Kinetic study and modelling of the UV photo-degradation of thiabendazole

• A mid-pressure multi-wavelength lamp was used to degrade thiabendazole.
• A reaction mechanism was proposed, matching zero-, pseudo-first- and first-order kinetic.
• The radiant power absorbed by the solution was evaluated.
• The kinetic constants were obtained for aqueous solutions.
• All the kinetics were obtained for pH 3, 4 and 5 and temperatures from 8 to 45 °C.
• The dependence of the absorbed radiation on the thiabendazole concentration was evaluated.

A consequence of the massive use of pesticides in fruit harvesting is that many fruit juices contain pesticide traces that can be hazardous to the health of consumers. The wastewater generated in the fruit process after cleaning the fruit also contains pesticides in concentrations that cannot be dumped into the environment so these substances have to be previously eliminated. As thermal and the biological treatments do not degrade most pesticides used, an alternative treatment has to be applied to eliminate these toxic compounds both in fruit juices and wastewater. In the present work, a photochemical treatment with UV radiation was applied to eliminate thiabendazole from aqueous solutions at different pH and temperatures, using a medium-pressure mercury lamp that emitted in the range of wavelengths between 255 and 750 nm. The absorbed radiation was calculated as a function of the concentration of thiabendazole. A reaction mechanism was proposed, so combining it with the mathematical relation found between the absorbed radiation and thiabendazole concentration suggests a pseudo-first-order kinetic model that, for the range of concentrations studied, can be simplified to a zero-order kinetic model, both of which fit the experimental data obtained well.