Modeling the degradation of herbicide 2,4-D in aqueous media by Ozonation and Ozonation combined with UV radiation

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

Rio de Janeiro

Congreso; VI Encontro sobre Aplicações Ambientais de Processos Oxidativos Avançados; 2011

The herbicide 2,4-D is extensively used as a plant growth regulator for agricultural and non-agricultural purposes. 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. The reaction of ozone with organic substrates follows two reaction mechanisms: (i) direct reaction of molecular ozone and (ii) indirect reactions involving OH? radicals formed in the ozone decomposition in water. The direct oxidation by ozone molecule is selective to unsaturated electron-rich bonds contained in specific functional groups, but relatively slow. Indirect oxidation reaction by means of OH? radicals proceeds at a faster rate with low selectivity. OH? radicals can be produced in the aqueous media from Ozone by pH modification, by combining Ozone with Hydrogen Peroxide or by the combination with UV radiation from a low pressure mercury lamp. It was developed a comprehensive mathematical model, which represents 2,4-D decomposition, using a kinetic scheme that considers all the parallel paths of attack of O3, in addition to the photolysis of O3 and its spontaneous decomposition in water. The effects of different operating variables were investigated and oxidation by-products were identified and quantified, in order to develop an operative reaction scheme.