Effects of Anions on Heat-assisted Persulfate Oxidation of Trichloroethylene (TCE) in Aqueous System

• Main Authors: Pek-Hoon Lim, 林佩雲
• Other Authors: Tsair-Fuh Lim
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/66627672668579966813

碩士 === 國立成功大學 === 環境工程學系碩博士班 === 93 === 　The kinetics on heat-assisted persufate oxidation of trichloroethene (TCE) in aqueous solutions at various oxidant concentrations (persulfate/TCE ratio = 20 and 60), ionic strength and ionic kinds was studied. The decomposition of persulfate was found to follow a first-order decay kinetic model in deionized water, and the rate constant was larger in unbuffered condition of at around 0.0030 hr-1 than that in buffered condition at 0.0011 hr-1. The difference may be attributed to that no acid-catalyzed reaction was present in the buffered condition as the pH remained always constant at 6.6, and higher ionic strength in the condition. A higher persulfate/TCE molar ratio in the oxidation experiments resulted higher efficiencies of TCE destruction by persulfate at 40 �aC. Three models were proposed to simulate the kinetic data of both persulfate and TCE. Model 3, which considered the effect of persulfate decomposition, methanol oxidation, and TCE degradation, was able to simulate all the experimental data to a reasonable degree. The determined rate constants (0.016 M-1s-1 and 0.023 M-1s-1 for TCE, and 0.034 hr-1 and 0.050 hr-1 for persulfate), were close in different experimental conditions, indicating that the model and the extracted parameters may be appropriate for extrapolating into other systems. The oxidation of TCE by persulfate was influenced at different degree by the presence of three anions, nitrate, chloride, and bromide. For nitrate, the influence is the smallest and may be attributed to the effect of increasing ionic strength. For both chloride and bromide, in addition to the ionic strength effect, it is speculated that the two anions were radical scavengers that caused additional reduction of reaction rates. A simplified model (model 2) was employed to simulate the kinetics of both persulfate and TCE concentration changes with the presence of the three anions in the systems. Excellent model fits to the experimental data was obtained in this study. Compared to the case without the presence of the three anions (k3 = 0.023 M-1s-1), the rate constants for TCE degradation were much smaller at 0.0044 M-1s-1, 0.0004 M-1s-1 and 0.0006 M-1s-1 for chloride cases at 0.01, 0.1, and 0.5 M, respectively, and were 0.0003 M-1s-1 and 0.009 M-1s-1, for bromide and nitrate cases at 0.5M, respectively. Although the rate constants are different under different experimental conditions, the determined rate constants may provide basis for estimating the reaction rate under the influence of different anions.