Effect of Hydrogen on Reductive Dechlorination of Chlorinated Ethenes

Abstract

A methanogenic fluidized bed reactor (FBR) fed with lactate and tetrachloroethene (PCE) was operated for 14 months to study the effect of electron donor and PCE loading on chloroethene dechlorination rates. Lactate was fed continuously at 200 mg/L (2.2 mmol/L), and the influent PCE feed concentration was increased stepwise from 3.5 to 160 µmol/L. Vinyl chloride (VC) and ethene accounted for 80% and 20%, respectively, of the PCE dechlorination. Batch tests with various electron donors showed that H 2 , propionate, and lactate supported dechlorination of PCE, trichloroethene (TCE), cis-dichloroethene (c-DCE), and VC, whereas no dechlorination was observed with acetate or in the absence of an electron donor. Different short-term steady H 2 concentrations were obtained by adjusting the FBR influent lactate feed concentration, and the effect of H 2 concentration on the rate of chloroethene dechlorination was determined. Dechlorination rates for PCE, TCE, c-DCE, and VC showed a Michaelis-Menten relationship with H 2 partial pressure. The half-velocity coefficients for H 2 utilization by dechlorinators ranged from 12 to 28 ppm for the chloroethenes and are at least an order of magnitude lower than values reported for methanogens. This implies that dechlorinating bacteria can out-compete methanogens for H 2 utilization at low H 2 concentration.

Kinetic and phylogenetic characterization of an anaerobic dechlorinating microbial community

“…Thus, the higher rate with no lag phase when H 2 substituted the methanol supports the hypothesis that also in the PCE/methanol-fed consortium, the actual source of reducing equivalents for RD is H 2 , as reported in the literature (Ballapragada et al, 1997;DiStefano et al, 1992;Maymó -Gatell et al, 1995;Tandoi et al, 1994). Because methanol is the only electron donor given to the consortium (with the exception of a small amount of yeast extract), the observed behaviour is also consistent with the hypothesis that H 2 is formed by methanol-utilizing micro-organisms.…”

Identification of abiotic and biotic reductive dechlorination in a chlorinated ethene plume after thermal source remediation by means of isotopic and molecular biology tools

“…According to laboratory and field observations, PCE could undergo reductive dechlorination in virtually all anaerobic conditions while reductive TCE, cDCE and VC dechlorination would generally occur in more reduced conditions, such as ironreducing for TCE and ideally sulfate-reducing to methanogenic for cDCE and VC (Vogel et al, 1987;Chapelle, 1996;Bradley, 2000;Tiehm and Schmidt, 2011). The presence of and competition for molecular hydrogen (H 2 ), a key electron donor, can also be a determining factor (Ballapragada et al, 1997). Depending on its mineralogy, the presence of iron may also induce competitive inhibition of chlorinated ethene biotic reductive dechlorination (Paul et al, 2013).…”

Enrichment and Characterization of a Trichloroethene-Dechlorinating Consortium Containing Multiple “Dehalococcoides” Strains

“…Hence, hydrogenotrophs such as methanogens and sulfate-reducing bacteria (SRB) compete with ''Dehalococcoides'' populations in mixed cultures. [11][12][13][14][15][16] In contrast, interspecies hydrogen transfer from the aceticlastic methanogen Methanosarcina to VC-dechlorinating ''Dehalococcoides'' has been documented. 17) Methanosarcina spp.…”