Photodegradation performance of 1,1,1-trichloroethane in aqueous solution: In the presence and absence of persulfate

Photodegradation of 1,1,1-trichloroethane (TCA), a chlorinated solvent, with VUV and VUV/S2O82- processes was investigated. The effects of various parameters including solution pH, Cl− and HCO3- anions, and humic acid (HA) were evaluated. The results indicated that TCA can be effectively removed under VUV irradiation, and the addition of S2O82-, significantly enhanced TCA removal. TCA decomposition in both processes follows the pseudo-first-order kinetic model. In the pH adjusted solutions (from pH 3 to 11), maximum TCA degradation rate occurred at pH 3 and remarkable inhibition at pH 11 in the two processes. Both Cl− and HCO3- anions, as well as HA, adversely affected TCA degradation performance. Moreover, TCA degradation in the VUV/S2O82- process was more sensitive to all the influence factors than in the VUV process. The organic chlorine in TCA was released completely to chloride ion as a final product in both processes. Several reaction intermediates, including 1,1-dichloroethylene, 1,1,1,2-tetrachloroethane, perchloroethylene, carbon tetrachloride, chloroform, and dichloromethane were identified during TCA degradation in the presence of S2O82-. In summary, it can be concluded that the presence of persulfate was much more effective than the VUV alone, but the latter was more environmentally friendly due to the formation of nontoxic intermediates.

• 1,1,1-Trichloroethane is frequently detected in contaminated groundwater with recalcitrant characteristics.
• VUV/S2O82-, a novel photochemical technology, is developed and compared with VUV process for 1,1,1-TCA degradation.
• VUV/S2O82- process is more effective in TCA decomposition, but more sensitive to the solution matrix than VUV process.
• Several intermediates are detected in VUV/S2O82- process, while none in VUV process.