Oxygen effect in photocatalytic reactions: application to degradation of dichloroacetic acid

C.S. ZALAZAR; C.A. MARTÍN; A.E. CASSANO

USA

Conferencia; The Ninth International Conference on TiO2 Photocatalysis: Fundamentals and Applications (TiO2-9)” and “The Tenth International Conference on Advanced Oxidation Technologies for Water and Air Remediation (AOTs-10)”; 2004

The effect of oxygen concentration on the photocatalytic oxidation of low concentration, aqueous solutions of dichloroacetic acid (DCA) - a typical by product of chlorine disinfection - was studied employing titanium dioxide and UV radiation. The study aims at the development of an intrinsic and complete reaction kinetics (apt for scaling-up purposes) that will consider also the oxygen demand as one of the design variables, particularly important for liquids having a very high COD. Using the mass action law and the micro steady state approximation, a kinetic model was developed starting from a complete reaction sequence based on the direct hole attack of DCA and the participation of oxygen as the main electron acceptor. The obtained representation gives reaction rates for the DCA and oxygen disappearance as well as chloride ion formation. The model includes the local rate of photon absorption numerically obtained employing the Discrete Ordinate Method. The employed reactor (a cylinder with a volume of 110 cm3) irradiated from both sides with tubular lamps and parabolic reflectors was part of a recycling system. Experiments were conducted at different experimental conditions (DCA, catalyst and oxygen concentrations as well as Incident Radiation were independent variables). The mass balance for DCA degradation, chloride ion formation and oxygen consumption was closed with very small error. Finally, using the kinetic model, the mass balance for the recycling system and the experimental data, upon application of the Levenberg-Marquardt optimization algorithm, the kinetic constants were obtained and then experimental data were compared with theoretical predictions from the reactor-reaction kinetic model obtaining very good agreement.