Optimal control of urban sewer systems under enhanced water quality modeling

Abstract

Agricultural lands usually carry a considerable amount of phosphorous and nitrogen. This is due to the routinely added chemical fertilizers. Phosphorous is identified as a non-point source pollutant that causes eutrophication in surface waters. Even though, phosphorous is less mobile than nitrogen, soil erosion in agricultural lands leads to increase the phosphorous levels in surface water. Therefore, it is always better to consider phosphorous concentration when considering the receiving water quality due to combined sewer overflows (CSOs). Rathnayake and Tanyimboh’s optimal control model for urban sewer systems is capable of assessing water quality in receiving water due to CSOs. However, it only includes the concentrations of total suspended solids (TSS), chemical oxygen demand (COD), nitrates and nitrites (NOX), five-day biochemical oxygen demand (BOD) and total Kjeldahl nitrogen (TKN). Therefore, there is a necessity to improve the water quality analysis in Rathnayake and Tanyimboh’s optimal model. This paper presents an enhanced water quality approach, including phosphorous concentrations, in control of urban sewer networks. The enhanced model is applied to a real world combined sewer network. Results show that the enhanced model produces better approach compared to the existing Rathnayake and Tanyimboh’s control model.