Degradation of pesticides chlorpyrifos, cypermethrin and chlorothalonil in aqueous solution by TiO_2 photocatalysis

摘要

Degradation of pesticides chlorpyrifos, cypermethrin and chlorothalonil in aqueous solution by TiO_2 photocatalysis under UVA (365 nm) irradiation was examined. Enhancement of degradation and improvement in biodegradability index (BOD5/COD ratio) by H_2O_2 addition were also evaluated. UVA irradiation per se produced insignificant degradation of the pesticides. In UV/TiO_2 photocatalysis (TiO_2 1.5 g L~(-1) pH 6 and 300 min irradiation), COD and TOC removal were 25.95 and 8.45%, respectively. In UV/ TiO_2/H_2O_2 photocatalysis (TiO_2 1.5 g L~(-1) H_2O_2 100 mg L~(-1), pH 6 and 300 min irradiation), COD and TOC removal were 53.62 and 21.54%, respectively and biodegradability index improved to 0.26. Ammonia-nitrogen (NH3-N) decreased from 22 to 7.8 mg L~(-1) and nitrate-nitrogen (NO_3~--N) increased from 0.7 to 13.8 mg L~(-1) in 300 min, indicating mineralization. Photocatalytic degradation followed pseudo-first order kinetics with rate constant (k) of 0.0025 and 0.0008 min~(-1) for COD and TOC removal, respectively. FTIR spectra indicated degradation of the organic bonds of the pesticides. UV/TiO_2/H_2O_2 photocatalysis is effective in degradation of pesticides chlorpyrifos, cypermethrin and chlorothalonil in aqueous solution. UV/TiO_2/H_2O_2 photocatalysis may be applied as pretreatment of a chlorpyrifos, cypermethrin and chlorothalonil pesticide wastewater at pH 6, for biological treatment.