Degradation and byproduct formation of parathion in aqueous solutions by UV and UV/H2O2 treatment

• Published in: Water research (Oxford) 2008-12, Vol.42 (19), p.4780-4790
• Main Authors: Wu, Changlong, Linden, Karl G
• Format: Article
• Language: English
• Subjects: Applied sciences; aqueous solutions; byproducts; chemical treatment; degradation; Exact sciences and technology; hydrogen peroxide; nitrates; optimization; Other industrial wastes. Sewage sludge; oxidation; p-nitrophenol; paraoxon; parathion; phosphates; photolysis; Pollution; pressure; sulfates; ultraviolet radiation; Wastes; water pollution; water treatment; Water treatment and pollution
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2008.08.023

The photodegradation of parathion, a US EPA Contaminant Candidate List pesticide, in aqueous solutions by UV and UV/H 2 O 2 processes in batch reactors was evaluated. Direct photolysis of parathion both by LP (low pressure) and MP (medium pressure) lamps at pH 7 were very slow with quantum yields of 6.67 ± 0.33 ×10 −4 and 6.00 ± 1.06 ×10 −4 mol E −1 , respectively. Hydrogen peroxide enhanced the photodegradation of parathion through the reaction between UV generated hydroxyl radical and parathion with a second-order reaction rate constant of 9.70 ± 0.45×10 9 M −1 s −1 . However, addition of hydrogen peroxide did not result in a linear increase in the degradation rate. An optimum molar ratio between hydrogen peroxide and parathion was determined to be between 300 – 400. Photodegradation of parathion yielded several organic byproducts, of which the paraoxon, 4-nitrophenol, O,O,O-triethyl thiophosphate and O,O diethyl-methyl thiophosphate were quantified and their occurrence during UV/H 2 O 2 processes were discussed. NO 2 − , PO 4 3− , NO 3 − and SO 4 2− were the major anionic byproducts of parathion photodegradation and their recover ratio were also discussed. A photodegradation mechanism scheme suggesting three simultaneous pathways was proposed in the study.