UV-bubble column reactor (UV-BCR) for photolytic removal of tetrachloroethylene (PCE) from the vapor phase: Methodological approach

Chlorinated volatile organic compounds (CVOCs) such as tri- and tetrachloroethylene (TCE and PCE) are common contaminants of ground water and soil. Numerous studies have been carried out with the long-term objective of the development of efficient, destructive on-site technologies for their removal. The so-called advanced oxidation processes (AOPs) were applied in the liquid and in the gas, but were shown to have limited application. In the liquid phase the efficiency was limited due to the presence of OH radical scavengers and UV light absorbers; and in the gas phase due to the production of stable intermediates. A new photochemical reactor system is described, in which the polluted air (from the air stripper or SVE unit) is absorbed into a bubble column reactor equipped with the UV light (UV-BCR) containing only distilled water and H2O2 as a reacting medium. The experiments showed that the oxidation of model pollutant PCE in a liquid phase occurred approximately 6 times faster in an OH radical scavenger-free environment compared to the experiments in which the OH radical scavenger concentration was adjusted to a level usually found in ground waters. It was also observed, that for the certain PCE concentration, there exists an optimal hydrogen peroxide concentration above and below which the rate is reduced and could be predicted by the kinetic model under operational conditions of this work. For the experiments in which PCE gas was absorbed into the UV-BCR, the influences of the two critical parameters, gas flow rate and the hydrogen peroxide concentration, were investigated using the experimental design methodology. There has been observational evidence of the efficiency of the process (cca 75%-80% PCE gas removal efficiency in one flow through the UV-BCR) but the operational parameters still need to be optimized.