The present paper presents a submerged anaerobic membrane bioreactor (SAnMBR) as a sustainable approach for urban wastewater treatment at 33 and 20 degrees C, since greenhouse gas emissions are reduced and energy recovery is enhanced. Compared to other anaerobic systems, such as UASB reactors, the membrane technology allows the use of biogas-assisted mixing which enhances the methane stripping from the liquid phase bulk. The methane saturation index obtained for the whole period (1.00 +/- 0.04) evidenced that the equilibrium condition was reached and the methane loss with the effluent was reduced. The methane recovery efficiency obtained at 20 degrees C (53.6%) was slightly lower than at 33 degrees C (57.4%) due to a reduction of the treatment efficiency, as evidenced by the lower methane production and the higher waste sludge per litre of treated wastewater. For both operational temperatures, the methane recovery efficiency was strongly affected by the high sulphate concentration in the influent wastewater. (C) 2012 Elsevier Ltd. All rights reserved.