To tackle the widespread problem of subsurface chlorinated ethene contamination, some studies have reported that naturally-occurring biotic (microbial reductive dechlorination, MRD) and abiotic (<i>in situ </i>biogeochemical transformation) degradation processes can be used in concert to reach remediation targets. Owing to the ubiquity of subsurface iron- and sulfate-reducing bacteria (IRB, SRB), the formation of reduced iron sulfide (FeS) minerals that can completely reduce chlorinated ethenes to benign end products (e.g. acetylene) are common.  Bacteria capable of MRD of chlorinated ethenes are also native to many sites or can be added to stimulate bioremediation; however, sulfide (5mM) produced under sulfate-reducing conditions has been shown to impede or inhibit MRD in microcosm studies.<br/> In this work, the potential for concomitant iron- and sulfate- reduction and MRD of tetrachloroethene (PCE) was evaluated in 15 cm columns packed with iron-coated sand, and flushed continuously with reduced media containing 200 μM PCE,5 mM sulfate, and 5mM each of lactate and acetate as electron donor and carbon sources. Two experiments were performed, each consisting of two columns operated in parallel. In the first experiment, one column was inoculated with a PCE-to-ethene dechlorinating consortium (BDI-SZ), while the second was inoculated with both BDI-SZ and IRB. Dechlorination of PCE (expressed as moles of Cl removed) was 2% higher in the IRB-containing column, which also yielded 6.5% more ethene compared to the BDI-SZ-only column, presumably due to more reduced conditions. In the second experiment, columns were both inoculated with BDI-SZ, IRB, and SRB, and MRD was monitored as ferrous iron and sulfide production progressed. Additional sulfate and sulfide were also provided to the columns to assess the effects of elevated sulfide on MRD. Effects on PCE dechlorination (e.g., decreased transformation to vinyl chloride and ethene) were not detected until influent sulfide concentrations exceeded 10 mM.  Iron-reduction and FeS formation decreased aqueous sulfide concentrations, and allowed for MRD to proceed at sulfide concentrations that were twice the dosage applied in previous batch reactor studies. However, as sulfide concentrations exceeded 10mM, the pH concurrently increased up to 9.5. Therefore, observed effects on MRD caused by elevated by pH (&gt; 8.0) and potentially sulfide concentrations exceeding the sequestration capacity of the system were indistinguishable.<br/>

Microbial reductive dechlorination of tetrachloroethene under iron- and sulfate-reducing conditions

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.