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.