Enrichment of Dehalococcoides mccartyi spp. from a municipal activated sludge during AQDS-mediated bioelectrochemical dechlorination of 1,2-dichloroethane to ethene

Current advances of chlorinated organics degradation by bioelectrochemical systems: a review

Chlorinated organic compounds (COCs) are typical refractory organic compounds, having high biological toxicity. These compounds are a type of pervasive pollutants that can be present in polluted soil, air, and various types of waterways, such as groundwater, rivers, and lakes, posing a significant threat to the ecological environment and human health. Bioelectrochemical systems (BESs) are an effective strategy for the degradation of bio-refractory compounds. BESs improve the waste treatment efficiency through the application of weak electrical stimulation. This review discusses the processes of BESs configurations and degradation performances in different environmental media including wastewater, soil, waste gas and groundwater. In addition, the degradation mechanisms and performance-enhancing additives are summarized. The future challenges and perspectives on the development of BES for COCs removal are briefly discussed.

Bioelectrochemically-assisted degradation of chloroform by a co-culture of Dehalobacter and Dehalobacterium

Using bioelectrochemical systems (BESs) to provide electrochemically generated hydrogen is a promising technology to provide electron donors for reductive dechlorination by organohalide-respiring bacteria. In this study, we inoculated two syntrophic dechlorinating cultures containing Dehalobacter and Dehalobacterium to sequentially transform chloroform (CF) to acetate in a BES using a graphite fiber brush as the electrode. In this co-culture, Dehalobacter transformed CF to stoichiometric amounts of dichloromethane (DCM) via organohalide respiration, whereas the Dehalobacterium-containing culture converted DCM to acetate via fermentation. BES were initially inoculated with Dehalobacter, and sequential cathodic potentials of -0.6, -0.7, and -0.8 V were poised after consuming three CF doses (500 μM) per each potential during a time-span of 83 days. At the end of this period, the accumulated DCM was degraded in the following seven days after the inoculation of Dehalobacterium. At this point, four consecutive amendments of CF at increasing concentrations of 200, 400, 600, and 800 μM were sequentially transformed by the combined degradation activity of Dehalobacter and Dehalobacterium. The Dehalobacter 16S rRNA gene copies increased four orders of magnitude during the whole period. The coulombic efficiencies associated with the degradation of CF reached values > 60% at a cathodic potential of -0.8 V when the degradation rate of CF achieved the highest values. This study shows the advantages of combining syntrophic bacteria to fully detoxify chlorinated compounds in BESs and further expands the use of this technology for treating water bodies impacted with pollutants.

Natural Magnetite Minerals Enhance 1,2-Dichloroethane Reductive Dechlorination

Contamination of soil and groundwater by chlorinated solvents is an environmental issue of primary concern. Recently, electrically conductive iron particles have been proposed as a novel approach to accelerate anaerobic bioremediation processes. In fact, it was demonstrated that conductive particles facilitate the exchange of electrons between microorganisms via Direct Interspecies Electron Transfer (DIET) processes, thus enhancing the pollutant-degrading potential of the microbial community. However, the use of natural minerals in this context has not been reported so far. In this study, we applied, for the first time, natural magnetite and hematite to accelerate the reductive dechlorination of 1,2-dichloroethane by an enrichment culture in lab-scale anaerobic microcosms. After four feeding cycles, low magnetite-amended microcosms (13 mg/L) yielded the highest rate of 1,2-DCA reductive dechlorination and reduced methanogenic activity. By contrast, hematite did not display any apparent stimulatory effect. Surprisingly, in the presence of higher amounts of iron oxides, a weaker effect was obtained, probably because iron(III) present in the minerals competed for the electrons necessary for reductive dechlorination. For all microcosms, the concentration of the toxic byproduct vinyl chloride was negligible throughout the whole study. The SEM/EDS analysis confirmed the close interaction between the conductive iron oxide particles and the dechlorinating bacteria. This work opens the possibility of using natural conductive minerals for bioremediation applications as well as shedding light on the previously unrecognized role of such minerals in contaminated ecosystems.

Soil microorganisms facilitated the electrode-driven trichloroethene dechlorination to ethene by Dehalococcoides species in a bioelectrochemical system

Bioelectrochemical dechlorination using organohalide-respiring bacteria (ORBs) is a promising technique for remediating contaminated groundwater. Generally, a longer enrichment period is required for selecting the ORB consortia to achieve bioelectrochemical dechlorination. However, the full dechloriantion is difficult to be achieved due to the absence of functional species (e.g. Dehalococcoides) in previously used enrich cultures. To overcome these challenges, bioelectrochemical dechlorination using a culture enriched with the pre-augmented Dehalococcoides was performed for the first time in this study. A two-chamber bioelectrochemical system (BES) inoculated with a pure Dehalococcoides culture and paddy soil with an applied voltage of -0.3 V (versus a standard hydrogen electrode) as the sole electron donor was used to achieve dechlorination. The ethene formation rate was 10-100 times higher than that in previous studies, indicating that inoculating the system with a pure Dehalococcoides culture and soil microorganisms gave effective full dechlorination performance. Microbial community analysis and bioelectrochemical analysis indicated that Desulfosporosinus species may have facilitated dechlorination through syntrophic interactions with Dehalococcoides. The results indicated that adding Dehalococcoides cells before operating a bioelectrochemical system is an effective way of achieving full dechlorination.

Bioelectrochemical system for dehalogenation: A review

Halogenated organic compounds are persistent pollutants, whose persistent contamination and rapid spread seriously threaten human health and the safety of ecosystems. It is difficult to remove them completely by traditional physicochemical techniques. In-situ remediation utilizing bioelectrochemical technology represents a promising strategy for degradation of halogenated organic compounds, which can be achieved through potential modulation. In this review, we summarize the reactor configuration of microbial electrochemical dehalogenation systems and relevant organohalide-respiring bacteria. We also highlight the mechanisms of electrode potential regulation of microbial dehalogenation and the role of extracellular electron transfer in dehalogenation process, and further discuss the application of bioelectrochemical technology in bioremediation of halogenated organic compounds. Therefore, this review summarizes the status of research on microbial electrochemical dehalogenation systems from macroscopic to microscopic levels, providing theoretical support for the development of rapid and efficient in situ bioremediation technologies for halogenated organic compounds contaminated sites, as well as insights for the removal of refractory fluorides.

Enhanced dechlorination of 1,2-dichloropropane to propene in a bioelectrochemical system mediated by Dehalogenimonas

Bioelectrochemical systems (BES) are promising technologies to enhance the growth of organohalide-respiring bacteria and to treat chlorinated aliphatic hydrocarbons. In this study, two carbon-based cathodic electrode materials, a graphite brush and a carbon cloth, were used as hydrogen suppliers to couple growth of Dehalogenimonas and dechlorination of 1,2-DCP to nontoxic propene in the cathode vessel. The BES with graphite brush electrode consumed ~4000 µM 1,2-DCP during 110 days and exhibited a degradation rate 5.6-fold higher than the maximum value obtained with the carbon cloth electrode, with a cathode potential set at -0.7 V. Quantitative PCR confirmed that Dehalogenimonas gene copies increased by two orders of magnitude in the graphite brush BES, with an average yield of 1.2·10⁸±5·10⁷ cells per µmol of 1,2-DCP degraded. The use of a pulsed voltage operation (cathode potential set at -0.6 V for 16 h and -1.1 V for 8 h) increased the coulombic efficiency and degradation of 1,2-DCP when compared with a continuous voltage operation of -1.1 V. Bacterial cell aggregates were observed in the surface of the graphite brush electrodes by electron scanning microscopy, suggesting biofilm formation. This study expands the range of chlorinated compounds degradable and organohalide-respiring bacteria capable of growing in BES.

Characterization and Performance of Lactate-Feeding Consortia for Reductive Dechlorination of Trichloroethene

Understanding the underlying mechanism that drives the microbial community mediated by substrates is crucial to enhance the biostimulation in trichloroethene (TCE)-contaminated sites. Here, we investigated the performance of stable TCE-dechlorinating consortia by monitoring the variations in TCE-related metabolites and explored their underlying assembly mechanisms using 16S rDNA amplicon sequencing and bioinformatics analyses. The monitoring results indicated that three stable TCE-dechlorinating consortia were successfully enriched by lactate-containing anaerobic media. The statistical analysis results demonstrated that the microbial communities of the enrichment cultures changed along with time and were distinguished by their sample sources. The deterministic and stochastic processes were simultaneously responsible for shaping the TCE-dechlorinating community assembly. The indicator patterns shifted with the exhaustion of the carbon source and the pollutants, and the tceA-carrying Dehalococcoides, as an indicator for the final stage samples, responded positively to TCE removal during the incubation period. Pseudomonas, Desulforhabdus, Desulfovibrio and Methanofollis were identified as keystone populations in the TCE-dechlorinating process by co-occurrence network analysis. The results of this study indicate that lactate can be an effective substrate for stimulated bioremediation of TCE-contaminated sites, and the reduction of the stochastic forces or enhancement of the deterministic interventions may promote more effective biostimulation.

Impact of electrical stimulation modes on the degradation of refractory phenolics and the analysis of microbial communities in an anaerobic-aerobic-coupled upflow bioelectrochemical reactor

An electrically stimulated anaerobic-aerobic coupled system was developed to improve the biodegradation of refractory phenolics. Expected 4-nitrophenol, 2, 4-dinitrophenol, and COD removals in the system with aerobic cathodic and anaerobic anodic chambers were approximately 53.7%, 45.4%, 22.3% (intermittent mode) and 37.9%, 19.8%, 17.3% (continuous mode) higher than that in the control system (26.0 ± 6.4%, 30.7 ± 7.1%, 49.8 ± 3.0%). 2, 4-dichlorophenol removal in the system with aerobic anodic and anaerobic cathodic chambers was approximately 28.5% higher than that in the control system (71.4 ± 5.7%). The contribution of the aerobic cathodic/anodic chambers to the removal of phenolic compounds was higher than that of the anaerobic cathodic/anodic chambers. The species related to phenolic biodegradation (Rhodococcus, Achromobacter, PSB-M-3, and Sphingobium) were enriched in the cathodic and anodic chambers of the system. These results showed that intermittent electrical stimulation could be a potential alternative for the efficient degradation of refractory phenolics.

A review and perspective of recent research in biological treatment applied in removal of chlorinated volatile organic compounds from waste air

Chlorinated volatile organic compounds (Cl-VOCs) waste air is a kind of typical recalcitrant organic compounds, which poses a great threat to the ecological environment and human health. At present, the biotechnology is considered as a potential strategy for the Cl-VOCs removal due to the advantages of low energy consumption and less possibility of secondary pollution. This work summarizes the recent researches on strains, bioreactors and technology integration. The dominant pure strains for biodegradation of Cl-VOCs are first outlined with a special focus on the co-metabolism of multi-components. It then summarizes two bioreactors (optimized airlift reactor (ALR) and two-phase partitioning bioreactor (TPPB)) and strategy (addition of surfactant) for improvement of biotrickling filter (BTF), which are benefit to achieve the mass transfer enhancement in the removal of hydrophobic Cl-VOCs from waste air. After that, the integration technologies, such as magnetic field (MF)-BTF, non-thermal plasma (NTP)/ultraviolet light (UV)-BTF, and microbial electrolytic cells (MEC), are elucidated, which provide opportunities for complete mineralization of Cl-VOCs in a more efficient, energy-saving and economical way. Finally, current challenges and a perspective of future research on biotechnology for Cl-VOCs removal are thoroughly discussed.

Bioelectrochemical Systems for Groundwater Remediation: The Development Trend and Research Front Revealed by Bibliometric Analysis

: Due to the deficiency of fresh water resources and the deterioration of groundwater quality worldwide, groundwater remedial technologies are especially crucial for preventing groundwater pollution and protecting the precious groundwater resource. Among the remedial alternatives, bioelectrochemical systems have unique advantages on both economic and technological aspects. However, it is rare to see a deep study focused on the information mining and visualization of the publications in this field, and research that can reveal and visualize the development trajectory and trends is scarce. Therefore, this study summarizes the published information in this field from the Web of Science Core Collection of the last two decades (1999–2018) and uses Citespace to quantitatively visualize the relationship of authors, published countries, organizations, funding sources, and journals and detect the research front by analyzing keywords and burst terms. The results indicate that the studies focused on bioelectrochemical systems for groundwater remediation have had a significant increase during the last two decades, especially in China, Germany and Italy. The national research institutes and universities of the USA and the countries mentioned above dominate the research. Environmental Science & Technology, Applied and Environmental Microbiology, and Water Research are the most published journals in this field. The network maps of the keywords and burst terms suggest that reductive microbial diversity, electron transfer, microbial fuel cell, etc., are the research hotspots in recent years, and studies focused on microbial enrichment culture, energy supply/recovery, combined pollution remediation, etc., should be enhanced in future.

Response of humic-reducing microorganisms to the redox properties of humic substance during composting

Humic substance (HS) could be utilized by humus-reducing microorganisms (HRMs) as the terminal acceptors. Meanwhile, the reduction of HS can support the microbial growth. This process would greatly affect the redox conversion of inorganic and organic pollutants. However, whether the redox properties of HS lined with HRMs community during composting still remain unclear. This study aimed to assess the relationships between the redox capability of HS [i.e. humic acids (HA) and fulvic acids (FA)] and HRMs during composting. The results showed that the changing patterns of electron accepting capacity and electron donating capacity of HS were diverse during seven composting. Electron transfer capacities (ETC) of HA was significantly correlated with the functional groups (i.e. alkyl C, O-alkyl C, aryl C, carboxylic C, aromatic C), aromaticity and molecular weight of HA. Aromatic C, phenols, aryl C, carboxylic C, aromaticity and molecular weight of HS were the main structuralfeatures associated with the ETC of FA. Ten key genera of HRMs were found significantly determine these redox-active functional groups of HS during composting, thus influencing the ETC of HS in composts. In addition, a regulating method was suggested to enhance the ETC of HS during composting based on the relationships between the key HRMs and redox-active functional groups as well as environmental variables.

Opportunities for groundwater microbial electro-remediation

Groundwater pollution is a serious worldwide concern. Aromatic compounds, chlorinated hydrocarbons, metals and nutrients among others can be widely found in different aquifers all over the world. However, there is a lack of sustainable technologies able to treat these kinds of compounds. Microbial electro‐remediation, by the means of microbial electrochemical technologies (MET), can become a promising alternative in the near future. MET can be applied for groundwater treatment in situ or ex situ, as well as for monitoring the chemical state or the microbiological activity. This document reviews the current knowledge achieved on microbial electro‐remediation of groundwater and its applications.