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Widespread pesticide use in agriculture is a major source of soil pollution, driving biodiversity loss and posing serious threads to human health. The recalcitrant nature of most of these pesticides demands for effective remediation strategies. In this study, we assess the ability of soil microbial fuel cell (SMFC) technology to bioremediate soil polluted by the model pesticide atrazine. To elucidate the degradation mechanism and consequently define effective implementation strategies, we provide the first comprehensive investigation of the SMFC performance, in which the monitoring of the electrochemical performance of the system is combined with Quadrupole Time-of-Flight (QTOF) mass spectrometry and microbial analyses. Our results show that, while both SMFC and natural attenuation lead to a reduction on atrazine levels, the SMFC modulates the activity of different microbial pathways. As a result, atrazine degradation by natural attenuation leads to high levels of deisoproylatrazine (DIPA), a very toxic degradation metabolite, while DIPA levels in soil treated by SMFC remain comparatively low. The beta diversity and differential abundance analyses revealed how the microbial community evolves over time in the SMFCs degrading atrazine, demonstrating the enrichment of electroactive taxa on the anode, and the enrichment of a mixture of electroactive and atrazine-degrading taxa at the cathode. The detection and taxonomic classification of peripheral atrazine degrading genes, atzA, atzB and atzC, was carried out in combination with the differential abundance analysis. Results revealed that these genes are likely harboured by members of the order Rhizobiales enriched at the cathode, thus promoting atrazine degradation via the conversion of hydroxyatrazine (HA) into N-isopropylammelide (NIPA), as confirmed by mass spectrometry data. Overall, the comprehensive approach adopted in this work, provides fundamental insights into the degradation pathways of atrazine in soil by SMFC technology, which is critical for practical applications, thus suggesting an effective approach to advance research in the field.

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In recent years, owing to the overuse and improper handling of antibiotics, soil antibiotic pollution has become increasingly serious and an environmental issue of global concern. It affects the quality and ecological balance of the soil and allows the spread of antibiotic resistance genes (ARGs), which threatens the health of all people. As a promising soil remediation technology, bioelectrochemical systems (BES) are superior to traditional technologies because of their simple operation, self-sustaining operation, easy control characteristics, and use of the metabolic processes of microorganisms and electrochemical redox reactions. Moreover, they effectively remediate antibiotic contaminants in soil. This review explores the application of BES remediation mechanisms in the treatment of antibiotic contamination in soil in detail. The advantages of BES restoration are highlighted, including the effective removal of antibiotics from the soil and the prevention of the spread of ARGs. Additionally, the critical roles played by microbial communities in the remediation process and the primary parameters influencing the remediation effect of BES were clarified. This study explores several strategies to improve the BES repair efficiency, such as adjusting the reactor structure, improving the electrode materials, applying additives, and using coupling systems. Finally, this review discusses the current limitations and future development prospects, and how to improve its performance and promote its practical applications. In summary, this study aimed to provide a reference for better strategies for BES to effectively remediate soil antibiotic contamination.

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Soil microbial fuel cells (SMFCs) are bioelectrical devices powered by the oxidation of organic and inorganic compounds due to microbial activity. Seven soils were randomly selected from Bergen Community College or areas nearby, located in the state of New Jersey, USA, were used to screen for the presence of electrogenic bacteria. SMFCs were incubated at 35-37 °C. Electricity generation and electrogenic bacteria were determined using an application developed for cellular phones. Of the seven samples, five generated electricity and enriched electrogenic bacteria. Average electrical output for the seven SMFCs was 155 microwatts with the start-up time ranging from 1 to 11 days. The highest output and electrogenic bacterial numbers were found with SMFC-B1 with 143 microwatts and 2.99 × 109 electrogenic bacteria after 15 days. Optimal electrical output and electrogenic bacterial numbers ranged from 1 to 21 days. Microbial DNA was extracted from the top and bottom of the anode of SMFC-B1 using the ZR Soil Microbe DNA MiniPrep Protocol followed by PCR amplification of 16S rRNA V3-V4 region. Next-generation sequencing of 16S rRNA genes generated an average of 58 k sequences. BLAST analysis of the anode bacterial community in SMFC-B1 demonstrated that the predominant bacterial phylum was Bacillota of the class Clostridia (50%). However, bacteria belonging to the phylum Pseudomonadota (15%) such as Magnetospirillum sp. and Methylocaldum gracile were also part of the predominant electrogenic bacterial community in the anode. Unidentified uncultured bacteria accounted for 35% of the predominant bacterial community. Bioelectrical devices such as MFCs provide sustainable and clean alternatives to future applications for electricity generation, waste treatment, and biosensors.

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Microbial-mineral interaction has a broad application prospect in the field of environmental remediation of organic pollutants. However, the disadvantages of long repair cycle and low repair rate limit its industrial application. In this study, natural hematite was used as an auxiliary material for soil remediation in a bio-electrochemical system. It was found that the power density of soil microbial fuel cell (SMFC) system composed of 2.0 mm hematite was 2.889 mW/m2, which is 2.7 times compared with the blank group (1.068 mW/m2) in the particle size optimization experiment. A similarly increased power density (1.068 to 2.467 mW/m2) was observed when the hematite content changed from 0 to 20% in the concentration optimization experiment. Under 20% and 2.0-mm hematite condition, the phenol removal rate was closed to 99% after 7 days, which is 1.9-folds compared with blank control (53%). These results suggest that addition of hematite enhances soil porosity and conductivity, and increases the number of electron acceptors in soil. These findings inspire that this economic and abundant natural mineral is expected to be a potential auxiliary material in the field of soil organic pollutant purification, and expand the understanding of interactions between hematite and microorganisms in nature.

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Increasing energy demands and environmental pollution concerns press for sustainable and environmentally friendly technologies. Soil microbial fuel cell (SMFC) technology has great potential for carbon-neutral bioenergy generation and self-powered electrochemical bioremediation. In this study, an in-depth assessment on the effect of several carbon-based cathode materials on the electrochemical performance of SMFCs is provided for the first time. An innovative carbon nanofibers electrode doped with Fe (CNFFe) is used as cathode material in membrane-less SMFCs, and the performance of the resulting device is compared with SMFCs implementing either Pt-doped carbon cloth (PtC), carbon cloth, or graphite felt (GF) as the cathode. Electrochemical analyses are integrated with microbial analyses to assess the impact on both electrogenesis and microbial composition of the anodic and cathodic biofilm. The results show that CNFFe and PtC generate very stable performances, with a peak power density (with respect to the cathode geometric area) of 25.5 and 30.4 mW m-2, respectively. The best electrochemical performance was obtained with GF, with a peak power density of 87.3 mW m-2. Taxonomic profiling of the microbial communities revealed differences between anodic and cathodic communities. The anodes were predominantly enriched with Geobacter and Pseudomonas species, while cathodic communities were dominated by hydrogen-producing and hydrogenotrophic bacteria, indicating H2 cycling as a possible electron transfer mechanism. The presence of nitrate-reducing bacteria, combined with the results of cyclic voltammograms, suggests microbial nitrate reduction occurred on GF cathodes. The results of this study can contribute to the development of effective SMFC design strategies for field implementation.

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Soil microbial fuel cells (MFCs) have been increasingly studied in recent years and have attracted significant attention as an environmentally sustainable bioelectrochemical technology. However, the poor conductivity of the soil matrix and the neglect of the cathodic function have limited its application. In this study, quartz sand and activated carbon were subjected to investigation on their influence on atrazine degradation. Atrazine was introduced in different layers (cathode, upper layer) to explore the cathodic effect on atrazine removal. The results revealed that activated carbon could reduce the internal resistance (693 Ω) and generate the highest power density (25.51 mW/m2) of the soil MFCs, and thus increase the removal efficiency (97.92%) of atrazine. The dynamic degradation profiles of atrazine were different for different adding layers. The cathode electrode acted as an electron donor could increase the distance of the effective influence of the soil MFCs' cathode from the middle to the cathode layer. The cathode (region) and the region close to the cathode could degrade atrazine with the atrazine removal efficiencies ranging from 60.67% to 92.79%, and the degradation ability of the cathode was stronger than that of other layers. The degradation effect followed the order: cathode > upper > lower > middle). Geobacter, Desulfobulbus, and Desulfuromonas belonging to the δ-Proteobacteria class were identified as the dominant electroactive microorganisms in the anode layer, while their relative abundances are quite low in the upper and cathode layers. Pseudomonas is an atrazine-degrading bacterium, but its relative abundance was only 0.13-0.51%. Thus, bioelectrochemistry rather than microbial degradation was the primary driving force.

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Soil microbial fuel cells (SMFCs) are an innovative device for soil-powered biosensors. However, the traditional SMFC sensors relied on anodic biosensing which might be unstable for long-term and continuous monitoring of toxic pollutants. Here, a carbon-felt-based cathodic SMFC biosensor was developed and applied for soil-powered long-term sensing of heavy metal ions. The SMFC-based biosensor generated output voltage about 400 mV with the external load of 1000 Ω. Upon the injection of metal ions, the voltage of the SMFC was increased sharply and quickly reached a stable output within 2~5 min. The metal ions of Cd2+, Zn2+, Pb2+, or Hg2+ ranging from 0.5 to 30 mg/L could be quantified by using this SMFC biosensor. As the anode was immersed in the deep soil, this SMFC-based biosensor was able to monitor efficiently for four months under repeated metal ions detection without significant decrease on the output voltage. This finding demonstrated the clear potential of the cathodic SMFC biosensor, which can be further implemented as a low-cost self-powered biosensor.

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The soil microbial fuel cell (SMFC) is a new device that was originally designed to generate electricity from organic matter in soil using microorganisms. Currently, SMFC based biosensors are emerging as a new and promising research direction for real-time and rapid monitoring of soil quality or soil pollution. Compared to conventional biosensors, SMFC based biosensors exhibit advantages such as low-cost, simple design, in-situ, and long-term self-powering monitoring, which makes it become attractive devices for in-situ long-term soil quality or soil pollution monitoring. Thus, this review aims to provide a comprehensive overview of SMFC based biosensors. In this review, different prototypes of SMFC based biosensors developed in recent years are introduced, the biosensing mechanisms and the roles of SMFC are highlighted, and the emerging applications of these SMFC based biosensors are discussed. Since the SMFC based biosensors are applied in open-air conditions, the effects of different environmental factors on the biosensing response are also summarized. Finally, to further expand the understanding and boost the practical application of the SMFC based biosensors, future perspectives including fundamental mechanism exploration and investigation of the full-scale application are proposed.

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The cost-effective and eco-friendly approaches are needed for decontamination of polluted soils. The bio-electrochemical system, especially microbial fuel cells (MFCs) offer great promise as a technology for remediation of soil, sediment, sludge and wastewater. Recently, soil MFCs (SMFCs) have been attracting increasing amounts of interest in environmental remediation, since they are capable of providing a clean and inexhaustible source of electron donors or acceptors and can be easily controlled by adjusting the electrochemical parameters. In this review, we comprehensively covered the principle of SMFCs including the mechanisms of electron releasing and electron transportation, summarized the applications for soil contaminants remediation by SMFCs with highlights on organic contaminants degradation and heavy metal ions removal. In addition, the main factors that affected the performance of SMFCs were discussed in details which would be helpful for performance optimization of SMFCs as well as the efficiency improvement for soil remediation. Moreover, the key issues need to be addressed and future perspectives are presented.

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Bioelectrochemical approaches offer a simple, effective, and environmentally friendly solution to pollutant remediation. As a versatile technology, although many studies have shown its potential in soil heavy metal(loid) remediation, the mechanism behind this process is not simple or well-reviewed. Thus, in this review we summarized the impacts of the microbial fuel cells (MFCs) on metal (loids) movement and transformation in the soil environment in terms of changes in soil pH, electromigration, and substrate competition between anode-respiring bacteria and the soil microbial community. Furthermore, the progress of MFCs in the fixation/removal of different elements from the soil environment is described. Hence, this review provides critical insight into the use of the MFC for soil metal(loid) bioremediation.

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The increase in toxic heavy metal pollutants in rice paddies threatens food safety. There is an urgent need for lnow-cost remediation technology for immobilizing these trace metals. In this study, we showed that the application of the soil microbial fuel cell (sMFC) can greatly reduce the accumulation of Cd, Cu, Cr, and Ni in the rice plant tissue. In the sMFC treatment, the accumulation of Cd, Cu, Cr, and Ni in rice grains was 35.1%, 32.8%, 56.9% and 21.3% lower than the control, respectively. The reduction of these elements in the rice grain was due to their limited mobility in the soil porewater of soils employing the sMFC. The restriction in Cd, Cu, Cr, and Ni bioavailability was ascribed to the sMFC ability to immobilize trace metals through both biotic and abiotic means. The results suggest that the sMFC may be used as a promising technique to limit toxic trace metal bioavailability and translocation in the rice plants.

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Soil bioelectrochemical systems (BESs) utilize indigenous microorganisms to generate biocurrent/electric fields that stimulate the degradation of organic pollutants, exhibiting great potential in the removal of petroleum hydrocarbons from soils. In this study, a horizontal bioelectric field was constructed to investigate the conversion of carbon and nitrogen in a soil BES. After 182 days, the degradation rates of total petroleum hydrocarbons, alkanes, and aromatics were promoted by 52 %, 38% and 136%, respectively. Meanwhile, the bioelectric field accelerated NH4+-N production near the cathode, whereas NH4+-N consumption near the anode indicated that the bioelectric field promoted the cathode-dominated ammoniation process and the anode-dominated denitrification process. Additionally, a distinctive microbial community was formed under the bioelectric field, and the improved degradation on the cathode and the anode relied on special functional bacteria (typically, cathode, Alcanivorax; anode, Marinobacter). The dramatic enrichment in anodic denitrifying bacteria, including Pontibacillus, Sediminimonas, Georgenia, etc., explained the enhanced denitrification process under the bioelectric field. This study simultaneously clarified the carbon and nitrogen conversion processes and corresponding bacterial community occurring under the bioelectric field for the first time, helping to form regulation strategies in the practical application of soil BESs and providing a new perspective for removing petroleum hydrocarbons from soils.

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Arsenic (As) mobility in paddy soils is mainly controlled by iron (Fe) oxides and iron reducing bacteria (IBR). The Fe reducing bacteria are also considered to be enriched on the anode of soil microbial fuel cells (sMFC). Thus, the sMFC may have an impact on elements' behavior, especially Fe and As, mobilization and immobilization in paddy soils. In this study, we found dissolved organic matter (DOC) abundance was a major determinate for the sMFC impact on Fe and As. In the constructed sMFCs with and without water management, distinctive behaviors of Fe and As in paddy soil were observed, which can be explained by the low or high DOC content under different water management. When the sMFC was deployed without water management, i.e. DOC was abundant, the sMFC promoted Fe and As movement into the soil porewater. The As release into the porewater was associated with the enhanced Fe reduction by the sMFC. This was ascribed to the acidification effect of sMFC anode and the increase of Fe reducing bacteria in the sMFC anode vicinity and associated bulk soil. However, when the sMFC was coupled with alternating dry-wet cycles, i.e. DOC was limited, the Fe and As concentrations in the soil porewater dramatically decreased by up to 2.3 and 1.6 fold, respectively, compared to the controls under the same water management regime. This study implies an environmental risk for the in-situ application of sMFC in organic matter rich wetlands and also points out a new mitigation strategy for As management in paddy soils.

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A microbial fuel cell (MFC) is a very promising way to remove organic pollutants. Hexachlorobenzene (HCB) is a widely used agricultural pesticide. In this study, single-chamber and membrane-less soil MFCs were constructed. The HCB was degraded to pentachlorobenzene (PeCB), tetrachlorobenzene (TeCB), and trichlorobenzene (TCB) in sequence by a reductive dechlorination process in soil MFCs. The influences of the external resistance, concentration of phosphate buffer, and electrode spacing in soil MFCs on the degradation rate and removal efficiency of HCB were analyzed. The results showed that the degradation rate and removal efficiency of HCB were increased when the external resistance decreased from 2000 to 20Ω, and also when the concentration of phosphate buffer increased. The anode area played a significant role in dechlorination of HCB. Altering the spacing of the reducing electrode resulted in a lower ohmic resistance in the soil MFCs. The ohmic resistance was negatively correlated with the removal efficiency and degradation rate (P<0.05). In conclusion, HCB removal efficiency could be enhanced by soil MFCs, the performance of which was improved by a decrease in external resistance and internal resistance, and an increase in phosphate buffer concentration, rather than just by shortening the electrode spacing.

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The electrical conductivity (EC) of soil is generally measured after soil extraction, so this method cannot represent the in situ EC of soil (e.g., EC of soils with different moisture contents) and therefore lacks comparability in some cases. Using a resistance measurement apparatus converted from a configuration of soil microbial fuel cell, the in situ soil EC was evaluated according to the Ohmic resistance (Rs) measured using electrochemical impedance spectroscopy. The EC of soils with moisture content from 9.1% to 37.5% was calculated according to Rs. A significant positive correlation (R² = 0.896, p < 0.01) between the soil EC and the moisture content was observed, which demonstrated the feasibility of the approach. This new method can not only represent the actual soil EC, but also does not need any pretreatment. Thus it may be used widely in the measurement of the EC for soils and sediments.

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The formation of the Amazon Dark Earths was a model of sustainable soil management that involved intensive composting and charcoal (biochar) application. Biochar has been the focus of increasing research attention for carbon sequestration, although the role of compost or humic substances (HS) as they interact with biochar has not been much studied. We provide a perspective that biochar and HS may facilitate extracellular electron transfer (EET) reactions in soil, which occurs under similar conditions that generate the greenhouse gases methane and nitrous oxide. Facilitating EET may constitute a viable strategy to mitigate greenhouse gas emission. In general, we lack knowledge in the mechanisms that link the surface chemical characteristics of biochar to the physiology of microorganisms that are involved in various soil processes including those that influence soil organic matter dynamics and methane and nitrous oxide emissions. Most studies view biochar as a mostly inert microbial substrate that offers little other than a high sorptive surface area. Synergism between biochar and HS resulting in enhanced EET provides a mechanism to link electrochemical properties of these materials to microbial processes in sustainable soils.