Optimal Water Quality Management Considering Spatial and Temporal Variations in a Tidal River

There is an increasing need to establish wastewater treatment facilities for improving water quality of heavily polluted rivers in rapidly urbanizing areas. Optimization models are widely used to determine the pollutant removal levels at different pollution sources, with the aim of minimizing the wastewater treatment cost and satisfying certain water quality criteria. Water quality is usually evaluated in a prescribed space or time point. Thus it cannot reflect the overall status of a tidal river that has significant spatio-temporal variations. In this paper, new spatio-temporal water quality criteria, which consider the water quality violation against specified water quality standards during the whole simulation period of time for the entire river simulated, are proposed and then applied to optimization of a wastewater treatment system in Shenzhen, China. The results indicate that the optimization based on the proposed criteria facilitates an improved performance of wastewater treatment systems in terms of water quality along the whole river during a long time period, instead of just in a prescribed space or time point. Furthermore, use of the new criteria derives a better Pareto front of cost and water quality in terms of convergence and coverage compared with the conventional criteria and thus they are recommended as the water quality criteria to measure spatial and temporal variation in a tidal river for wastewater treatment system planning.