Evaluation of the treatment effects of pesticide production wastewater under direct and indirect discharge modes

The wastewater treatment of pesticide enterprises is one of the key issues in terms of environmental protection and cleaner agricultural production. Fully understanding the water quality characteristics and treatment processes of pesticide production wastewater is of great significance to the management of stable and compliant discharge up to standards for pesticide enterprises. In this study, the water qualities, treatment processes and removal efficiencies of wastewater from six typical pesticide enterprises under two dominant discharge modes across China were investigated. The results revealed that the organic pollution of pesticide production wastewater was serious and their biodegradability were generally bad (B/C ≤ 0.25). Among them, the situation in enterprises producing paraquat was the most obvious. The concentrations of chemical oxygen demand (COD_Cr), 5-day biochemical oxygen demand (BOD₅), total organic carbon (TOC) and total dissolved solids (TDS) in the wastewater of this enterprise reached 95,600 mg/L, 48,400 mg/L, 16,400 mg/L and 336,000 mg/L, respectively. The sewage discharge limits for direct discharge enterprises (DDEs) were stricter than those for indirect discharge enterprises (IDEs). As a result, the sewage treatment processes of DDEs were more complex, leading to a higher average pollutant removal efficiency (DDEs, 85.50%; IDEs, 73.13%) and a higher compliance rate (DDEs, 100%; IDEs, 75%). Finally, the wastewater treatment processes of the six pesticide enterprises were evaluated and suggestions were given on the improvement of pollutant removal efficiencies and avoidance of resource waste. It was suggested that DDEs should add corresponding adsorption process in the pretreatment stage, and that the chemical industry parks (CIPs), where IDEs were located should conduct water quality assessment upstream, classify enterprises according to pollution degree, and add toxicity index assessment to pesticide industry standards. The results of this study systematically and comprehensively revealed the current situation of pesticide wastewater treatment in China, and provided important references for the formulation of national pesticide industry discharge standards.