Effects of methanogen inhibition on the enhancement of reductive dechlorination of TCE

• Main Authors: Zong-Ting Lin, 林宗廷
• Other Authors: Chih-Ming Kao
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/yskzn6

碩士 === 國立中山大學 === 環境工程研究所 === 106 === Chlorinated organics have characteristics of high solubility, low vapor pressure, and high boiling point, and they belong to the dense non-aqueous phase liquids (DNAPLs). Trichloroethylene (TCE) is one of the chlorinated organics that has been proven to be harmful to humans and the environments. TCE is often found at the bottom of aquifers, which is difficult for remediation. Therefore, the use of biological remediation is a more feasible remediation method. Supplement of substrates can enhance the in situ activity of Dehalococcoides (Dhc), and adding Clostridium can improve the hydrogen production rates, and thus, the reductive dichlorination of TCE can be enhanced. There are many strains in the natural environment including methanogens, which can compete hydrogen with Dhc, and this would inhibit the TCE dechlorination efficiency. Although methanogens have a competitive relationship with Dhc, they cannot be completely inhibited. This is due to the effect that the presence of methanogens can provide the micronutrients required by Dhc. Therefore, the purpose of this study is to add Clostridium and methane inhibitors to create a suitable environment for the growth of Dhc. In this study, the degree of degradation of TCE and the accumulation of by-products were observed and real-time quantitative polymerase chain reaction (qPCR) was used to assess the change of bacterial species. Results show that more electron donor addition can increase the dechlorination efficiency and Dhc rowth. Adding 5% of Clostridium can increase the removal rate by 80% to 88%. In batch experiments with 0.5, 1, and 5% of Clostridium addition, approximately 2.3×101, 4.7×101, and 3.8×102 gene copies/mL of Dhc can be observed after 20 dys of incubation. The above results show that Clostridium addition can enhance Dhc activity. In the methane inhibitor group, 2-bromoethanesulfonate (BES) and 2-chloroethanesulfonate (CES) addition showed effective methane production inhibition, and there was a lower accumulation of dichloroethylene (DCE) and vinyl chloride (VC), and a large amount of ethylene was detected. Thus, reduction of methanogens can enhance the efficiency of complete reduction and dichlorination. Propynoic acid (PA) could acidify the environment and have toxic effects on Dhc. Molybdate (Mo) is a micronutrients of methanogen at low concentrations, and inhibits methanogen activity at high concentrations. According to the qPCR tests the Dhc of the BES and CES groups increased to 5 orders, the PA group increased to the 3 orders, and the Mo group increased to the 4 orders, indicating that the Dhc gene copies had an upward trend. The above results show that adding of Clostridium can increase the efficiency of TCE reductive dechlorination. Moreover, methanogen inhibitors can effectively inhibit methane production. Because methanogen can provide micronutrients, complete methanogen inhibition is not allowed. Therefore, adding enough Clostridium and methanogens inhibtition can achieve the goal of complete reduction dichlorination of TCE. The results of this study will be helpful in developing an effective green remediation technology for TCE dechlorination. Keywords: trichloroethylene, Clostridium, methanogen inhibitor, bioremediation, biostimulation