Microbial Reductive Dechlorination in Large-Scale Sandbox Model
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Microbial reductive dechlorination is a naturally occurring transformation process tetrachloroethene (PCE) undergoes in aquifers. It contributes significantly to natural attenuation of chlorinated solvents. Stimulation of this process has been considered as a method of enhanced bioremediation. Experiments on the stimulation of reductive dechlorination were carried out in a large-scale quasi-2D sandbox model. The transformation of PCE to cis-1,2-dichloroethene (DCE) was attempted by inoculation with Dehalospirillum multivorans and that of DCE to ethene with a mixed culture. Ethanol used as the electron donor was introduced into the inlet of the domain, whereas water loaded with PCE was injected into a well. Limitations due to insufficient mixing could not be observed as high-permeability lenses enhanced the transverse exchange of the compounds. Both reductive dechlorination and competitive microbial reactions led to the acidification of the domain. The artificial aquifer was buffered by the concurrent injection of sodium sulfide with the electron donor. Under these conditions bioaugmentation of Dehalospirillum multivorans was successful, whereas stable dechlorination of DCE could not be achieved.Keywords:
Reductive Dechlorination
Bioaugmentation
Electron donor
Dehalococcoides
Human decontamination
Bioaugmentation
Dehalococcoides
Reductive Dechlorination
Strain (injury)
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Bioaugmentation
Dehalococcoides
Reductive Dechlorination
Biostimulation
Human decontamination
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At the Department of Energy's (DOE) Savannah River Site (SRS) in Aiken, SC there are a number of sites contaminated with Chlorinated Ethenes (CE) due to past disposal practices. Sediments from two CE contaminated SRS locations were evaluated for trichloroethylene (TCE) biodegradation through anaerobic laboratory microcosms. The testing included addition of amendments and bioaugmentation of sediments. The anaerobic microcosms were first amended with substrates including acetate, lactate, molasses, soybean oil, methanol, sulfate, yeast extract, Regenesis HRC(R), and MEAL (methanol, ethanol, acetate, lactate mixture). Microcosms were analyzed after biostimulation for 9 months and no significant TCE biodegradation was observed. At 10 months, additional TCE, fresh amendments, and a mixed culture containing Dehalococcoides ethenogenes were added to active microcosms. A significant decrease in TCE concentrations and an increase in biodegradation products cis-dichloroethylene (cDCE) and vinyl chloride (VC) were noted within 2 weeks of bioaugmentation. Microcosms amended with lactate and sulfate showed complete transformation of TCE (3 ppm) to ethene within 40 days after bioaugmentation. Microcosms amended with other substrates - soybean oil, acetate, yeast extract, and methanol - also show enhanced biodegradation of TCE to ethene. Microcosms amended with molasses and Regenesis HRC showed limited TCE transformation. No TCE transformation was seenmore » in killed control microcosms. On the basis of these successful results, plans are underway for field-scale in-situ deployment of biostimulation/bioaugmentation at SRS.« less
Bioaugmentation
Microcosm
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Reductive Dechlorination
Dehalococcoides
Amendment
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A trichloroethylene (TCE) dechlorinating enrichment (Dehalococcoides spp.), which was isolated from soil of chlorinated ethene contaminated site, was used to investigate whether nano-scale zero valent iron (NZVI) could serve as electron donor for this consortium via cathodic H2 production during anaerobic corrosion. The results show that in the presence of methanol serving as electron donor, dechlorinating culture of 25 fold dilution [(2.0 +/- 0.44) x 10(5) cell/mL] degraded 20 mg/L TCE completely in 96 h, which was accompanied by the production of 2.706 micromol ethene in 190 h. Methanol-free control caused partial degradation of TCE to primarily cis-DCE in 96 h, with only 0.159 micromol ethene produced in 190 h. This indicates bacteria cannot reduce TCE to ethene without electron donor. But when 4 g/L NZVI was added as sole electron donor, this dechlorinating culture degraded 20 mg/L TCE into ethene and vinyl chloride (VC) in 131 h at a speed higher than that by NZVI alone. Compared to 2.706 micromol ethene produced by Dehalococcoides spp. with methanol added as the electron donor, there was only 1.187 micromol ethene produced by bacteria with NZVI serving as the electron donor, which means NZVI has a potential toxicity on Dehalococcoides spp.. At the meantime, 0.109 micromol acetylene was produced in 190 h, which was relatively lower than 0.161 micromol produced by NZVI alone, indicating bacteria competed with NZVI under electron deficient condition. In conclusion, NZVI could serve as electron donor and support dechlorination activity for Dehalococcoides spp. which could enhance the application of NZVI and usage of dechlorinating culture as a polishing strategy in future ground water remediation.
Dehalococcoides
Electron donor
Reductive Dechlorination
Zerovalent iron
Enrichment culture
Tetrachloroethylene
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Bioaugmentation
Reductive Dechlorination
Dehalococcoides
Microcosm
Electron donor
Tetrachloroethylene
Enrichment culture
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Dehalococcoides
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Reductive Dechlorination
Biostimulation
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Abstract : Successful anaerobic bioremediation at chlorinated solvent sites relies on the presence of bacteria, such as Dehalococcoides (Dhc), capable of organohalide respiration (i.e., respiratory reductive dechlorination or [de]chlororespiration). Nucleic acid-based assays like the quantitative real-time polymerase chain reaction (qPCR) technique detect and enumerate Dhc in soil or groundwater samples by targeting Dhc-specific biomarker genes, including the 16S rRNA gene and the tceA, bvcA, and vcrA reductive dechlorinase (RDase) genes implicated in chlorinated ethene reductive dechlorination. The results of nucleic acid-based tests, like the qPCR approach, are expected to assist site managers and practitioners to identify sites where implementation of long-term monitored natural attenuation (MNA) will be effective; where biostimulation will achieve complete dechlorination without DCE/VC stall; and where bioaugmentation is required.
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Dehalococcoides
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Abstract Large laboratory columns (15.2 cm diameter, 183 cm long) were fed with groundwater containing trichloroethylene (TCE), were biostimulated and bioaugmented, and were monitored for over 7.5 years. The objective of the study was to observe how the selection of the carbon and energy source, i.e., whey, Newman Zone ® standard surfactant emulsified oil and Newman Zone nonionic surfactant emulsified oil, affected the rate and extent of dechlorination. Column effluent was monitored for TCE and its degradation products, redox indicators (nitrate‐N, Fe(II), sulfate), and changes in iron mineralogy. Total bacteria and Dehalococcoides mccartyi strains were quantified using q‐PCR. Complete dechlorination was only observed in the whey treated columns, occurring 1 year after bioaugmentation with addition of a culture known to dechlorinate TCE to ethene, and 3 years later in the non‐bioaugmented column. The addition of the emulsified oils with or without bioaugmentation resulted in dechlorination only through cis‐DCE and vinyl chloride. While Dehalococcoides mccartyi strains are the only known bacteria that can fully dechlorinate TCE, their presence, either natural or augmented, was not the sole determiner of complete dechlorination. The establishment of a supporting microbial community and biogeochemistry that developed with continuous feeding of whey, in addition to the presence of D. mccartyi , were necessary to support complete reductive dechlorination. Results confirm that careful selection of a biostimulant is critical to the success of TCE dechlorination in complex soil environments.
Bioaugmentation
Reductive Dechlorination
Biostimulation
Dehalococcoides
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Bioaugmentation
Microcosm
Reductive Dechlorination
Dehalococcoides
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Dehalococcoides
Reductive Dechlorination
Electron donor
Electron acceptor
Dehalogenase
Zerovalent iron
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