Photodegradation of Chlorinated Organic Pollutants in Wastewater in the Absence of Dissolved Oxygen

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Photodegradation of organic pollutants of chlorinated aliphatic and aromatic hydrocarbons in water by irradiation of ultraviolet aiming a wastewater treatment was studied. The point of this study is to propose a novel technique of photodegradation of the compounds under free of dissolved oxygen (DO). The results obtained by this study are as follows.(1) The irradiation of ultraviolet (wavelength of 185nm + 254nm) without DO remarkably accelerated the degradation rates of aliphatic compounds having only single bond in their structures, such as carbon tetrachloride, chloroform, 1,2-dichloroethane, 1,1,1-trichloroethane, and 1,1,2-trichloroethane. Removing DO was not so effective for tetrachloroethylene, trichloroethylene and chlorobenzene having double bond in their structures.(2) The irradiation of ultraviolet (185nm + 254nm) to water saturated with oxygen caused the decrease of DO. On the other hand ultraviolet of 254nm did not cause such decrease of DO.(3) These results strongly lead us to a following conclusion for photodegradation under free of DO. The energy of ultraviolet of 185nm is strong enough to break the bond of hydrocarbons directly. In the presence of DO, however, the energy is consumed by DO to be converted into other species.This study shows us a high potential of this novel technique for wastewater treatment.