Anaerobic biotransformation of polychlorinated methane and ethene under various redox conditions

Doong, Ruey‐an; Wu, Shang-Chuen; Chen, Tsu-feng

doi:10.1016/0045-6535(95)00349-5

“…Due to the fact that degradation only happened in the presence of Ti (III) citrate, we consider Ti (III) citrate and not acetate to be the electron donor in our systems. Correlating with this result, depletion of CCl 4 under redox potentials ranging from ϩ188 to Ϫ263 mV has been observed [21]. Addition of 300 M Ti (III) citrate was found to increase CCl 4 degradation rates by autoclaved sludge [22].…”

Section: Discussionsupporting

confidence: 57%

“…Purely chemical degradation of chlorinated hydrocarbons has been previously related to iron metal and/or Fe 2ϩ [21,26,27]. The degradation rates of the abiotic samples were low in comparison with the live and heat-killed sludge samples (Table 3).…”

Section: Live and Heat-resistant Catalystsmentioning

confidence: 94%

The Influence of Redox Potential on the Degradation of Halogenated Methanes

Olivas¹,

Dolfing²,

Smith³

2002

Environ Toxicol Chem

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To determine the influence of redox potential on the reaction mechanism and to quantify kinetics of the dechlorination by digester sludge, the test compounds trichlorofluoromethane (CFCl3), carbon tetrachloride (CCl4), and chloroform (CHCl3) were incubated in the presence of sludge and variable concentrations of reducing agent. Different sources of dehalogenation were examined, including live sludge and heat-killed sludge, and abiotic mechanisms were quantified in the absence of sludge. Batch incubations were done under redox conditions ranging from +/-534 to -348 mV. The highest rates for the dehalogenation of the three compounds were observed at -348 mV. The dechlorination rate of all the compounds by the heat-resistant catalysts was approximately twofold higher than the live treatments. It was proposed that the higher degradation rates by heat-killed sludge were due to the absence of physical barriers such as cell wall and cell membranes. There was no abiotic dechlorination of CFCl3, whereas CCl4 and CHCl3 were both reduced in the absence of sludge catalyst by Ti (III) citrate at > or =2.5 mM. The degradation pathways of CFCl3 and CHCl3 appeared to be only partially reductive since the production of reduced metabolites was low in comparison with the total amount of original halogenated compounds degraded. For CFCl3, the partial reductive degradation implied that different intra- and extracellular pathways were concurrent. The Gibbs free energy and the redox potential for the dehalogenation reactions utilizing Ti (III) citrate and acetate as electron donors are reported here for the first time.

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“…Due to the fact that degradation only happened in the presence of Ti (III) citrate, we consider Ti (III) citrate and not acetate to be the electron donor in our systems. Correlating with this result, depletion of CCl 4 under redox potentials ranging from +188 to ‐263 mV has been observed [21]. Addition of 300 μMTi (III) citrate was found to increase CCl 4 degradation rates by autoclaved sludge [22].…”

Section: Discussionmentioning

confidence: 90%

“…Purely chemical degradation of chlorinated hydrocarbons has been previously related to iron metal and/or Fe 2+ [21,26,27]. The degradation rates of the abiotic samples were low in comparison with the live and heat‐killed sludge samples (Table 3).…”

Section: Discussionmentioning

confidence: 97%

The influence of redox potential on the degradation of halogenated methanes

Olivas¹,

Dolfing²,

Smith³

2002

Enviro Toxic and Chemistry

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To determine the influence of redox potential on the reaction mechanism and to quantify kinetics of the dechlorination by digester sludge, the test compounds trichlorofluoromethane (CFCl3), carbon tetrachloride (CCl4), and chloroform (CHCl3) were incubated in the presence of sludge and variable concentrations of reducing agent. Different sources of dehalogenation were examined, including live sludge and heat-killed sludge, and abiotic mechanisms were quantified in the absence of sludge. Batch incubations were done under redox conditions ranging from +/-534 to -348 mV. The highest rates for the dehalogenation of the three compounds were observed at -348 mV. The dechlorination rate of all the compounds by the heat-resistant catalysts was approximately twofold higher than the live treatments. It was proposed that the higher degradation rates by heat-killed sludge were due to the absence of physical barriers such as cell wall and cell membranes. There was no abiotic dechlorination of CFCl3, whereas CCl4 and CHCl3 were both reduced in the absence of sludge catalyst by Ti (III) citrate at > or =2.5 mM. The degradation pathways of CFCl3 and CHCl3 appeared to be only partially reductive since the production of reduced metabolites was low in comparison with the total amount of original halogenated compounds degraded. For CFCl3, the partial reductive degradation implied that different intra- and extracellular pathways were concurrent. The Gibbs free energy and the redox potential for the dehalogenation reactions utilizing Ti (III) citrate and acetate as electron donors are reported here for the first time.

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“…Fe(III)-reducing conditions are prevalent in subsurface environments, but the effect of Fe(III) reduction on complete TCE degradation has often been reported using field data or laboratory data in which understanding the dynamic between these processes was not the goal. Iron-bearing minerals are abundant in natural environments, and Fe(III) compounds are present in aquifer and lake sediments. , Fe(III) reduction has been documented during natural attenuation of chlorinated ethenes and during TCE bioremediation where high concentrations of electron donor were added to stimulate reductive dechlorination. − However, previous studies of the effects of alternative electron acceptors on reductive dechlorination have focused on nitrate, sulfate, or carbon dioxide (methanogenesis); − few, if any, data are available as to the effect of Fe(III) despite its significance.…”

Section: Introductionmentioning

confidence: 99%

Influence of Ferric Iron on Complete Dechlorination of Trichloroethylene (TCE) to Ethene: Fe(III) Reduction Does Not Always Inhibit Complete Dechlorination

Wei

¹

,

Finneran

²

2011

Environ. Sci. Technol.

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The effects of Fe(III) reduction on TCE, cis-DCE, and VC dechlorination were studied in both contaminated aquifer material and enrichment cultures. The results from sediment batch experiments demonstrated that Fe(III) reduction did not inhibit complete dechlorination. TCE was reduced concurrently with Fe(III) in the first 40 days of the incubations. While all incubations (plus and minus Fe(III)) generated approximately the same mass of ethene within the experimental time frame, Fe(III) speciation (ferrihydrite versus Fe(III)-NTA) had an impact on daughter product distribution and dechlorination kinetics. 16S rRNA gene clone library sequencing identified Dehalococcoides and Geobacteraceae as dominant populations, which included G. lovleyi like organisms. Quantitative PCR targeting 16S rRNA genes and Reductive Dehalogenase genes (tceA, bvcA, vcrA) indicated that Dehalococcoides and Geobacteraceae were enriched concurrently in the TCE-degrading, Fe(III)-reducing sediments. Enrichment cultures demonstrated that soluble Fe(III) had a greater impact on cis-DCE and VC reduction than solid-phase Fe(III). Geobacteraceae and Dehalococcoides were also coenriched in the liquid cultures, and the Dehalococcoides abundance in the presence of Fe(III) was not significantly different from those in the cultures without Fe(III). Hydrogen reached steady-state concentrations most amenable to complete dechlorination very quickly when Fe(III) was present in the culture, suggesting that Fe(III) reduction may actually help dechlorination. This was contrasted to hydrogen levels in nitrate-amended enrichments, in which hydrogen concentration was too low for any chlororespiration.

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Anaerobic biotransformation of polychlorinated methane and ethene under various redox conditions

Cited by 10 publications

References 37 publications

The Influence of Redox Potential on the Degradation of Halogenated Methanes

The Influence of Redox Potential on the Degradation of Halogenated Methanes

The influence of redox potential on the degradation of halogenated methanes

Influence of Ferric Iron on Complete Dechlorination of Trichloroethylene (TCE) to Ethene: Fe(III) Reduction Does Not Always Inhibit Complete Dechlorination

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