| Summary: | 碩士 === 國立中興大學 === 環境工程學系所 === 105 === Pentachlorophenol(PCP) is a persistent organic pollutant that is very difficult to be degraded. If PCP leaks into the soil and groundwater, it will accumulate by the food chain and cause a potential risk to human being. The main source of pollution is extensively used as herbicide, agricultural pesticide, and as common wood-preservation in industries. In China, PCP is used for epidemic prevention of pesticides. However, in Taiwan, the most famous case is China Petrochemical Development Corporation An-shun Plant at Tainan. These source of pollutions mainly leakage into the soil through the factory manufacturing, improper storage and transport process, and they result the long-term pollution.
Electrokinetic remediation technology is a kind of in-situ remediation process. It has the most effective treatment for low permeability soil. Sodium persulfate (SPS) is a common reagent on in-situ chemical oxidation. It has the advantage of high solubility, and it will not cause the secondary pollution after the reaction, Nevertheless, its reaction rate is so slow that it needs to be activated by using electricity, heat, transition metal, alkali or other method to generate sulfate radicals. The permeable reactive barriers (PRB) contains the reactive media in the ground to intercept contaminants. The PRB use the zero-valent iron to redox pollutant to form stable products or less hazardous substances in situ, for the purpose of achieving the remediation pollution of groundwater. Therefore, this study applies electrokinetic method that use electromigration of persulfate and PCP into PRB , and the persulfate is activated in the PRB to degrade PCP.
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The study progam would be divided into four parts. The first part used magnesium chloride(MgCl2) and acetic acid(HAc) as the electrolyte, in order to investigate the advantages and disadvantages, and simultaneously to understand the distribution of PCP in soil column, to determinate the PRB location. The second part and the third part used only SPS and PRB respectively, in order to investigate the independent removal rate. The fourth part is to investigate the degradation rates with different concentrations of persulfate coupled with PRB.
The results of the first group (Test 1 and Test 2) show that the removal rates were 23.58% and 24.46%, and the region where PCP accumulated at 7/10 distance normalized from anode, so the PRB was installed at the position of 6/10 ~ 8/10 distance normalized from anode. Test 3 contains 500 ppm SPS in the anode, the degradation rate was 51.04%. Test 4 is the case of only installed PRB without SPS, the removal rate was 52.8%, and agglomeration of zero-valent iron was observed in PRB. Test5 to Test7 is compared with different concentrations of SPS coupled with PRB , the overall degradation rate range was 55% to 65%.
In general, Test 7 had the best degradation efficiency, using acetic acid as the electrolyte, and 1000 ppm SPS into the anode coupled with PRB. This study proves that the electrokinetic/PRB approach with SPS is effective for the remediation of PCP contaminated soil.
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