“Degradation of Chloride Pollutants in Water using UV/H2O2. Reaction Mechanism and Kinetics”,

CRISTINA ZALAZAR, MARISOL LABAS, RODOLFO BRANDI, ALBERTO CASSANO

Bilbao (España)

Congreso; Chemical Reaction Entineering XI Green Chemical Reactor Engineering; 2007

Pollution control is subject of increasingly growing importance. New technologies are being studied in substitution of established ones that normally do not produce the complete destruction of the existing toxic compounds. Dichloroacetic acid (DCA) is a pollutant that can be found in water as a byproduct of chlorine disinfection (DBPs). DCA can also be detected in waste waters resulting from the degradation of others chlorinated compounds. Activated carbon adsorption and air stripping technologies are not good options for DCA due to its very high solubility in water and very low vapour pressure. Thus the combination UV/H2O2 should be a suitable process for treating this type of pollutants. This work was planned with two specific purposes: (i) to know the best operating conditions for the complete degradation of DCA using UVC radiation (253.7 nm). In particular, the optimal ratio of hydrogen peroxide to DCA concentrations and (ii) to derive, from a plausible reaction sequence, a mathematical and complete model able to represent the kinetics of DCA oxidation  and validate its quality with experiments. The kinetic model must be independent of the shape, size and configuration of the laboratory reactor in order to be apt for scaling up purposes. The employed experimental device was a cylinder, with two parallel, flat windows made of quartz. Each window was irradiated with a tubular, germicidal lamp. Experiments were made under different operating conditions of the involved variables. On the basis of the proposed reaction sequence, the developed expression for the reaction kinetics incorporates the radiation intensity effect, which was calculated by solving the radiation balance in the experimental reactor. The mass balance for the laboratory reactor was then combined with the obtained kinetic model rendering a complete description of the reactor performance. Experimental date agree well with theoretical predictions employing just two kinetic lumped constants.