Photochemical degradation of vinyl chloride with an Advanced Reduction Process (ARP) - Effects of reagents and pH

摘要

A new treatment technology, called an Advanced Reduction Process (ARP), was developed by combining UV irradiation with reducing reagents to produce highly reactive reducing free radicals that degrade contaminants. Batch experiments were performed under anaerobic conditions to investigate the degradation of vinyl chloride (VC) by this ARP. All degradation reactions were found to follow a pseudo-first-order decay model and the rate constants (k_(obs)) were characterized for all experimental conditions. The influence of pH on k_(obs) was studied in experiments with direct photolysis as well as experiments with ARPs using reagents activated by ultraviolet (UV) light. Values for k_(obs) in direct photolysis were found to be 0.012, 0.011, and 0.018 min~(-1) at pH 3, 7 and 10, respectively. Values of most of the k_(obs) in experiments with ARP increased at all pH values compared with corresponding values obtained for direct photolysis. The increase in k_(obs) was due to the production of reactive species produced by photochemical reaction of the reducing reagents with UV light. The pH effect on k_(obs) observed with the ARP can be explained in terms of changes in the absorption spectra of the reagents at various pH. The rate of light absorption determines the rate of formation of the reactive species which determines the rate of contaminant degradation. Chloride ion and chloroethane were detected as the products of VC degradation. The increase in pH value was shown to promote the transformation of VC to chloride.