Quantitatively updating sewage discharge standard of wastewater treatment plants: Starting from the estimation of water environment capacity

Abstract

To protect aquatic environment and human health, determining the optimal sewage discharge standard for wastewater treatment plants (WWTPs) is important to reduce pollutant discharge into natural ecosystems. In this study, a novel quantitative assessment method combining water environment capacity (WEC) estimation and feasibility analysis was introduced for the selection of WWTP sewage discharge standard. A certain WWTP executing national Grade 1-B discharge standard in China’s southern coast was selected as a case study. First of all, pollution sources of receiving water were investigated. More than 69.0% of nutrients (nitrogen, phosphorus) came from WWTP effluent, while non-point pollution contributed 58.3% of organic pollutants. Next, the WEC of receiving water was estimated via multiple mathematical models. It was speculated that the WEC of TP may be completely depleted by 2020 if still executing national Grade 1-B discharge standard. The maximum acceptable pollutant concentration of WWTP effluent are determined with chemical oxygen demand (COD) 86.05 mg/L, total nitrogen (TN) 19.38 mg/L, ammonium (NH4+-N)4.87 mg/L, and total phosphorus (TP) 0.67 mg/L to maintain water self-purification. Finally, after further economic/technical feasibility analysis, an optimal sewage discharge standard was recommended: 40 mg COD/L, 15 mg TN/L, 4.0 mg NH4+-N/L, and 0.3 mg TP/L.