Photoassisted iron compound catalytic degradation of organophosphorous pesticides with hydrogen peroxide

The photocatalytic degradation of organophosphorous pesticides(OPPs), such as methamidophos, malathion, diazion, phorate and EPN was studied using UV radiation in combination with hydrogen peroxide. The influence of iron compounds, including ferrous and zero-valent iron on the degradation of OPPs was also examined. Results of the experiment showed that the addition of iron compounds (Fe-0, Fe2+) can enhance the degradation efficiency of OPPs. Nearly complete removal was exhibited when the system was amended with iron compounds and illuminated with UV light. The degradation efficiency of OPPs in the UV/Fe/H2O2 system was more effective than that of OPPs in the UV/H2O2 system. The ferrous ion, produced from the surface oxidation of Fe-0, reached a maximum concentration of 21.6 mu M at 160 minutes and rapidly converted to Fe3+ within 25 minutes. The degradation process of OPP appeared to follow pseudo-first-order equation, with the rate constants ranging from 0.004 to 0.026 min(-1). Also, the order of reactivity of OPP was phorate > methamidophos > EPN > diazion > malathion. This study indicates that the addition of zero-valent iron is a feasible alternative in the pretreatment of wastewater containing organophosphorous pesticides. (C) 1998 Elsevier Science Ltd. All rights reserved.