Degradation of the Herbicida Atrazina saw Processes Advanced of Oxidation / DegradaÃÃo do Herbicida Atrazina via Processos AvanÃados de OxidaÃÃo

AUTOR(ES)

Josà TibÃrio GonÃalves de Miranda

DATA DE PUBLICAÇÃO

2004

RESUMO

Herbicide contamination of the aquatic environment is widespread, particularly that caused by the triazine group herbicide Atrazine, which is used for weed-control in sugar-cane crops in the State of Pernambuco in Brazil. Atrazine is a âpriority pollutantâ since it is carcinogenic and is highly resistant to biological breakdown, with a 12 months half-life in water. The Environmental Pollution Agency (EPA) suggests an atrazine limit concentration of 3 μg.L-1 in surface water. In this work, the Advanced Oxidation Processes Ozone/UV and Hydrogen Peroxide/UV, were used to degrade atrazine in aqueous solution. Atrazine direct photolysis at 253,70 nm and direct ozonization of atrazine were attained through the synergistic nature of the possible oxidation routes a molecule of this herbicide can follow in the Ozone/UV and Hydrogen Peroxide/UV processes. Kinetic aspects were studied for the atrazine degradation reaction and the efficiency of ozone transfer to pure water (direct ozonization process) and aqueous atrazine (direct ozonization and ozone-UV processes). An homogeneous reaction system was used, in which an absorber (a co-current downflow column with swirl-flow) was linked in series with an annular photo-reactor. Precise models were developed for the distribution of radiant energy and the concentration of atrazine and oxidants, based on the transport phenomena principles. The Linear Spherical Source Emission (LSSE) model was applied to provide the valour of the incident radiation at the wall of the photo-reactor quartz tube. Mechanistic models for the rate of atrazine degradation reaction were developed and used in all the processes studied except for atrazine direct photolysis at 253.70 nm, where a simple phenomenological model was used. The models allow good representation of the reaction evolution in the atrazine initial concentration range tested. The degradation reaction rate in the direct photolysis, ozone/UV and hydrogen peroxide/UV processes was found to be dependent on the total energy absorbed by the reacting mixture, on the atrazine and oxidant quantum yields and on the concentration of atrazine and oxidants; whereas the degradation reaction rate for the direct ozonization of atrazine was found to be dependent on the concentrations of atrazine, ozone and products. To obtain the kinetic parameters and the overall mass transfer gas-liquid coefficient, experimental data were fit with a multiparameter, non-linear regression algorithm, coupled with the Levenberg-Marquardt optimisation routine. The PAO Ozone- UV was more efficient than the PAO H2O2-UV to degrade the atrazine herbicide.

ASSUNTO(S)

atrazine ultraviolet radiation radiaÃÃo ultravioleta ozÃnio ozone modelagem c-current downflow bubble column with swirl flow fotorreator anular hydrogen peroxide annular photoreactor coluna de borbulhamento co-corrente de fluxo descendente atrazina perÃxido de hidrogÃnio engenharia quimica modelling

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