Decomposition of aqueous chlorinated contaminants by UV irradiation with H_2O_2

摘要

In the present study, the decomposition rates of carbon tetrachloride (CCl_4) and 2,4-dichlorophenol (2,4-DCP) in water by the ultraviolet (UV) light irradiation alone and H_2O_2/UV were experimentally investigated. The detailed experimental studies have been conducted for examining treatment capacities of the two different ultraviolet light sources (low and medium pressure Hg arc) in H_2O_2/UV processes. The low or medium UV lamp alone resulted in a 60%-90% decomposition of 2,4-DCP while a slight addition of H_2O_2 resulted in a drastic enhancement of the 2,4-DCP decomposition rate. The decomposition rate of 2,4-DCP with the medium pressure UV lamp alone was about 3-6 times greater than the low pressure UV lamp alone. In the direct photolysis of aqueous CCl_4, the medium pressure UV lamp had advantage over the low pressure UV lamp because the molar extinction coefficient of CCl_4 at shorter wavelength (210-220 nm) is about 20 to 50 times higher than that at 254 nm. However, adding H_2O_2 to the medium pressure UV lamp system rendered a negative oxidation rate because H_2O_2 acted as a UV absorber being competitive with CCl_4 due to negligible reaction between CCl_4 and OH radicals. The results from the present study indicated significant influence of the photochemical properties of the target contaminants on the photochemical treatment characteristics for designing cost-effective UV-based degradation of toxic contaminants.