Status : Verified
| Personal Name | Lim, Justine Kei T. |
|---|---|
| Resource Title | Evaluation of sustained persulfate oxidant release for remediating trichloroethylene contaminated low permeability silty soil in the phreatic zone |
| Date Issued | 31 July 2023 |
| Abstract | Desorption and back diffusion of a chlorinated solvent such as trichloroethylene (TCE) from the low permeability zone (LPZ) to the transmissive zone in the subsurface exhibits a challenge in remediation. The study was to investigate the in situ chemical oxidation (ISCO) using a sodium persulfate sustained-release rod (SPS SR-rod) for potential remediation application of TCE contamination in the LPZ within a two-dimensional sand tank. The objective was to determine the SPS concentration distribution contour when placing the SPS SR-rod atop and within the LPZ. A laboratory scale, 2D tank system (100 cm L x 5 cm W x 50 cm H) represents a distinct type of LPZ in the geologic settings, exhibiting a saturated dual permeability porous media. The SPS SR-rod placed within the LPZ released an average ~625 mg L-1 concentration contour from at least 10 to 15 cm lateral distance from the rod. When the rod placement was atop LPZ, continuous determination of persulfate concentrations at an average value of ~57 mg L-1 within the LPZ was observed comparably at low and high hydraulic gradients of 0.01 and 0.05, respectively. A separate evaluation of both SPS SR-rod placements in the 2D sand tank injected with pure TCE is conducted to test if the oxidant perfusion can address the difficulties in destroying soil-sorbed TCE. It took five days for sorption-desorption from the injection point to occur. On the 10th and 15th days, the concentrations of TCE exceed the groundwater limit of 0.05 mg L-1 set by Taiwan. Comparably lower concentrations are observed in the HPZ following back diffusion and concentration gradient principles where lower mass flux results in lower resultant aqueous concentration. In the presence of an SPS SR-rod, TCE concentration measures up to 0.6 mg L-1 versus 1.4 mg L-1 when no SPS rod is present. The persistence of persulfate in the LPZ and its slow release in the subsurface supports that the SPS SR-rod may be an efficiently controlled release material in extending the ISCO remediation of TCE in low-concentration scenarios in LPZ and its surrounding environment. This approach allows for efficient and effective remediation and limited loss of oxidant mass during delivery while minimizing the risk of adverse effects or excessive chemical usage. |
| Degree Course | Master of Science in Environmental Engineering |
| Language | English |
| Keyword | Contaminant rebound; Controlled release; Groundwater contamination; In Situ Chemical Oxidation (ISCO); Long term remediation; Trichloroethylene |
| Material Type | Thesis/Dissertation |
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