This study was conducted to investigate the effects of sulfate on propionate degradation and higher organic loading rate (OLR) achievement in a thermophilic AnMBR for 373 days using coffee grounds, milk and waste activated sludge (WAS) as the co-substrate. Without the addition of sulfate, the anaerobic system failed at an OLR of 14.6 g-COD/L/d, with propionate accumulating to above 2.23 g-COD/L, and recovery by an alkalinity supplement was not successful. After sulfate was added into substrates at a COD/SO42- ratio of 200: 1 to 350: 1, biogas production increased proportionally with OLR increasing from 4.06 to 15.2 g-COD/L/d. Propionic acid was maintained at less than 100 mg-COD/L due to the effective conversion of propionic acid to methane after the sulfate supplement was added. The long-term stable performance of the AnMBR indicated that adding sulfate was beneficial for the degradation of propionate and achieving a higher OLR under the thermophilic condition. (C) 2015 Elsevier Ltd. All rights reserved.