TiO2-Based Heterogeneous Photocatalytic Treatment Combined With Ozonation For Carbendazim Degradation

The degradation of pesticide Carbendazim was investigated by combination of TiO₂-based photocatalysis and ozonation. A batch annular photoreactor has been used for carrying out the combined process and the influence of TiO₂ concentration, ozone dose and pH were investigated. The results showed that the removal rate increased with increase in ozone dosage upto 0.48 g/h and decreased above 1g/L of TiO₂. At optimum pH=6, with 1g/L TiO₂ and with 0.48g/h ozone dose, 88% COD removal was achieved in 3 hours by the combined photocatalytic ozonation process, where as 54% and 67% COD removal was observed with each photocatalysis and ozonation process, respectively. BOD5/COD ratio was enhanced to 0.38 and TOC removal was 80% in 180 min of combined treatment. Carbendazim was quickly degraded by the combined photocatalytic ozonation process and followed pseudo-first order kinetics. The kinetic study showed that degradation rate constant of Carbendazim with TiO₂/UV/O3 to be 1.5 times higher than that & O3 with the same ozone dose and 2.2 times higher than that of TiO₂/UV. A mechanism involving the formation of an ozonide radical previous to the generation of hydroxyl radicals is suggested to explain the synergistic effect between ozone and TiO₂ under illumination. The laboratory study has also demonstrated that a combination of TiO₂-based photocatalysis and ozonation will overcome the disadvantage of the selectivity of ozonation and the lower efficiency of TiO₂ photocatalysis.

Keywords
Pesticide, Photocatalysis, Ozonation, Photocatalytic Ozonation, Synergistic effect, Carbendazim