The performance of a pilot scale anaerobic membrane bioreactor (AnMBR), comprising an upflow anaerobic sludge blanket (UASB) reactor coupled to an external ultrafiltration membrane treating municipal wastewater at 18 +/- 2 degrees C, was evaluated over three years of stable operation. The reactor was inoculated with a mesophilic inoculum without acclimation. The AnMBR supported a tCOD removal efficiency of 87 +/- 1% at hydraulic retention time (HRT) of 7 h, operating at a volumetric loading rate (VLR) of between 2 and 2.5 kg tCOD/m(3) d, reaching effluent tCOD concentrations of 100-120 mg/L and BOD5 concentrations of 35-50 mg O-2/L. Specific methane yield varied from 0.18 to 0.23 Nm(3) CH4/kg CODremoved depending on the recirculation between the membrane module and the UASB reactor. The permeate flow rate, using cycles of 15 s backwash, 7.5 min filtration, and continuous biogas sparging (40-60 m/h), ranged from 10 to 14 Lm(2)/h with trans-membrane pressure (TMP) values of 400-550 mbar. (C) 2015 Elsevier Ltd. All rights reserved.