Achieving low effluent BOD5 concentrations and stable performance while treating municipal wastewater at ambient temperature has been difficult for anaerobic biotechnology without using membranes. Membrane operation has typically required energy inputs greater than traditionally needed for activated sludge aeration, thus defeating one main objective of utilizing anaerobic biotechnology. However, new low-energy membrane operational strategies are being evaluated to make anaerobic membrane bioreactors (AnMBR) more energy efficient. In this study, four 3.3 L bench-scale AnMBRs using external crossflow tubular membranes were fed synthetic and real municipal wastewater at 10 and 25 degrees C and evaluated on the basis of energy demand and organic removal. The membranes were operated at atypically low crossflow velocities of 0.018-0.3 m/s, and with or without fluidized GAC, to reduce AnMBR energy demand. Use of GAC in membranes allowed for significant reduction in crossflow velocity without reducing membrane run-time between cleanings and resulted in energy demands of 0.05-0.13 kWh/m(3). The AnMBRs were able to produce permeate BOD5 <= 10 mg/L at bioreactor HRTs of 4.2-9.8 h, even at 10 degrees C. When factoring in theoretical energy production, the AnMBR described herein is estimated to require 70-100% less energy compared to activated sludge, indicating net neutral energy demand may be feasible for BOD5 and nutrient removal from municipal wastewater. (C) 2016 Elsevier B.V. All rights reserved.