Pollutant Reduction Systems for Controlling Agricultural Non-Point-Source Pollution in Town District of River Network Area Based on Reuse of Wastewater and Nutrient: A Case Study in Xinjian Town, Taihu Lake

In river network areas, the control of agricultural non-point source pollution (ANPSP)should consider not only the pollutant removal effect and cost but also the resource utilization efficiency. Taking Xinjian Town, Yixing City on the west bank of Taihu Lake as an example, the volume of wastewater and the pollutant loads discharged from three pollution sources (crop farming, livestock and aquaculture)were investigated. The demand of water for irrigation and the potential reuse of wastewater for irrigation and the potential reuse of nitrogen (N)and phosphorus (P)from manure and wastewater for fertilizing cropland were also estimated. The performance of two schemes of ANPSP control system (Scheme Ⅰ:reuse of all livestock wastewater and manure; Scheme Ⅱ:reuse of all livestock wastewater and manure and some aquaculture wastewater)on pollutant reduction efficiency (TN, TP, NH₃-N, and COD)and economic cost were evaluated. The results show that if all the livestock wastewater (71.96×10³ m³) and some aquaculture wastewater (2 277.11×10³ m³)were reused for irrigation after processing could meet the total irrigation water demand in Xinjian Town (Scheme Ⅱ). The removal efficiencies of Scheme Ⅱ for the pollutants TN, TP, NH₃-N, and COD were 84.3%, 94.2%, 89.6% and 94.0%, respectively. In addition, Scheme Ⅱ could reduce the use of chemical fertilizers by nearly 81.8 kg·hm^-2 of N and 39.9 kg·hm^-2 of P annually. In order to reduce costs, Scheme Ⅰ that only reuse livestock wastewater (71.96×10³ m³)for irrigation after processing could only meet with 3% of irrigation water demand. The removal efficiencies of Scheme Ⅰ for the pollutants TN, TP, NH₃-N, and COD were 83.0%, 93.7%, 88.7% and 93.7%, respectively, and the use of N and P fertilizers can be reduced by nearly 52.0 and 34.2 kg·hm^-2 annually. The proposed two schemes of ANPSP control system with consideration of nutrients and wastewater recycling may provide a reference for the construction of pollution control projects in Xinjian Town.