| Summary: | 碩士 === 國立中山大學 === 環境工程研究所 === 92 === In this study, potassium permanganate was used as the oxidant to remediate TCE–contaminated groundwater. The objectives of this bench-scale oxidation study include the following: (1) evaluate the overall TCE oxidation rate with the presence of KMnO4, (2) assess the consumption rate of KMnO4, (3) evaluate the effect of the oxidation by-product, manganese dioxide (MnO2), on the TCE oxidation rate. The control factors in this study include (1) four different molar ratios of KMnO4 to TCE [designated as P, (KMnO4/TCE) = 2, 5, 10, and 20]; (2) four different TCE concentration (0.5, 5, 20, and 100 ppm); (3) three different initial pH values (2.1, 6.3, and 12.5); (4) three different oscillator mix rate (0, 50, and 200 rpm); (5) four different molar ratios of dibasic sodium phosphate (Na2HPO4) to Mn2+ [designated as D, (Na2HPO4/Mn2+) = 0, 50, 100, and 300D], and (6) two different medium solutions [deionized (DI) water and groundwater]. Moreover, the effects of D values on TCE oxidation rate and KMnO4 consumption rate were also evaluated.
Experimental results indicate that a second-order reaction model could be applied to express the oxidation reaction of TCE by KMnO4, and the calculated rate constant equals 0.8 M-1s-1. Results also show that the higher the P value, the higher the TCE oxidation rate. Moreover, TCE oxidation rate was not affected under low pH conditions (pH = 2.10 and 6.3). However, TCE oxidation rate dropped under high pH condition (pH 12.5) due to the transformation of KMnO4 to manganese dioxide.
The following three pathways would cause the production of manganese dioxide: (1) direct oxidation of TCE by KMnO4, (2) production of Mn2+ after the oxidation of TCE by KMnO4, and Mn2+ was further oxidized by KMnO4 to form manganese dioxide, and (3) transformation of KMnO4 to manganese dioxide under high pH condition. Results also show that more manganese dioxide was produced while groundwater was used as the medium solution.
Results show that the produced manganese dioxide was 47.2% - 81.5% less with the addition of dibasic sodium phosphate. Moreover, the variations in D values would not affect the TCE oxidation rate. However, the increase in D value would decrease the consumption of KMnO4. Results also reveal that significant inhibition of manganese dioxide production was observed under low pH condition. Furthermore, no TCE oxidation byproducts were detected after the oxidation reaction.
Key words: KMnO4, TCE, manganese dioxide and dibasic sodium phosphate
|
|---|
