Kinetics of degradation of dichloroacetic acid in aqueous solution by UV/ Hydrogen Peroxide

CRISTINA S. ZALAZAR; MARISOL D. LABAS; RODOLFO J. BRANDI; ALBERTO E. CASSANO

Campinas, Brasil

Congreso; III EPOA Encontro Sobre Aplicações Ambientais de Processos Oxidativos Avançados; 2005

Dichloroacetic acid (DCA) can be found anywhere in nature today, because it is a metabolite of different chlorinated substances such as trichloroacetic acid, perchloroethylen and others. In addition to this, DCA is a disinfection by product (DBPa) that have been classified as possible carcinogenic compound by the US Environmental Protection Agency (USEPA). Conventional methods such as air stripping or adsorption by activated carbon are not good alternatives for DCAdue to its high solubility in water and low vapour pressure. Thus, the combination of H2O2/UV is a suitable process to remove DCA. The intrinsic reaction kinetics of the photochemical degradation of DCA in aqueous solution in presence of hydrogen peroxide was studied. The optimum concentration of hydrogen peroxide wasestablished using laboratory studies for the pollutant in question. Also the effect of the pH was studied. Using the mass action law and the micro steady state approximation a kinetic model was developed starting from a complete reaction sequence. The kinetic model incorporates the radiation intensity effect, which was calculated by solving the radiation balance in the experimental reactor. The experimental setup employed was a cylinder with two flat windows of quartz irradiated with germicidal lamps (l = 253.7 nm). The reactor was part of a recycle that includes a heat exchanger, a pump and a well stirred tank with provisions for sampling. Experiments were conducted under different operating conditions. The mass balance for the laboratory y reactor was then combined with the obtained kinetic model recdering a complete description of the reactor performance. The kinetics parameters of the DCA degradation were obtained by comparing predicted concentrations with the experimental values employing a multiparameter non linear regression analysis.