Electrochemically Active Bacteria Research Articles

Constructed wetland coupled microbial fuel cell (CW-MFC) with Phragmites australis planted for hexavalent chromium removal and electricity generation

Hexavalent chromium (Cr(VI)) in aqueous solution is characterized by strong mobility, high solubility, and significant biological toxicity. In this study, four constructed wetland combined with microbial fuel cell (CW-MFC) systems were established to explore the changes in electricity generation, water purification, and microbial community structure under the influence of plant, bioelectrochemical, and Cr(VI) stress. The planted CW-MFC (total Cr: 97.5 %, Cr(VI): 99.2 %) and non-planted CW-MFC (total Cr: 95.3 %, Cr(VI): 97.3 %) showed significantly higher Cr removal efficiency than open circuit CW-MFC (total Cr: 86.9 %, Cr(VI): 84.8 %). The presence of plants and Cr(VI) increased the average voltage and power density of CW-MFC. Additionally, plants, bioelectrochemistry, and Cr(VI) improved COD removal and significantly enhanced the abundance and diversity of microorganisms in the system during long-term domestication. The Cr(VI)-reducing bacterium Exiguobacterium was least abundant in non-Cr(VI) containing CW-MFC system. The abundance of the electrochemically active bacteria (EAB) Geobacter increased under bioelectrochemistry and Cr(VI).

Insights into the efficient electricity production performance using acid-treated straw in MFCs

In this study, a mixed electrogenic culture (RS) was successfully enriched from cow rumen fluid which produced a maximum current density of 634 ± 58 μA cm−2 using carboxymethyl cellulose (CMC) as the substrate in a three-electrode system. Furthermore, in the microbial fuel cells (MFCs) system, RS as the inoculum was able to generate electricity using treated corn straw instead of CMC as substrates. Power densities of 550 ± 25 mW m−2 from the alkali-treated straw, 842 ± 35 mW m−2 from neutral-treated straw, and 1377 ± 20 mW m−2 from acid-treated straw for RS were obtained with RS, respectively, which are all much higher than that of 110 ± 15 mW m−2 using untreated straw as the substrate. It can be found that the electricity generation performance of RS in MFCs using straw treated by different methods varied significantly. Among them, the power density using acid-treated straw was 1.64 and 2.50 times higher than that using neutral-treated and alkali-treated straw, respectively. Meanwhile, the power density of RS using acid-treated straw was 1.36 times and 1.58 times higher than that of RS using CMC and that of G. sulfurreducens PCA using small molecule acetic acid as the substrate, respectively. Microbial community composition analysis of the RS enriched using differently treated straw revealed that the relative abundances of 47.1 % for Geobacter and 14.7 % for Wolinella were dominant in the acid-treated straw RS by comparison of 1.9 %, 11.3 % and 14.0 %, 4.2 % for RS using alkali-treated and neutral-treated straw, respectively. In addition, the metabolite analysis of RS during electricity generation revealed that the RS enriched from acid-treated straw contained a higher amount of acetic acid (9.3 ± 0.4 mmol/L) as the carbon source for electrochemically active bacteria (EAB), such as G. sulfurreducens PCA, which was higher than the values of 4.3 ± 0.4 mmol/L (alkali-treated) and 0.34 ± 0.04 mmol/L (neutral-treated) straw. Therefore, these results implied that the degraded organic matters in the acid-treated straw contains more acetic acid, which is accessible to RS, enabling higher electricity production by enriching more efficient EAB. It can be seen that the acid-treated method for straw can effectively degrade the straw to low molecules (more acetic acid) which will improve the microbial community composition to produce higher electricity current. This study offers a promising practical method for recovery energy using straw in MFCs system in the future.

Bidirectional extracellular electron transfers by Stenotrophomonas sp. and by Serratia marcescens via tunable extracellular polymeric substances at low or at high solution conductivity

Unearthing robust electrochemically active bacteria (EAB) with bidirectional extracellular electron transfer (EET) is increasingly attractive for the treatment of wastewaters characterized by a diversity of ions and limited by either carbon/electron sources or electron acceptors in single-chamber bioelectrochemical systems (BESs). Here, both Stenotrophomonas sp. YS1 and Serratia marcescens Q1 biofilms were demonstrated to be switchable and thus capable of bidirectional EET metabolizing either organic (acetate) or inorganic species (NaHCO3) in single-chamber BESs. The electron uptake (inward EET) by Q1 was more efficient than that of YS1 while, YS1 was more efficient than Q1 for outward EET. Higher solution conductivity significantly increased the EET activities of both strains, although, Q1 was more affected than YS1 during outward EET, while YS1 was more impacted than Q1 during inward EET. Experiments performed at low (5.8 mS/cm) and at high (103 mS/cm) solution conductivity with inward and outward EET evidenced the variable amount and compositional diversity of extracellular polymeric substances (EPS) released by Q1 and YS1 biofilms and plankton cells during inward or outward EET, demonstrating the regulative manipulation of these EAB via adaptive electrochemically-tunable EPS components. This study demonstrates EET between Stenotrophomonas sp. or S. marcescens and the electrodes is bidirectional and switchable with dependence on solution conductivity via the response of EPS amount and compositional diversity, giving a comprehensive appreciation of the bacteria behaviour through tunable EPS in response to the altered solution conductivity widening our knowledge on EAB bidirectional EET in single-chamber BESs.

Isolation of Electrochemically Active Bacteria from an Anaerobic Digester Treating Food Waste and Their Characterization.

Studies have used anaerobic-digester sludge and/or effluent as inocula for bioelectrochemical systems (BESs), such as microbial fuel cells (MFCs), for power generation, while limited studies have isolated and characterized electrochemically active bacteria (EAB) that inhabit anaerobic digesters. In the present work, single-chamber MFCs were operated using the anaerobic-digester effluent as the sole source of organics and microbes, and attempts were made to isolate EAB from anode biofilms in MFCs by repeated anaerobic cultivations on agar plates. Red colonies were selected from those grown on the agar plates, resulting in the isolation of three phylogenetically diverse strains affiliated with the phyla Bacillota, Campylobacterota and Deferribacterota. All these strains are capable of current generation in pure-culture BESs, while they exhibit different electrochemical properties as assessed by cyclic voltammetry. The analyses of their cell-free extracts show that cytochromes are abundantly present in their cells, suggesting their involvement in current generation. The results suggest that anaerobic digesters harbor diverse EAB, and it would be of interest to examine their ecological niches in anaerobic digestion.

Extracellular electron transfer explained

Extracellular electron transfer explained Arpita Bose, PhD from Washington University in St. Louis, guides us through host-associated impacts and biotechnological applications of extracellular electron transfer in electrochemically active bacteria. Electron flow and oxidative and reductive reactions, referred to as “redox reactions,” collectively impact the outcomes of biochemical pathways essential for cell growth, energy conservation, and stress response throughout various organisms. An example of these organisms is electrochemically active bacteria (EAB), which can link internal redox reactions with external electron acceptors or donors via a process known as extracellular electron transfer (EET).

Biological mechanisms affecting the release of greenhouse gases from microbial fuel cell-constructed wetland by simultaneously altering structure and electron shuttles

The utilization of microbial fuel cells (MFCs) for regulating greenhouse gas (GHG) emissions in constructed wetlands (CW) has attracted significant attention. The impact of structural modifications, the introduction of iron-carbon materials on pollutant removal and GHG release from MFC-CW has not been systematically studied. In this study, four types of MFC-CWs were constructed, including MFC-CW with separated aerobic and anaerobic zones (SC), MFC-CW with unseparated aerobic and anaerobic zones (IC), SC added with iron-carbon (SFC), and IC added with iron-carbon (IFC). The aim was to investigate the effects of structural changes and electron shuttle additions on the GHG release. The results revealed that IFC simultaneously enhanced pollutant removal and GHG emissions reduction, compared to IC. However, no significant enhancements were observed in SC and SFC. The cumulative emissions of nitrous oxide (N2O) and methane (CH4) in SC were reduced by 51.83% and 89.33% respectively, compared to IC. The modifications made to the structure of MFC-CWs influenced the relationship between functional bacteria (Chlorobium, Azospira, and Denitratisoma) and electrochemically active bacteria (EAB), resulting in increased values of nirS/nosZ and pmoA/mcrA. Comparing the SFC and IFC, despite an improvement in denitrogenation efficiency, the effect of structural alteration on N2O reduction was slight. The electrons in the iron-mediated process were not effectively used for N2O reduction. This study confirmed the crucial involvement of electron shuttles and the structure of MFC-CWs in controlling contaminant removal and GHG emissions.

Efficient phosphate and hydrogen recovery from sludge fermentation liquid by sacrificial iron anode in electro-fermentation system

Electro-fermentation (EF) has been extensively studied for recovering hydrogen and phosphorus from waste activated sludge (WAS), while was limited for the further application due to the low hydrogen yield and phosphorus recovery efficiency. This study proposed an efficient strategy for hydrogen and vivianite recovery from the simulated sludge fermentation liquid by sacrificial iron anode in EF. The optimum hydrogen productivity and the utilization efficiency of short chain fatty acids (SCFAs) reached 45.2 mmol/g COD and 77.6% at 5 d in pH 8. Phosphate removal efficiency achieved at 90.8% at 2 d and the high crystallinity and weight percentage of vivianite (84.8%) was obtained. The functional microbes, i.e., anaerobic fermentative bacteria, electrochemical active bacteria, homo-acetogens and iron-reducing bacteria were highly enriched and the inherent interaction between the microbial consortia and environmental variables was thoroughly explored. This work may provide a theoretical basis for energy/resource recovery from WAS in the further implementation.

Synergistic reduction of pollution and carbon mitigation in constructed wetlands-microbial fuel cell using sludge-derived biochar

Integrating microbial fuel cells (MFC) into constructed wetland systems (CW) has been an efficient wastewater treatment to improve the pollutants removal and regenerate power energy. This study fabricated a sludge biochar material (SBM) to sequestrate the carbon of residual sludge. Thereafter used SBM and modified SBM as the substrate materials to construct three groups of CW-MFC for decreasing the greenhouse gas (GHG) emission. The water quality improvement in removal efficiency achieved (2.59 %, 3.10 %, 5.21 % for COD; 3.31 %, 3.60 %, 6.71 % for TN; 1.80 %, 7.38 %, 4.93 % for TP) by the application of MFC, SBM, and modified SBM in wastewater treatment, respectively. Additionally, the reduction in global warming potential (GWP) realized 17.2 %, 42.2 %, and 64.4 % resulting from these applications. The carbon flow and fate diagrams showed MFC shifted the gas phase‑carbon flow from CH4 to CO2, and SBM promoted this shift trends. Microbial diversity indicated enrichment of electrochemically active bacteria (EAB), denitrifying bacteria, and phosphate accumulating organisms (PAOs) by SBM. Metabolic pathways analysis showed that introduction of MFC and SBM exhibited significant increases of key functional genes in metabolic pathway of anaerobic oxidation of methane (AOM). This study highlights the benefit of CW-MFC in and provides a new strategy for removing pollutants and abating GHG emissions in wastewater treatment.

Promoting bioremediation of brewery wastewater, production of bioelectricity and microbial community shift by sludge microbial fuel cells using biochar as anode

Seeking low-cost and eco-friendly electrode catalyst of microbial fuel cell (MFC) reactor has received extensive attention in recent decades. In this study, a sludge MFC was coupled with biochar-modified-anode (BC-300, BC-400, and BC-500) for actual brewery wastewater treatment. The physicochemical properties of biochar largely depended on the pyrolysis temperature, further affecting the removal efficiency of wastewater indicators. BC-400 MFC proved to be efficient for TN and NH4+-N removal, while the maximum removal efficiencies of COD and TP were achieved by BC-500 MFC, reaching respectively 97.14 % and 89.67 %. Biochar could promote the degradation of dissolved organic matter (DOM) in wastewater by increasing the electrochemical performances of MFC. The maximum output voltage of BC-400 MFC reached 410.24 mV, and the maximum electricity generation of 108.05 mW/m2 was also obtained, surpassing the pristine MFC (BCC-MFC) by 4.67 times. High-throughput sequencing results illustrated that the enrichment of electrochemically active bacteria (EAB) and functional bacteria (Longilinea, Denitratisoma, and Pseudomonas) in BC-MFCs, contributed to pollutants degradation and electron transfer. Furthermore, biochar affected directly the electrical conductivity of wastewater, simultaneously changing microbial community composition of MFC anode. Considering both enhanced removal efficiency of pollutants and increased power generation, the results of this study would offer technical reference for the application of biochar as MFC catalyst for brewery wastewater treatment.

Selective colonization of multifunctional microbes that facilitates caproate production in microbial electrosynthesis system

As promising and value-added platform chemicals, the biosynthesis of medium-chain fatty acids (MCFAs, C6-C12) via chain elongation (CE) in microbial electrosynthesis systems (MES) has recently garnered significant attentions due to the unique bioelectrocatalytic behaviors and the reduction of exogenous electron donors (EDs). Caproate-synthesizing bacteria (CSB) played a crucial role in the generation of acetyl-CoA, which subsequently underwent reverse β oxidation to synthesize MCFAs. However, the presence of electrochemically active bacteria (EAB) was also pivotal for MES as they generated hydrogen in the cathodic electron transfer pathways, the specific colonization patterns of key symbionts remained unknown. The aim of this study was to investigate the selective colonization of EAB and CSB on the performance of caproate production in MES. The reactors colonized EAB and CSB achieved the maximum caproate concentration of 5332.5 mg COD/L, which was 7.9 and 1.3 times higher compared to that inoculated with either sole EAB or CSB, respectively. Moreover, the reactors colonized with mixed culture exhibited a clear redox peak and preferable electron transfer efficiency. CSB and EAB mutually interacted in metabolic activities, thereby resulting in increased substrate utilization and caproate production. The findings of this study provide a new strategy and insights for value-added chemicals recovery in microbial electrosynthesis platform.

Effects of simulated microgravity on current generation of electrochemically active bacteria: Insights from case-control study using random positioning machine

Electrochemically active bacteria (EAB) exhibit promising prospects for space exploration and life support systems. However, the effects of the space environment on EAB are unclear. In this study, the effects of simulated microgravity on the current generation of mixed-culture EAB were illustrated, and the underlying mechanism was elucidated. The results demonstrated that the electrochemical activity of mixed-culture EAB was enhanced, which was mainly due to the enrichment of Geobacter and the increase in EAB biomass. Additionally, the genes and proteins of the biofilm changed obviously under simulated microgravity conditions, including: I) genes related to signal transfer, II) genes related to cell wall synthesis, and III) genes related to riboflavin synthesis. This study first revealed the enrichment in EAB abundance, the increase in EAB biomass, and the promotion of current generation under simulated microgravity.

An overview of agro-industrial wastewater treatment using microbial fuel cells: Recent advancements

Discharge of agro-industrial wastewater causes severe damage to the environment due to the various hazardous components it contains. Progressive circular agriculture and industry involve closed cycles and zero-waste principles; therefore, waste treatment for subsequent reuse is of great interest. The microbial fuel cell (MFC) is a promising sustainable technology capable of treating wastewater at low cost without greenhouse gas (GHG) emissions while simultaneously producing electricity. The principle behind MFCs is based on the conversion of chemical energy into electricity using electrochemically active bacteria (EAB) as a biocatalyst. This article presents an overview of the progress and recent advancements in MFCs as a pivotal technology for agro-industrial wastewater treatment with production of sustainable electricity, compared to conventional treatment processes. Furthermore, the fundamental aspects of the design, configuration, operation, and application of MFCs in wastewater treatment (i.e., removal of inorganic nutrients, nitrate, phosphate, sulfate, sulfide, ammonium, organics, dyes, carbohydrates, fatty acids, and petroleum) are comprehensively discussed. Despite the viability and potential of MFCs in treating agro-industrial wastewater and producing electricity, they face various limitations and significant challenges, which are highlighted in this review. Future opportunities and perspectives on MFC applications are also discussed. Further research is required to address MFC limitations, which could make them feasible and practicable for real-world applications. However, MFC technology is clearly an excellent option for simultaneous wastewater treatment and electricity production without the need for external energy sources.

Effects of long-term and incremental exposure to toxic pollutants on the current generation and microbial communities of electrochemically active bacteria

The study first reveals the long-term effects of toxic exposure on the current generation and the microbial communities of EAB. Acute toxicity inhibits the current generation in the early stage but gradually diminish during the middle and end stages.

Resorufin retainment by extracellular DNA ensures efficient extracellular electron transfer of Geobacter biofilm

Electrochemically active bacteria (EAB) have promising applications in renewable energy recovery, biofuel production, environmental remediation, and wastewater treatment. Resazurin (RZ) is an effective exogenous electron mediator to facilitate extracellular electron transfer (EET) in EAB, but it is not fully understood that how it catalyzes EET within thick electroactive biofilm. Using Geobacter sulfurreducens as a model EAB, this study investigated the effect and mechanisms of RZ-mediated electron transfer in anode biofilm in a bioelectrochemical system. It was found that the amendment of RZ substantially enhanced current generation of anode biofilm, and the facilitating effect of RZ remained even after fresh electrolyte replacement without RZ replenishment. As an intermediate product of RZ, resorufin (RR) was the actual electron shuttle retained within the entire anode biofilm, responsible for the observed stable electron shuttling efficiency. The retention of RR in anode biofilm might be the consequences of insoluble RR deposition and RR binding with extracellular DNA (eDNA) through intercalative interactions. This study provided in vivo and in vitro evidences for the first time that eDNA provided binding sites for RR in Geobacter biofilm, and proposed a novel electron shuttling mechanism of phenoxazine catalyzing efficient EET of electroactive biofilm.

Rapid screening of electrochemically active bacteria based on a biocathode-functional bipolar electrode-electrochemiluminescence platform.

A functional bipolar electrode-electrochemiluminescence (BPE-ECL) platform based on biocathode reducing oxygen was constructed for detecting electrochemically active bacteria (EAB) in this paper. Firstly, thiolated trimethylated chitosan quaternary ammonium salt (TMC-SH) layer was assembled on the gold-plated cathode of BPE. TMC-SH contains quaternary ammonium salt branch chain, which can inhibit the growth of microorganisms on the surface or in the surrounding environment while absorbing bacteria. Then, the peristaltic pump was used to flow all of the samples through the cathode, and the EAB was electrostatically adsorbed on the electrode surface. Finally, applying a constant potential to the BPE, bacteria can catalyze electrochemical reduction of O2, and decrease the overpotential of O2 reduction at the cathode, which in turn generates an ECL reporting intensity change at the anode. In this way, live and dead bacteria can be distinguished, and the influence of complex food substrates on detection can be greatly reduced.

Selective Sensing in Microbial Fuel Cell Biosensors: Insights from Toxicity-Adapted and Non-Adapted Biofilms for Pb(II) and Neomycin Sulfate Detection.

This study introduces the utilization of self-powered microbial fuel cell (MFC)-based biosensors for the detection of biotoxicity in wastewater. Current MFC-based biosensors lack specificity in distinguishing between different pollutants. To address this limitation, a novel approach is introduced, capitalizing on the adaptive capabilities of anodic biofilms. By acclimating these biofilms to specific pollutants, an enhancement in the selectivity of MFC biosensors is achieved. Notably, electrochemically active bacteria (EAB) were cultivated on 3D porous carbon felt with and without a model toxicant (target analyte), resulting in the development of toxicant-resistant anodic biofilms. The model toxicants, Pb2+ ions and the antibiotic neomycin sulfate (NS), were deployed at a concentration of 1 mg L-1 during MFC operation. The influence of toxicity on biofilm growth and power production was investigated through polarization and power density curves. Concurrently, the electrochemical activity of both non-adapted and toxicity-adapted biofilms was investigated using cyclic voltammetry. Upon maturation and attainment of peak powers, the MFC reactors were evaluated individually as self-powered biosensors for pollutant detection in fresh wastewater, employing the external resistor (ER) mode. The selected ER, corresponding to the maximum power output, was positioned between the cathode and anode of each MFC, enabling output signal tracking through a data logging system. Subsequent exposure of mature biofilm-based MFC biosensors to various concentrations of the targeted toxicants revealed that non-adapted mature biofilms generated similar current-time profiles for both toxicity models, whereas toxicity-adapted biofilms produced distinctive current-time profiles. Accordingly, these results suggested that merely by adapting the anodic biofilm to the targeted toxicity, distinct and identifiable current-time profiles can be created. Furthermore, these toxicity-adapted and non-adapted biofilms can be employed to selectively detect the pollutant via the differential measurement of electrical signals. This differentiation offers a promising avenue for selective pollutant detection. To the best of our current knowledge, this approach, which harnesses the natural adaptability of biofilms for enhanced sensor selectivity, represents a pioneering effort in the realm of MFC-based biosensing.

Instant water toxicity detection based on magnetically-constructed electrochemically active biofilm

Water toxicity determination with electrochemically active bacteria (EAB) is promising in the early warning of water pollution. However, limited by tedious biofilm formation, natural EAB biofilms are uncapable of the instant detection of water toxicity, resulting in the failure for the emergency monitoring of water pollution. To solve this problem, a novel method for the rapid construction of EAB biofilms using magnetic adsorption was established, and the performance of instant water toxicity detection with magnetically-constructed EAB biofilm was investigated. The results demonstrate that EAB biofilms were magnetically constructed in less than 30 min, and magnetically-constructed EAB biofilm generated stable currents even under continuous flow conditions. Magnetically-constructed EAB biofilms realized instant water toxicity detection, and the sensitivity increased with the decrease of magnetic field intensity. Low magnetic field intensity resulted in a loose biofilm structure, which is conducive to toxic pollutant penetration. The detection limit for Cu2+, phenol, and Cd2+ achieved 0.07 mg/L with optimal magnetic field intensity, and the detection time was less than 30 min. This study broadens the application of water toxicity determination with EAB, and establishes a foundation for the instant and continuous detection of water toxicity with EAB.

Fat, oil, and grease as new feedstock towards bioelectrogenesis in microbial fuel cells: Microbial diversity, metabolic pathways, and key enzymes

Microbial fuel cells (MFCs) are a well-known technology used for bioelectricity production from the decomposition of organic waste via electroactive microbes. Fat, oil, and grease (FOG) as a new substrate in the anode and microalgae in the cathode were added to accelerate the electrogenesis. The effect of FOG concentrations (0.1%, 0.5%, 1%, and 1.5%) on the anode chamber was investigated. The FOG degradation, volatile fatty acid (VFAs) production, and soluble chemical oxygen demand along with voltage output kinetics were analyzed. Moreover, the microbial community analysis and active functional enzymes were also evaluated. The maximum power and current density were observed at 0.5% FOG which accounts for 96 mW m−2 (8-folds enhancement) and 560 mA m−2 (3.7-folds enhancement), respectively. The daily voltage output enhanced upto 2.3-folds with 77.08% coulombic efficiency under 0.5% FOG, which was the highest among all the reactors. The 0.5% FOG was degraded >85%, followed by a 1% FOG-loaded reactor. The chief enzymes in β-oxidation and electrogenesis were acetyl-CoA C-acetyltransferase, riboflavin synthase, and riboflavin kinase. The identified enzymes symbolize the presence of Clostridium sp. (>15%) and Pseudomonas (>10%) which served as electrochemical active bacteria (EAB). The major metabolic pathways involved in electrogenesis and FOG degradation were fatty acid biosynthesis and glycerophospholipid metabolism. Utilization of lipidic-waste (such as FOG) in MFCs could be a potential approach for simultaneous biowaste utilization and bioenergy generation.

Synergic mechanisms of electricity generation and bisphenol a degradation in a novel photocatalytic-microbial fuel cell equipped with a TiO2-C-BiVO4 photo-anode and a biofilm-anode

To provide a promising strategy for coping with the issues of energy shortage and wastewater treatment, a novel single-chamber photocatalytic-microbial fuel cell (PC-MFC) equipped with a photo-anode and a biofilm-anode was firstly established to degrade bisphenol A (BPA). The results showed that due to the ex-situ dual-anode configuration, the output voltage increased rapidly and maintained for three cycles with the maximum voltage of 0.55 V. In addition to the electrochemically-active bacteria (EAB) including Geobacter and Pseudomonas, TiO2-C-BiVO4 with Z-scheme was induced into PC-MFC as photoanode, which not only contributed the photoelectrons to electricity generation, but also functioned as redox mediator to regulate extracellular electron transfer (EET) processes. Within 12 h, the degradation and mineralization efficiency of BPA achieved 96.98% and 82.80%, respectively. Under the simulated solar irradiation, extra reactive oxygen species (ROS) induced by TiO2-C-BiVO4 and extracellular polymeric substances (EPS) in the biofilm contributed primarily to BPA degradation, assisted by the biodegradation of the functional bacteria and algae. The degradation routes of BPA were revealed based on the degradation intermediates detected by UPLC-MS and DFT calculation. Moreover, the toxicity of BPA was almost eliminated according to ECOSAR procedure, since the toxic intermediates can be fixed onto EPS as the microbial protective layer, and further degraded by ROS into the products with relatively high bioavailability, which enhanced the electricity generation. Thus, this study provided a novel way for advanced treatment of organic chemicals and power recovery from the wastewater to boost carbon neutralization.

Fe2O3 micron particles are critical for electron transfer and the distribution of electrochemically active bacteria in soil MFCs

Fe2O3 plays a complex role in soil electron transfer. A microbial fuel cell (MFC) was constructed to drive the directional transfer of electrons in soil, and the results revealed that Fe2O3 acts first as a capacitor, intercepting and reserving the electrons produced by electrochemically active bacteria (EAB) in the soil, which leads to a decrease in hexachlorobenzene (HCB) removal efficiency with increasing proportions of Fe2O3 dosing (R2 = 0.85). The Fe2O3 then exerted its semiconductor properties in synergy with dissolved Fe2+ as an electron mediator to promote the flow of electrons in the soil. Power generation by the MFC was significantly and positively correlated with the concentration of dissolved Fe2+ (r = 0.51) and the Fe2O3 dosing proportion (r = 0.97). The higher HCB removal efficiency, spatial distribution of intercepted electrons, and abundance of electron transfer metabolic pathways confirmed that Fe2O3 promoted electron-flow fluxes in soil. Additionally, Geobacter sp., (direct electron transfer) and Pseudomonas sp., (indirect electron transfer) were the dominant electrochemically active bacteria in the anode and soil of MFC, respectively. In this study, both dissolved (Fe2+) and solid state (Fe2O3) electron mediators functioned as electron transporters in soil, we propose an internal “electron internet” of soil consisting of points and lines.