Study on the enhanced biological nitrogen and phosphorus removal in a full-scale wastewater treatment plant with modified carrousel oxidation ditch process

In order to solve the increasingly serious problem of eutrophication in China, the government had issued a new wastewater discharge standard that focuses on reducing the nutrients from effluents (TN <; 15 mg/L, TP <; 0.5 mg/L). These stringent new requirements had resulted in the need for improved nutriment removal from existing full-scale wastewater treatment plants. In this study a series of reform were carried out in a full-scale wastewater treatment plant with modified carrousel oxidation ditch process located in Henan province of China. In order to improve the nutriment removal efficiency, low oxygen control strategy was adopted and the gas supply of aerobic zone was optimized y. By reducing the quantity of aeration in the front of the oxidation ditch and controlling the DO between 1 and 1.5 mg/L in the export, the anoxic zone was formed in the front of the oxidation ditch. The run way of modified oxidation ditch was changed from anoxic/anaerobic/aerobic to anoxic/anaerobic/anoxic/aerobic. After adjusting, the effluent quality was substantially improved. The concentrations of COD, NH₄⁺-N, TN and TP in the effluent were below 30 mg/L, 2 mg/L, 15 mg/L and 0.5 mg/L, respectively. All of these indicators met the new wastewater discharge standards enacted in China.