Abstract: Wastewater is treated by promoting the presence and growth of BPR organisms, which have the ability to absorb and retain an amount of phosphorus in excess of the amount required by the BPR organisms for metabolism and cell growth. In the process, a mixture of influent wastewater (10) and activated sludge (14) containing BPR organisms is first subjected to a period of incubation in an anoxic zone (20) followed by a period of incubation in an anaerobic zone (30). Volatile fatty acids (VFA's) (16) are added in the anaerobic zone (30). The mixture is then subjected to an aerobic zone (41). The wastewater mixture (46) leaving the aerobic zone is clarified in a clarifier (50), causing activated sludge to settle. The activated sludge contains BPR organisms which are engorged with phosphorus absorbed from the wastewater. The clarified wastewater (52) becomes effluent from the system. The activated sludge (54) is removed from the clarifier (50).