Detoxication of organophosphate pesticides in source waters by incorporation of an alkaline hydrolysis procedure in conventional drinking water treatment processes

Abstract

Organophosphorus pesticides (OPPs) in source waters are a potential threat to drinking water safety. Although these chemicals could be removed upon chlorination in conventional water treatment, the formation of toxic decomposition products, i.e., oxons, can increase the toxicity of finished water. To address this problem, this study proposed a simple and practical treatment method for detoxifying OPPs by incorporating an alkaline hydrolysis procedure after pre-chlorination in the conventional treatment process. The experimental results showed that pre-chlorination with a chlorine dose of 1.5 mg/L could transform 87 %–92 % of OPPs with initial concentrations <50 μg/L into oxons, resulting in a significant increase in toxicity. However, by adjusting solution pH to around 11 through addition of a base fostered hydrolysis reactions of the chlorinated by-products, reducing the toxicity of the treated solution to about 0 % after a 30-minute reaction. Furthermore, the present study demonstrated that, even at a higher OPPs concentration (e.g., 100 μg/L for individual OPPs), a complete detoxification of the treated water could be achieved via adjusting pre-chlorination dose or reaction time, or hydrolysis reaction time. The presence of the common inorganic ions and organic matter in the source water matrix has negligible effects on the degradation and detoxication of OPPs. This study thus demonstrated that a combined pre-chlorination and alkaline hydrolysis process could be an effective and efficient treatment protocol for both degradation and detoxication of OPPs in water treatment.