Biological reductive dechlorination of tetrachloroethylene and trichloroethylene to ethylene under methanogenic conditions

Abstract

A biological process for remediation of groundwater contaminated with tetrachloroethylene (PCE) and trichloroethylene (TCE) can only be applied if the transformation products are environmentally acceptable. Studies with enrichment cultures of PCE-and TCE-degrading microorganisms provide evidence that, under methanogenic conditions, mixed cultures are able to completely dechlorinate PCE and TCE to ethylene, a product which is environmentally acceptable. Radiotracer studies with [14C]PCE indicated that ['4C]ethylene was the terminal product; significant conversion to 14Co2 or 14CH4 was not observed. The rate-limiting step in the pathway appeared to be conversion of vinyl chloride to ethylene. To sustain reductive dechlorination of PCE and TCE, it was necessary to supply an electron donor; methanol was the most effective, although hydrogen, formate, acetate, and glucose also served. Studies with the inhibitor 2-bromoethanesulfonate suggested that methanogens played a key role in the observed biotransformations of PCE and TCE.

Inhibition of methanogenesis by C1‐ and C2‐polychlorinated aliphatic hydrocarbons

“…Reductive dechlorination of PCE and TCE by methanogenic cultures has been well documented [3,[15][16][17], and our results ( Figs. 3 and 4) are consistent with those reports.…”

“…Chemically, the tri-and tetrachlorinated aliphatic hydrocarbons are highly oxidized and therefore are resistant to biological oxidation but are susceptible to reductive dechlorination by some anaerobic bacteria. There have been a number of observations of reductive dechlorination of polychlorinated hydrocarbons either by complex methanogenic cultures [2][3][4][5][6] or by pure cultures of methanogenic bacteria [6,[7][8][9][10][11][12]. Chloroform is mostly dechlorinated by methanogens to DCM [6,11], which can be further degraded slowly by acetogens in mixed methanogenic cultures [13,14].…”

Aerobic biodegradation of the chloroethenes: pathways, enzymes, ecology, and evolution

“…In contrast, the tri-and tetra-chlorinated ethenes and ethanes are used effectively by many bacteria as electron acceptors via reductive dechlorination and dihaloelimination processes (Vogel et al, 1987). Anaerobic dechlorinating bacteria are promising agents for the bioremediation of chloroethene-contaminated sites because they appear to be widespread, they are active under the anoxic conditions typically encountered in the subsurface, and some can catalyze the complete reduction of PCE and TCE to ethene (Freedman & Gossett, 1989;Maymó-Gatell et al, 1997;Parkin, 1999;Bradley, 2003), which is considered an innocuous end product (although this is controversial; see above). Anaerobic dechlorination of chloroethenes has been thoroughly reviewed elsewhere (Bradley, 2003;Cupples, 2008;Futagami et al, 2008), and so only a brief overview is provided here.…”

Stochastic dynamics of intermittent pore‐scale particle motion in three‐dimensional porous media: Experiments and theory

“…Understanding how flow and transport through porous media are regulated by structural features of the pore space is a problem of central concern for many environmental matters not limited to the following: reactive transport in groundwater [Neuman, 1990;Willmann et al, 2010;Dentz et al, 2011], environmental remediation [Freedman and Gossett, 1989;Zhang, 2003], nuclear waste disposal [McCarthy et al, 1978;Helton, 1993], and oil recovery [Hiorth et al, 2010;Armstrong and Wildenschild, 2012]. Predicting flow behavior in heterogeneous porous media from measurable structural properties remains a challenge, given that the relationship between structure and function is tenuously understood.…”