Wastewaters are treated by an activated sludge process that includes combining wastewater with bacteria-laden sludge in an activated sludge tank to form a mixed liquor, separating the mixed liquor into a clear effluent and activated sludge stream, pretreating at least a portion of the activated sludge stream in a conditioning tank, transferring at least a portion of the activated sludge stream in the conditioning tank to an interchange bioreactor operating in batch or continuous flow mode, processing the activated sludge stream within the interchange bioreactor by selecting desired growth conditions to cultivate at least one type of bacteria in the activated sludge stream, and returning at least a portion of the activated sludge stream in the bioreactor to the activated sludge tank. The process may further include a sidestream reactor to remove phosphates from the activated sludge stream leaving the interchange bioreactor.