A new treatment technology, called Advanced Reduction Process (ARP), was developed by combining UV irradiation with reducing reagents to produce highly reactive species that degrade contaminants rapidly. Vinyl chloride (VC) and 1,2-dichloroethane (1,2-DCA) pose threats to humans and the environment due to their high toxicity and carcinogenicity. In this study, batch experiments were conducted under anaerobic conditions to investigate the degradations of VC and 1,2-DCA with various ARP that combined UV with dithionite, sulfite, sulfide or ferrous iron. Complete degradation of both target compounds was achieved by all ARP and the reactions were found to follow pseudo-first-order decay kinetics. The effects of pH, sulfite dose, UV light intensity and initial contaminant concentration on the degradation kinetics were investigated in the photochemical degradation of VC and 1,2-DCA by the sulfite/UV ARP. The rate constants were generally promoted by raising the solution pH. The optimal pH conditions for VC and 1,2-DCA degradation were pH 9 and pH 11,respectively. Higher sulfite dose and light intensity were found to increase the rate constants linearly for both target contaminants. A near reciprocal relation between the rate constant and initial concentration of target compounds was observed in the degradation of 1,2-DCA. The rate constant was observed to be generally independent of VC concentration, but with a slight increase at lower concentrations. A degradation mechanism was proposed that described reactions between target contaminants and reactive species such as the sulfite radical and hydrated electron that were produced in the photolysis of sulfite solution. A mechanistic model that described major reactions in the ARP system was developed and explained the dependence of the rate constant on those experimental factors. Chloride ion and chloroethane were detected as the major degradation products at acid and neutral pH. An increase in pH promoted the extent of dechlorination with complete dechlorination being observed at pH 11 for both VC and 1,2-DCA. Due to the rapid degradation kinetics in these ARPs, this new treatment technology may be applied to remove various contaminants in water and wastewater.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/150992 |
| Date | 16 December 2013 |
| Creators | Liu, Xu |
| Contributors | Batchelor, Bill, Abdel-Wahab, Ahmed, Boulanger, Bryan, Ying, Qi, Huang, Yongheng |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Thesis, text |
| Format | application/pdf |
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