning had to be undertaken every 3-5 days at shorter sludge retention times (typically an SRT of five days and a flux of 143 l/m(2)/h at 30 degrees C). In this study, fouling materials were removed efficiently through chemical cleaning, with an average permeablity recovery of 87 +/- 11 %.