A Pilot Study on Nitrogen and Phosphorus Removal in Modified Phostrip Process

초록

A pilot-scale plant with a capacity of 20-30m3/day was operated for 10 months for the simulataneous removal of nitrogen and phosphorus using Modified-Phostrip process. In the process, a denitrification tank was installed before an aeration tank in the Phostrip process, which was developed mainly for the phosphorus removal. To maintain the effluent TKN in the range of 1-3 mg/L, the allowable maximum TKN loading rate in the aeration tank was found to be 0.065 kg TKN/kg MLSS.d. The nitrification rate in the aeration tank increased as the influent COD/TKN ratio declined. The optimum ratio of the internal sludge recycle from the aeration tank to the anoxic basin was appropriate to be at the nitrate-nitrogen loading equvalent to the one-fourths of the influent COD. The optimal internal recycling ratio from the aeration tank to the denitrifier was obtained to be 2Q, when the yearly average COD and TKN concentrations of influent was 197 mg/L and 37.1 mg/L, respectively. To keep the effluent T-P concentration below 1 mg/L, T-P loading to the aeration tank should be less than 0.008 kg T-P/kg MLSS.d at the internal recycle ratio from the 2nd clarifier to P-stripper, 0.3Q. However, the loading should be kept at less than 0.0065 kg T-/kg MLSS.d at the internal recycle ratio of 0.15Q.