This study was conducted to investigate the ratios of phosphorus release to COD uptake, phosphorus release to nitrate removal, and phosphorus uptake to phosphorus release by DNPAOs(denitrifying phosphate accumulating organisms). In case I～IV, influent 1 were fed with synthetic wastewater with influent 2 NO3--N injection to anoxic zone and the case V were fed with municipal wastewater with side stream oxic zone instead of influent 2 NO3--N injection. As a result, the ratio of phosphorus release to carbon uptake was increased in accordance with nitrate supply. The DNPAOs simultaneously took up phosphate and removed nitrate from the anoxic reactor. In case I～IV, with above 20 mg/L of sufficient NO3--N supply, phosphate was taken up excessively by the DNPAOs in anoxic condition. The large amount of both uptake and release of phosphorus occurred above 20 mg/L of nitrate supply, achieving the ratio of phosphorus uptake to phosphorus release to be 1.05.
In case V, phosphate luxury uptake was not occurred in system due to 6.98 mg/L of insufficient NO3--N supply and the ratio of phosphorus uptake to phosphorus release was 0.98. Consequently, if nitrate as the electron acceptor was sufficient in anoxic zone, the ratio was found to be high.

• 김홍태(경북대학교 건설공학부 토목공학) | Hong Tae Kim
• 김경호(경북대학교 건설공학부 토목공학) | Kyeong Ho Kim Corresponding Author