Degradation Of Tetrachloroethylene Research Articles

Cometabolic biodegradation of chlorinated ethenes with methanotrophs in anaerobic/aerobic simulated aquifer

Aim: This study explores anaerobic/aerobic biodegradation efficiencies of aerobic cometabolism with methanotrophs when contaminants trichloroethylene (TCE) and cis-1,2-dichloroethylene (cDCE) are present individually or in tandem. Methodology: Batch tests and an anaerobic/aerobic column system were used to simulate saturated, contaminated aquifers. A brown glass bottle with an effective volume of 44 m l-1 was prepared for the batch test. An integrated one-dimensional sequential anaerobic/aerobic column system was used to simulate the accumulative intermediates such as TCE, cDCE and VC caused by incomplete degradation of PCE during the upgradient anaerobic stage in the saturated aquifer. In the downgradient aquifer, aerobic cometabolism was employed to degrade the intermediates. Methanotrophs in the aerobic aquifer were inoculated to degrade the by-products of incomplete degradation of PCE by aerobic cometabolism. Results: In the batch test, biodegradation of TCE was significantly inhibited by cDCE. However, biodegradation of cDCE was not significantly inhibited by TCE. In the simulated aquifer test, aerobic cometabolism completely degraded intermediates (TCE, cDCE, and VC) produced by incomplete anaerobic degradation of tetrachloroethylene (PCE). The results showed that methane, a by-product of anaerobic reductive dechorination of PCE, was used as a primary substrate for aerobic degradation, at a utilization rate of almost 100%. Interpretation: Biodegradation of TCE was significantly inhibited by cDCE. Bioremediation should have sufficient oxygen and methane at aerobic stage to ensure that chlorinated ethenes fully mineralize.

Degradation of tetrachloroethylene by zero valent iron nanoparticles in the presence of a natural groundwater bacterial biofilm in a sandy porous media

Biofilms are naturally present in aquifers and can interact with zero valent iron nanoparticles (nZVI) used as remediation agents in contaminated groundwater; thereby they may alter nZVI reactivity towards targeted contaminants in porous media. Laboratory scale experiments using columns filled with sand (50 cm long and 5.2 cm in diameter) were performed to investigate the impact of natural biofilms on nZVI reactivity towards tetrachloroethylene (PCE) in conditions simulating an unconsolidated sandy aquifer. Solutions containing PCE were injected through the sand columns in the presence or absence of biofilm and nZVI. Concentrations in PCE and its metabolites were monitored during 45 days in dissolved and gas phases. PCE concentrations decreased at the column outlets due both to its reductive dechlorination by nZVI (~30% of injected PCE) and its sorption or deposition (as PCE-DNAPL) on sand (~35% of injected PCE). No significant differences in PCE concentrations were found in presence or absence of biofilm. However, biofilm presence affected the nature of PCE metabolites. A higher release of ethene in the column containing biofilm was observed, whereas ethane was dominant in the absence of biofilm. Microbes consumed H2 released by the corrosion of nZVI limiting the hydrogenation of ethene to ethane. The consequences of biofilm development in porous media should be taken into account when considering treatment with nZVI, as it may affect the nature of produced metabolites.

Survival, metabolic rates and locomotory activities of a groundwater-obligate copepod species under long-term exposures to tetrachloroethylene

Volatile organic compounds (VOCs) are known to potentially cause a severe change in the respiratory metabolism of freshwater species, however the effect of these contaminants on groundwater-obligate species has not been investigated to date. Tetrachloroethylene (TCE) is a VOC frequently found in the groundwater bodies of industrialized areas, even years after a contamination event because TCE degradation takes several decades to occur. Contamination from TCE is considered persistent and difficult to remediate. Its high density favors a gravity-driven vertical infiltration into groundwater bodies. The TCE threshold value is 1.1 μg/L in groundwater bodies of Italy. TCE concentration in many Italian groundwater bodies is widely over this legal limit. In this study, we investigated the effect of 1.1 μg/L TCE on the survival, oxygen consumption, and locomotory activities of a groundwater-obligate copepod species. The specimens required for the trials were collected in the Antro del Corchia Cave (Tuscany). We measured the individual-based oxygen consumption of this species as a proxy of possible metabolic reactions to long-term (5 days) exposures to TCE at 8.0°C that is the mean annual temperature of groundwater flowing in the cave. To this end, we used a sealed glass microplate equipped with 24-planar oxygen sensor spots with optical isolation glued onto the bottom of 80-μL wells (Loligo Systems, Denmark) integrated with a 24-channel fluorescence-based respirometry system (SDR Sensor Dish Reader, PreSens, Germany). The system allows simultaneous measurement of 20 replicates and 4 controls. Survival and locomotory activity assessments were performed by counting the number of alive individuals and measuring the number of moving animals in 5 mL glass vials each containing 20 individuals. Preliminary results showed a decreasing in oxygen consumption of the organisms exposed to 1.1 μg/L TCE for 5 days at 8°C respect to the control. However, neither survival nor locomotory activities appeared to have been affected by exposure to TCE. See Suppl. material 1.

To postpone the precipitation of manganese oxides in the degradation of tetrachloroethylene by controlling the permanganate concentration

ABSTRACTControlled-release permanganate (CRP) is a relatively new technology used to treat contaminated groundwater. This study tested the encapsulation of permanganate using stearic acid to realize controlled-release properties. Batch experiments were conducted to investigate the performance of manganese oxides (MnO2) in the reaction between CRP and the contaminant of interest: tetrachloroethylene (PCE). The results showed that higher ionic strengths (I = 0.1 mol/L) cause earlier precipitation of MnO2 colloids. Using CRP to degrade PCE could decrease the amount of MnO2 colloids produced and postpone precipitation compared to raw potassium permanganate (KMnO4) under high ionic strength conditions by controlling the KMnO4 concentration in the solution. The amount of MnO2 colloids produced and the time of precipitation depended more on the CRP grain size than on the CRP mass ratio. Controlling the KMnO4 concentration used in the reaction could control the formation of MnO2 precipitates in the premise of guarantee the removal rate of PCE.

活性汚泥由来微生物の生成物によるテトラクロロエチレンの分解

高濃度のテトラクロロエチレン（PCE）に長期間馴養した活性汚泥は，PCEを好気的条件で減少させることが分かった．さらに，菌体除去後の濾液でもPCEを0.61 ㎎減少させた．よって，PCEの減少が活性汚泥中のフロックや微生物への吸着ではないこと，活性汚泥中の微生物の生成物質がPCE 減少に関与していることが示された．この濾液を熱処理や活性炭処理するとPCE 減少が認められなかった．また，このPCE 減少に関与する物質はタンパク質様物質であった．分画分子量3,000の限外濾過液においてもPCE が減少したことから，分子量3,000以下の低分子のペプチド様物質であると考えられた．PCEの分解産物は各種GC（FID，MS，TCD 等）やイオンクロマトなどでは検出できなかったが，シンクロトロン光によるＸ線吸収微細構造解析の結果，C-Cl 結合が切断され，塩素原子が共有結合ではなく，イオン状態での存在が確認され，新たなPCE 分解機構の存在が示唆された．

Effect of Spherosome on Degradation of Tetrachloroethylene in Soil

The fate of spherosome on the degradation of tetrachloroethylene in soil was investigated for 38 days. The time needed to become the half value of the initial concentration is 8 days for the case with spherosome and 15 days for the case without spherosome. The time needed for complete degradation is 25 days for the case with spherosome and 38 days for the case without spherosome. The degradation of tetrachloroethylene appeared to be essentially due to the biological activity of the soil. Spherosome should enhance the rate of tetrachloroethylene destruction.

Ultrastructure of a bio-electrolytic methanogenic/methanotrophic granular biofilm for the complete degradation of tetrachloroethylene in contaminated groundwater

The electrolytical methanogenic/methanotrophic coupling (eMaMoC) process was tested in a laboratory-scale single-stage reactor for the treatment of tetrachloroethene (PCE)-contaminated waters. A water electrolysis cell was placed directly in the effluent recirculation loop for the supply of both O2 and H2 to the system: H2 serving as the electron donor for both carbonate reduction into CH4 and reductive dechlorination. The concurrent presence of O2 and CH4 could be used by the methanotrophs for co-metabolically oxidising the chlorinated intermediates left over by the anaerobic transformation of PCE. At a PCE inlet of 33-52 microM and a hydraulic residence time (HRT) of 5.6 days, PCE reductive dechlorination to dichloroethene (DCE) was over 95% with a maximum DCE mineralisation of 83%. Fluorescence in situ hybridisation with 16S rRNA probes related to type I and type II methanotrophic bacteria were utilised to localise the methanotrophic communities in the anaerobic/aerobic granules. It evidenced that with operational time, along with increasing oxygenation rate, methanotrophic communities were specifically colonising onto the outermost layer of the anaerobic/aerobic granule.

Photocatalytic Degradation of Tetrachloroethylene in Gas Phase on TiO2 Films: A Kinetic Study

Fil: Imoberdorf, Gustavo Eduardo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Desarrollo Tecnologico para la Industria Quimica. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnologico para la Industria Quimica; Argentina

Resonance-enhanced multiphoton ionization for real-time monitoring of trichloroethylene formed by degradation of tetrachloroethylene using zero-valent zinc

Resonance-enhanced multiphoton ionization (REMPI) is investigated as a potential technique for real-time monitoring of selected volatile organochloride compounds (VOCs). In a proof-of-concept experiment, the progress of the reductive-degradation of tetrachloroethylene (PCE) to trichloroethylene (TCE) by zero-valent zinc was monitored by REMPI measurements performed in the headspace above the PCE solution. Two-photon resonant REMPI spectra of TCE and PCE were recorded over the wavelength range 305-320 nm. The concentrations of PCE and TCE in the headspace were monitored by measurement of the ionization signal with 315.64- and 310.48-nm excitation for PCE and TCE, respectively. Calibration curves yielded a linear range of more than 2 orders of magnitude for both compounds. The REMPI headspace results agreed well with the solution-phase results from gas chromatography analysis, which was used for independent verification of the progress of the reaction.

Kinetics of tetrachloroethylene (PCE) gas degradation and byproducts formation during UV/H 2O 2 treatment in UV-bubble column reactor

The UV/H 2O 2 process is commonly used for the remediation of drinking and groundwater pollution with chlorinated volatile organic compounds. In direct treatment, its efficiency can be lowered in the presence of radical scavengers and/or UV light absorbers. This research is focused on the improvement of the UV/H 2O 2 photolytic process, due to the reduction of OH radical scavengers and UV absorbers in the reacting system. Degradation of tetrachloroethylene (PCE) gas, which was absorbed into a bubble column reactor equipped with UV light (UV-BCR), containing distilled water and H 2O 2 as the reacting medium, was studied in a one flow-through mode. Degradation of PCE in the liquid phase was found to follow pseudo-first-order kinetics and apparent rate constants in the order of 0.02 s −1 have been observed. An absorption-reaction model based on slow reaction in the bulk liquid was proposed, and it fitted the experimental data reasonably well. However, when sequence making internal (designed as to prolong the gas pathway through the reactor) was in the system in addition to the relatively high PCE concentrations (500 ppm) , production of the byproduct chloroform was observed, indicating that some reaction might have occurred in the gas phase. The addition of term for a reaction in the gas phase was able to account for the reaction due to direct absorption of PCE.

Reductive Dechlorination of Tetrachloroethylene by Fe(II) in Cement Slurries

Fe(II) is a potentially effective reductant for treating chlorinated organics in soils by degradative solidification/stabilization (DS/S) process. DS/S is a modification of conventional S/S that promotes degradation of organic contaminants while immobilizing inorganic contaminants. In this study, degradation of tetrachloroethylene (PCE) by Fe(II) in the presence of cement hydration products was characterized by using batch slurry reactors. Cement has been found to catalyze or participate in the PCE degradation reactions over the pH range investigated (10.6−13.8), and the degradation kinetics can generally be described by a pseudo-first-order rate law. PCE degradation rate was greatest at pH ∼12.1 with a half-life of 4.1 days when [PCE]0 = 0.245 mM and [Fe(II)]0 = 39.2 mM. Under this condition, 98% of the PCE initially present in the system transformed to nonchlorinated products (acetylene, ethylene, ethane) with acetylene being predominant, implying that elimination pathways were favored in the cement systems at high pH. Production of chlorinated intermediates was minimal in Fe(II)/cement systems. Addition of Fe(III) to Fe(II)/cement systems increased PCE degradation rates by factors of ∼2 to 3, suggesting Fe(II)-Fe(III) (hydr)oxides might have been reactive agents. Three hypotheses for the reaction mechanisms are discussed.

Sequential anaerobic/aerobic degradation of tetrachloroethylene in a soil enrichment culture.

An enrichment culture taken from a contaminated site could efficiently degrade tetrachloroethylene (PCE) under a sequential anaerobic/aerobic condition. Under an anaerobic condition using citrate as a carbon source and yeast extract as a nutritional requirement, the enrichment culture could transfer 60 μM of PCE nearly stoichiometrically to cis-1, 2-dichloroethylene (cis-DCE) via trichloroethylene (TCE) within 3 days. A solution of 19.6% H2O2 was added atfinal concentration of 1.0% (v/v) to change the anaerobic condition of medium to aerobic one. Under the aerobic condition, more than 80% of cis-DCE accumulated was co-metabolized by indigenous phenol degrading bacteria in the enrichment culture. During the co-oxidation in the aerobic condition, all of phenol (125 mg/liter) added were completely consumed and population of phenol degrading bacteria was increased. The degradation of cis-DCE was affected by H2O2 (0.1-2.0% (v/v) ) and phenol (0-250 mg/liter) concentrations, indicating that the optimum doses of H2O2 and phenol are very important to lead successful co-metabolisms of less chlorinated ethylenes under aerobic conditions. The results from this research suggested that the sequential anaerobic/aerobic biostimulation would be viable as a cost-effective and safe bioremediation technique for degradation of PCE and less chlorinated metabolites. But it should need thorough investigation of microbial populations and their interactions for degrading chlorinated ethylenes under anaerobic and aerobic environments of contaminated sites.

Degradation of Tetrachloroethylene by Granular Biological Activated Carbon under an Anaerobic Condition

Degradation of Tetrachloroethylene by Granular Biological Activated Carbon under an Anaerobic Condition

テトラクロロエチレンの分解除去を目的とした嫌気性ろ床のスタートアップと処理特性

テトラクロロエチレンの分解除去を目的とした嫌気性ろ床のスタートアップと処理特性

Tetrachloroethylene Degradation by Culture Supernatant of the Anaerobic Bacterium, Strain T.

Degradation of tetrachloroethylene (PCE) by a gram negative, anaerobic bacterium strain T isolated from sludge in drainage from a laundry was examined. The activity of degradation was obtained in the culture supernatant of strain T, but not in the cell-extract by sonication. The reaction was optimal between pH 7.0 and 8.0 and at a temperature of 37°C. The activity was unstable in oxygen, heat labile and inhibited not only by trypsin and chymotrypsin but also by thiol inhibitors such as N-ethylmaleimide and p-hydroxymercuribenzoic acid. The substance degrading PCE in the culture supernatant of a gram negative anaerobic bacterium strain T might be a protein with the thiol group as an active site.