title: Inhibition of iron (III) minerals and acidification on the reductive dechlorination of trichloroethylene.
abstract: Reductive dechlorination of chlorinated ethenes is inhibited by acidification and by the presence of Fe (III) as a competitive electron acceptor. Synergism between both factors on dechlorination is predicted as reductive dissolution of Fe (III) minerals is facilitated by acidification. This study was set-up to assess this synergism for two common aquifer Fe (III) minerals, goethite and ferrihydrite. Anaerobic microbial dechlorination of trichloroethylene (TCE) by KB-1 culture and formate as electron donor was investigated in anaerobic batch containers at different solution pH values (6.2-7.2) in sand coated with these Fe minerals and a sand only as control. In the absence of Fe, lowering substrate pH from 7.2 to 6.2 increased the time for 90% TCE degradation from 14±1d to 42±4d. At pH 7.2, goethite did not affect TCE degradation time while ferrihydrite increased the degradation time to 19±1d compared to the no Fe control. At pH 6.2, 90% degradation was at 78±1 (ferrihydrite) or 131±1d (goethite). Ferrous iron production in ferrihydrite treatment increased between pH 7.2 and 6.5 but decreased by further lowering pH to 6.2, likely due to reduced microbial activity. This study confirms that TCE is increasingly inhibited by the combined effect of acidification and bioavailable Fe (III), however no evidence was found for synergistic inhibition since Fe reduction did not increase as pH decreases. To the best of our knowledge, this is the first study where effect of pH and Fe (III) reduction on TCE was simultaneously tested. Acid Fe-rich aquifers need sufficient buffering and alkalinity to ensure swift degradation of chlorinated ethenes.
authors.affiliation: Division of Soil and Water Management, Department of Earth and Environmental Sciences, KU Leuven, Kasteelpark Arenberg 20, B-3001 Heverlee, Belgium. Electronic address: laiby.paul@ees.kueuven.
authors.forename: Laiby
authors.initials: L
authors.lastname: Paul
authors.affiliation: Division of Soil and Water Management, Department of Earth and Environmental Sciences, KU Leuven, Kasteelpark Arenberg 20, B-3001 Heverlee, Belgium. Electronic address: erik.smolders@ees.kuleuven.be.
authors.forename: Erik
authors.initials: E
authors.lastname: Smolders
mesh_terms: D001421:Bacteria, Anaerobic / Q000378:metabolism; D001673:Biodegradation, Environmental; D005290:Ferric Compounds / Q000737:chemistry*; D054879:Halogenation; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry*; D010084:Oxidation-Reduction; D014241:Trichloroethylene / Q000737:chemistry* / Q000378:metabolism; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005290:Ferric Compounds; D058085:Iron Compounds; D008903:Minerals; D014874:Water Pollutants, Chemical; C094886:goethite; D014241:Trichloroethylene; C092844:ferric oxyhydroxide
keywords: Acidification; Fe (III) oxides; Reductive dechlorination; Reductive dissolution; Trichloroethylene; pH inhibition