| 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.
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