Evaluation of nutrients removal in full-scale modified oxidation ditch system in the ambient conditions

A modified oxidation ditch process is applied in a full-scale municipal wastewater treatment plant. Compared with the conventional oxidation ditch, the modified oxidation ditch adds some microporous aerators to improve oxygen utilization. The measures bring about a further improvement of nitrogen and phosphorus in the urban wastewater. The monitoring results for one year show that the influent concentrations of SS, COD, NH₄-N and TP are 160-320, 170-320, 8-16, 2.5-4.0 mg/L, respectively. And the influent pH and temperature are 7.0-8.5 and 17-27°C. Afte the treatment of modified oxidation ditch process, the average effluent concentrations of SS, COD, NH₄-N, TP are 18, 20, 2.4, 0.8 mg/L, and the average removal rates are 92%, 90%, 80%, 60%, respectively. The effluent pH is consisted with the influent pH. The removal efficiency of nitrogen and phosphorus can be kept at good efficiency, in spite of the fluctuation of temperature. The effluent quality meets the 1 B level discharging criteria in China.