The photodegradation and modeling of a typical NAPL trichloroethene, by monochromatic UV irradiations.

In this study, the photodegradation of a typical nonaqueous phase liquid (NAPL)-trichloroethene (TCE) by ultraviolet irradiation was investigated. The decay of NAPL-TCE was studied in a RPR-200 Rayonet photochemical reactor, at three different monochromatic UV lamps (254, 300, and 350 nm). Among the three UV wavelengths used, the highest photodecay rate was obtained at 254 nm. The effect of the initial NAPL dosage was also analyzed to determine the photodecay of NAPL-TCE in batch experiments by ultraviolet irradiation at preselected wavelengths. The direct photolysis of NAPL-TCE followed two-stage pseudo first-order decay kinetics. The photodegradation rates of TCE were found to decrease with the increment of NAPL dosage. It is interesting to find that the NAPL dosage is critical to determine the process performance due to the NAPL size or cage effect, which will control the diffusion of TCE/intermediates between NAPL and aqueous phases and therefore the overall reaction rates. Mathematical models were developed for the prediction of the two-stage photodegradation, in which the remaining fraction of TCE (C/C0) in the system becomes predictable.