BACKGROUNDIn this study the performance of a membrane bioreactor (MBR) pilot plant treating industrial wastewater at the Heraklion Industrial Park, at three different sludge retention times (SRTs), was investigated. Membrane fouling in the MBR was monitored through the transmembrane pressure build up and by measuring accumulation of extracellular polymeric substances (EPS) and soluble microbial products (SMP). The effect of hydraulic residence time (HRT) on effluent quality and membrane fouling was examined as well. RESULTSThe highest removal efficiencies (COD, TN, P) of the order of 99.2%, 94.3% and 89.3%, respectively, as well as moderate formation of EPS and SMPs were observed at a SRT of 20 days. Changes in HRT had a small effect on carbon and ammonium removal, but a strong impact on denitrification and phosphate removal. Total EPS and SMP were higher at higher SRTs in contrast to reported common observations. However, the shorter SRT of 15 days led to a more rapid increase of TMP. CONCLUSIONThe system's performance regarding COD, TN and P removal was very good despite the high COD/N input ratio and the huge variations in influent quality. The observed membrane fouling behavior reflects the complexity of the biological process. (c) 2014 Society of Chemical Industry