Open-circuit Control Research Articles

Viral community and antibiotic resistance genes carried by virus in soil microbial fuel cells

Soil microbial fuel cells (MFCs) can control the horizontal transfer of antibiotic resistance genes (ARGs) by reducing the abundance of mobile genetic elements. However, little is known about the effect of soil MFCs on the horizontal transfer pathway of ARGs transduced by viruses. In this study, the average abundance of ARGs in soil MFCs was 11 % lower than that in the open-circuit control. Lower virus abundance in soil MFCs suggested less detriment of microbial communities. The structure of the viral community was respectively shifted by the introduction of electrodes and the stimulation of biocurrent, especially for the top three viral genera Oslovirus, Tequatrovirus and Incheonvrus in soil. The ARGs aac(6)-I, cat chloramphenicol acetyltransferase, qnrA and vanY were found as the highest health risk (Rank I), and their total abundance showed the lowest in MFCs, with a decrease of 91–99 % compared to the controls. As the main carrier of ARGs, the abundance of Caudoviricetes showed a significant positive correlation with ARGs. Viral integrase was identified respectively coexisting with arnA and vanR (Rank III) in the same contig, which might aggravate their horizontal transfer. Proteobacteria was the main host of viruses carrying ARGs, which exhibited the lowest abundance in the soil MFC. The genus Pseudomonas was the host of viruses carrying ARGs, whose amount reduced by soil MFCs. This study provides an insight into the bioelectrochemical control of ARGs horizontal transfer.

Lithium-Mediated Nitrogen Reduction in a Flow Electrolyzer Cell Using Gas Diffusion Electrodes with Carbon-Based Electrocatalysts

Due to the sluggish kinetics in activating the chemically stable dinitrogen (N2) and the competing hydrogen evolution reaction in aqueous media, recent attention in the field of direct ammonia (NH3) electrosynthesis has been increasingly drawn to the lithium-mediated N2 reduction reaction (LNRR) in tetrahydrofuran (THF)-based non-aqueous electrolyte. In particular, near 100% faradaic efficiency (FE) and/or a current density (j) of 100 mA cm-2 has been demonstrated with unique electrolyte (proton-shuttle additive) and/or electrode designs (expansive electrochemical surface area) in single-compartment cells at elevated N2 pressure (5 – 20 bar).[1,2]A submerged electrode leads to electrolyte flooding and restricts to N2 mass transfer to the electrode surface where electrodeposited Li as an electron mediator is available.[3] However, flow cell electrolyzers containing gas-diffusion electrodes can improve this technology to practical relevance, which features the LNRR on the cathode and hydrogen oxidation reaction (HOR) on the anode. Differing from single-compartment cells, the HOR supplements the ethanol additive (<1 vol%) as the proton source, which not only prevents the oxidative electrolyte degradation but also reduces the energy consumption due to a lower equilibrium anode potential (E0 = 0 VRHE). Gas-diffusion electrodes (GDEs) are used in the few LNRR studies with flow cell configurations, which are prepared by electro- or electroless depositing electrocatalysts (e.g., Pt [4] or PtAu alloy [5]) onto a porous substrate.In this work, carbon-based electrocatalysts (Vulcan XC72R carbon black, battery-grade conductive carbon SUPER C45, and graphitic carbon SFG6L) as low-cost alternatives to previously studied precious metals are assessed for their LNRR performance in flow cells using an HOR anode. In comparison to Vulcan-supported Pt, XC72R and C45 can obtain similar NH3 production rates (rNH3 )and FE at the same . Continuous LNRR at -3 mA cm-2 was demonstrated with linearly increased NH3 production for over 8 h without catalyst layer detachment, which was also verified with open circuit and Ar control experiments (Fig. 1). By presenting the LNRR activity with GDEs spray-coated with carbon-based electrocatalysts, opportunities for future research are suggested, such as novel carbon materials and porous substrates other than SSC for facile N2 mass transfer and Li deposition.

Microbial electrochemical Cr(VI) reduction in a soil continuous flow system.

Microbial electrochemical technologies represent innovative approaches to contaminated soil and groundwater remediation and provide a flexible framework for removing organic and inorganic contaminants by integrating electrochemical and biological techniques. To simulate in situ microbial electrochemical treatment of groundwater plumes, this study investigates Cr(VI) reduction within a bioelectrochemical continuous flow (BECF) system equipped with soil-buried electrodes, comparing it to abiotic and open-circuit controls. Continuous-flow systems were tested with two chromium-contaminated solutions (20-50 mg Cr(VI)/L). Additional nutrients, buffers, or organic substrates were introduced during the tests in the systems. With an initial Cr(VI) concentration of 20 mg/L, 1.00 mg Cr(VI)/(L day) bioelectrochemical removal rate in the BECF system was observed, corresponding to 99.5% removal within nine days. At the end of the test with 50 mg Cr(VI)/L (156 days), the residual Cr(VI) dissolved concentration was two orders of magnitude lower than that in the open circuit control, achieving 99.9% bioelectrochemical removal in the BECF. Bacteria belonging to the orders Solirubrobacteriales, Gaiellales, Bacillales, Gemmatimonadales, and Propionibacteriales characterized the bacterial communities identified in soil samples; differently, Burkholderiales, Mycobacteriales, Cytophagales, Rhizobiales, and Caulobacterales characterized the planktonic bacterial communities. The complexity of the microbial community structure suggests the involvement of different microorganisms and strategies in the bioelectrochemical removal of chromium. In the absence of organic carbon, microbial electrochemical removal of hexavalent chromium was found to be the most efficient way to remove Cr(VI), and it may represent an innovative and sustainable approach for soil and groundwater remediation. Integr Environ Assess Manag 2024;20:2033-2049.© 2024 The Author(s). Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Study on the mechanism of mitigating membrane fouling in MFC-AnMBR coupling system treating sodium and magnesium ion-containing wastewater

ABSTRACT Anaerobic Membrane Bioreactors (AnMBR) offer numerous advantages in wastewater treatment, yet they are prone to membrane fouling after extended operation, impeding their long-term efficiency and stability. In this study, a coupled system was developed using modified conductive membranes as the filtration membrane for the AnMBR and as the anodic conductive membrane in the microbial electrochemical system, with a total volume of approximately 2.57 L. The research focused on understanding the membrane fouling characteristics of the AnMBR when treating wastewater containing sodium ion (Na+) and magnesium ion (Mg2+). When the system was treating wastewater containing Na+, organic pollutants such as proteins and polysaccharides were identified as the primary causes of membrane fouling. Three experimental groups generating different electric currents exhibited extended operational times compared to the open-circuit control group, with extensions of 30, 24, and 15 days, respectively. Conversely, when treating wastewater with Mg2+, organic–inorganic composite fouling, primarily driven by Mg2+ bridging, emerged as the key challenge, with the experimental groups showing operational extensions of 5, 8, and 23 days, respectively, in comparison to the control group. Analysis of proteins and polysaccharides indicated that electric current played a crucial role in reducing organic fouling in the sludge cake layer. When treating wastewater containing Na+, the effectiveness of membrane fouling control was directly proportional to the electric current, while when treating wastewater containing Mg2+, it was directly proportional to the voltage.

Removal of sulfur and nitrogen pollutants in a sediment microbial fuel cell coupled with Vallisneria natans: Efficiency, microbial community structure, and functional genes

The rapid development of the economy has led to an increase in the sulfur and nitrogen load in surface water, which has the potential to cause river eutrophication and the emission of malodorous gases. A lab-scale sediment microbial fuel cell coupled with Vallisneria natans (P-SMFC) was designed for surface water remediation. The enhancement of pollutant removal performance of P-SMFC was evaluated in contrast to the SMFC system without plants (SMFC), the open-circuit control system with plants (C–P), and the open-circuit control system without plants (C–S), while illustrating the mechanisms of the sulfur and nitrogen transformation process. The results demonstrated that the effluent and sediment of P-SMFC had lower concentrations of sulfide compared to other systems. Furthermore, P-SMFC exhibited higher removal efficiency for COD (73.1 ± 8.7%), NH4+-N (80.5 ± 19.8%), and NO3−-N (88.5 ± 11.8%) compared to other systems. The closed-circuit conditions and growth of Vallisneria natans create a favorable ecological niche for functional microorganisms involved in power generation, sulfur oxidation, and nitrogen transformation. Additionally, metagenomic analysis revealed that multifunctional bacteria possessing both denitrification and sulfur oxidation genes, such as Thiobacillus, Dechloromonas, and Bacillus, may play simultaneous roles in metabolizing sulfur and nitrogen, thus serving as integral factors in maintaining the performance of P-SMFC. In summary, these findings provide a theoretical reference for the concurrent enhancement of sulfur and nitrogen pollutants removal in P-SMFC and will facilitate its practical application in the remediation of contaminated surface water.

Simultaneous nitrification/denitrification in a single-chamber stainless steel bioelectrochemical reactor

The removal of nitrogen from wastewater with a low C/N ratio often requires additional carbon sources to address the shortage of electron donors, which increases the cost. We explored a simple and energy effecient means for treating wastewater with a high concentration of ammonia nitrogen under anoxic conditions without the addition of carbon sources. We constructed a stainless steel tube as an anaerobic single-chamber microbial electrolysis cell (MEC) for investigating autotrophic simultaneous nitrification/denitrification (SND). Two different structures (carbon brush vs. stainless-steel) were used to construct biocathodes and compared their performances under different voltages (1.8 V, 1.5 V, 1.2 V) applied by DC power. When voltage was applied at 1.5 V, the removal rates of TN and NH4+-N reached 19.68 ± 0.02 mg L−1 d−1 and 21.04 ± 0.17 mg L−1 d−1, respectively. Simultaneously, it achieved maximum TN and NH4+-N removal over 14 days (44.97 ± 0.28 %, 48.16 ± 0.32 %). These rates were 1.8 and 5 times of that obtained with the conventional carbon brush electrode and open-circuit control. Furthermore, microbial community and SEM analysis indicate that species of Thermomonas, Thibacillus and Thauera were the predominant autotrophic electroactive denitrifying bacteria in the reactors. Overall, we achieved a high rate of nitrogen removal, electron utilization and energy recovery in a single-chamber stainless steel MEC.

Evaluation of organic matter and nitrogen removals, electricity generation and bacterial community responses in sediment microbial fuel cell coupled with Vallisneria natans

With the development of industrial civilization, a large amount of carbon and nitrogen compounds from industrial, agricultural, and human activities are discharged into the environment, which has seriously affected the quality of the surface water. The current remediation methods, such as aeration or chemical addition, not only exhibit high energy consumption but may also lead to secondary pollution. This study constructed a sediment microbial fuel cell system coupled Vallisneria natans (P-SMFC) to remove surface water and sediment pollutants, generate electricity, and reduce the demand for additional oxygen supply. P-SMFC demonstrated excellent pollutant removal and power generation performance under three different pollution loads. P-SMFC exhibited a COD removal efficiency of 80.48% at organic loading rate of 10.64 g/(m3d), which was 10.01%, 26.01%, and 41.77% higher than that of normal SMFC system without plants (SMFC), open-circuit control system with plants (C-P), and open-circuit control system without plants (C-S), respectively. P-SMFC exhibited a TN removal efficiency of 92.61% at nitrogen loading rate of 1.06 g/(m3d), which was 17.31%, 9.92%, and 40.58% higher than that of SMFC, C-P, and C-S, respectively. The maximum power density of the P-SMFC was 45.36 mW·m−3, which was 18.57 mW·m-3 higher than that of the SMFC. The oxygen release and root secretion of organic substances by Vallisneria natans promoted the enrichment of microorganisms with power generation and nitrogen removal functions, such as Geobacter, Acidovorax, Nitrosomonas, Pseudomonas, and Delftia. This study developed a novel, sustainable, and low-cost technology for the in-situ remediation of contaminated surface water.

The effect of anode potential on electrogenesis, methanogenesis and sulfidogenesis in a simulated sewer condition

Methane emissions from the sewer system are considered to be a non-negligible source of aggravating the greenhouse effect. Meanwhile, the sewer system has long been plagued by sulfide-induced corrosion problems. This study explored the possibility of using a bioelectrochemical system to intensify the competition between electroactive bacteria, methanogens and sulfate-reducing bacteria, thereby reducing the production of methane and sulfide. Dual-chamber bioelectrochemical reactors were constructed and operated in fed-batch mode with the coexistence of Electroactive bacteria, Methanogenic archaea and Sulfate-reducing bacteria. Acetate was supplied as the sole carbon source. The results indicated that electrogenesis induced by the anode potentials of -0.42 V and -0.2 V (vs. Ag/AgCl) had advantages over methanogenesis and sulfidogenesis in consuming acetate. The stimulated electrogenesis by anode potentials resulted in a decrease in pH. Methane production was suppressed in the reactors with anode potentials of -0.42 and -0.2 V compared to open circuit controls. In contrast to methane, the capacity for sulfide production was facilitated in the reactors with the anode potentials of -0.42 V and -0.2 V compared to open circuit controls. 16s rRNA gene analysis showed that Geobacter was the most abundant genus on the anode biofilm in the anode potential-controlled reactor, while acetoclastic methanogens dominated in open circuit controls. Methanosaeta and Methanosarcina were the most abundant methanogens in open circuit controls. Collectively, our study demonstrates that the use of electrodes with anode potential control can help to control methane emissions, but could not yet prevent sulfide production, which requires further research.

Genome-Scale Mutational Analysis of Cathode-Oxidizing Thioclava electrotropha ElOx9T.

Extracellular electron transfer (EET) – the process by which microorganisms transfer electrons across their membrane(s) to/from solid-phase materials – has implications for a wide range of biogeochemically important processes in marine environments. Though EET is thought to play an important role in the oxidation of inorganic minerals by lithotrophic organisms, the mechanisms involved in the oxidation of solid particles are poorly understood. To explore the genetic basis of oxidative EET, we utilized genomic analyses and transposon insertion mutagenesis screens (Tn-seq) in the metabolically flexible, lithotrophic Alphaproteobacterium Thioclava electrotropha ElOx9T. The finished genome of this strain is 4.3 MB, and consists of 4,139 predicted ORFs, 54 contain heme binding motifs, and 33 of those 54 are predicted to localize to the cell envelope or have unknown localizations. To begin to understand the genetic basis of oxidative EET in ElOx9T, we constructed a transposon mutant library in semi-rich media which was comprised of >91,000 individual mutants encompassing >69,000 unique TA dinucleotide insertion sites. The library was subjected to heterotrophic growth on minimal media with acetate and autotrophic oxidative EET conditions on indium tin oxide coated glass electrodes poised at –278 mV vs. SHE or un-poised in an open circuit condition. We identified 528 genes classified as essential under these growth conditions. With respect to electrochemical conditions, 25 genes were essential under oxidative EET conditions, and 29 genes were essential in both the open circuit control and oxidative EET conditions. Though many of the genes identified under electrochemical conditions are predicted to be localized in the cytoplasm and lack heme binding motifs and/or homology to known EET proteins, we identified several hypothetical proteins and poorly characterized oxidoreductases that implicate a novel mechanism(s) for EET that warrants further study. Our results provide a starting point to explore the genetic basis of novel oxidative EET in this marine sediment microbe.

Plant nutrients recovery from agro-food wastewaters using microbial electrochemical technologies based on porous biocompatible materials

Microbial recycling cells (MRCs) are a category of microbial electrochemical technologies aimed at recovering plant nutrients from agro-food wastewater and recycling them as fertilizers. Here, we used terracotta as a biocompatible and low-cost material to fabricate porous air-water separators. At the interface, access to oxygen induces a red-ox gradients, facilitating nutrients deposition on the material itself. We tested: a) raw swine manure (rich in suspended solids, rich in mineral-N) and b) an artificial wastewater (suspended-solid-free, rich in mineral-P). Bioanodes (carbon cloths enriched in electroactive biofilm) were connected to air-exposed cathodes, generating currents of ≈ 2 mA and an electric field of ≈ 400 mV. Over 250 days, consistent amounts (up to 69%) of the main nutrients (N, P, K, Mg, Mn, Fe) were removed from the wastewater and deposited on the terracotta separators at significantly higher concentrations in presence of the electrochemical circuit (MRC), as compared to open-circuit controls. Cation and water electro-driven migration towards the cathode and high cathodic pH (up to 10.7) were favouring inorganic salts accumulation and precipitation on the porous surface. Accordingly, halophilic microbial species were populating the biofilm grown on the terracotta. In the case of SM, suspended-solids were also deposited on the surface (as revealed by microscope imaging), driving to recover organic forms of nutrients. Porous biocompatible materials (such as terracotta) can be enriched of nutrients from wastewaters, to be later re-used in agriculture as soil conditioners. Future studies on this concept should look at optimizing surface/volume ratios, to maximize nutrients recovery efficiencies.

Enhanced Electrochemical Treatment of Phenanthrene-polluted Soil using Microbial Fuel Cells

In this study, tubular microbial fuel cells (MFCs) were inserted into phenanthrene-contaminated water-logged soil in order to evaluate their treatment efficiency and overall system performance within 60 days’ incubation period. At day 10, phenanthrene degradation rates were found to decrease with increasing distance from the anodes from 50-55 % at 2 cm to 38-40 % at 8 cm. Bromate (used as a catholyte) removal in both MFCs was about 80-95 % on average which is significantly higher than the open circuit controls (15-40 %) over the 60day period. Total chemical oxygen demand removal (72.8 %) in MFCs amended with surfactants was significantly higher than MFCs without surfactant (20 %). This suggests that surfactant addition may have enhanced bioavailability of not only phenanthrene, but other organic matter present in the soil. The outcomes of this work has demonstrated the simultaneous removal of phenanthrene (86%) and bromate (95%) coupled with concomitant bioelectricity generation (about 4.69 mWm-2) using MFC systems within a radius of influence (ROI) up to 8 cm. MFC technology may be used for in situ decontamination of soils due to its potential detoxification capacity and could be deployed directly as a prototype-MFC design in field applications.

Electrochemical evidence for in situ microbial activity at the Deep Mine Microbial Observatory (DeMMO), South Dakota, USA.

The subsurface is Earth's largest reservoir of biomass. Micro-organisms are the dominant lifeforms in this habitat, but the nature of their in situ activities remains largely unresolved. At the Deep Mine Microbial Observatory (DeMMO) located in the Sanford Underground Research Facility (SURF) in Lead, South Dakota (USA), we performed in situ electrochemical incubations designed to assess the potential for deep groundwater microbial communities to utilize extracellular electron transfer to support microbial respiration. DeMMO 4 was chosen for its stable geochemistry and microbial community. Graphite and indium tin oxide electrodes poised at -200mV versus SHE were incubated along with open circuit controls and various minerals in a parallel flow reactor that split access to fluids across different treatments. From the patterns of net current over time (fluctuating between anodic and cathodic currents over the course of a few days to weeks) and the catalytic features measured using periodic cyclic voltammetry, evidence of both oxidative and reductive microbe-electrode interactions was observed. The predominant catalytic activity ranged from -210 to -120mV. The observed temporal variability in electrochemical activity was unexpected given the documented stability in major geochemical parameters. This suggests that the accessed fluids are more heterogeneous in electrochemically active microbial populations than previously predicted from the stable community composition. As previously reported, the fracture fluid and surface-attached microbial communities at SURF differed significantly. However, only minimal differences in community composition were observed between poised potential electrodes, open circuit electrodes, and mineral incubations. These data support that in this environment the ability to attach to surfaces is a stronger driver of microbial community structure than the type or reactivity of the surface. We demonstrate that insight into specific activities can be gained from electrochemical methods, specifically chronoamperometry coupled with routine cyclic voltammetry, which provide a sensitive approach to evaluate microbial activities in situ.

Electroactive microorganisms in mouse feces

The gut microbiome is not only an indicator of different pathologies, but it also influences metabolism and overall health of the host. Recently, microorganisms inherent to the gut microbiome, such as Listeria monocytogenes, Enterococcus faecalis and Clostridium cochlearium, were demonstrated to be electroactive, i.e. to perform extracellular electron transfer (EET). To further explore the presence of electroactive microorganisms in the gut microbiome electrochemical enrichment starting from mouse feces was performed. Open circuit, abiotic and autoclaved inoculum controls were run in parallel. A maximum current density of 122±23 µA cm−2 at low coulombic efficiency ( ̴1%) was achieved. The presence of biofilms at the anode and microbial electrochemical activity with a formal potential of EET of 0.23±0.01 V vs. Ag/AgCl sat. KCl was demonstrated using fluorescence microscopy and cyclic voltammetry. The 16S rRNA gene sequencing and PCR-free Nanopore sequencing showed the enrichment and dominance of Shigella flexneri.

Electrogenic Biofilm Development Determines Charge Accumulation and Resistance to pH Perturbation

The electrogenic biofilm and the bio-electrode interface are the key biocatalytic components in bioelectrochemical systems (BES) and can have a large impact on cell performance. This study used four different anodic carbons to investigate electrogenic biofilm development to determine the influence of charge accumulation and biofilm growth on system performance and how biofilm structure may mitigate against pH perturbations. Power production was highest (1.40 W/m3) using carbon felt, but significant power was also produced when felt carbon was open-circuit acclimated in a control reactor (0.95 W/m3). The influence of carbon material on electrogenic biofilm development was determined by measuring the level of biofilm growth, using sequencing to identify the microbial populations and confocal microscopy to understand the spatial locations of key microbial groups. Geobacter spp. were found to be enriched in closed-circuit operation and these were in close association with the carbon anode, but these were not observed in the open-circuit controls. Electrochemical analysis also demonstrated that the highest mid-point anode potentials were close to values reported for cytochromes from Geobacter sulfurreductans. Biofilm development was greatest in felt anodes (closed-circuit acclimated 1209 ng/μL DNA), and this facilitated the highest pseudo-capacitive values due to the presence of redox-active species, and this was associated with higher levels of power production and also served to mitigate against the effects of low-pH operation. Supporting carbon anode structures are key to electrogenic biofilm development and associated system performance and are also capable of protecting electrochemically active bacteria from the effects of environmental perturbations.

Effect of soil type on heavy metals removal in bioelectrochemical system

Microbial fuel cell (MFC) technology is widely used to remediate heavy metal pollution of soil, and the applicability of soils with different physical and chemical properties under micro-electric field has not been studied. In this study, copper was effectively removed in four typical soil-filled MFCs. The removal efficiencies of copper from closed-circuit MFCs filled with paddy, red, black and alluvial soils were 2.9, 1.50, 3.48 and 3.40 times higher than those in the open-circuit control group, respectively. However, the contributions of electromigration and diffusion mechanisms were different under different soil types. The greatest copper removal (19.3 ± 0.8%) was achieved based on electromigration of the electric field inside the paddy soil MFC in 63 days, while the greatest copper removal (25 ± 2%) was achieved under the action of diffusion mechanism inside the red soil MFC. According to redundancy analysis, the removal of copper by electromigration was positively correlated with electricity generation performance and acid extractable Cu content, whereas copper removal based on diffusion was positively related to soil pore volume and acid extractable Cu content. The cation exchange capacity and total organic carbon of soil were negatively correlated with the acid extractable Cu content, and electrical conductivity of soil was positively correlated with the MFC electricity generation performance. Furthermore, the directional movement of protons under an electric field alleviated the issue of soil acidification caused by citric acid.

Microbial Assisted Hexavalent Chromium Removal in Bioelectrochemical Systems

Groundwater is the environmental matrix that is most frequently affected by anthropogenic hexavalent chromium contamination. Due to its carcinogenicity, Cr(VI) has to be removed, using environmental-friendly and economically sustainable remediation technologies. BioElectrochemical Systems (BESs), applied to bioremediation, thereby offering a promising alternative to traditional bioremediation techniques, without affecting the natural groundwater conditions. Some bacterial families are capable of oxidizing and/or reducing a solid electrode obtaining an energetic advantage for their own growth. In the present study, we assessed the possibility of stimulating bioelectrochemical reduction of Cr(VI) in a dual-chamber polarized system using an electrode as the sole energy source. To develop an electroactive microbial community three electrodes were, at first, inserted into the anodic compartment of a dual-chamber microbial fuel cell, and inoculated with sludge from an anaerobic digester. After a period of acclimation, one electrode was transferred into a polarized system and it was fixed at −0.3 V (versus standard hydrogen electrode, SHE), to promote the reduction of 1000 µg Cr(VI) L−1. A second electrode, served for the set-up of an open circuit control, operated in parallel. Cr(VI) dissolved concentration was analysed at the initial, during the experiment and final time by spectrophotometric method. Initial and final microbial characterization of the communities enriched in polarized system and open circuit control was performed by 16S rRNA gene sequencing. The bioelectrode set at −0.3 V showed high Cr(VI) removal efficiency (up to 93%) and about 150 µg L−1 day−1 removal rate. Similar efficiency was observed in the open circuit (OC) even at about half rate. Whereas, purely electrochemical reduction, limited to 35%, due to neutral operating conditions. These results suggest that bioelectrochemical Cr(VI) removal by polarized electrode offers a promising new and sustainable approach to the treatment of groundwater Cr(VI) plumes, deserving further research.

Molecular Transformation of Crude Oil Contaminated Soil after Bioelectrochemical Degradation Revealed by FT-ICR Mass Spectrometry.

Bioremediation is a low-cost approach for crude oil spill remediation, but it is often limited by electron acceptor availability. In addition, the biodegradation products of crude oil contaminants are complex, and transformation pathways are difficult to decipher. This study demonstrates that bioelectrochemical systems (BESs) can be effective in crude oil degradation by integrating biological and electrochemical pathways, and more importantly, it provides the first understanding on the daughter products of bioelectrochemical hydrocarbon degradation. Using electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and two-dimensional gas chromatography (GC × GC), the results showed that the active BES reactor improved the total petroleum hydrocarbon (TPH) degradation by ∼70% than open circuit control reactors. After separating the daughter products into nine fractions (MA1-MA9) according to the molecular weight (m/z 200-1000) by modified aminopropyl silica (MAPS) fractionation, we found that active BES remediation resulted in 50% more polar, oxygen-containing naphthenic (NAP) acids. The MA4 fraction (centered at ∼550 Da) increased by 47%, and MA5 and MA7 fractions with higher molucular weight increased by a maximum of ∼7- and 9-fold, respectively. These results are in accordance with the variation of bulk elemental compositions in O2 species, where daughter transformation products doubled relative to parent oil extract. The contribution of newly generated NAP acids was mainly from higher-order oxygen species (O5-O6) with increased hydrophobicity in conjunction with a decreased abundance in lower-order oxygen species (O1). Overall, the study suggests that n-alkane degradation occurred via β-oxidation to oxygenated transformation products with lower molecular weight, such as n-alcohols in O1 class and subsequently to n-fatty acids in O2 class.

Performance of cathodic nitrate reduction driven by electricity generated from ANAMMOX sludge in anode

In this study, ANAMMOX sludge was used as anode microbial catalysts to drive electrocatalytic reduction of nitrate in the SnCu-Pd/CFC catalytic cathode with total nitrogen (TN) removal efficiency of ANAMMOX as well as generate electricity without additional carbon and energy source. The system operation with 1.74 Kg·N/m3·d as nitrogen loading rate (NLR) exhibited a TN removal efficiency of 96.3% and obtained the highest nitrogen removal rate (NRR, 1.69 Kg·N/m3·d), increased by 14.9% and 0.30 Kg·N/m3·d compared with open circuit (control group), respectively. Maximum voltage (39.8 mV) and power density (21.20 ± 0.05 mW/m3, standardized to anode surface area) were also observed. Additionally, microbial community analysis revealed community structure of S2anode had an obvious disparity compared with others as the predominant ANAMMOX bacteria (AnAOB) closed to anode surface was evolved from Candidatus_Kuenenia to Candidatus_Brocadia.

Electro-fermentation regulates mixed culture chain elongation with fresh and acclimated cathode

Chain elongation has been proposed as a novel secondary fermentation process for the production of medium chain fatty acids as organic waste valorization. However, a strategy to effectively control the product spectrum of the chain elongation process is required. This study evaluated the effect of electro-fermentation on the mixed culture chain elongation process in detail. The results showed that electro-fermentation with a fresh carbon felt cathode increased the caproate specificity by about 28%, compared with the open circuit control and without carbon felt control. With an acclimated cathode, the effect of electro-fermentation on caproate specificity depended on the substrate concentration. The majority of bacteria belonged to Firmicutes, Bacteroidetes, and Proteobacteria, the distribution of which under biofilm and planktonic conditions were shaped by the application of electro-fermentation. These findings suggested that microorganisms interacted electrochemically with the polarized fresh electrode for chain elongation. The synergistic effect between microorganisms and acclimated electrode was largely affected by elevated substrate concentrations, and thus resulted in a redirection of the fermentation pattern.

Removal of Hepatitis B virus surface HBsAg and core HBcAg antigens using microbial fuel cells producing electricity from human urine

Microbial electrochemical technology is emerging as an alternative way of treating waste and converting this directly to electricity. Intensive research on these systems is ongoing but it currently lacks the evaluation of possible environmental transmission of enteric viruses originating from the waste stream. In this study, for the first time we investigated this aspect by assessing the removal efficiency of hepatitis B core and surface antigens in cascades of continuous flow microbial fuel cells. The log-reduction (LR) of surface antigen (HBsAg) reached a maximum value of 1.86 ± 0.20 (98.6% reduction), which was similar to the open circuit control and degraded regardless of the recorded current. Core antigen (HBcAg) was much more resistant to treatment and the maximal LR was equal to 0.229 ± 0.028 (41.0% reduction). The highest LR rate observed for HBsAg was 4.66 ± 0.19 h−1 and for HBcAg 0.10 ± 0.01 h−1. Regression analysis revealed correlation between hydraulic retention time, power and redox potential on inactivation efficiency, also indicating electroactive behaviour of biofilm in open circuit control through the snorkel-effect. The results indicate that microbial electrochemical technologies may be successfully applied to reduce the risk of environmental transmission of hepatitis B virus but also open up the possibility of testing other viruses for wider implementation.