Electroactive Microorganisms Research Articles

Mechanical energy drives the growth and carbon fixation of electroactive microorganisms

Phototrophy and chemotrophy are two dominant types of microbial metabolism. However, to date, the potential of the ubiquitous and versatile mechanical energy as a renewable energy source to drive the growth of microorganisms has remained unknown and not utilized. Here, we present evidence in favor of a previously unidentified metabolic pathway, in which the electronic energy produced from mechanical energy by the piezoelectric materials is used to support the growth of microorganisms. When electroactive microorganism Rhodopseudomonas palustris (R. palustris; with barium titanate nanoparticles) was mechanically stirred, a powerful biohybrid piezoelectric effect (BPE) enabled sustainable carbon fixation coupled with nitrate reduction. Transcriptomic analyses demonstrated that mechanical stirring of the bacteria–barium titanate biohybrid led to upregulation of genes encoding functions involved in electron and energy transfer in R. palustris. Studies with other electroactive microorganisms suggested that the ability of microbes to utilize BPE may be a common phenomenon in the microbial world. Taken together, these findings imply a long-neglected and potentially important microbial metabolic pathway, with potential importance to microbial survival in the energy-limited environments.

Synergistic material–microbe interface toward deeper anaerobic defluorination

Per- and polyfluoroalkyl substances (PFAS), particularly the perfluorinated ones, are recalcitrant to biodegradation. By integrating an enrichment culture of reductive defluorination with biocompatible electrodes for the electrochemical process, a deeper defluorination of a C6-perfluorinated unsaturated PFAS was achieved compared to the biological or electrochemical system alone. Two synergies in the bioelectrochemical system were identified: i) The in-series microbial-electrochemical defluorination and ii) the electrochemically enabled microbial defluorination of intermediates. These synergies at the material-microbe interfaces surpassed the limitation of microbial defluorination and further turned the biotransformation end products into less fluorinated products, which could be less toxic and more biodegradable in the environment. This material-microbe hybrid system brings opportunities in the bioremediation of PFAS driven by renewable electricity and warrants future research on mechanistic understanding of defluorinating and electroactive microorganisms at the material-microbe interface for system optimizations.

Effect of Supporting Carbon Fiber Anode by Activated Coconut Carbon in the Microbial Fuel Cell Fed by Molasses Decoction from Yeast Production

A microbial fuel cell (MFC) is a bioelectrochemical system that generates electrical energy using electroactive micro-organisms. These micro-organisms convert chemical energy found in substances like wastewater into electrical energy while simultaneously treating the wastewater. Thus, MFCs serve a dual purpose, generating energy and enhancing wastewater treatment processes. Due to the high construction costs of MFCs, there is an ongoing search for alternative solutions to improve their efficiency and reduce production costs. This study aimed to improvement of MFC operation and minimize MFC costs by using anode material derived from by-products. Therefore, the proton exchange membrane (PEM) was abandoned, and a stainless steel cathode and a carbon anode were used. To improve the cell’s efficiency, a carbon fiber anode supplemented with activated coconut carbon (ACCcfA) was utilized. Micro-organisms were provided with molasses decoction (a by-product of yeast production) to supply the necessary nutrients for optimal functioning. For comparison, an anode made solely of carbon fibers (CFA) and an anode composed of activated carbon grains without carbon fibers (ACCgA) were also tested. The results indicated that the ACCcfA system achieved the highest cell voltage, power density, and COD reduction efficiency (compared to the CFA and ACCgA electrodes). Additionally, the study demonstrated that incorporating activated coconut carbon significantly enhances the performance of the MFC when powered by a by-product of yeast production.

Biochar alleviates inhibition effects of humic acid on anaerobic digestion: Insights to performances and mechanisms

To recover methane from waste activated sludge through anaerobic digestion (AD) is one promising alternative to achieve carbon neutrality for wastewater treatment plants. However, humic acids (HAs) are one of the major compositions in waste activated sludge, and their accumulation performs inhibition effects on AD. This study investigated the potentials of biochar (BC) in alleviating inhibition effects of HAs on AD. Results showed that although the accumulated HAs reduced methane yield by 9.37% compared to control, the highest methane yield, 132.6 mL CH4/g VSS, was obtained after adding BC, which was 45.9% higher than that in HA group. Mechanism analysis showed that BC promoted the activities of hydrolase such as protease and α-glucosidase, which were 69.7% and 29.7% higher than those in HA group, respectively. The conversion of short-chain fatty acids was accelerated. In addition, the evolutions of electroactive microorganisms like Clostridium_sensu_stricto_13 and Methanosaeta were consistent with the activitiies of electron transfer and the contents of cytochrome c. Furthermore, parts of HAs rather than all of them were adsorbed by BC, and the remaining free HAs and BC formed synergistic effects on methanogenesis, then both CO2 reduction and acetoclastic methanogenesis pathways were improved. The findings may provide some solutions to alleviate inhibition effects of HAs on AD.

Metabolism mechanisms of biogenic methane production by synergistic biodegradation of lignite and guar gum

Coalbed methane (CBM) presents a promising energy source for addressing global energy shortages. Nonetheless, challenges such as low gas production from individual wells and difficulties in breaking gels at low temperatures during extraction hinder its efficient utilization. Addressing this, we explored native microorganisms within coal seams to degrade guar gum, thereby enhancing CBM production. However, the underlying mechanisms of biogenic methane production by synergistic biodegradation of lignite and guar gum remain unclear. Research results showed that the combined effect of lignite and guar gum enhanced the production, yield rate and concentration of biomethane. When the added guar gum content was 0.8 % (w/w), methane production of lignite and guar gum reached its maximum at 561.9 mL, which was 11.8 times that of single lignite (47.3 mL). Additionally, guar gum addition provided aromatic and tryptophan proteins and promoted the effective utilization of CC/CH and OCO groups on the coal surface. Moreover, the cooperation of lignite and guar gum accelerated the transformation of volatile fatty acids into methane and mitigated volatile fatty acid inhibition. Dominant bacteria such as Sphaerochaeta, Macellibacteroides and Petrimonas improved the efficiency of hydrolysis and acidification. Electroactive microorganisms such as Sphaerochaeta and Methanobacterium have been selectively enriched, enabling the establishment of direct interspecies electron transfer pathways. This study offers valuable insights for increasing the production of biogenic CBM and advancing the engineering application of microbial degradation of guar gum fracturing fluid. Future research will focus on exploring the methanogenic capabilities of lignite and guar gum in in-situ environments, as well as elucidating the specific metabolic pathways involved in their co-degradation.

Inoculum source determines the stress resistance of electroactive functional taxa in biofilms: A metagenomic perspective

The inoculum has a crucial impact on bioreactor initialization and performance. However, there is currently a lack of guidance on selecting appropriate inocula for applications in environmental biotechnology. In this study, we applied microbial electrolysis cells (MECs) as models to investigate the differences in the functional potential of electroactive microorganisms (EAMs) within anodic biofilms developed from four different inocula (natural or artificial), using shotgun metagenomic techniques. We specifically focused on extracellular electron transfer (EET) function and stress resistance, which affect the performance and stability of MECs. Community profiling revealed that the family Geobacteraceae was the key EAM taxon in all biofilms, with Geobacter as the dominant genus. The c-type cytochrome gene imcH showed universal importance for Geobacteraceae EET and was utilized as a marker gene to evaluate the EET potential of EAMs. Additionally, stress response functional genes were used to assess the stress resistance potential of Geobacter species. Comparative analysis of imcH gene abundance revealed that EAMs with comparable overall EET potential could be enriched from artificial and natural inocula (P > 0.05). However, quantification of stress response gene copy numbers in the genomes demonstrated that EAMs originating from natural inocula possessed superior stress resistance potential (196 vs. 163). Overall, this study provides novel perspectives on the inoculum effect in bioreactors and offers theoretical guidance for selecting inoculum in environmental engineering applications.

Unravelling the mechanisms of organic micropollutant removal in bio-electrochemical systems: Insights into sorption, electrochemical degradation, and biodegradation processes

Bio-electrochemical systems (BESs) have recently been proposed as an efficient treatment technology to remove organic micropollutants from water treatment plants. In this study, we aimed to differentiate between sorption, electrochemical transport/degradation, and biodegradation. Using electro-active microorganisms and electrodes, we investigated organic micropollutant removal at environmentally relevant concentrations, clarifying the roles of sorption and electrochemical and biological degradation. The role of anodic biofilms on the removal of 10 relevant organic micropollutants was studied by performing separate sorption experiments on carbon-based electrodes (graphite felt, graphite rod, graphite granules, and granular activated carbon) and electrochemical degradation experiments at two different electrode potentials (−0.3 and 0 V).Granular activated carbon showed the highest sorption of micropollutants; applying a potential to graphite felt electrodes increased organic micropollutant removal. Removal efficiencies >80 % were obtained for all micropollutants at high anode potentials (+0.955 V), indicating that the studied compounds were more susceptible to oxidation than to reduction. All organic micropollutants showed removal when under bio-electrochemical conditions, ranging from low (e.g. metformin, 9.3 %) to exceptionally high removal efficiencies (e.g. sulfamethoxazole, 99.5 %). The lower removal observed under bio-electrochemical conditions when compared to only electrochemical conditions indicated that sorption to the electrode is key to guarantee high electrochemical degradation. The detection of transformation products of chloridazon and metformin indicated that (bio)-electrochemical degradation occurred. This study confirms that BES can treat some organic micropollutants through several mechanisms, which merits further investigation.

Distinct microbial communities enriched in water-saturated and unsaturated reactors influence performance of integrated hydroponics-microbial electrochemical technology

This study aimed to understand the wastewater treatment and electricity generation performance besides the microbial communities of the integrated Hydroponics-Microbial Electrochemical Technology (iHydroMET) systems operated with water-saturated and water-unsaturated reactors. The organics removal was slightly higher in the water-unsaturated system (93 ± 4 %) than in the water-saturated system (87 ± 2 %). The total nitrogen removal and electric voltage were considerably higher in the water-saturated system (42 ± 5 %; 111 ± 8 V per reactor) than in the water-unsaturated system (18 ± 3 %; 95 ± 9 V per reactor). The enhanced organics and nitrogen removal and high voltage output in respective conditions were due to the dominance of polysaccharide-degrading aerobes (e.g., Pirellula), anammox bacteria (e.g., Anammoximicrobium), denitrifiers (e.g., Thauera and Rheinheimera), and electroactive microorganisms (e.g., Geobacter). The differential performance governed by distinct microbial communities under the tested conditions indicates that an appropriate balancing of water saturation and unsaturation in reactors is crucial to achieving optimum iHydroMET performance.

Molecular biological mechanism of fillers with surface micro-electric field to enhance biodegradation of kitchen-oil wastewater

The kitchen-oil wastewater is characterized by a high concentration of organic matter, complex composition and refractory pollutants, which make wastewater treatment more difficult. Based on the study of using micro-electric field characteristic catalyst HCLL-S8-M to enhance the electron transfer between microorganisms in kitchen-oil wastewater which further improved the COD removal rate, we focus on the microbial community, intracellular metabolism and extracellular respiration, and make an in-depth analysis of the molecular biological mechanisms to microbial treatment in wastewater. It is found that electroactive microorganisms are enriched on the material surface, and the expression levels of cytochrome c and riboflavin genes related to electron transfer are up-regulated, confirming that the surface micro-electric field structure could enhance the electron transfer between microbial species and improve the efficiency of wastewater degradation. This study provides a new idea for the treatment of refractory organic wastewater.

Analysis of the contribution of different electron transfer pathways for hydrogen production in a bioelectrochemically assisted dark fermentation system

This research analyzed the contribution of different electron transfer pathways for H2 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 H2 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 H2 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 H2 production through the eEET pathway.

Accelerating cell division of Shewanella oneidensis to promote extracellular electron transfer rate for efficient pollution treatment

The slow rate of extracellular electron transfer (EET) of electroactive microorganisms (EAMs) remains a predominate bottleneck that restricts practical applications of bio-electrochemical systems. Cell division has significant effects on cell cycle, morphology, growth and metabolism. However, the relation between cell division and the EET rate of Shewanella oneidensis has not been established. Here, we employed modular engineering strategy to accelerate DNA replication in the C period and divisome formation in the D period of cell cycle, which decreased cellular volume and enhanced the EET efficiency. Assembly of the C and D period modules further decreased the cell volume by 82.0 % and enhanced power density by 3.12-fold. Electrophysiological and transcriptomic analyses synergistically revealed that the programmed cell volume decrease facilitated lactate uptake and cellular metabolism due to the increased specific surface area (SSA), which consequently reinforced intracellular electron generation. Moreover, the reduced cell size facilitated electroactive biofilm formation. Finally, programmed increase in riboflavin biosynthesis and transport further strengthened indirect EET and boosted output power density to 1537.8 ± 116.9 mW m−2, 21.1-fold of that of the WT. The engineered strains exhibited superior abilities for Cr6+ reduction and azo dyes degradation. This study shed light on the underlying mechanism how reduced cell size impacts electrophysiology of EAMs, and indicated accelerating cell division is a promising avenue to increase the EET of EAMs for efficient environmental pollution treatment.

Three-dimensional biochar aerogel anode derived from expired yogurt for enhancing power efficiency and electron transfer at the bacteria-anode interface in microbial fuel cells

Microbial fuel cells (MFCs) are a promising and sustainable form of fuel cells that utilize electroactive microorganisms to generate electricity. However, the practical application of MFCs is limited by their low power density, inadequate biocompatibility, and suboptimal electrochemical properties. To overcome these challenges, we developed a three-dimensional high performance biochar aerogel anode (YP) made from a mixture of expired yogurt and polyvinyl alcohol (PVA) and investigated its effect on the performance of the MFC. The incorporation of PVA into the YP anodes resulted in improved electrolyte wettability and hydrophilic surfaces, thereby enhancing biocompatibility and bacterial adhesion, especially with Geobacter, reaching up to 89.6% coverage. The biofilm content reached 68.1 mg, which is 1.7 times that of carbon cloth, which improved the electron transfer efficiency at the bacteria-anode interface. Moreover, the mechanical strength of the YP anodes was increased, improving anode stability and durability. In addition, the aerogel anode exhibited impressive power density and current density values of 15.87 W m−3 and 43.76 A m−3, respectively. These values are 3.16 times and 3.60 times higher than the 5.03 W m−3 and 12.13 A m−3 of carbon cloth. This study makes a significant contribution to improving power generation in MFCs, optimizing electron transfer at the bacteria-anode interface, and paving the way for future practical applications of MFCs.

Electron Transfer in the Biogeochemical Sulfur Cycle.

Microorganisms are key players in the global biogeochemical sulfur cycle. Among them, some have garnered particular attention due to their electrical activity and ability to perform extracellular electron transfer. A growing body of research has highlighted their extensive phylogenetic and metabolic diversity, revealing their crucial roles in ecological processes. In this review, we delve into the electron transfer process between sulfate-reducing bacteria and anaerobic alkane-oxidizing archaea, which facilitates growth within syntrophic communities. Furthermore, we review the phenomenon of long-distance electron transfer and potential extracellular electron transfer in multicellular filamentous sulfur-oxidizing bacteria. These bacteria, with their vast application prospects and ecological significance, play a pivotal role in various ecological processes. Subsequently, we discuss the important role of the pili/cytochrome for electron transfer and presented cutting-edge approaches for exploring and studying electroactive microorganisms. This review provides a comprehensive overview of electroactive microorganisms participating in the biogeochemical sulfur cycle. By examining their electron transfer mechanisms, and the potential ecological and applied implications, we offer novel insights into microbial sulfur metabolism, thereby advancing applications in the development of sustainable bioelectronics materials and bioremediation technologies.

Transitional bimetallic heterostructure catalyst modified anode for microbial fuel cell treatment of high-intensity wastewater

In this paper, transitional bimetallic catalysts (FeS2/MoS2) were prepared by a simple one-step hydrothermal method, which were directly applied to MFC anodes for the treatment of high-concentration wastewater with simultaneous biopower generation. The obtained catalysts were highly biocompatible and favorable for inducing the enrichment of electroactive microorganisms and shortening the initiation cycle. The maximum power density (Pmax) and current density of the obtained anode reached 2.87 W·m−2 and 4.37 A·m−2 under 4000 mg·L−1 influent, which were 171% and 65% higher than that of bare carbon cloth, respectively. The chemical oxygen demand (COD) removal rate reached 98.82%. 16 S rRNA gene sequence analysis showed that the main electrophilic microorganisms induced by FeS2/8%MoS2-modified anodes were Synergistota (30.94%) and Geoalkallbacter (15.93%) compared to CC anodes. The resulting anode possesses excellent redox activity and high biocompatibility, and is simple and inexpensive to prepare. More importantly, it accelerated the extracellular electron transfer rate at the interface between the electroactive bacteria and the anode, providing a new idea of choice for single-chamber microbial fuel cells for low-cost treatment of high-concentration wastewater.

Dissolved organic matter (DOM) enhances the competitiveness of weak exoelectrogens in a soil electroactive biofilm

Dissolved organic matter (DOM) as critical redox active soil carbon plays a crucial role in shuttling electrons between bacteria and solid electron acceptors, such as iron oxides. However, research on DOM as an electron shuttle has traditionally focused on its impact on typical iron-reducing bacteria, namely strong exoelectrogens, like Geobacter. Besides these strong exoelectrogens, there is a significant presence of weak exoelectrogens in the soil, but studies examining how DOM affects their survival and competitiveness are lacking. This study focused on exploring the influence of DOM on weak exoelectrogens like Bacillus in the soil. By utilizing soil-bioelectrochemical systems (s-BESs) to enrich soil electroactive microorganisms, it investigated the relationship between the abundance of strong and weak exoelectrogens under conditions rich in DOM and conditions lacking DOM. The results showed that in the rich DOM treatment, the abundance of Geobacter was relatively lower (12 ± 0.5% vs. 41 ± 3%), and there was a significant negative correlation between the abundance changes of 18 weak exoelectrogens and Geobacter. This suggests that DOM caused a decrease in the population of strong exoelectrogens (e.g., Geobacter) while simultaneously promoting the growth of weak exoelectrogens (e.g., Bacillus and Sedimentibacter). Based on this, we propose that DOM, acting as an electron shuttle, creates favorable ecological niches for the thriving and propagation of weak exoelectrogens, enhancing their competitiveness within the microbial community. This new understanding provides deeper insights into the significance of DOM electron shuttling in soil microbial ecology, and raises the question: is the role of weak exoelectrogens in soil iron cycling underestimated due to the existence of DOM?Graphical

Low temperature acclimation of electroactive microorganisms may be an effective strategy to enhance the toxicity sensing performance of microbial fuel cell sensors

Microbial fuel cell (MFC) sensing is a promising method for real-time detection of water biotoxicity, however, the low sensing sensitivity limits its application. This study adopted low temperature acclimation as a strategy to enhance the toxicity sensing performance of MFC biosensor. Two types of MFC biosensors were started up at low (10 °C) or warm (25 °C) temperature, denoted as MFC-Ls and MFC-Ws respectively, using Pb2+ as the toxic substance. MFC-Ls exhibited superior sensing sensitivities towards Pb2+ compared with MFC-Ws at both low (10 °C) and warm (25 °C) operation temperatures. For example, the inhibition rate of voltage of MFC-Ls was 22.81 % with 1 mg/L Pb2+ shock at 10 °C, while that of MFC-Ws was only 5.9 %. The morphological observation showed the anode biofilm of MFC-Ls had appropriate amount of extracellular polymer substances, thinner thickness (28.95 μm for MFC-Ls and 41.58 μm for MFC-Ws) and higher proportion of living cells (90.65 % for MFC-Ls and 86.01 % for MFC-Ws) compared to that of MFC-Ws. Microbial analysis indicated the enrichment of psychrophilic electroactive microorganisms and cold-active enzymes as well as their sensitivity to Pb2+ shock was the foundation for the effective operation and good performance of MFC-Ls biosensors. In conclusion, low temperature acclimation of electroactive microorganisms enhanced not only the sensitivity but also the temperature adaptability of MFC biosensors.

Nature inspired catalysts: A review on electroactive microorganism-based catalysts for electrochemical applications

The pursuit of efficient and sustainable electrochemical systems, that can generate green fuels and chemicals, stands as a primary contemporary challenge for sustaining a circular economy. As one of the main focuses in electrochemical systems, crafting robust electrocatalysts for various reactions, mostly based on expensive platinum group metals, has achieved plenty of attention in recent decades. To avoid the high cost and potential pollution associated with the synthesis of noble metal catalysts, nature-inspired catalysts, in particular catalysts based on electroactive microorganisms (EAM), serve as a valuable alternative for producing catalysts with intricate hierarchical structures and intrinsically scaling capability. This review aims to systematically detail the fundamental mechanisms of synthesis, potential applications, and future directions of EAM-based catalysts in electrochemical systems with emphasis on EAM-derived electrocatalysts and electrocatalysis. First, the synthesis methods, the mechanisms of synthesis, and the potential applications of EAM-derived electrocatalysts are discussed in detail. Second, the basics of microbial electrocatalysis, where EAM catalyzes various reactions at the electrodes of bioelectrochemical systems, are presented. The application of EAM catalysts in bioelectrochemical systems for organic matter degradation producing high current densities (> 2 A m−2), electrosynthesis of high-value chemicals from CO2, and the application of EAM-derived electrocatalysts for hydrogen/oxygen evolution reaction achieving comparable overpotentials to benchmark Pt/C and IrO2 catalyst (400 mV for HER and 370 mV for OER at 10 mA cm−2) are systematically summarized. Finally, challenges and new research directions are discussed, to shed light on the future implementation of EAM-based catalysts in sustainable electrochemical systems.

The promotion of the atrazine degradation mechanism by humic acid in a soil microbial electrochemical system

The enhancing effects of anodes on the degradation of the organochlorine pesticide atrazine (ATR) in soil within microbial electrochemical systems (MES) have been extensively researched. However, the impact and underlying mechanisms of soil microbial electrochemical systems (MES) on ATR degradation, particularly under conditions involving the addition of humic acids (HAs), remain elusive. In this investigation, a soil MES supplemented with humic acids (HAs) was established to assess the promotional effects and mechanisms of HAs on ATR degradation, utilizing EEM-PARAFAC and SEM analyses. Results revealed that the maximum power density of the MES in soil increased by 150%, and the degradation efficiency of ATR improved by over 50% following the addition of HAs. Furthermore, HAs were found to facilitate efficient ATR degradation in the far-anode region by mediating extracellular electron transfer. The components identified as critical in promoting ATR degradation were Like-Protein and Like-Humic acid substances. Analysis of the microbial community structure indicated that the addition of HAs favored the evolution of the soil MES microbial community and the enrichment of electroactive microorganisms. In the ATR degradation process, the swift accumulation of Hydrocarbyl ATR (HYA) was identified as the primary cause for the rapid degradation of ATR in electron-rich conditions. Essentially, HA facilitates the reduction of ATR to HYA through mediated bonded electron transfer, thereby markedly enhancing the efficiency of ATR degradation.

Electromagnetic Field Drives the Bioelectrocatalysis of γ-Fe2O3-Coated Shewanella putrefaciens CN32 to Boost Extracellular Electron Transfer.

The microbial hybrid system modified by magnetic nanomaterials can enhance the interfacial electron transfer and energy conversion under the stimulation of a magnetic field. However, the bioelectrocatalytic performance of a hybrid system still needs to be improved, and the mechanism of magnetic field-induced bioelectrocatalytic enhancements is still unclear. In this work, γ-Fe2O3 magnetic nanoparticles were coated on a Shewanella putrefaciens CN32 cell surface and followed by placing in an electromagnetic field. The results showed that the electromagnetic field can greatly boost the extracellular electron transfer, and the oxidation peak current of CN32@γ-Fe2O3 increased to 2.24 times under an electromagnetic field. The enhancement mechanism is mainly due to the fact that the surface modified microorganism provides an elevated contact area for the high microbial catalytic activity of the outer cell membrane's cytochrome, while the magnetic nanoparticles provide a networked interface between the cytoplasm and the outer membrane for boosting the fast multidimensional electron transport path in the magnetic field. This work sheds fresh scientific light on the rational design of magnetic-field-coupled electroactive microorganisms and the fundamentals of an optimal interfacial structure for a fast electron transfer process toward an efficient bioenergy conversion.

Denitrification reaction performance in three-dimensional biofilm electrode reactors using self-releasing carbon biofilm electrodes

Agricultural waste, corncobs, and sponge iron were used to develop a self-releasing carbon biofilm electrode (SRC-BE) and utilized for denitrification experiments in three-dimensional biofilm electrode reactors (3D-BERs). Fe2+ was released to enhance the extracellular electron transfer. Following an alkali treatment, SRC-BE were introduced into 3D-BERs of the electrode group (EG), with iron serving as the anode-cathode plate in the EG. Under a current density of 0.1 mA/cm2, hydraulic retention time of 2 h, and dissolved oxygen control at 0.5–1.0 mg/L, the removal rates were as follows: the highest removal rates were 71.09 % for total nitrogen, 40.26 % for NH4+-N, and 84.34 % for NO3−-N, with a stable 96.87 % removal rate for total phosphate. The effluent chemical oxygen demand in the EG remained stable at approximately 12 mg/L during the stable phase, thus reducing the risk of secondary pollution. The enrichment of electroactive microorganisms and functional genes related to C and N also verified their denitrification efficacy.