2,4-dichlorophenoxyacetic acid degradation in aqueous media: ozonation and ozonation combined with Ultraviolet radiation

M.E. LOVATO, C.A. MARTIN, A.E. CASSANO

Paris

Congreso; IOA IUVA World Congress & Exhibition; 2011

International Ozone Association

In this work, 2,4-Dichlorophenoxyacetic acid (2,4-D) was selected as model compound, and O3 and O3/UV as tentative oxidation technologies. 2,4-D is an herbicide widely used for the selective control of weeds in gardens and farming. Because it is poorly biodegradable, powerful oxidation and efficient methods for treating natural waters contaminated with this pollutant are required in order to ensure its absence in waters for domestic uses. Ozone is a strong oxidant; an important advantage is that it does not introduce new substances into the aqueous media. It could be applied alone or in combination with Hydrogen Peroxide or UV radiation. Two reactions of ozone with dissolved organic substances can be distinguished in water: at low pH, a highly selective attack of molecular Ozone, whereas free radicals from Ozone decomposition can also react non-selectively with organic compounds. Free radicals can be produced in the aqueous media from Ozone by pH modification, by combining Ozone with Hydrogen Peroxide or associated with UV radiation from a low pressure mercury lamp. A kinetic model was developed, which represents the reaction of decomposition of 2,4-D taking into account all the O3 parallel paths of attack among which, the direct photolysis and its spontaneous decomposition in water cannot be excluded. The kinetic model must represent the evolution of the pollutant, the principal reaction intermediates and the detectable end products concentrations