A Microcosm Treatability Study for Evaluating Wood Mulch-Based Amendments as Electron Donors for Trichloroethene (TCE) Reductive Dechlorination

Abstract

In this study, wood mulch-based amendments were tested in a bench-scale microcosm experiment in order to assess the treatability of saturated soils and groundwater from an industrial site contaminated by chlorinated ethenes. Wood mulch was tested alone as the only electron donor in order to assess its potential for stimulating the biological reductive dechlorination. It was also tested in combination with millimetric iron filings in order to assess the ability of the additive to accelerate/improve the bioremediation process. The efficacy of the selected amendments was compared with that of unamended control microcosms. The results demonstrated that wood mulch is an effective natural and low-cost electron donor to stimulate the complete reductive dechlorination of chlorinated solvents to ethene. Being a side-product of the wood industry, mulch can be used in environmental remediation, an approach which perfectly fits the principles of circular economy and addresses the compelling needs of a sustainable and low environmental impact remediation. The efficacy of mulch was further improved by the co-presence of iron filings, which accelerated the conversion of vinyl chloride into the ethene by increasing the H2 availability rather than by catalyzing the direct abiotic dechlorination of contaminants. Chemical analyses were corroborated by biomolecular assays, which confirmed the stimulatory effect of the selected amendments on the abundance of Dehalococcoides mccartyi and related reductive dehalogenase genes. Overall, this paper further highlights the application potential and environmental sustainability of wood mulch-based amendments as low-cost electron donors for the biological treatment of chlorinated ethenes.

Sequential Anaerobic/Aerobic Microbial Transformation of Chlorinated Ethenes: Use of Sustainable Approaches for Aquifer Decontamination

“…Chen and colleagues [98] observed at a microcosm scale that molasses induced a higher dechlorination rate with respect to acetate and soybean oil, but the rapid H 2 release induced a higher production of methane. Wood mulch and whey enhanced complete microbial dechlorination to ethene but increased the production of methane after 90 days of incubation [109,110] and sulfide [111], respectively. At the field scale, whey addition coupled with the addition of a dechlorinating bacterial consortium allowed the completion of the process [112].…”

“…This correspondence is not always respected. In many field-based experiments, Dehalococcoides and Dehalococcoida biomarker quantification is not consistent with biodegradation rates, thus indicating that OHR can be carried out by a wider range of microorganisms [109,145]. In contaminated groundwater, four known OHRBs (Dehalococcoides, Desulfitobacterium, Dehalobacter, and Dehalogenimonas) were quantified [146].…”

Combined Strategies to Prompt the Biological Reduction of Chlorinated Aliphatic Hydrocarbons: New Sustainable Options for Bioremediation Application

“…In general, the addition is carried out by direct push/injection wells, by the construction of biowalls, or by injection/extraction wells to recirculate and improve the distribution of the amendments [32]. For the success of biological metabolism, the use of a slow-release, low-solubility substrate for hydrogen donation should be a valuable approach (e.g., HRC™ or vegetable oils) [33]. When injected into the aquifer, these substrates slowly hydrolyze to form more soluble compounds that are transported along the contamination plume.…”