This study compares membrane fouling and removal efficiencies of organic and nitrogen in thermophilic (47 and 60 degrees C) and mesophilic (30 degrees C) aerobic sidestream airlift membrane bioreactors (SA-MBRs). These reactors were fed with high strength molasses-based synthetic wastewater at an organic loading rate (OLR) of 24.75 kg COD/m(3) d. Removal efficiencies of COD, NH(4)(+) and TKN were compared. The sidestream filtration was conducted with microfilter and ultrafilter. SA-MBRs with microfilter were operated in continuous and intermittent operation modes, while with the ultrafilter only continuous operation mode was employed. The excessive membrane fouling observed in thermophilic SA-MBRs with microfilter under continuous filtration mode, could be significantly reduced by the application of cake layer pre-coating or replacing microfilter with ultrafilter. This membrane fouling under the thermophilic condition could be linked to higher protein generation within the reactors. Soluble COD removal efficiencies were higher in thermophilic conditions while the sludge yields were significantly low in thermophilic SA-MBRs.(C) 2010 Elsevier Ltd. All rights reserved.