Abstract: The biological process is for treating wastewater in order to remove the phosphorus therefrom and thus obtain clarified water. The process is using two sequencing batch reactors (SBR) in series filled with a sludge-mixed liquor. The process consists of: continuously feeding wastewater into the first (SBR) operating under anaerobic conditions for equalization and anaerobic treatment by controlling in-time any fermentation reaction occurring therein in order to produce an acidogenesis fermenting phase of organic materials and prevent the methanogenesis phase. Then, the fermented wastewater from the first SBR is rapidly transferred by batch into the second SBR. In the second SBR, the wastewater is first anaerobically treated to store a maximum amount of volatile fatty acids (VFAs) in the phosphorus removal biomass.