An Optimization Model for Waste Load Allocation under Water Carrying Capacity Improvement Management, A Case Study of the Yitong River, Northeast China

In this study, a two-stage stochastic programming (TSP) model was developed for supporting regional waste load(chemical oxygen demand (COD) and NH3-N) allocation in four main pollution departments (industry, municipal, livestock breeding, and agriculture), constrained by the water carrying capacity, which can be improved by ecological restoration engineering, in the nine function zones of the Yitong River. A number of scenarios corresponding to different stream flow levels were examined. The results revealed that the carrying capacity of COD and NH3-N has a similar tendency with a positive correlation to stream flow levels. The allocation amount of each pollutant for the four departments was obtained differently in each zone, and ecological restoration engineering solutions were obtained for different zones to improve the carrying capacity of the pollutants in order to meet the permitted emission allocation and water qualities. The results are helpful in establishing a rational discharge permit system of each pollution unit under water quality targets, and provide a basis for production plans of these pollution units.