Process based on the capacity of some microorganisms to accumulate phosphate (as polyphosphate) in excess of their normal metabolic requirements. These microorganisms store substrate (PHB) anaerobicly which is oxidized in a phase where a electron acceptor like oxygen ore nitrate is present. In the presence of nitrate ore oxygen phosphate is stored by the microorganisms. By extracting excess sludge from the anoxic or aerobic phase, phosphate is removed from the system.