【作者】 李烨；

【导师】 沈照理； 刘菲；

【作者基本信息】 中国地质大学（北京） ， 环境工程， 2006， 博士

【摘要】 四氯乙烯（PCE）是一种广泛用于干洗和脱脂的有机溶剂,是地下水中常见的污染物。关于PCE的处理引起了广泛关注,目前有物理、化学和生物三种处理方法。生物法最大的优点是可以实现无害化,无二次污染,处理成本低,是一种较经济的污染处理措施。PCE只能在厌氧条件下发生共代谢降解,本文主要对较弱的还原环境,包括硫酸盐还原、铁还原、反硝化、混和电子受体和天然地下水环境的PCE脱氯性能进行研究。 本实验采用的是室内培养微生物的方式,当系统中的微生物活性较高时,以醋酸为共代谢基质,进行驯化实验,为了消除地下水中硝酸根和硫酸根的干扰,同时以实验配水和天然地下水为基础培养液,加入相应的电子受体营造不同的还原环境。 当所营造的还原环境已经形成,而且微生物可以适应浓度为120.0μg/L的PCE之后,对PCE在不同厌氧条件下的降解情况进行研究。研究结果表明,铁还原环境比天然地下水环境的PCE脱氯效果要好,到实验的第13天,去除率分别为90.00%以上和84.71%。在这两个环境中,可以使PCE很快转化为三氯乙烯（TCE）,并可以进一步转化为二氯乙烯（DCEs）。根据实验结果进行拟合,PCE的降解和TCE的产生均符合准一级反应动力学方程。 在混和电子受体环境、硫酸盐还原环境和反硝化环境,PCE的去除率主要都以挥发为主,降解只占很小的比例,而且最终的降解产物只有TCE。根据实验第13天PCE的去除率来衡量其它各个环境的PCE降解性能,反硝化环境PCE的降解能力最差;混和电子受体环境次之;硫酸盐还原环境最好。相比较而言,硫酸盐初始浓度低的微环境比硫酸盐初始浓度高的微环境,PCE的降解效果好一些。 在以实验配水营造的铁还原环境PCE的降解性能最好,选择该环境作PCE的影响因素分析,结果表明,PCE在脱氯过程中受温度、pH值、电子受体的影响。温度为20℃时脱氯能力较强,半衰期为2.78天,温度为12℃时PCE仍可以脱氯,半衰期为6.45天;到实验结束时,初始pH值在6.00～8.00之间的微环境,PCE的去除率达到90.00%以上;pH值在5.00左右,铁还原作用较强烈,产生的Fe（Ⅱ）浓度为67.71mg/L,PCE的去除率为34.52%;而当pH值>9.00时,铁还原作用不明显,产生的Fe（Ⅱ）浓度为4.52mg/L,而且PCE的去除率不足20.00%。加入硝酸盐和硫酸盐后,会使PCE的脱氯受到抑制,而且抑制作用与加入的硝酸盐和硫酸盐浓度成正比。实验结束时,未加N_<sub>3^-的微环境中,PCE的反应速率常数是NO₃^-浓度为500.0mg/L的环境中的5.12倍;未加入SO₄^2-的微环境中,PCE去除率达到了100.0%,而在SO₄^2-初始浓度为100.0mg/L的微环境中,PCE的去除率仅为47.79%。更多还原

【Abstract】 Tatrachloroethylene（PCE）, which is a chlorinated aliphatic compound essentially used as a degreasing and dry-cleaning solvent, has become a major contaminant of soil and groundwater due to leakages from storage tanks and improper handling and disposal. The suspicion that this contaminant is a carcinogen led to an urgent necessity to efficiently remove this compound from contaminated sites. So far, physical, chemical and biological techniques are three PCE removal methods, and the most cost-efficient way to remove PCE is biological method, that is biodegradation. The bioremediation technique has a great potential to replace physical and chemical techniques, which are processes that do not destroy the harmful contaminant, but instead transfer it from one part of the environment to another.PCE does not appear to be biodegradable under aerobic conditions, but it can be reductively dechlorinated into trichloroethylene（TCE）, dichloroethylene（DCE） isomers, vinyl chloride（VC） and/or ethene under anaerobic conditions. Since PCE can be biodegraded only in anaerobic conditions, the research aims at dechlorination efficiency in different redox environments, including denitrifying, iron reducing, sulfate reducing, mixing electron acceptors and natural groundwater condition.Microorganisms were cultured in the lab;anaerobic sewage was inoculated to mixture of groundwater and soil, which was from a garden. When there was enough microorganism population, acclimation experiment was carried out with acetate acid as co metabolism substrate, and different electron acceptors were added to create corresponding reducing environment. When the reducing environments have been created, and microorganism can adapt target contaminant of 120.0μg/L, the degradation experiment was carried out. The best environment for PCE dechlorination was chose to carry out effect factors experiment.According to the results, iron reducing environment is the best condition for PCE dechlorination, followed with natural groundwater condition. The degradation products are TCE and DCEs. It is difficult for PCE dechlorination in denitrifying, sulfate reducing, and mixing electron acceptors conditions, and the degradation product is TCE.The results showed that PCE was dechlorinated to TCE and DCEs in the presence of-ferric iron. The degradation rate of PCE is 0.2489d^-1 and the half life was 2.78 days when the temperature is 20℃. Since the temperature in groundwater is about 12℃, theexperiment was carried out in 12°C. The half life is 6.45 days, and the degradation rates 0.1073d’1 when the temperature is 12"C, which was lower than that in 20°C. The optimal pH and temperature during this experiment was 7 and 20 °C respectively in this experiment. When pH>9.00, extra anaerobic mix-culture consortia were added in the bottle, PCE dechlorination rate was still very slow, which shows that the microorganism can not adapt the environment. PCE dechlorination rate in microcosm with pH=5.00±0.1 was faster slightly than that with pH>9.00.Since nitrate is a strong oxidant and can form a high ORP in the microcosm, nitrate effects on PCE dechlorination was evaluated. Different initial nitrate concentrations were added into the microcosms. When nitrate concentration was 5.00mg/L, degradation rate of PCE was 0.1899d’’, while nitrate concentration was 500.0mg/L, degradation rate of PCE was 0.0486d’1, which shows that the PCE dechlorination rates are decreased with increasing nitrate concentrations, which indicates that for PCE dechlorination bacteria the low ORP conditions are favorable. The removal efficiency of PCE is 100.0% in the environment without SO42", while the removal efficiency is 47.79% in the environment added SO42" with initial concentration of lOO.Omg/L.更多还原