Anaerobic membrane bioreactor (AnMBR) is a promising process to recover energy and water resource from domestic wastewater; however, its energy-efficiency needs substantial improvement for real applications. In this study, based on the methanogenic activity batch tests and critical flux determination, an optimization protocol for AnMBRs is reported and a flux-centered energy balance analysis is conducted. The results demonstrate that organic loading rate by sludge (OLRsludge) should be controlled within 0.43-0.90 kgCOD/(kgVSS.d), and the corresponding sludge retention time (SRT) should be in the range of 50 d to infinity. Energy balance analysis shows that the AnMBR systems at the temperature of 35 degrees C and 25 degrees C could achieve net energy recovery. For realizing energy-neutral operation, the corresponding fluxes should range from 8.3 to 9.5 Li(m(2).h) at 35 degrees C and 6.0 to 6.7 L/(m(2).h) at 25 degrees C, respectively. In the process design and operation, a relatively short hydraulic retention time (HRT) and an SRT close to 50 d should be considered in order to achieve an energy-efficient AnMBR performance. (C) 2016 Elsevier Ltd. All rights reserved.