Acetate versus Hydrogen as Direct Electron Donors To Stimulate the Microbial Reductive Dechlorination Process at Chloroethene-Contaminated Sites

Abstract

A study to evaluate the dechlorination end points and the most promising electron donors to stimulate the reductive dechlorination process at the chloroethene-contaminated Bachman Road site in Oscoda, MI, was conducted. Aquifer materials were collected from inside the plume and used to establish microcosms under a variety of electron donor conditions using chlorinated ethenes as electron acceptors. All microcosms that received an electron donor showed dechlorination activity, but the end points depended on the sampling location, indicating a heterogeneous distribution of the dechlorinating populations in the aquifer. Interestingly, several microcosms that received acetate as the only electron donor completely dechlorinated PCE to ethene. All acetate-amended microcosms rapidly converted PCE to cis-DCE, whereas PCE dechlorination in H2-fed microcosms only occurred after a pronounced lag time and after acetate had accumulated by H2/CO2 acetogenic activity. The microcosm experiments were corroborated by defined co-culture experiments, which demonstrated that H2 sustained PCE to cis-DCE dechlorination by acetotrophic populations in the presence of H2/CO2 acetogens. In sediment-free nonmethanogenic enrichment cultures derived from ethene-producing microcosms, acetate alone supported complete reductive dechlorination of chloroethenes to ethene, although the addition of H2 resulted in higher cis-DCE and VC dechlorination rates. Measurements of H2 production and consumption suggested that syntrophic acetate-oxidizing population(s) were active in the enrichment cultures. These findings demonstrated that either acetate or H2 alone can be sufficient to promote complete

Identification and Environmental Distribution ofdcpA, Which Encodes the Reductive Dehalogenase Catalyzing the Dichloroelimination of 1,2-Dichloropropane to Propene in Organohalide-Respiring Chloroflexi

“…Details on sample collection and site information are provided in the supplemental material and given in Table 1. Microcosms were prepared inside an anoxic chamber (N 2 /H 2 , 97%/3% [vol/vol]) by using established procedures (13), with the following modifications. One-gram (wet weight) samples of solids were transferred to sterile 60-ml (nominal capacity) glass serum bottles containing 40 ml of defined, completely synthetic reduced mineral salts basal salts medium (14) amended with 5 mM lactate, 30 mM bicarbonate (pH 7.2), 0.2 mM Na 2 S · 9H 2 O, resazurin (0.25 mg liter Ϫ1 ), vitamins (15), and 0.2 mM 1,2-D. Microcosms established with groundwater were initiated with 20 ml of groundwater plus 20 ml of medium.…”

The Role of Syntrophic Associations in Sustaining Anaerobic Mineralization of Chlorinated Organic Compounds

“…Complete biodegradation of these compounds at contaminated sites is often limited by the availability of a suitable electron donor (He et al 2002). A number of microbial populations that use PCE as the terminal electron acceptor in dehalorespiration couple the reduction of chlorinated ethenes to the oxidation of hydrogen (H 2 ).…”

“…A number of microbial populations that use PCE as the terminal electron acceptor in dehalorespiration couple the reduction of chlorinated ethenes to the oxidation of hydrogen (H 2 ). Thus, although the direct involvement of organic electron donors, especially acetate, in dehalorespiration has been demonstrated at some contaminated sites (He et al 2002), it is generally believed that H 2 serves as the ultimate electron donor for reduction of PCE in most cases (Fennell et al 1997; Yang and McCarty 1998). However, sustaining degradation of chlorinated ethenes through the delivery of H 2 in engineered in situ bioremediation scenarios is complicated by the presence of a variety of hydrogenotrophic populations that use nonchlorinated electron acceptors, such as sulfate and carbon dioxide (CO 2 ), in contaminated anaerobic environments and the competition of these populations with PCE-degrading organisms for H 2 .…”

Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment

“…Chlororespiring populations depend on the activity of fermentative organisms to convert (complex) organic materials into suitable electron donors (e.g., hydrogen or acetate) (DiStefano et al 1992; He et al 2002). A variety of substrates including pentanol, ethanol, lactate, propionate, butyrate, and oleate have been shown to produce suitable electron donors (e.g., acetate, hydrogen) to support chlororespiring populations (Carr and Hughes 1998; Fennell and Gossett 1998; He et al 2002; Yang and McCarty 1998, 2002). Alternative amendment strategies that supply slow-release, nonsoluble substrates for example, olive oil, chitin, polylactate esters [e.g., Hydrogen Release Compound (HRC; Regenesis Bioremediation Products, San Clemente, CA)], have also been successfully, used (Koenigsberg and Farone 1999; Yang and MacCarty 2002).…”

“…Chlororespiring populations are highly competitive hydrogen users and outcompete methanogens, acetogens, and sulfate-reducing populations for this electron donor (Löffler et al 1999). Thus, substrates that result in slow release (or production) of hydrogen are advantageous because most reducing equivalents are directed toward the process of interest (Ballapragada et al 1997; Fennell et al 1997; Fennell and Gossett 1998; He et al 2002; Smatlak et al 1996). It should be noted that any approach that increases the flux of hydrogen in a subsurface environment will also result in an increased flux of acetate, which has been implicated as a relevant source of low concentrations of hydrogen through syntrophic oxidation (He et al 2002; Schink 1997).…”