Abstract: A process is disclosed for decreasing the phosphorus content of an aqueous influent stream containing biodegradable substrates, comprising adding to said stream previous aerobically enhanced and anaerobically stressed bacteria; dividing said stream into separate first and second streams; treating the first stream in an aerobic zone, in the presence of sufficient oxygen, for a time sufficient to cause enhancement of the bacteria to take-up phosphorus in excess of their growth requirements; treating the second stream in an anaerobic zone containing less than about 1 ppm of oxygen, for a time sufficient to stress the bacteria and cause release of phosphorus which is nonessential for the bacteria growth requirements; intimately mixing said treated first and second stream; holding said mixed first and second streams to allow settling of precipitants; removing liquid effluent from the upper portion of the settled stream; removing high solids content sludge, containing bacteria and phosphorus from the lower portion