| dc.description.abstract | The objective of this study was aimed to investigate the elimination of trichloroethylene (TCE) in contaminated water by the zero-valent iron reactive barrier. The column experiments were carried out to simulate the operation of reactive barrier. Physical factors including iron surface per porosity volume (S/V) or arranged amounts of zero-valent iron, the thickness of barriers, inlet concentration of TCE and superficial velocity were studied to understand the performance of reactive barrier. Moreover, the reaction mechanism of reductive dechlorination and the feasibility of long-term operation were also investigated in this study.
Results indicated the removal of TCE could be simulated by the first-order equation. The reaction rate constant increased as S/V of iron were increased, and excellent linear relationship between them was obtained in this study. However, the value of S/V should be lower than 747 m2/L to maintain enough permeability(>10-2cm/sec) in the reactive barrier. Also, the increase extent of rate constant would decrease as higher S/V was arranged in the barriers. This fact suggested the removal of TCE would be limited by the rate of dechlorination. The relationship of rate constant and S/V could be modified to the model of K(S/V) / Ks + (S/V), where the K was the maximum rate constant and the Ks (S/V at 1/2 K)represented the affinity between the iron and TCE. Meanwhile, when the S/V was set to 121.3 m2/L, the reaction rate was similar even the inlet concentration of TCE was increased to be as high as 72.5 mg/L. Effect of superficial velocity was also minimal on the removal of TCE.
In addition, by the analysis of intermediate and chlorine ion, experimental results also suggested the reactive products would release to the bulk solution until the TCE was dechlorinated completely in the grains of iron. Furthermore, the rate constant of chlorinated ethene increased generally with the increase of chlorine numbers or reduction potential. However, for the dichloroethylene (DCE), the removal efficiency of cis-DCE was lower than that of tran-DCE greatly and this fact was suggested due to the characteristics of molecular structure and the direction of collision between the DCE and iron surface. Therefore, in order to enhance the removal of cis-DCE in contaminated water, increasing the thickness of barriers or the arranged amounts of iron was necessary. On the other hand, the removal efficiency of PCE was reduced by the competition inhibition when PCE and TCE coexisted in the contaminated water. Since the rate constant of PCE was still greater than that of TCE, the effect of competition inhibition could be ignored for the design of reaction barriers. The performance of column experiments was excellent and stable during 90 days of period. Thus, the reactive barrier exhibited great potential in the long-term operation. | en_US |