The Effect of Malathion on the Activity and Performance of Activated Sludge

Decontamination activities following a chemical weapons incident may generate significant quantities of contaminated wash water that may enter the wastewater collection system either intentionally or accidentally. This raises concerns about the effect of chemical warfare agents (CWAs) on the operation of a biological wastewater treatment plant. The goal of the study was to evaluate the effect of malathion on the activity and performance of activated sludge. Malathion is an organophosphate (OP) and is considered an environmental surrogate for VX. This study employed respirometry, short term batch tests, and long term exposure experiments to investigate the effects of different concentrations of malathion on bioreactor performance. Short-term exposure to malathion may depress microbial respiration, however, short-term batch tests showed that chemical oxygen demand (COD) removal was not negatively impacted by the presence of malathion concentrations of 0.1 or 3 mg/L. Unlike COD removal, ammonia-N removal was slowed by the presence of malathion at both 0.1 and 3 mg/L with a positive correlation of the removal rate to the quantity of total suspended solids. Long-term exposure experiments demonstrated that both COD removal and Nitrate production were negatively affected at concentrations of 3.0 mg/L and unaffected at concentrations of 0.1 mg/L.
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