Kinetics of tetrachloroethylene (PCE) gas degradation and by products formation during UV/H₂O₂ treatment in UV-bubble column reactor

The UV/H₂O₂ process is commonly used for the remediation of drinking and groundwater pollution with chlorinated volatile organic compounds. In direct treatment, its efficiency can be lowered in the presence of radical scavengers and/or UV light absorbers. This research is focused on the improvement of the UV/H₂O₂ photolytic process, due to the reduction of OH radical scavengers and UV absorbers in the reacting system. Degradation of tetrachloroethylene (PCE) gas, which was absorbed into a bubble column reactor equipped with UV light (UV-BCR), containing distilled water and H₂O₂ as the reacting medium, was studied in a one flow-through mode. Degradation of PCE in the liquid phase was found to follow pseudo-first-order kinetics and apparent rate constants in the order of 0.02 s^-1 have been observed. An absorption-reaction model based on slow reaction in the bulk liquid was proposed, and it fitted the experimental data reasonably well. However, when sequence making internal (designed as to prolong the gas pathway through the reactor) was in the system in addition to the relatively high PCE concentrations (500 ppm), production of the byproduct chloroform was observed, indicating that some reaction might have occured in the gas phase. The addition of term for a reaction in the gas phase was able to account for the reaction due to direct absorption of PCE.