Process Modeling and Its Application in Municipal Wastewater Treatment Plant Based on Seasonal Temperature Variations: A Case Study in Eastern China

Based on the impact of seasonal temperature variations on wastewater treatment plants (WWTPs), a mathematical model of the Anaerobic–Anoxic–Oxic (AAO) process at a municipal WWTP in Eastern China was developed using GPS-X 8.5 software. A sensitivity analysis was conducted on 128 parameters, and key influential parameters were identified and adjusted accordingly. The model’s accuracy was validated using historical monitoring data, and the validation confirmed its ability to reflect operational conditions across different seasons. To address seasonal challenges observed in historical data, several scenarios were simulated. The results show that the maximum treatment capacity of the WWTP is approximately 125% of the design capacity. Under low winter temperatures, the treatment efficiency can be enhanced by reducing the dissolved oxygen (DO) levels in the oxic tank to 1.5–2 mg/L and increasing both the internal reflux ratios to approximately 150% and external reflux ratios to 100%. During summer rainstorms, the risk of exceeding the discharge limits can be mitigated by appropriately increasing the dosage of the flocculant poly-aluminum chloride (PAC). Additionally, carbon source supplementation strategies were proposed based on varying influent carbon-to-nitrogen ratios (C/N). These findings provided precise operational strategies for the WWTP, effectively reducing the effluent concentrations of COD, TN, NH4+-N, and TP by 3.1%, 12.7%, 24.1%, and 18.9%, respectively, while also achieving a 24.2% reduction in the carbon source dosage.