| 英文摘要 |
Soil and groundwater at many existing and former industrial areas and disposal sites is contaminated by halogenated organic compounds that were released into the environment. Halogenated organic compounds are heavier than water. When they are released into the subsurface, they tend to adsorb onto the soils and cause the appearance of DNAPL (dense-non-aqueous phase liquid) pool. Thus, a combination of several different treatment technologies is required to remediate DNAPL contaminated soil and groundwater. Among those halogenated organic compounds, trichloroethylene is more difficult to treat compared to other organics. Thus, TCE is used as the target compound in this study, .
The objective of this study is to assess the potential of combining three different treatment processes to clean up DNAPL contaminated sites. In this study, a concept of “treatment train” has been proposed. The first remedial phase applies surfactant flushing to remove the major amount of DNAPL in the groundwater. Thus, more than 50 to 60% of the TCE can be reduced in groundwater. After the flushing with the surfactant, the groundwater permeability would decrease due to the clogging. This would be minimized after the subsequent oxidation process. The second phase is the chemical oxidation process applying potassium permanganate (KMnO4) technique. Approximately 20 to 30% of the remaining TCE could be reduced after the oxidation process. The residual 10 to 20% of the TCE would be remediated by the third process, which is biological permeable reactive wall.
In the first surfactant flushing stage, three different surfactants were evaluated including Tween80, Triton X-100, and Simple Green (SG). Results from the bench-scale study indicate that Tween80 and Triton X-100 had higher TCE removal efficiencies. However, SG is selected for the following column study based on the effects that SG is more biodegradable and cost effective. Results from the oxidation experiments show that higher TCE oxidation efficiency was achieved when 0.1 wt% of SG was mixed in potassium permanganate solution. This is due to the effects that SG is able to enhance the transport of potassium permanganate, and thus, enhance the oxidation efficiency. TCE oxidation can be further confirmed by the analyses of chloride concentrations and rates of potassium permanganate consumption Results of this study will aid in designing a system for field application. The proposed treatment scheme would be expected to provide a more efficient and cost-effective alternative to remediate TCE contaminated sites. The following operational steps are recommended for the future application on TCE contaminated sites: flushing with site groundwater, followed by SG (0.1 wt%) flushing, and oxidation by potassium permanganate containing with 0.1 wt% SG.
Results from the column experiment indicate that approximately 90% of TCE could be removed after the groundwater and surfactant flushing. The potassium permanganate (KMnO4) oxidation is able to remove 7.2% of the remaining TCE. The residual TCE could be further remediated via the biological permeable reactive wall process. Thus, more than 97% of initial TCE could be removed using the three-stage treatment scheme. Results of this study will aid in designing a system for field application. The proposed treatment scheme would be expected to provide a more efficient and cost-effective alternative to remediate TCE contaminated sites. This developed remedial scheme can also be applied for other DNAPL contaminated sites. Because the developed integrated remediation system is able to remediate the TCE contaminated soil and groundwater effectively, this system would be accepted as a sound technology in the remediation market. Moreover, this system would not cause any adverse impact on the subsurface environment, and thus, it would be a more environmentally friendly technology compared to other technologies currently in use.
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