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The influence of redox potential on the degradation of halogenated methanes

Lookup NU author(s): Dr Jan Dolfing

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Abstract

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 greater than or equal to2.5 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.


Publication metadata

Author(s): Olivas Y, Dolfing J, Smith GB

Publication type: Article

Publication status: Published

Journal: Environmental Toxicology and Chemistry

Year: 2002

Volume: 21

Issue: 3

Pages: 493-499

Print publication date: 01/02/2002

ISSN (print): 0730-7268

ISSN (electronic): 1552-8618

URL: http://dx.doi.org/10.1897/1551-5028(2002)021<0493:TIORPO>2.0.CO;2

DOI: 10.1897/1551-5028(2002)021<0493:TIORPO>2.0.CO;2

Notes: Times Cited: 2 Cited Reference Count: 30 English Article ENVIRON TOXICOL CHEM 524GE


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