Feasibility of an AnMBR demonstration plant treating urban wastewater (UWW) at temperatures around 25-30 ºC was assessed during a 350-day experimental period. The plant was fitted with industrial-scale hollow-fiber membranes and fed with the effluent from the pre-treatment of a full-scale municipal WWTP. Biodegradability of the UWW reached values up to 87%, although a portion of the biodegradable COD was consumed by sulfate reducing organisms. Effluent COD remained below effluent discharge limits, achieving COD removals above 90%. System operation resulted in a reduction of sludge production of 36-58% compared to theoretical aerobic sludge productions. The membranes were operated at gross transmembrane fluxes above 20 LMH maintaining low membrane fouling propensities for more than 250 days without chemical cleaning requirements. Thus, the system resulted in net positive energy productions and GHG emissions around zero. The results obtained confirm the feasibility of UWW treatment in AnMBR under mild and warm climates.