Application of gamma poly-glutamic acid to enhance the bioremediation efficiency of TCE-contaminated in groundwater

• Main Authors: Chiao-An Wang, 王喬安
• Other Authors: Chih-Ming Kao
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/q68u65

碩士 === 國立中山大學 === 環境工程研究所 === 106 === Trichloroethene(TCE) is a type of recalcitrant contaminant commonly found in groundwater. Provide carbon sources for a long period of time for TCE-bioremediation is necessary . Related research indicates that acidification problems often be accompanied with injecting substrate and that problems inhibits biological dechlorination mechanisms. The gamma poly-glutamic acid (γ-PGA) is a biopolymer synthesized by biochemical processes. In addition, its characteristics of moisture resistance, no toxicity, and chelating ability with metals. In this study, column experiments and field scale test were performed to evaluate the feasibility of using γ-PGA as a primary substrate to enhance the dechlorinating process of TCE degradation under anaerobic conditions. The predominant bacterial species and change of bacterial diversity during TCE bioremediation were using different molecular biology techniques to analyses, it were including denaturing-gradient gel electrophoresis (DGGE), next generation sequencing (NGS), and real-time PCR (qPCR). Among them, qPCR observed the change trend of Dehalococcoides(Dhc). Result of particle size showed that the γ-PGA could distribution well in soil particles. The results of column experiments showed that when γ-PGA were useded as a carbon source in the column, the acidity of the outflow water was not monitored during the reaction to maintain the neutral environment. Because γ-PGA contains an amine function group, and the amine group was dissolved after add system, and the formation of alkaline substance ammonia in water neutralizes the release of organic acid by the microorganism. The TCE concentration of the outflow of the column is reduced from 1.6 to 0.009 mg/L after 50 days of reaction, and the degradation efficiency is as high as 99%. The DGGE results show that γ-PGA could increase the abundance of bacteria in the environment. The data of qPCR for Dhc showed that the initial bacterial amount is about 4.6×103gene copies/g soil, and the amount of bacteria reaches 3.1×106gene copies/g soil on the 90th day. The results of field scale test showed that the initial concentration of TCE in the injection well was 0.127 mg/L. After the 75th day of the infusion, the TCE concentration was decreased to 0.008 mg/L (degradation efficiency was 93.7%). The TCE concentration of the downstream monitoring well (1 m from the injection well) were decreased from 0.149 mg/L to 0.035 mg/L within 5 weeks (degradation rate was about 63.6%). It was also found that the pH of the groundwater did not acidify. According to the identification results of NGS strains, the site contains strains that can completely reduce dechlorination, strains that can dechlorinate iii chlorinated aliphatic hydrocarbons, synthetic coenzymefactor B12 to create strains suitable for the growth environment of dechlorination bacteria, and produce hydrogen that coluld accelerate the reduce dechlorination of dechlorination bacteria effectively degrade TCE to ethylene.qPCR results show that the amount of the initial Dhc in the injection well was 1.0×103gene copies/L, and the amount of bacteria increased to 5.63×107gene copies/L on the 75th day. The results show that γ-PGA has a pH buffering effect, provides a carbon source that promotes the growth of dechlorination bacteria. The γ-PGA also can maintains an anaerobic reduction environment and bacterial abundance. The result of field scale test data showed that γ-PGA can effectively promote the biodegradation of TCE in situ, making the matrix system of γ-PGA a more economical and environmentally friendly green remediation method.