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The anaerobic treatment is a potential way to realize the energy production in wastewater treatment. However, it is necessary to increase the organic matter concentration in municipal wastewater. In this study, we proposed a wastewater treatment system that involved an anaerobic membrane bioreactor (AnMBR) combined with a forward osmosis (FO) process to concentrate the wastewater. The energy balance of this system was estimated by the calculation based on the FO condensation test and batch methane fermentation test. The methane yield from the condensed municipal wastewater in the batch methane fermentation test at 40°C was 0.22 m3 -CH4 /kg-CODCr_rem, putting CODCr as the chemical oxygen demand was determined by chromium oxidation method. The energy generated from the yielded methane was estimated to be 0.33 kWh/m3. Nevertheless, the total energy consumption was 0.39 kWh/m3, which was higher than 0.2 kWh/m3 of a conventional activated sludge process. It was found that it is possible to get a net energy if the fermentation temperature in the AnMBR process can be reduced to below 34°C. [ABSTRACT FROM AUTHOR]