Increasing electron donor concentration does not accelerate complete microbial reductive dechlorination in contaminated sediment with native organic carbon

Abstract

Experiments with Fe(III)-rich, chloroethene-contaminated sediment demonstrated that trichloroethylene (TCE) and vinyl chloride (VC) were completely reduced to ethene regardless of whether electron donor(s) were added at 1 × stoichiometry or 10 × stoichiometry relative to all-electron acceptors. Unamended controls uniformly reduced TCE to ethene with a mean time to complete dechlorination (operationally defined as the presence of stoichiometric ethene production) of 79 days. Adding 1 × and 10 × acetate hindered the rate and extent of TCE and VC reduction relative to unamended controls, with several only partially reduced when the experiments were terminated. Adding high molecular mass (soybean oil derivative) substrates did not increase microbial reductive dechlorination relative to unamended incubations, and in many cases, hindered microbial dechlorination in favor of methanogenesis. The mean time to complete dechlorination was comparable between low (× 1) and high (× 10) electron donor concentration for all lipid-based electron donors tested. Those tested included Newman Zone® Standard without sodium lactate (96 vs. 75 days, respectively), CAP 18 ME (85 vs. 94 days, respectively), EOS 598B42 (68 vs. 72 days, respectively), and acetate (134 vs. 125 days, respectively). These data suggest that the addition of an electron donor does not always increase the rate and extent of reductive dechlorination but will increase costs. In particular, increasing the concentration of electron donors higher than the stoichiometric demand only decreased complete microbial reductive dechlorination, which is the opposite of most standard “more time and more electrons” approaches. These data argue that site-specific electron donor demands must be evaluated, and in some cases, a monitored natural attenuation (MNA) approach is most favorable.

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Acknowledgements

This project was funded by Clemson University external faculty grants. The authors want to specifically acknowledge Bob Borden (EOS), Matthew Dingens (CAP 18), and William Newman (Newman Zone) for providing the vegetable oils used in this research. The results and conclusions presented herein are those of the authors and do not necessarily represent those of Clemson University, and no endorsement of the described technology is implied. This paper has not been subjected to peer review within Clemson University or by any of the Vendors who provided materials for this study, and the conclusions stated here do not necessarily reflect the official views of the University or the Vendors, nor does this document constitute an official endorsement by the University or the Vendors. The authors thank the anonymous reviewers for their feedback.

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Haluska, A.A., Finneran, K.T. Increasing electron donor concentration does not accelerate complete microbial reductive dechlorination in contaminated sediment with native organic carbon. Biodegradation (2021). https://doi.org/10.1007/s10532-021-09953-y

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Keywords

  • Microbial reductive dechlorination
  • Trichloroethylene
  • Vinyl chloride
  • Emulsified vegetable oils