Early warning and management of excessive discharge of water pollutants in municipal wastewater treatment plants based on fluctuation coefficients

Constructing an exceedance early warning mechanism based on the fluctuation coefficients (FCs) of water pollutants is critical for maintaining stable and compliant effluent discharge at municipal wastewater treatment plants (WWTPs). In this study, nine municipal WWTPs in China's Taihu Basin were selected, and one year of continuous online monitoring data for water pollutant effluent discharge was analyzed. By deriving a set of formulas, FCs for four water pollutants within their normal discharge concentration ranges were calculated, and their variations and seasonal characteristics were examined. Subsequently, an exceedance early warning mechanism was developed according to the critical warning thresholds of each plant. The results indicate that FCs vary among pollutants and exhibit pronounced seasonal fluctuations. The proposed tiered early warning mechanism can promptly detect all potential exceedance risks and dynamically adjust warning levels, thereby effectively capturing abnormal pollutant discharge events over short timeframes. Specifically, low-level warnings constituted 47.4% of all warning events, and 74% of dynamic warnings were ultimately downgraded to lower warning levels. This approach provides essential technical support for the timely detection and control of exceedance risks and has important implications for safeguarding the ecological security of aquatic environments.