This work investigates operation of a laboratory scale membrane bioreactor (MBR) in the continuous mode for distillery wastewater (spentwash) treatment using submerged 30 mu m nylon mesh filters. The inoculum was municipal activated sludge,which was first acclimatized in a fed-batch reactor over a period of 102 days, before initiating continuous operation. Critical flux for this wastewater-filter combination was measured by flux stepping method, and the MBR was operated under subcritical flux conditions. Organic loading rates ranging from 3 to 5.71 kg m(-3) day(-1) were investigated and the performance was analyzed in terms of COD removal and biomass growth in the reactor. Up to 41% COD removal was obtained over 245 days of reactor operation. The molecular weight profiles of the untreated and treated effluent suggested that the degradation of low molecular weight compounds occurred in the reactor while the high molecular weight compounds comprising the colour imparting melanoidins remained unaffected. Up to 100% suspended solid retention (average 87%) was obtained and the system could be operated up to 2 weeks without significant flux drop. (C) 2008 Elsevier B.V. All rights reserved.