Bioelectrochemical dechlorination of trichloroethene: From electron transfer mechanisms to process scale-up

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Membrane-less bioelectrochemical reactor for the treatment of groundwater contaminated by toluene and trichloroethene

To address the ever-growing environmental problem of groundwater contamination, microbial electrochemical technologies (METs) are being studied as promising substitutes for traditional remediation techniques. Among their many advantages, they possess the capability of providing a virtually inexhaustible electron acceptor (or donor) directly in the aquifer without addition of air, oxygen or other chemicals. In this way, they can promote microbially-driven oxidation and/or reduction of contaminants in-situ, in a more sustainable and cost-effective way

Field distribution and activity of chlorinated solvents degrading bacteria by combining CARD-FISH and real time PCR

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Coupling of bioelectrochemical toluene oxidation and trichloroethene reductive dechlorination for single-stage treatment of groundwater containing multiple contaminants

Bioremediation of groundwater contaminated by a mixture of aromatic hydrocarbons and chlorinated solvents is typically challenged because these contaminants are degraded via distinctive oxidative and reductive pathways, thus requiring different amendments and redox conditions. Here, we provided the proof-of-concept of a single-stage treatment of synthetic groundwater containing toluene and trichloroethene (TCE) in a tubular bioelectrochemical reactor, known as a “bioelectric well”. Toluene was degraded by a microbial bioanode (up to 150 μmol L−1 d−1) with a polarized graphite anode (+0.2 V vs. SHE) serving as the terminal electron acceptor. The electric current deriving from microbially-driven toluene oxidation resulted in (abiotic) hydrogen production (at a stainless-steel cathode), which sustained the reductive dechlorination of TCE to less-chlorinated intermediates (i.e., cis-DCE, VC, and ETH), at a maximum rate of 500 μeq L−1 d−1, in the bulk of the reactor. A phylogenetic and functional gene-based analysis of the “bioelectric well” confirmed the establishment of a microbiome harboring the metabolic potential for anaerobic toluene oxidation and TCE reductive dechlorination. However, Toluene degradation and current generation were found to be rate-limited by external mass transport phenomena, thus indicating the existing potential for further process optimization

Syntrophy drives the microbial electrochemical oxidation of toluene in a continuous-flow "bioelectric well"

Microbial electrochemical technologies (MET) are promising for the remediation of groundwater pollutants such as petroleum hydrocarbons (PH). Indeed, MET can provide virtually inexhaustible electron donors or acceptors directly in the subsurface environment. However, the degradation mechanisms linking contaminants removal to electric current flow are still largely unknown, hindering the development of robust design criteria. Here, we analysed the degradation of toluene, a model PH, in a bioelectrochemical reactor known as "bioelectric well"operated in continuous-flow mode at various influent toluene concentrations. With increasing concentration of toluene, the removal rate increased while the current tended to a plateau, hence the columbic efficiency decreased. Operation at open circuit confirmed that the bioelectrochemical degradation of toluene proceeded via a syntrophic pathway involving cooperation between different microbial populations. First of all, hydrocarbon degraders quickly converted toluene into metabolic intermediates probably by breaking the aromatic ring upon fumarate addition. Subsequently, fermentative bacteria converted these intermediates into volatile fatty acids (VFA) and likely also H2, which were then used as substrates by electroactive microorganisms forming the anodic biofilm. As toluene degradation is faster than subsequent conversion steps, the increase in intermediate concentration could not result in a current increase. This work provides valuable insights on the syntrophic degradation of BTEX, which are essential for the application of microbial electrochemical system to groundwater remediation of petroleum hydrocarbons

Biotechnologies for Marine Oil Spill Cleanup : Indissoluble Ties with Microorganisms

The ubiquitous exploitation of petroleum hydrocarbons (HCs) has been accompanied by accidental spills and chronic pollution in marine ecosystems, including the deep ocean. Physicochemical technologies are available for oil spill cleanup, but HCs must ultimately be mineralized by microorganisms. How environmental factors drive the assembly and activity of HC-degrading microbial communities remains unknown, limiting our capacity to integrate microorganism-based cleanup strategies with current physicochemical remediation technologies. In this review, we summarize recent findings about microbial physiology, metabolism and ecology and describe how microbes can be exploited to create improved biotechnological solutions to clean up marine surface and deep waters, sediments and beaches. Cleaning up oil spills in marine environments ultimately relies on microbial metabolism of HC, which complements the current chemicophysical techniques used in emergency response.Consolidated biotechnologies include microbial communities biostimulation, biosurfactant supplementation and bioaugmentation HC-degrading microbial cells.The effectiveness of biotechnologies is limited by our understanding of the microbial ecology of polluted marine systems. We lack knowledge on how environmental factors, such as hydrostatic pressure, temperature and dispersant toxicity, affect microbial successions.The recent availability of meta-omics data and the improved understanding of microbial metabolism are leading to novel biotechnologies for marine oil spill cleanup, such as slow-release particles for efficient biostimulation and bioelectrochemical approaches for sediment cleanup

A microcosm treatability study for evaluating wood mulch-based amendments as electron donors for trichloroethene (Tce) reductive dechlorination

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