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Farre MJ, Franch MI, Malato S, Ayllon JA, Peral J, Domenech X:
"Biodegradability of treated aqueous solutions of biorecalcitrant pesticides by means of photocatalytic ozonation",
In CEST2005: 402-406, (Sep 2005)

Keywords	Photo-Fenton,TiO2-photocatalysis, ozone coupling, pesticide degradation
Abstract	Photo-Fenton/ozone (PhFO) and TiO2-photocatalysis/ozone (PhCO) coupled systems are used as Advanced Oxidation Processes for the degradation of the following biorecalcitrant pesticides: alachlor, atrazine, chlorfenvinfos, diuron, isoproturon and pentachlorophenol. These organic compounds are considered Priority Hazardous Substances by the Water Framework Directive of the European Comission. This work has been performed in the frame of the CADOX EU project (EVK1-CT-2002-00122), that is currently working in the design of the coupling between an advanced oxidation and an aerobic biological treatment steps, for the degradation of toxic and biorecalcitrant organic contaminants. The aim of the project is to find the optimal experimental conditions for the application of a chemical step previous to the biological treatment of the contaminated effluent, in order to obtain a detoxified water able to be treated by a conventional aerobic biological treatment. In the present communication two photocatalytic processes coupled with ozone have been used. These two chemical processes produce in situ OH radicals under very mild experimental conditions. It is observed that the addition of ozone in the system working in both Photo-Fenton and TiO2-photocatalysis conditions, enhances the production of OH radicals that leads to an important increment of TOC removal for the different pesticide aqueous solutions investigated. The degradation process of the different pesticides, that occurs through oxidation of the organic molecules by means of their reaction with generated OH radical, follows a first and zero-order kinetics, when PhFO and PhCO are applied, respectively. The best results of pesticide mineralization are obtained when PhFO is applied. For this system the following order of initial rate degree of mineralization is obtained, PCP > chlorfenvinfos > diuron > isoproturon > alachlor > atrazine while in the case of application of PhCO, the rate of mineralization of the different pesticides investigated is almost the same, except for atrazine which shows a much lower degradation rate. The toxicity of the pesticide solutions treated with PhFO have been assessed. It has been observed that all pesticide solutions become detoxyfied except in the case of atrazine and alachlor aqueous solutions for which no detoxification is achieved at the experimental conditions used in the work, at least after 2 and 3 h of treatment, respectively.
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