Effect of pH on the Degradation of Aqueous Organophosphate (methylparathion) in Wastewater by Ozonation

Degradation of O,O-dimethyl -O-4-nitrophenylphosphorothioate (methylparathion) by ozonation in aqueous solution was studied in a batch reactor under constant ozone dosage and variable pH conditions. The effectiveness of the process was estimated based on the degree of COD (chemical oxygen demand) reduction and conversion of methylparathion. It was observed that ozonation is more effective at alkaline reaction of medium than other conditions. The degree of methylparathion conversion achieved after 120 minutes of the process at pH 9 was 98% compared to 81% and 60% at pH 7 and 3, respectively. Another parameter used to quantify the methylparathion during ozonation was the pseudo first order rate constant k (1/min). Results showed that the rate constant of the process was approximately much higher at pH 9 compared to pH 7 and 3. A significant improvement in chemical oxygen demand removal was observed at pH above 7. At pH 9, the reduction in chemical oxygen demand at the end of the process reached 93%. The methylparathion degradation intermediate products were analyzed by gas chromatography–mass spectrometry (GC–MS). The main intermediate product was p-nitrophenol. The result of the study concludes that ozonation is an effective process for the treatment of organophosphate (methylparathion) contaminated wastewater.