The specification discloses a method for treating and digesting organic wastes in a wastewater stream. A first wastewater influent stream is mixed with an activated sludge biomass in an aerobic digestion zone, so that least a portion of the organic wastes in the first wastewater influent stream are digested by activated sludge biomass. The first wastewater influent stream is separated from the activated sludge biomass in a first separation zone to recover activated sludge biomass and to provide a wastewater effluent stream. The second wastewater influent stream is mixed with recovered activated sludge biomass from the aerobic digestion zone in a substantially anaerobic adsorption zone so that at least a portion of the organic wastes in the second wastewater influent stream are adsorbed by the activated sludge biomass. The second wastewater influent stream and the activated sludge biomass are then separated in a second separation zone to recover the activated sludge biomass and organic wastes adsorbed thereto from the anaerobic adsorption zone and to provide a substantially liquid wastewater stream which is recycled to the aerobic digestion zone. Finally, at least a portion of the activated sludge biomass and adsorbed organic wastes from the anaerobic adsorption zone are digested under substantially anaerobic conditions so as to recover a combustible gas stream. An apparatus for carrying out the method is also disclosed.