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

Revealing chlorinated ethene transformation hotspots in a nitrate-impacted hyporheic zone

“…Overall, the reductive dechlorination potential of the hyporheic zone appears to be limited to cDCE production with only minor concentrations of VC detected which is consistent with previous results (Weatherill et al, 2014). This incomplete natural attenuation may be ascribed to the presence of residual DO concentrations, a lack of suitable cDCE dechlorinator populations or competition for reducing equivalents by metal-reducing bacteria (Chambon et al, 2013;Paul et al, 2016). The presence of both NH and CH4 in hypoxic samples may favour alternative cometabolic pathways for cDCE and VC mineralisation at the interface between hypoxic and oxic flow paths (Mattes et al, 2010).…”

“…However, considerable overlap in H2 thresholds are observed experimental studies under metal-reducing conditions with mineral bioavailability playing an important role (Paul et al, 2016). Our findings suggest that reduction of NO and TCE to cDCE dechlorination occur independently of one another which is supported by the PCA results in Fig.…”

Natural attenuation of chlorinated ethenes in hyporheic zones: A review of key biogeochemical processes and in-situ transformation potential

“…whereas LCE reduction overlaps with sulfate reduction and methanogenesis (Paul et al, 2016). Overlap of TEAP H 2 thresholds are commonly observed in experimental studies (e.g.…”

“…Overlap of TEAP H 2 thresholds are commonly observed in experimental studies (e.g. Jakobsen and Postma, 1999;Aulenta et al, 2008;Paul et al, 2016) with lower levels than predicted from thermodynamic considerations (Heimann et al, 2009). This phenomenon has been attributed to kinetic effects arising from the relative efficiencies in H 2 producers and consumers in microbial consortia (Richardson, 2016).…”

“…Heimann et al (2006) suggested that acetoclastic methanogenesis may enhance VC dechlorination by providing additional H 2 during acetate cleavage. The observed H 2 thresholds for hydrogenotrophic methanogenesis (5-100 nM) are considerably greater than OHR (0.1-2.5 nM) (Paul et al, 2016) and OHRB have been shown to out-compete hydrogenotrophic methanogens for reducing equivalents at low H 2 concentrations (Ballapragada et al, 1997;Yang and McCarty, 1998;Azizian et al, 2010). CEs on the other hand have been shown to have direct inhibitory effect on methanogenesis through enzyme inactivation although the effect is less pronounced than for other organohalides such as chlorinated methanes (Chan and Radom, 2011).…”