Degradation of trichloroethylene in wastewater by heat and uv activated persulfate oxidation

Abstract

Trichloroethylene (TCE) has been used as a component of industrial cleaning solution and as a universal degreasing agent. TCE is of concern due to its widdspread use and highly adverse effects, especially a potential human carcinogen. TCE degradation by chemical oxidation processes can be by hydrogen peroxide, Fenton's reagent, potassium permanganate, or ozone. However, these processes have some limitations when applied to contaminated sites such as unstability and requirement for specific conditions. The main objective of this study was to compare the performance of heat and UV activated persulfate oxidations. This research tried to enhance the efficiency of the heat and UV activate persulfate oxidation methods by determining the optimal oxidant/TCE molar ratio to degrade the contaminant in different ranges of TCE concentration. The optimum temperature of heat persulfate oxidation obtained from Liang et al. (2003)'s study was 40C. In UV persulfate oxidation system, average UV intensity was 10.96 u Einstein/s as was measured by ferrioxalate actinometer. The TCE degradation by heat and UV activated persulfate oxidations was found to follow a pseudo-first-order reaction. The most effective condition in this study was heat activated persulfate oxidation at 40C using persulfate/TCE molar ratio of 15:1 with 99.9% of TCE removal and 1.40 hr-1 of rate constant within 5 hrs (initial TCE concentration of 10 ppm). For the UV activated persulfate oxidation, the optimal concdition was persulfate/TCE molar ratio of 10:1 at UV intensity of 10.96 u Einstein/s with 99.8% of TCE removal and 1.35 hr-1 of rate constant within 5 hrs (initial TCE concentration of 10 ppm). In the degradation of 50 ppm and 100 ppm TCE, heat persulfate oxidation was able to degrade tCE effectively. Fr UVpersulfate oxidation, the efficiency was obviously decreased when increasing TCE concentration. The factors that limited the perfoemance of heat and UV activated persulfate oxidation might be persulfate concentration, and UV intensity or lamp power, respectively. For energy consumption aspect, the UV persulfate oxidation system was more effective because it required much less energy (180 kj for 20 W system and 9,000 kj for 1kW system) comparing with the heat activated persulfate oxidation system (62,760 kJ) for 1 m3 of wastewater.