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

Abstract

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.

Reductive Dechlorination of Trichloroethylene (TCE) in Competition with Fe and Mn Oxides—Observed Dynamics in H2-dependent Terminal Electron Accepting Processes

“…In contrast to this study, a complete dechlorination of TCE to ethene with simultaneous iron reduction process is observed by Wei and Finneran (2011) and Azizian et al (2008), as the donor was a slow-fermenting substrate and was provided in excess. Thus, the extent and ultimate effect of the competition on the outcome of the dechlorination may also depend on the amount and type of electron donor compared to the amount of alternative TEA's.…”

“…Most of the previous studies conducted for determining H 2 thresholds during dechlorination reactions e.g., Lu et al (2001), Luitjen et al (2004), Wei and Finneran (2011) utilized a slow-release H 2 donor or were measured in ground water systems where electron donor is usually limited. However, the choice of formate has been made after different trials using different electron donors, due to the capability of formate in maintaining the pH of the medium for a long running experiment of dechlorination where pH is a very important factor that affects the rate of reaction.…”

“…It has been shown that reductive dechlorination of TCE does occur under Fe(III) reducing conditions (Azizian et al, 2008;Paul et al, 2013;Wei and Finneran, 2011) while a few other studies indicate that concomitant Fe(III)-reduction poses a competitive inhibition to the dechlorination process, especially on cis-DCE and VC dechlorination (Dupont et al, 2003;Evans and Koenigsberg, 2001;Paul et al, 2013;Yager et al, 1997). Different approaches have been used to assess the redox conditions during transformation of TCE such as the concentration of either the parent compound or electron donor or of reduced species such as Fe 2+ , HS -and CH 4 (Damgaard et al, 2013;Hunkeler et al, 2011).…”

Identification of chlorinated solvents degradation zones in clay till by high resolution chemical, microbial and compound specific isotope analysis

“…Heimann et al, 2005;Wei and Finneran, 2011). Several studies suggest that chlorinated ethenes and ethanes can undergo abiotic degradation through reactions with reduced iron minerals (e.g.…”

“…The sequential dechlorination requires anaerobic conditions (iron-reducing to methanogenic) (Hoelen and Reinhard, 2004;MaymoGatell et al, 1995;Wei and Finneran, 2011), a hydrogen donor (e.g. lactate, Aulenta et al, 2007) and a certain composition of the bacterial community (Duhamel et al, 2002).…”