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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. [ABSTRACT FROM AUTHOR]

ABSTRACT Bioelectrochemical systems (BESs) offer a sustainable method for chemical production, including the enhanced production of succinic acid. By combining fermentation with BES, it could be possible to achieve sustainable succinic acid production and CO2 fixation using Actinobacillus succinogenes. In literature, the potential application of BES is commonly associated with increased succinate yields, as it is expected to enhance the availability of NADH, thereby influencing the intracellular nicotinamide adenine dinucleotide (NADH/NAD+) balance. However, it remains unclear whether BES can improve NADH regeneration and achieve higher NADH/NAD+ ratios across all growth phases of A. succinogenes. This study investigates the impact of an applied electrical potential on the intracellular NADH/NAD+ ratio during an electrochemical‐assisted fermentation process. Using an adapted high‐performance liquid chromatography method with a Supelcosil LC‐18‐T column, it was demonstrated that NADH availability in BES, particularly during the stationary growth phase, improved by up to 1.98‐fold compared to the control. This enhancement in reducing power led to a succinate yield of 0.747 ± 0.01 g g−1, representing a 15.65% increase compared to a fermentation without electrochemical assistance. These findings support the expectation that the use of BES could enhance the competitiveness of bio‐based succinate production. [ABSTRACT FROM AUTHOR]

Industrial applications of microbial electrochemical systems will require regular maintenance shutdowns, involving inspections and component replacements to extend the lifespan of the system. Here, we examined the impact of such shutdowns on the performance of three electrode materials (i. e., platinized titanium, graphite, and nickel) as cathodes in a microbial electrochemical system that would be used for electromethanogenesis in power‐to‐gas applications. We focused on methane (CH4) production from hydrogen (H2) and carbon dioxide (CO2) using Methanothermobacter thermautotrophicus. We showed that the platinized titanium cathode resulted in high volumetric CH4 production rates and Coulombic efficiencies. Using a graphite cathode would be more cost‐effective than using the platinized titanium cathode in microbial electrochemical systems, but showed an inferior performance. The microbial electrochemical system with the nickel cathode showed improvements compared to the graphite cathode. Additionally, this system with a nickel cathode demonstrated the fastest recovery during a shutdown experiment compared to the other two cathodes. Fluctuations in pH and nickel concentrations in the catholyte during power interruptions affected CH4 production recovery in the system with the nickel cathode. This research enhances understanding of the integration of biological and electrochemical processes in microbial electrochemical systems, providing insights into electrode selection and operating strategies for effective and sustainable CH4 production. [ABSTRACT FROM AUTHOR]

Pb-contaminated soil poses inherent risks for the spread of antibiotic resistance genes (ARGs). However, few reports have investigated the distribution of lead resistance genes (LRGs), particularly their role in ARGs dynamics during Pb-contaminated soil remediation. This study explored the mechanisms driving ARGs variation under different remediation strategies. The results indicated that an increase in the total abundance of ARGs after applying montmorillonite (Imvite), the composite remediation agents of MgO and Ca(H2PO4)2 (MgO-Ca(H2PO4)2), and the composite remediation agents of montmorillonite, MgO, and Ca(H2PO4)2 (Imvite-MgO-Ca(H2PO4)2). Bioelectrochemical systems (BES) effectively reduced ARGs abundance, and when combined with Imvite-MgO-Ca(H2PO4)2, lowered the risk of ARGs proliferation linked to antibiotic deactivation. Changes in Pb concentration and pH reshaped microbial communities, impacting both LRGs and ARGs. To reduce the risk of ARGs proliferation and transmission during, various control strategies, such as modifying Pb stress, adjusting pH, and manipulating microbial community structure, have been proposed. The study provided theoretical foundation and practical strategies for controlling ARGs dissemination during the remediation of heavy metal-contaminated soil. [ABSTRACT FROM AUTHOR]

Fossil resources must be replaced by renewable resources in production systems to mitigate green-house gas emissions and combat climate change. Electrofermentation utilizes a bioelectrochemical system (BES) to valorize industrial and municipal waste. Current electro-fermentation research is mainly focused on microbial electrosynthesis using CO2 for producing commodity chemicals and replacing petroleum-based infrastructures. However, slow production rates and low titers of metabolites during CO2 -based microbial electrosynthesis impede its implementation to the real application in the near future. On the other hand, CO is a highly reactive gas and an abundant feedstock discharged from fossil fuel-based industry. Here, we investigated CO and CO2 electro-fermentation, using a CO-enriched culture. Fresh cow fecal waste was enriched under an atmosphere of 50% CO and 20% CO2 in N2 using serial cultivation. The CO-enriched culture was dominated by Clostridium autoethanogenum (≥89%) and showed electroactivity in a BES reactor with CO2 sparging. When 50% CO was included in the 20% CO2 gas with 10  mA applied current, acetate and ethanol were produced up to 12.9  ±  2.7  mM and 2.7  ±  1.1  mM, respectively. The coulombic efficiency was estimated to 148%  ±  8% without an electron mediator. At 25  mA, the culture showed faster initial growth and acetate production but no ethanol production, and only at 86%  ±  4% coulombic efficiency. The maximum optical density (OD) of 10  mA and 25  mA reactors were 0.29  ±  0.07 and 0.41  ±  0.03, respectively, whereas it was 0.77  ±  0.19 without electric current. These results show that CO electro-fermentation at low current can be an alternative way of valorizing industrial waste gas using a bioelectrochemical system. [ABSTRACT FROM AUTHOR]

Plastic wastes, widely distributed in the environment, can be transformed into microplastics, posing a huge threat to ecosystems and human health due to their stability and adsorbability to other toxic pollutants (e.g., heavy metals and antibiotics). Recently, microbial degradation of (micro)plastics has gained widespread attention because of its green and sustainable properties. Microbial degradation of (micro)plastics is based on the cascade effects of various enzymes secreted by microorganisms, which can convert (micro)plastics into oligomers and monomers, or even mineralize them into CO2 and H2O. The microbial degradation of (micro)plastics is affected by multiple factors, such as microbial species, plastic properties, and environmental conditions. Currently, limited efficient plastic-degrading microorganisms have been discovered, and their degradation mechanisms are still unclear. Furthermore, the efficiency of microbial degradation needs to be improved for future application. Therefore, this review systematically summarizes the sources and properties of existing plastics, identifies pure cultures and mixed cultures for plastic degradation, and examines their influencing factors. In particular, the microbial degradation behaviors of (micro)plastics, including relevant enzymes, degradation efficiency, and degradation mechanisms, were thoroughly discussed. Additionally, the augmentation technologies coupling with microbial degradation, such as advanced oxidation, electrochemical, and genetic engineering technologies, were introduced and highlighted for their potential prospects. This review provides a reference for future research and development of (micro)plastic biodegradation technology. [ABSTRACT FROM AUTHOR]

Cable bacteria are filamentous bacteria that couple the oxidation of sulfide in sediments to the reduction of oxygen via long-distance electron transport over centimeter distances through periplasmic wires. However, the capability of cable bacteria to perform extracellular electron transfer to acceptors, such as electrodes, has remained elusive. In this study, we demonstrate that living cable bacteria actively move toward electrodes in different bioelectrochemical systems. Carbon felt and carbon fiber electrodes poised at +200 mV attracted live cable bacteria from the sediment. When the applied potential was switched off, cable bacteria retracted from the electrode. qPCR and scanning electron microscopy corroborated this finding and revealed cable bacteria in higher abundance present on the electrode surface compared with unpoised controls. These experiments raise new possibilities to study metabolism of cable bacteria and cultivate them in bioelectrochemical devices for bioelectronic applications, such as biosensing and bioremediation. [ABSTRACT FROM AUTHOR]

Carbon dioxide can be relatively easily reduced to organic matter in a bioelectrochemical system (BES). However, due to insufficient reduction force from in‐situ hydrogen evolution, it is difficult for nitrogen reduction. In this study, MoS2 was firstly used as an electrocatalyst for the simultaneous reduction of CO2 and N2 to produce microbial protein (MP) in a BES. Cell dry weight (CDW) could reach 0.81±0.04 g/L after 14 d operation at −0.7 V (vs. RHE), which was 108±3 % higher than that from non‐catalyst control group (0.39±0.01 g/L). The produced protein had a better amino acid profile in the BES than that in a direct hydrogen system (DHS), particularly for proline (Pro). Besides, MoS2 promoted the growth of bacterial cell on an electrode and improved the biofilm extracellular electron transfer (EET) by microscopic observation and electrochemical characterization of MoS2 biocathode. The composition of the microbial community and the relative abundance of functional enzymes revealed that MoS2 as an electrocatalyst was beneficial for enriching Xanthobacter and enhancing CO2 and N2 reduction by electrical energy. These results demonstrated that an efficient strategy to improve MP production of BES is to use MoS2 as an electrocatalyst to shift amino acid profile and microbial community. [ABSTRACT FROM AUTHOR]

In all variants where carbon felt was present, imidacloprid degradation by the microflora of bottom sediments was many times higher than in the control, reaching 84.0 ± 1.7% under the polar connection of an external voltage source (1.2 V). When Shewanella oneidensis MR-1 was introduced, almost complete degradation of the pollutant was observed, while in the control without electrodes, it was 29.7 ± 6.0%. The relative representation of the genes of the MtrB transmembrane protein of the respiratory chain, which is associated with exoelectrogenesis, depended on the external chain and had a maximum value when the voltage source was connected polarly, correlating with the pesticide degradation by the autochthonous microflora, similar to the DyP-type peroxidase genes. The introduction of S. oneidensis MR-1 resulted in an almost tenfold increase in the relative representation of DyP-type peroxidase genes. In all experimental variants, the values of the DyP relative representation were significantly higher than in the control without carbon felt, as well as the degree of imidacloprid degradation under these experimental conditions. [ABSTRACT FROM AUTHOR]

Cupriavidus necator, despite lacking direct electron transfer capabilities, demonstrates efficient reduction of various redox mediators in oxygen‐free cultivation within bioelectrochemical systems. This study investigates the reduction site of ferricyanide through inhibition and expression rate analysis of oxygen and nitrate respiration chain complexes, comparing aerobic cultivation conditions with fructose as carbon and electron donor to autotrophic (CO2/H2/O2) and anodic cultivation conditions (fructose/anode). Azide inhibition identified cytochrome c oxidase as the primary complex facilitating electron transfer to ferricyanide, with a secondary role proposed for nitrite reductase NirS, demonstrating a 3.9±1.1‐fold higher expression when exposed to anodic conditions. The 2.9±0.6‐fold increase in the expression of the natural porin OmpA under anodic conditions implies its potential involvement in ferricyanide uptake. Additionally, chemically permeabilizing cell membranes with cetyltrimethylammonium bromide doubles ferricyanide reduction rates without an anode present, offering insights for optimizing redox mediation in C. necator based bioelectrochemical systems. This study opens up new possibilities for the targeted optimization of mediated electron transfer in C. necator and other organisms. [ABSTRACT FROM AUTHOR]

Abstract Industrial applications of microbial electrochemical systems will require regular maintenance shutdowns, involving inspections and component replacements to extend the lifespan of the system. Here, we examined the impact of such shutdowns on the performance of three electrode materials (i. e., platinized titanium, graphite, and nickel) as cathodes in a microbial electrochemical system that would be used for electromethanogenesis in power‐to‐gas applications. We focused on methane (CH4) production from hydrogen (H2) and carbon dioxide (CO2) using Methanothermobacter thermautotrophicus. We showed that the platinized titanium cathode resulted in high volumetric CH4 production rates and Coulombic efficiencies. Using a graphite cathode would be more cost‐effective than using the platinized titanium cathode in microbial electrochemical systems, but showed an inferior performance. The microbial electrochemical system with the nickel cathode showed improvements compared to the graphite cathode. Additionally, this system with a nickel cathode demonstrated the fastest recovery during a shutdown experiment compared to the other two cathodes. Fluctuations in pH and nickel concentrations in the catholyte during power interruptions affected CH4 production recovery in the system with the nickel cathode. This research enhances understanding of the integration of biological and electrochemical processes in microbial electrochemical systems, providing insights into electrode selection and operating strategies for effective and sustainable CH4 production.

The embryonic technology of microbial electrosynthesis (MES) possesses the potential to alleviate global CO2 concentration with concomitant recovery of valuables. However, due to the significant bottlenecks of inferior yield of valuables and higher capital cost, its potential has not been fully realized at a larger scale till date. With the aim of bridging this lacuna, a first of its kind pilot-scale MES (PSMES) was designed and operated to yield acetic acid from biogas. The PSMES was able to produce 70.55 g m−2.day of acetic acid in its extraction chamber with the coulombic efficiency of 77.8 % for an imposed cathode potential of −1.0 V vs. standard hydrogen electrode. Moreover, life cycle assessment (LCA) and economic analysis of the PSMES was also conducted to elucidate the economic and environmental feasibility of the same. From the LCA and economic analysis of the PSMES, it was inferred that acrylic sheet and carbon felt used during the fabrication of PSMES were the major culprit in terms of both environmental and economic sustainability and thus should be replaced with greener but cost-effective materials. Therefore, these results would guide the budding scholars in designing more economical and environment friendly scaled-up MES, thus paving towards the commercialization of this ingenious technology.

This research analyzed the contribution of different electron transfer pathways for H 2 production in a bioelectrochemicallly assisted dark fermentation system (BEDF), and compared to an electric field-driven dark fermentation (EFDF) reactor. The results showed that intrinsic extracellular electron transfer (iEET) via dark fermentation accounted for 76.3% of the H 2 production in the BEDF reactor. In comparison, the extracellular electron transfer (bEET) pathway via the bioelectrode enhanced by the bioelectrochemical system and the electric field-driven extracellular electron transfer (eEET) in the bulk solution accounted for 5% and 18.7%, respectively. This suggests that the main electron transfer pathway for H 2 production comes from the bulk solution rather than that on the bioelectrodes. Under the condition of electric field, extracellular polymeric substances (EPS) were secreted in large quantities in the bulk solution, and electroactive microorganisms such as Proteobacteria were significantly enriched, which further promote the H 2 production through the eEET pathway. [Display omitted] • H 2 production was increased by electric field rather than that on bioelectrode. • BEET and eEET pathways account for 5% and 18.7% of total hydrogen production. • Electric fields activate more hydrogen-producing microbial metabolic pathways. • Electric field enriches bacteria that affect EPS secretion in bulk solution. [ABSTRACT FROM AUTHOR]

A significant variation in the relative representation of copies of bacterial genes of dye-decolorizing DyP peroxidases typical for the genus Shewanella and a number of other microorganisms was found in the bottom sediments of freshwater reservoirs. It was found that the specific rate of decolorization of crystal violet in a laboratory bioelectrochemical system by a mixed culture of bottom sediments, which showed the highest representation of DyP genes, depended on the method of electrical stimulation of the external circuit and the concentration of the dye. After an increase in the concentration of more than 20 microns, the maximum speed was achieved in the presence of an ionistor polarly connected to the external electrical circuit of the bioelectrochemical system and amounted to 3.23 ± 0.11 μM/h, while with the opposite polarity connection, a minimum value of 2.07 ± 0.08 μM/h was observed. In the case of an open circuit and a resistor, similar indicators occurred with 2.88 ± 0.09 and 2.67 ± 0.12 μM/h, respectively. When analyzing the decolorization products, a consistent decrease in the maxima of the absorption bands of the dye was noted, indicating its more complete degradation by the mixed culture. The results may be of interest for the development of methods to improve the efficiency of bioelectrochemical methods of environmental biotechnology by electrostimulation of the external circuit. [ABSTRACT FROM AUTHOR]

Degradation of oil hydrocarbons artificially introduced into bottom sediments in a bioelectrochemical system of a membrane-free (silt) type was studied. Passive bioelectrochemical stimulation by means of electrodes connected by an external circuit with a resistance of 1 kΩ, with an average electric current of ~85 µA was found to cause an increase in degradation during two months from 23.0 to 57.9%. Contamination of bottom sediments with oil (1.32 g/kg) slightly decreased the current in the external circuit of the bioelectrochemical system. The relationship was revealed between the degree of oil degradation and predominant utilization of the lighter n-alkanes in the C14H30–C30H62 series, compared with both the original oil and the residual hydrocarbons of the control. An increase in the representation of the alkB alkane monooxygenase genes relative to the 16S rRNA gene in the total DNA isolated from the sediments was induced by the introduction of hexadecane, both in the case of electrochemical stimulation and in the control. The results may be of interest for the development of new methods of bioelectrochemical removal of organic pollutants from anaerobic environments. [ABSTRACT FROM AUTHOR]

Municipal solid waste incineration (MSWI) fly ash is classified as hazardous waste due to high leachable heavy metals, and incineration leachate belongs to organic wastewater with high biodegradability. Electrodialysis (ED) has shown potential for the removal of heavy metals from fly ash, and bioelectrochemical system (BES) employs biological and electrochemical reactions to generate electricity and remove contaminants from a wide range of substrates. In this study, the ED-BES coupled system was constructed for the co-treatment of fly ash and incineration leachate, where the ED was driven by BES. The treatment effect of fly ash by varying additional voltage, initial pH and liquid-to-solid (L/S) ratio was evaluated. Results showed that the highest removal rates of Pb, Mn, Cu and Cd were 25.43%, 20.13%, 32.14% and 18.87% after 14 days treatment of the coupled system, respectively. These values were obtained under 300 mV of additional voltage, L/S 20 and initial pH3. After the treatment of the coupled system, the fly ash leaching toxicity was lower than the threshold of GB5085.3-2007. The highest energy saving for removed Pb, Mn, Cu and Cd were 6.72, 15.61, 8.99 and 17.46 kWh/kg, respectively. The ED-BES can be considered a cleanliness approach to treating fly ash and incineration leachate simultaneously. [ABSTRACT FROM AUTHOR]

Bioelectrochemical systems (BESs) are an innovative technology for the efficient degradation of antibiotics. Shewanella oneidensis (S. oneidensis) MR-1 plays a pivotal role in degrading sulfamethoxazole (SMX) in BESs. Our study investigated the effect of BES conditions on SMX degradation, focusing on microbial activity. The results revealed that BESs operating with a 0.05 M electrolyte concentration and 2 mA/cm2 current density outperformed electrolysis cells (ECs). Additionally, higher electrolyte concentrations and elevated current density reduced SMX degradation efficiency. The presence of nutrients had minimal effect on the growth of S. oneidensis MR-1 in BESs; it indicates that S. oneidensis MR-1 can degrade SMX without nutrients in a short period of time. We also highlighted the significance of mass transfer between the cathode and anode. Limiting mass transfer at a 10 cm electrode distance enhanced S. oneidensis MR-1 activity and BES performance. In summary, this study reveals the complex interaction of factors affecting the efficiency of BES degradation of antibiotics and provides support for environmental pollution control. [ABSTRACT FROM AUTHOR]

Fossil resources must be replaced by renewable resources in production systems to mitigate green-house gas emissions and combat climate change. Electro-fermentation utilizes a bioelectrochemical system (BES) to valorize industrial and municipal waste. Current electro-fermentation research is mainly focused on microbial electrosynthesis using CO2 for producing commodity chemicals and replacing petroleum-based infrastructures. However, slow production rates and low titers of metabolites during CO2-based microbial electrosynthesis impede its implementation to the real application in the near future. On the other hand, CO is a highly reactive gas and an abundant feedstock discharged from fossil fuel-based industry. Here, we investigated CO and CO2 electro-fermentation, using a CO-enriched culture. Fresh cow fecal waste was enriched under an atmosphere of 50% CO and 20% CO2 in N2 using serial cultivation. The CO-enriched culture was dominated by Clostridium autoethanogenum (≥89%) and showed electro-activity in a BES reactor with CO2 sparging. When 50% CO was included in the 20% CO2 gas with 10 mA applied current, acetate and ethanol were produced up to 12.9 ± 2.7 mM and 2.7 ± 1.1 mM, respectively. The coulombic efficiency was estimated to 148% ± 8% without an electron mediator. At 25 mA, the culture showed faster initial growth and acetate production but no ethanol production, and only at 86% ± 4% coulombic efficiency. The maximum optical density (OD) of 10 mA and 25 mA reactors were 0.29 ± 0.07 and 0.41 ± 0.03, respectively, whereas it was 0.77 ± 0.19 without electric current. These results show that CO electro-fermentation at low current can be an alternative way of valorizing industrial waste gas using a bioelectrochemical system.

Abstract Cupriavidus necator, despite lacking direct electron transfer capabilities, demonstrates efficient reduction of various redox mediators in oxygen‐free cultivation within bioelectrochemical systems. This study investigates the reduction site of ferricyanide through inhibition and expression rate analysis of oxygen and nitrate respiration chain complexes, comparing aerobic cultivation conditions with fructose as carbon and electron donor to autotrophic (CO2/H2/O2) and anodic cultivation conditions (fructose/anode). Azide inhibition identified cytochrome c oxidase as the primary complex facilitating electron transfer to ferricyanide, with a secondary role proposed for nitrite reductase NirS, demonstrating a 3.9±1.1‐fold higher expression when exposed to anodic conditions. The 2.9±0.6‐fold increase in the expression of the natural porin OmpA under anodic conditions implies its potential involvement in ferricyanide uptake. Additionally, chemically permeabilizing cell membranes with cetyltrimethylammonium bromide doubles ferricyanide reduction rates without an anode present, offering insights for optimizing redox mediation in C. necator based bioelectrochemical systems. This study opens up new possibilities for the targeted optimization of mediated electron transfer in C. necator and other organisms.

Pb-contaminated soil poses inherent risks for the spread of antibiotic resistance genes (ARGs). However, few reports have investigated the distribution of lead resistance genes (LRGs), particularly their role in ARGs dynamics during Pb-contaminated soil remediation. This study explored the mechanisms driving ARGs variation under different remediation strategies. The results indicated that an increase in the total abundance of ARGs after applying montmorillonite (Imvite), the composite remediation agents of MgO and Ca(H2PO4)2 (MgO-Ca(H2PO4)2), and the composite remediation agents of montmorillonite, MgO, and Ca(H2PO4)2 (Imvite-MgO-Ca(H2PO4)2). Bioelectrochemical systems (BES) effectively reduced ARGs abundance, and when combined with Imvite-MgO-Ca(H2PO4)2, lowered the risk of ARGs proliferation linked to antibiotic deactivation. Changes in Pb concentration and pH reshaped microbial communities, impacting both LRGs and ARGs. To reduce the risk of ARGs proliferation and transmission during, various control strategies, such as modifying Pb stress, adjusting pH, and manipulating microbial community structure, have been proposed. The study provided theoretical foundation and practical strategies for controlling ARGs dissemination during the remediation of heavy metal-contaminated soil.

Bioelectrochemical systems (BESs) that combine electrochemistry with biological methods have gained attention in the remediation of polluted environments, including wastewater, sludge, sediments, and soils. The most attractive advantage of BESs is that the solid electrode is used as an inexhaustible electron acceptor or donor, and biocurrent directly converted from organics can afford the reaction energy of contaminant breakdown, crossing the internal energy barrier of endothermic degradation, which achieves a continuous biodegradation process without the simultaneous use of exogenetic chemicals and bioelectricity recovery. However, soil BESs are hindered by expensive electrode materials, difficult pollutant and electron transfer, low microbial competitive activity, and biocompatibility in contamination remediation. Fortunately, introducing biochar into soil BESs could reveal a high potential in addressing these BES inadequacies. The characteristics of biochar, e.g., conductivity, transferability, high specific surface area, high porosity, large functional groups, and biocompatibility, can improve the performance of soil BESs. In fact, biochar not only carries electrons but also transfers nutrients, pollutants, and even bacteria by facilitating transmission in the bioelectric field of BESs. Consequently, the abilities of biochar make for better functionality of BESs. This review collates information on the roles, application, and progress of biochar in soil BESs, and future prospects are given. It is beneficial for environmental researchers and engineers to extend BES application in environmental remediation and to assist the progress of carbon sequestration and emission reduction based on the inertia of biochar and the blocking of electron flow to form methane. A feature comparison between BES and conventional techniques was made. Biochar characteristics match the deficiencies of bioelectrochemical remediation. Behind roles of biochar in the contamination remediation were summarized. Application potential and direction of biochar in BES were emphasized. [ABSTRACT FROM AUTHOR]

Bioelectrochemical systems based on electroactive processes in the root environment of plants are a promising direction for the combined production of green electricity and plant products. The dynamics of the electric potential differences formation in the root environment, diffuse reflection indices, fluorescence parameters of leaves, and morphometric and biochemical characteristics of lettuce varieties Chinese curly, Chinese red-green, Ballet, Cocarde, Mercury, Dubrava, Robin, and Solos F1 hybrid are studied. The maximum electric potential difference of 430 mV was typical for the Mercury variety, and the minimum of 352 mV for the Chinese Curly variety. According to the sum of the parameters, in addition to the electrical ones, including the morphometric, biochemical, and photosynthetic characteristics, the lettuce Ballet variety was the best. In the future, based on the data obtained, it will be possible to create agrophytocenoses, including plants capable of high and stable electricity generation together with high productivity and good quality of the plant products obtained, due to the effective assimilation and conversion of light energy. [ABSTRACT FROM AUTHOR]

Bioelectrochemical systems with Cupriavidus necator present a viable solution for harnessing H2/CO2 mixtures as substrates, employing mediated electron transfer to an infinite electron acceptor in the form of an anode instead of O2. Fourteen redox mediators were spectroelectrochemically characterized, and their efficiency was evaluated through screening with C. necator in common cuvettes with screen printed electrodes (e-Cuvettes). Key performance indicators, including total turnover number, reduction rate, and growth, were analyzed. Ferricyanide emerged as highly effective for anodic respiration, reaching a total turnover number of 8.38 over 120 h of cultivation. On the other hand, phenazine methosulfate exhibited the highest reduction rate at 2.49 mM h−1 with a total of 5.16 turnovers. Contrary, growth impairment is reported for menadione, possibly leading to deficient anodic electron transfer. The utilization of a broad spectrum of these shuttle molecules highlights the potential for optimizing bioelectrochemical applications involving C. necator.

Microbial electrosynthesis (MES) has been highlighted as a means to valorize inorganic gaseous carbon, such as CO2, into value-added chemicals using electricity as the reducing power. Electrode-based electron transfer delivers respiratory electrons to a live-cell biocatalyst through a biofilm matrix or via electron shuttle molecules. The addition of artificial mediators, such as neutral red (NR) and 2-hydroxy-1,4-naphthoquinone (HNQ), increased acetate synthesis significantly, suggesting that these mediators improve the electron transport capability between the suspended cells and electrode. Regular media replacement also improves MES by adapting mediator-utilizing species in the reactor. MES without a mediator initially produced acetate at a reasonable rate (5.1 ± 0.2 mmol/l/day), but the rate became negligible in the later stage. In contrast, MES with NR or HNQ showed a higher acetate production rate (4.6 ± 0.4 vs. 7.4 ± 0.4 mmol/l/day, respectively) as the media replacement progressed. Confocal laser scanning microscopy and 3D imaging showed that the biofilm matrix consisted of live and dead cells, while the composition was different in the MES with and without a mediator. Microbial community analysis by next-generation sequencing (NGS) showed that acetogenic Acetobacterium (in suspension) and Sporomusa (in both suspension and biofilm) were dominant during the 96 days of operation. The biofilm and planktonic community interacted dynamically under MES conditions. This result provides a realistic model of biofilms and planktonic cells in the MES. The interaction of the suspended cells with the biofilm-forming electrode via electron shuttles could improve volumetric acetate production and stabilize the MES performance.

Plastic wastes, widely distributed in the environment, can be transformed into microplastics, posing a huge threat to ecosystems and human health due to their stability and adsorbability to other toxic pollutants (e.g., heavy metals and antibiotics). Recently, microbial degradation of (micro)plastics has gained widespread attention because of its green and sustainable properties. Microbial degradation of (micro)plastics is based on the cascade effects of various enzymes secreted by microorganisms, which can convert (micro)plastics into oligomers and monomers, or even mineralize them into CO2 and H2O. The microbial degradation of (micro)plastics is affected by multiple factors, such as microbial species, plastic properties, and environmental conditions. Currently, limited efficient plastic-degrading microorganisms have been discovered, and their degradation mechanisms are still unclear. Furthermore, the efficiency of microbial degradation needs to be improved for future application. Therefore, this review systematically summarizes the sources and properties of existing plastics, identifies pure cultures and mixed cultures for plastic degradation, and examines their influencing factors. In particular, the microbial degradation behaviors of (micro)plastics, including relevant enzymes, degradation efficiency, and degradation mechanisms, were thoroughly discussed. Additionally, the augmentation technologies coupling with microbial degradation, such as advanced oxidation, electrochemical, and genetic engineering technologies, were introduced and highlighted for their potential prospects. This review provides a reference for future research and development of (micro)plastic biodegradation technology.

In this work, the ferrous (Fe2+) and graphitic N modified graphene-based composite cathode materials (N-rGO/Fe3O4) were developed through an in-situ reduction method, aiming to facilitate the two-electron pathway in the oxidation-reduction process. This approach generated a specific concentration of H2O2, enabling the construction of a sediment bio-electro-Fenton system using Fe2+ released from the cathode materials. Notably, this system operates without the need for proton exchange membranes. During the cathode material preparation, the utilization of Fe2+ as a reduction agent for graphene oxide (GO), triggered ammonia water to form graphitic N in graphene sheets. This addition enhanced the two-electron pathway, resulting in increased H2O2 production. Specifically, when the Fe2+ concentration was maintained at 0.1 mol/L, precise preparation of N-rGO/Fe3O4 occurred, leading to a maximum output voltage of 0.528 V and a maximum power density of 178.17 mW/m2. The degradation of methyl orange (MO) reached 68.91% within a 25-h period, a phenomenon contributed to the presence of graphitic N in the graphene sheets. H2O2, a byproduct of the two-electron pathway in cathode oxidation reduction reaction, played a crucial role in constructing the bio-electro-Fenton system. This system, in conjunction with Fe2+ released from N-rGO/Fe3O4, facilitated the complete degradation process of MO.

Microbial electrosynthesis (MES) is a promising carbon utilization technology, but the low-value products (i.e., acetate or methane) and the high electric power demand hinder its industrial adoption. In this study, electrically efficient MES cells with a low ohmic resistance of 15.7 mΩ m2 were operated galvanostatically in fed-batch mode, alternating periods of high CO2 and H2 availability. This promoted acetic acid and ethanol production, ultimately triggering selective (78% on a carbon basis) butyric acid production via chain elongation. An average production rate of 14.5 g m−2 d−1 was obtained at an applied current of 1.0 or 1.5 mA cm−2, being Megasphaera sp. the key chain elongating player. Inoculating a second cell with the catholyte containing the enriched community resulted in butyric acid production at the same rate as the previous cell, but the lag phase was reduced by 82%. Furthermore, interrupting the CO2 feeding and setting a constant pH2 of 1.7–1.8 atm in the cathode compartment triggered solventogenic butanol production at a pH below 4.8. The efficient cell design resulted in average cell voltages of 2.6–2.8 V and a remarkably low electric energy requirement of 34.6 kWhel kg−1 of butyric acid produced, despite coulombic efficiencies being restricted to 45% due to the cross-over of O2 and H2 through the membrane. In conclusion, this study revealed the optimal operating conditions to achieve energy-efficient butyric acid production from CO2 and suggested a strategy to further upgrade it to valuable butanol.

The electroenzymatic hydroxylation of 4-ethylbenzoic acid catalyzed by the recombinant unspecific peroxygenase from the fungus Agrocybe aegerita (r Aae UPO) was performed in a gas diffusion electrode (GDE)-based system. Enzyme stability and productivity are significantly affected by the way the co-substrate hydrogen peroxide (H 2 O 2) is supplied. In this study, two in-situ electrogeneration modes of H 2 O 2 were established and compared. Experiments under galvanostatic conditions (constant productivity of H 2 O 2) were conducted at current densities spanning from 0.8 mA cm−2 to 6.4 mA cm−2. For comparison, experiments under H 2 O 2 -stat mode (constant H 2 O 2 concentration) were performed. Here, four H 2 O 2 concentrations between 0.06 mM and 0.28 mM were tested. A maximum H 2 O 2 productivity of 5.5 µM min−1 cm−2 and productivity of 10.5 g L−1 d−1 were achieved under the galvanostatic condition at 6.4 mA cm−2. Meanwhile, the highest total turnover number (TTN) of 710,000 mol mol−1 and turnover frequency (TOF) of 87.5 s−1 were obtained under the H 2 O 2 -stat mode at concentration limits of 0.15 mM and 0.28 mM, respectively. The most favorable outcome in terms of maximum achievable TTN, TOF and productivity was found under the H 2 O 2 -stat mode at concentration limit of 0.2 mM. Here, a TTN of 655,000 mol mol−1, a TOF of 80.3 s−1 and a productivity of 6.1 g L−1 d−1 were achieved. The electrochemical H 2 O 2 -stat mode not only offers a promising alternative reaction concept to the well-established galvanostatic mode but also enhances the process performance of unspecific peroxygenases. [Display omitted] • In-situ electrochemical H 2 O 2 -stat mode as a promising alternative reaction concept. • Combination of electrochemical H 2 O 2 -stat mode with an enzymatic hydroxylation. • Enhancement of process performance of unspecific peroxygenase. • Achievement of TTN up to 710,000 mol mol−1 and TOF as high as 87.5 s−1 [ABSTRACT FROM AUTHOR]

BACKGROUND: In biodesulphurisation processes, sulphide oxidising bacteria (SOB) convert toxic sulphide to sulphur. Haloalkalophilic SOB are known to anaerobically remove sulphide from solution and release electrons when subsequently exposed to an electrode. This makes SOB able to spatially decouple sulphide removal and current production, thereby acting as sulphide shuttles. Little is known about the kinetics of electron release by sulphide shuttling SOB. To gain more insight into the sulphide shuttling mechanism and electron release, current production of abiotic sulphide and sulphide shuttling SOB was compared. RESULTS: SOB communities dominated by Thioalkalivibrio sulfidophilus were incubated with sulphide in batch experiments. After sulphide was removed, SOB were discharged in an electrochemical cell. Anode potential, sulphide load and biomass concentration were varied. Current was produced at potentials of −0.2 V versus Ag/AgCl and higher, and at a potential of 0.1 V a coulombic efficiency of 70% was reached in 30 min. The maximum charge recovered from biologically stored sulphide was 4900 ± 810 mC mgN−1. Discharge kinetics were not affected by biomass concentration or degree of sulphide removal and kinetics of biotic and abiotic current production were similar. CONCLUSION: Current production of sulphide shuttling SOB and abiotic sulphide was highly similar. This implies that sulphide shuttling is based on sorption to the biomass, and that shuttled sulphide converts to sulphur directly at the electrode surface. Therefore, the sulphide shuttling strategy is not sufficient to prevent electrode passivation, and different strategies need to be applied in the design of a sulphur‐producing bioelectrochemical desulphurisation process. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Standalone and combined leachate treatment mechanisms suffer from low treatment efficiencies due to leachate's complex, toxic, and recalcitrant nature. Bioelectrochemical system (BES) was used for the first time to investigate the treatment of leachate mixed wastewater (WW) (i.e., diluted leachate, DL) (DL ≈ L:WW = 1:4) to minimize these complexities. A natural clay (palygorskite) was used as adsorbent material for further treatment on the BES effluent (EBES) while using two different masses and sizes (i.e., 3 g and 6 g of raw crushed clay (RCC) and 75 μ of sieved clay (75 μSC)). According to bioelectrochemical performance, BES, when operated with low external resistance (Rext = 1 Ω) (BES 1), showed a high removal of COD and NH3-N with 28% and 36%, respectively. On the other hand, a high Rext (100 Ω, BES 100) resulted in low removal of NH3-N with 10% but revealed high COD removal by 78.26%. Moreover, the 6 g doses of 75 μSC and RCC showed the maximum COD removals of 62% and 38% and showed the maximum removal of NH3-N with an average range of 40% for both sizes. After efficient desorption, both clay sizes resulted in regeneration performance which was observed with high COD (75%) and NH3-N (34%) on EBES. Therefore, when BES and clay adsorption technique sequentially treated and achieved with combined removal of ~ 98% for COD and ~ 80% of NH3-N, it demonstrated an efficient treatment method for DL treatment. [ABSTRACT FROM AUTHOR]

The effect of bioelectrochemical anaerobic digestion (BEAD) on the methanogenic performance of brewery wastewater at different organic loading rates (OLRs) was investigated and compared to conventional anaerobic digestion. A continuous BEAD reactor was used to treat brewery wastewater at different OLRs of 2, 4, 8, 16, and 20 g COD/L.d. The experimental results showed that the methane production was gradually increased from 0.48 L/L.d at an OLR of 2 g COD/L.d to 5.64 L/L.d at an OLR of 20 g COD/L.d. The methane production of the BEAD system was significantly higher than that of the conventional anaerobic reactor, indicating that BEAD has a better treatment effect for brewery wastewater. The performance of the conventional anaerobic reactor was significantly reduced especially at an OLR of 16 g COD/L.d, while the BEAD system could withstand a higher OLR. Bioelectrochemical systems provide a completely new platform for the anaerobic treatment of brewery wastewater and greatly improve the operation of anaerobic processes. [ABSTRACT FROM AUTHOR]

Composites of polyurethane and graphite and polyurethane and carbon nanofibers (PU/Graphite 0.5% and PU/CNF 1%) were synthesized and used as anodes in dual-compartment microbial fuel cells (MFCs) for municipal wastewater treatment; electrical energy generation and organic matter removal were assessed. The maximum power density, coulombic efficiency and chemical oxygen demand (COD) removal efficiency in the MFCs packed with the PU/Graphite 0.5% and PU/CNF 1% composites were 232.32 mW/m3 and 90.78 mW/m3, 5.87 and 4.41%, and 51.38 and 68.62%, respectively. In addition, the internal resistance of the MFCs with the best bioelectrochemical performance (PU/Graphite 0.5%) was 1051.11 Ω. The results obtained in this study demonstrate the feasibility of using these types of materials in dual-compartment MFCs for wastewater treatment with electric power generation. [ABSTRACT FROM AUTHOR]

In view of increasing threats arising from the shortage of fresh water, there is an urgent need to propose sustainable technologies for the exploitation of unconventional water sources. As a derivative of microbial fuel cells (MFCs), microbial desalination cell (MDC) has the potential of desalinating saline/brackish water while simultaneously generating electricity, as well as treating wastewater. Therefore, it is worth investigating its practicability as a potential sustainable desalination technology. This review article first introduces the fundamentals and annual trends of MDCs. The desalination of diverse types of solutions using MDCs along with their life cycle impact assessment (LCIA) and economic analysis is studied later. Finally, limitations and areas for improvement, prospects, and potential applications of this technology are discussed. Due to the great advantages of MDCs, improving their design, building materials, efficiency, and throughput will offer them as a significant alternative to the current desalination technologies. [ABSTRACT FROM AUTHOR]

Abstract It is of great significance to utilize CO2 as feedstock to synthesize biobased products, particularly single cell protein (SCP) as the alternative food and feed. Bioelectrochemical system (BES) driven by clean electric energy has been regarded as a promising way for Cupriavidus necator to produce SCP from CO2 directly. At present, the key problem of culturing C. necator in BES is that reactive oxygen species (ROS) generated in cathode chamber are harmful to bacterial growth. Therefore, it is necessary to find a solution to mitigate the negative effect of ROS. In this study, we constructed a number of C. necator strains displayed with superoxide dismutase (SOD), which allowed the decomposition of superoxide anion radical. The effects of promoters and signal peptides on the cell surface displayed SOD were analyzed. The proteins displayed on the surface were further verified by the fluorescence experiment. Finally, the growth of C. necator CMS incorporating a pBAD-SOD-E-tag-IgAβ plasmid could achieve 4.9 ± 1.0 of OD600 by 7 days, equivalent to 1.7 ± 0.3 g/L dry cell weight (DCW), and the production rate was 0.24 ± 0.04 g/L/d DCW, around 2.7-fold increase than the original C. necator CMS (1.8 ± 0.3 of OD600). This study can provide an effective and novel strategy of cultivating strains for the production of CO2-derived SCP or other chemicals in BES. Graphical Abstract

Bioelectrochemical systems (BESs) are an innovative technology for the efficient degradation of antibiotics. Shewanella oneidensis (S. oneidensis) MR-1 plays a pivotal role in degrading sulfamethoxazole (SMX) in BESs. Our study investigated the effect of BES conditions on SMX degradation, focusing on microbial activity. The results revealed that BESs operating with a 0.05 M electrolyte concentration and 2 mA/cm2 current density outperformed electrolysis cells (ECs). Additionally, higher electrolyte concentrations and elevated current density reduced SMX degradation efficiency. The presence of nutrients had minimal effect on the growth of S. oneidensis MR-1 in BESs; it indicates that S. oneidensis MR-1 can degrade SMX without nutrients in a short period of time. We also highlighted the significance of mass transfer between the cathode and anode. Limiting mass transfer at a 10 cm electrode distance enhanced S. oneidensis MR-1 activity and BES performance. In summary, this study reveals the complex interaction of factors affecting the efficiency of BES degradation of antibiotics and provides support for environmental pollution control.

In a microbial electrolysis cell (MEC), the oxidization of organic compounds is facilitated by an electrogenic biofilm on the anode surface. The biofilm community composition determines the function of the system. Both deterministic and stochastic factors affect the community, but the relative importance of different factors is poorly understood. Anode material is a deterministic factor as materials with different properties may select for different microorganisms. Ecological drift is a stochastic factor, which is amplified by dispersal limitation between communities. Here, we compared the effects of three anode materials (graphene, carbon cloth, and nickel) with the effect of dispersal limitation on the function and biofilm community assembly. Twelve MECs were operated for 56 days in four hydraulically connected loops and shotgun metagenomic sequencing was used to analyse the microbial community composition on the anode surfaces at the end of the experiment. The anode material was the most important factor affecting the performance of the MECs, explaining 54–80 % of the variance observed in peak current density, total electric charge generation, and start-up lag time, while dispersal limitation explained 10–16 % of the variance. Carbon cloth anodes had the highest current generation and shortest lag time. However, dispersal limitation was the most important factor affecting microbial community structure, explaining 61–98 % of the variance in community diversity, evenness, and the relative abundance of the most abundant taxa, while anode material explained 0–20 % of the variance. The biofilms contained nine Desulfobacterota metagenome-assembled genomes (MAGs), which made up 64–89 % of the communities and were likely responsible for electricity generation in the MECs. Different MAGs dominated in different MECs. Particularly two different genotypes related to Geobacter benzoatilyticus competed for dominance on the anodes and reached relative abundances up to 83 %. The winning genotype was the same in all MECs that were hydraulically connected irrespective of anode material used.

Abstract In view of increasing threats arising from the shortage of fresh water, there is an urgent need to propose sustainable technologies for the exploitation of unconventional water sources. As a derivative of microbial fuel cells (MFCs), microbial desalination cell (MDC) has the potential of desalinating saline/brackish water while simultaneously generating electricity, as well as treating wastewater. Therefore, it is worth investigating its practicability as a potential sustainable desalination technology. This review article first introduces the fundamentals and annual trends of MDCs. The desalination of diverse types of solutions using MDCs along with their life cycle impact assessment (LCIA) and economic analysis is studied later. Finally, limitations and areas for improvement, prospects, and potential applications of this technology are discussed. Due to the great advantages of MDCs, improving their design, building materials, efficiency, and throughput will offer them as a significant alternative to the current desalination technologies.

The industrial adoption of microbial electrosynthesis (MES) is hindered by high overpotentials deriving from low electrolyte conductivity and inefficient cell designs. In this study, a mixed microbial consortium originating from an anaerobic digester operated under saline conditions (∼13 g L−1 NaCl) was adapted for acetate production from bicarbonate in galvanostatic (0.25 mA cm−2) H-type cells at 5, 10, 15, or 20 g L−1 NaCl concentration. The acetogenic communities were successfully enriched only at 5 and 10 g L−1 NaCl, revealing an inhibitory threshold of about 6 g L−1 Na+. The enriched planktonic communities were then used as inoculum for 3D printed, three-chamber cells equipped with a gas diffusion biocathode. The cells were fed with CO2 gas and operated galvanostatically (0.25 or 1.00 mA cm−2). The highest production rate of 55.4 g m−2 d−1 (0.89 g L−1 d−1), with 82.4% Coulombic efficiency, was obtained at 5 g L−1 NaCl concentration and 1 mA cm−2 applied current, achieving an average acetate production of 44.7 kg MWh−1. Scanning electron microscopy and 16S rRNA sequencing analysis confirmed the formation of a cathodic biofilm dominated by Acetobacterium sp. Finally, three 3D printed cells were hydraulically connected in series to simulate an MES stack, achieving three-fold production rates than with the single cell at 0.25 mA cm−2. This confirms that three-chamber MES cells are an efficient and scalable technology for CO2 bio-electro recycling to acetate and that moderate saline conditions (5 g L−1 NaCl) can help reduce their power demand while preserving the activity of acetogens.

Sulfur emission creates many health as well as environmental problem after release of sulfur compounds. Many approaches have been applied for the treatment of sulfur compounds via physical, chemical, and biological approaches; these techniques have some advantages as well disadvantages. But for as effective treatment of sulfur compounds biological approach put termendeous impact on environment as well as on human health. Different reseracher work on different methods available in the scope of biological approach current review emphasis on Bio-electrochemcial System. In this review study cover the application of Microbial Fuel Cell (MFC) for treating sulfur present in fossil fuel as well as waste stream couple with the changes in ecosystem. One of the latest approaches for sustainable way for treating wastewater stream is the use of MFCs. With this technique, the current work focuses on the mitigation of sulfur compounds in MFC. In addition, there are challenges and perspectives of using MFCs for sulfur removal. [ABSTRACT FROM AUTHOR]

Heavy metal pollution caused due to various industrial and mining activities poses a serious threat to all forms of life in the environment because of the persistence and toxicity of metal ions. Microbial-mediated bioremediation including microbial biofilms has received significant attention as a sustainable tool for heavy metal removal as it is considered safe, effective, and feasible. The biofilm matrix is dynamic, having microbial cells as major components with constantly changing and evolving microenvironments. This review summarizes the bioremediation potential of bacterial biofilms for different metal ions. The composition and mechanism of biofilm formation along with interspecies communication among biofilm-forming bacteria have been discussed. The interaction of biofilm-associated microbes with heavy metals takes place through a variety of mechanisms. These include biosorption and bioaccumulation in which the microbes interact with the metal ions leading to their conversion from a highly toxic form to a less toxic form. Such interactions are facilitated via the negative charge of the extracellular polymeric substances on the surface of the biofilm with the positive charge of the metal ions and the high cell densities and high concentrations of cell–cell signaling molecules within the biofilm matrix. Furthermore, the impact of the anodic and cathodic redox potentials in a bioelectrochemical system (BES) for the reduction, removal, and recovery of numerous heavy metal species provides an interesting insight into the bacterial biofilm-mediated bioelectroremediation process. The review concludes that biofilm-linked bioremediation is a viable option for the mitigation of heavy metal pollution in water and ecosystem recovery. [ABSTRACT FROM AUTHOR]

Nutrient-rich waste streams from domestic and industrial sources and the increasing application of synthetic fertilizers have resulted in a huge-scale influx of reactive nitrogen and phosphorus in the environment. The higher concentrations of these pollutants induce eutrophication and foster degradation of aquatic biodiversity. Besides, phosphorus being non-renewable resource is under the risk of rapid depletion. Hence, recovery and reuse of the phosphorus and nitrogen are necessary. Over the years, nutrient recovery, low-carbon energy, and sustainable bioremediation of wastewater have received significant interest. The conventional wastewater treatment technologies have higher energy demand and nutrient removal entails a major cost in the treatment process. For these issues, bio-electrochemical system (BES) has been considered as sustainable and environment friendly wastewater treatment technologies that utilize the energy contained in the wastewater so as to recovery nutrients and purify wastewater. Therefore, this article comprehensively focuses and critically analyzes the potential sources of nutrients, working mechanism of BES, and different nutrient recovery strategies to unlock the upscaling opportunities. Also, economic analysis was done to understand the technical feasibility and potential market value of recovered nutrients. Hence, this review article will be useful in establishing waste management policies and framework along with development of advanced configurations with major emphasis on nutrient recovery rather than removal from the waste stream. [ABSTRACT FROM AUTHOR]

Bioelectrochemical system is a novel method for controlling down nitrate pollution, yet the feasibility of using methane as the electron donors for denitrification in this system remains unknown. In this study, using the effluent from mother BESs as inocula, a denitrifying anaerobic methane oxidation bioelectrochemical system was successfully started up in 92 days. When operated with 50 mmol/L phosphate buffer solution at pH 7 and 30°C, the maximum methane consumption, nitrate, and total nitrogen removal load reached 0.23 ± 0.01 mmol/d, 551.0 ± 22.1 mg N/m3/d, and 64.0 ± 18.8 mg N/m3/d, respectively. Meanwhile, the peak voltage of 93 ± 4 mV, the anodic coulombic efficiency of 6.99 ± 0.20%, and the maximum power density of 219.86 mW/m3 were obtained. The metagenomics profiles revealed that the dominant denitrifying bacteria in the cathodic chamber reduced most nitrate to nitrite through denitrification and assimilatory reduction. In the anodic chamber, various archaea including methanotrophs and methanogens converted methane via reverse methanogenesis to form formate (or H2), acetate, and methyl compounds, which were than utilized by electroactive bacteria to generate electricity. Practitioner Points: A denitrifying anaerobic methane oxidation BES was successfully started up in 92 d.Simultaneous removal of methane and nitrate was achieved in the DAMO‐BES.Functional genes related to AMO and denitrification were detected in the DAMO‐BES.Methylocystis can mediate AMO in the anode and denitrification in the cathode. [ABSTRACT FROM AUTHOR]

Oxygen reduction reactions (ORRs) are unanimously a key factor of system performances in bioelectrochemical systems (BESs), low-temperature fuel cells, and generally in several electrochemical platforms. Platinum (Pt)-based catalyst is the finest electrocatalyst for ORR in BESs; however, it is constrained by its low abundance, high price, and poor catalytic durability in an electrochemical setup for cathodic reaction kinetics. In recent years, significant efforts in trimming the metal-based catalyst up to nanoscale to cater high performance of ORR have been explored. Still, there are many opportunities to improve catalyst performance at cathode through proper selection of an efficient low-cost metal-based ORR catalyst. Molybdenum (Mo) with its multi-dimensional form as 2D and 3D layers and synergistic combination with other non-metals offers prospects of extraordinary performance as low-cost metal-based ORR catalyst over the Pt in delivering enhanced ORR potential. The present review throws light on current requirements of a sturdier catalyst material and thus provides a comprehensive review on the continuing efforts in exploring the possibility of Mo as a low-cost metal-based ORR catalyst. This literature analysis would enlighten the significance of ORR in BESs, followed by the electrochemistry of Mo-based cathodic catalyst, its underlying mechanism and performance limiting factors in the operation of ORR. Moreover, the extensive and systematic acumen in the context of Mo-based catalytic formulations for increased ORR potentials including nano-composite Mo-cathode catalyst; development of Mo-catalyst with varied configurations; carbon-supported Mo-catalyst; morphological changes; surface area modifications; and Mo-coupling with other transition metal and its derivatives were discussed in great detail to provide prospective application of Mo-based catalyst. Lastly, numerous opportunities and projections for future research in fabrication, juxtaposition, and implementation of Mo-based cathodic catalysts and consequent recommendations were discussed as conclusive remarks for bringing out the state-of-the-art review on this subject. [ABSTRACT FROM AUTHOR]

Electrochemically active bacteria (EAB) are capable of electrically interacting with electrodes, enabling their application in bioelectrochemical systems (BESs). As the performance of BES is related to the metabolic activities of EAB, the development of methods to control their metabolic activities is important to facilitate BES applications. A recent study found that the EAB Shewanella oneidensis MR-1 uses the Arc system to regulate the expression of catabolic genes in response to electrode potentials, suggesting that a methodology for electrical control of gene expression in EAB, referred to as electrogenetics, can be developed by using electrode potential-responsive, Arc-dependent transcriptional promoters. Here, we explored Arc-dependent promoters in the genomes of S. oneidensis MR-1 and Escherichia coli to identify electrode potential-responsive promoters that are differentially activated in MR-1 cells exposed to high- and low-potential electrodes. LacZ reporter assays using electrode-associated cells of MR-1 derivatives revealed that the activities of promoters located upstream of the E. coli feo gene (P feo) and the MR-1 nqrA2 (SO_0902) gene (P nqr2) were significantly increased when S. oneidensis cells were exposed to electrodes poised at +0.7 V and −0.4 V (versus the standard hydrogen electrode), respectively. Additionally, we developed a microscopic system for in situ monitoring of promoter activity in electrode-associated cells and found that P nqr2 activity was persistently induced in MR-1 cells associated with an electrode poised at −0.4 V. Our results indicate that these electrode potential-responsive promoters enable efficient regulation of gene expression in EAB, providing a molecular basis for the development of electrogenetics. [Display omitted] [ABSTRACT FROM AUTHOR]

It is of great significance to utilize CO2 as feedstock to synthesize biobased products, particularly single cell protein (SCP) as the alternative food and feed. Bioelectrochemical system (BES) driven by clean electric energy has been regarded as a promising way for Cupriavidus necator to produce SCP from CO2 directly. At present, the key problem of culturing C. necator in BES is that reactive oxygen species (ROS) generated in cathode chamber are harmful to bacterial growth. Therefore, it is necessary to find a solution to mitigate the negative effect of ROS. In this study, we constructed a number of C. necator strains displayed with superoxide dismutase (SOD), which allowed the decomposition of superoxide anion radical. The effects of promoters and signal peptides on the cell surface displayed SOD were analyzed. The proteins displayed on the surface were further verified by the fluorescence experiment. Finally, the growth of C. necator CMS incorporating a pBAD-SOD-E-tag-IgAβ plasmid could achieve 4.9 ± 1.0 of OD600 by 7 days, equivalent to 1.7 ± 0.3 g/L dry cell weight (DCW), and the production rate was 0.24 ± 0.04 g/L/d DCW, around 2.7-fold increase than the original C. necator CMS (1.8 ± 0.3 of OD600). This study can provide an effective and novel strategy of cultivating strains for the production of CO2-derived SCP or other chemicals in BES. [ABSTRACT FROM AUTHOR]

Rumen fermentation (RF) is a complex system of oxidation–reduction reactions governed by the rumen microbiota, and its end-products are the volatile fatty acids (VFAs) which constitute the main energy source for the host animal. We speculated that the process could be manipulated through electrofermentation (EF) by utilizing solid-state electrodes as electron sources. This study aimed to evaluate the effects of single-chamber EF applied (0.4 vs. 0.9 V) for 6, 12, or 24 h to rumen fluid on the resulting microbial biomass, dry matter digestibility (DMD), VFA production, NADH/NAD ratio, and composition of the rumen fluid's bacterial communities. The application of a 0.9 V electric potential for 24 h produced the most significant changes in RF compared to the control treatment (0V), increasing microbial biomass (12%), DMD (58%), and VFA concentrations (~84%), and reducing NAD/NADH ratio (~50%) without a significant impact on bacterial diversity. These results suggest that the application of a 0.9 V electric potential allows the microbiota to better hydrolyze and digest the feed's components and could offer an electron sink for the production of VFAs. Hence, EF can provide innovative solutions to a range of challenges that limit the RF process. Nonetheless, more studies are needed to understand how the solid electrodes and external electric energy function. [ABSTRACT FROM AUTHOR]

The effect of the polarity of the electrical stimulation of the external circuit of the bioelectrochemical systems, as well as the immobilization of Shewanella oneidensis MR-1 cells containing the DyP peroxidase gene on the rate of discoloration of dyes of different types, was found. For the crystal violet triphenylmethane dye, the maximum decolorization rate by suspended S. oneidensis MR-1 cells of 2.05 ± 0.07 μM/h was noted when connecting a 1.2 V direct polarity DC voltage source. One of the minimum rates was observed with reverse polarity of the connection. For cells immobilized on the anode, the rate was higher, reaching 2.91 ± 0.09 μM/h and did not decrease with increasing substrate concentration. The lowest values were also noted for the reverse connection of the voltage source. For the azo dye congo red, the maximum rate was found for a source with direct connection and an open circuit (0.26 ± 0.01 and 0.29 ± 0.02 μM/h, respectively); the minimum value was 0.11 ± 0.02 μM/h for a reverse connection. For crystal violet decolorization products, a significant decrease in the intensity of the main absorption peak at 590 nm band was found, with no notable hypsochromic shift. The qualitative changes in the decolorization product composition were indicated by the appearance, with a direct polarity of the ionistor connection, of a new absorption maximum in the region of 360 nm. The results may be of interest for the development of new methods of bioelectrochemical cleaning. [ABSTRACT FROM AUTHOR]