Diversity in mechanisms of natural humic acid enhanced current production in soil bioelectrochemical systems.

The quinoid component of humic acids (HAs) had been studied as exogenous electron mediators (EMs), but the redox-mediating abilities of other functional groups remained unclear. This study evaluated the effects of various HAs functional groups on cellular respiration and extracellular electron transfer. The three EMs increased the current density compared to the control. Current density increased significantly after adding ultraviolet-irradiated HAs (UV-HAs), suggesting that nitrogenous group-mediated redox reactions contributed to high-density current generation. Structural equation model (SEM) results indicated that the contribution of nitrogen-containing groups to electron transfer could exceed 20%. This study proposed a synergistic mechanism: in the soil microbial fuel cells (soil-MFCs), HAs accelerated their component evolution through irreversible redox reactions and promoted extracellular electron transfer. Additionally, HAs-induced high expression of c-Cyts could further enhance high-density current generation. This study demonstrates that humic acids enhance electron transfer and current in bioelectrochemical systems, aiding sustainable energy optimization.

Material modification of electrodes in microbial electrochemical system to enhance electrons utilization on the electrode and its impact on microorganisms.

Previous research has established a MES embedding a microbial electrode to facilitate the degradation of antibiotics in water. We modified microbial electrodes in the MES with PEDOT and rGO to enhance electron utilization on electrodes and to further promote antibiotic degradation. Density functional theory calculations on the SMX molecule indicated that the C4-S8 and S8-N27 bonds are the most susceptible to electron attack. The introduction of various functional groups and multivalent elements enhanced the electrodes' capacitance and electron mediation capabilities. This led to enhance both electron utilization on the electrodes and the removal efficiency of SMX. After 120 h, the degradation efficiency of SMX by PEDOT and rGO-modified electrodes increased by 45.47 % and 25.19 %, respectively, compared to unmodified electrodes. The relative abundance of sulfate-reducing and denitrifying bacteria significantly increased in PEDOT and rGO-modified electrodes, while the abundance of nitrifying bacteria and potential antibiotic resistance gene host microbes significantly decreased. The impact of PEDOT modification positively influenced microbial Cellular Processes, including cell growth, death, and motility. This study provides insights into the mechanisms of direct electron involvement in antibiotic degradation steps in microbial electrochemistry, and provides a possible path for improved strategies in antibiotic degradation and sustainable environmental remediation.

The promotion of the polycyclic aromatic hydrocarbons degradation mechanism by humic acid as electron mediator in a sediment microbial electrochemical system.

To enhance the removal efficiencies of polycyclic aromatic hydrocarbons (PAHs) in sediments and to elucidate the mechanisms by which microbial electrochemical action aids in the degradation of PAHs, humic acid was used as an electron mediator in the microbial electrochemical system in this study. The results revealed that the addition of humic acids led to increases in the removal efficiencies of naphthalene, phenanthrene, and pyrene by 45.91%, 97.83%, and 85.56%, respectively, in areas remote from the anode, when compared to the control group. The investigation into the microbial community structure and functional attributes showed that the presence of humic acid did not significantly modify the microbial community composition or its functional expression at the anode. However, an examination of humic acid transformations demonstrated that humic acid extended the electron transfer range in sediment via the redox reactions of quinone and semiquinone groups, thereby facilitating the PAHs degradation within the sediment.

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

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.

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.

Study on influencing parameters and long-term operation of electrocoagulation phosphorus removal from small rural domestic sewage.

Excessive discharge of phosphorus can produce eutrophication in aquatic environments, damaging public health, the living environment, and the economy. The conventional mechanical-biological phosphorus removal methods are not suitable for small rural domestic sewage due to the features of small scale, scattered distribution, intermittent emission, and large fluctuation. This work evaluated electrocoagulation (EC) with industrial steel as electrodes on small rural domestic sewage. Results showed that the best performance was achieved at a current density of 1 mA/cm2, electrode distance of 2 cm, electrode number of 2, pH of 7, and Hydraulic Retention Time of 30 min, respectively. Under optimum conditions, the EC process removed 93.91% phosphorus while consuming around 0.25 kWh/m3 of electricity. In addition, the electrode passivation of EC was further investigated; the long-term research found that the phosphorus removal efficiency only decreased by 4.34% after 10 days of continuous flow operation, and the operational energy consumption was 0.07 kWh/m3 at a Cl- concentration of 500 mg/L.

Performance and mechanism of microbial fuel cell coupled with anaerobic membrane bioreactor system for fouling control.

To remove membrane fouling, a bio-electrochemical system that can generate a micro-electric field and micro-current was constructed. After 11 days of operation, the trans-membrane pressure difference of membrane modules in the open- and closed-circuit groups increased by 35.8 kPa and 6.2 kPa, respectively. The concentrations of total polysaccharide and protein in the open-circuit group were 1.8 and 1.1 times higher than those in the closed-circuit group, respectively. In addition, X-ray photoelectron spectroscopy and thermogravimetric analysis showed that inorganic crystals such as calcium carbonate were present on the membrane surface, and the concentration of calcium ion in the control group was 14.7 times that of the experimental group. High-throughput sequencing demonstrated that the enrichment of some electroactive bacteria and other microorganisms has a positive effect on the control of membrane fouling. Therefore, this system can effectively alleviate membrane fouling of a bioreactor, by targeting the membrane foulants.

Stimulation of atrazine degradation by activated carbon and cathodic effect in soil microbial fuel cell.

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.

Simultaneous removal of sediment and water contaminants in a microbial electrochemical system with embedded active electrode by in-situ utilization of electrons.

In the water environment such as lakes, there is a phenomenon that the sediment and overlying water are polluted at the same time. In this study, A microbial electrochemical system with an embedded active electrode was developed for simultaneous removal of polycyclic aromatic hydrocarbons in sediment and antibiotics in overlying water by in-situ utilization of electrons. In the closed-circuit group, the pyrene concentration in sediment decreased from 9.94 to 2.08 mg/L in 96 d, and the sulfamethoxazole concentration in water decreased from 5.12 to 1.12 mg/L in 168 h. These values were 18.71 % and 31.21 % higher, respectively, than those of the open-circuit group. The pyrene degradation pathway may be from polycyclic aromatic substances to low-cyclic aromatic hydrocarbons via successive breakdown of benzene rings. Multiple metabolites produced by reduction verified that SMX or its intermediates were reductively degraded in water. On the active electrode, the relative abundances of Acetobacterium and Piscinibacter, which were genera related to SMX degradation, was promoted, while the electricity-producing genus Pseudomonas was inhibited. ccdA, pksS, torC, and acsE genes related to extracellular electron transport may accelerate electron transport. Electrons could be transferred to SMX under the influence of proteins involved in extracellular electron transport, and SMX could be degraded reductively as an electron acceptor by microbes. Generation of electrons and in-situ utilization for simultaneous removal of solid-liquid two-phase pollutants will provide mechanistic insight into pollutant biodegradation by microbial electrochemistry and promote the development of sustainable bioremediation strategies for surface water.

Study on the performance and mechanism of bio-electrochemical system to mitigate membrane fouling in bioreactors.

To alleviate membrane fouling, a membrane of the membrane bioreactor was directly used as the anode of the bio-electrochemical system. On the 14th day, the control group had blocked, while the experimental group with a current of 0.44 mA, the increase in ΔTMP was only 2.2 kPa. The polysaccharide and protein concentrations in the open-circuit group were 4.2 and 2.9 times higher than those in the closed-circuit group, respectively. Three-dimensional fluorescence spectroscopy and gas chromatography mass spectrometry showed that most of the deposition in the control group contained high-molecular-weight compounds, especially long-chain ester derivatives, phenols, and complex hydrocarbons, whereas the experimental group was the opposite. Therefore, current (electrons) can change the composition of the cake layer. High-throughput sequencing indicated that a significantly higher abundance of electroactive microorganisms on the experimental than control group. Two-dimensional correlation spectroscopy showed that electrons promote the degradation of polysaccharides, thereby alleviating membrane fouling.

Application of microbial fuel cell technology to the remediation of compound heavy metal contamination in soil.

Exploring the removal rules of MFC on composite heavy metal pollution is very important for the future development and field application of MFC. We constructed a three-chamber soil MFC and the results showed that with the gradual deterioration of soil heavy metal contamination from single heavy metal to metals in different oxidation states (e.g., copper (II), lead (II), and chromium (III) compounds), the internal resistance of the soil MFC increased by 2.16-2.71 times, which significantly inhibited the power production performance of the MFC. After 59 days of remediation, the migration removal efficiencies of total Cu, total Cr and total Pb from the soil under composite conditions were 36.69%, 52.35% and 19.67%, respectively. The main removal mechanisms included both electromigration and diffusion, where electromigration contributed 74.41%, 31.48% and 97.67% to the removal of total Cu, Cr and Pb, respectively. The removal of composite heavy metals was affected by adsorption-desorption competition and synergism. The competition of Pb for specific adsorption sites in soil leads to the increase of mobility of Cr and Cu, which is conducive to migration and removal. The migration of Cu and Pb ions to the cathode inhibited the diffusion of Cr to the anode; however, it drove the synergistic migration of Pb ions to the cathode. For the heavy metals migrated from the soil into the catholyte, only Cu2+ with high redox potential is reduced to copper at the cathode.

Efficient use of electrons in a double-anode microbial fuel cell-biofilm electrode reactor self-powered coupled system for degradation of azo dyes.

A coupled system consisting of a double-anode microbial fuel cell (MFC) unit and a biofilm electrode reactor (BER) has been applied to degrade the azo dye reactive brilliant red X-3B. In this system, the MFC effluent was used as the input of the BER. The MFC preliminarily degraded X-3B while generating electricity, and the BER obtained electrons from the MFC through the external circuit to continue degrading pollutants without the need for an external power supply. The X-3B removal efficiency was 41.93% higher in the coupled system than the control when the X-3B concentration was 3000 mg/L. The analysis of intermediate products showed that the azo bond of X-3B broke in the MFC, generating a large number of complex intermediates such as anthraquinones, which were further degraded into simple organic compounds in the BER. Meanwhile, the abundance of microbial taxa related to the degradation of refractory organics in the MFC was high, as was that of microbial taxa related to the degradation of simple organics in the BER. Furthermore, the abundance of microorganisms related to power generation in the MFC increased. These results provided an efficient strategy for improving electron utilization efficiency in the coupling system of bioelectrochemical system.

Effect of starch-derived organic acids on the removal of polycyclic aromatic hydrocarbons in an aquaculture-sediment microbial fuel cell.

This study constructed sediment microbial fuel cells (SMFCs) for polycyclic aromatic hydrocarbons (PAHs) removal in contaminated aquaculture sediment. Starch, a waste deposited in aquaculture sediment, was employed as the co-substrate for electricity generation and PAHs removal, and the effect of starch-derived organic acids on SMFC performance was assessed. The results indicated that sufficient starch promoted PAHs removal (69.9% for naphthalene, 55.6% for acenaphthene, and 46.8% for pyrene) in dual-chamber SMFC, whereas excessive starch attenuated SMFC performance because the organic acids accumulation reduced anode pH, decreased species diversity, and changed the microbial communities. The electricity generation and PAHs removal were positively correlated (R > 0.96), and both of them were related to Macellibacteroides belonging to Bacteroidetes. However, a larger single-chamber SMFC device did not obtain enhanced PAHs removal owing to the restricted "effective range" of the anode. Hence, more challenges need to be addressed to realize the practical application of SMFC.

Effects of carbon source on electricity generation and PAH removal in aquaculture sediment microbial fuel cells.

Sediment microbial fuel cells (SMFCs) have been used for treating pollutants in sediment or overlying water. This study investigated the feasibility of constructing SMFCs under aquaculture conditions by employing indigenous carbohydrates as substrates to enhance the removal efficiency of polycyclic aromatic hydrocarbons (PAHs) in sediment, as well as the correlation between PAHs removal and electricity generation in SMFCs. The results showed that adding glucose could allow SMFCs to generate more electrical power and increase the removal efficiency of PAHs (by 57.2% for naphthalene, 41.3% for acenaphthene, and 36.5% for pyrene). In addition, starch enhanced PAHs removal by 49.9%, 35.8%, and 31.2%, respectively, whereas cellulose enhanced removal by 44.3%, 29.3%, and 26.9%, respectively. Pearson correlation coefficients between the level of electrical power generated and the removal masses of the three PAHs were 0.485, 0.830**, and 0.851**. Thus, the use of SMFCs could be an effective approach for PAH treatment in aquaculture, and the electrical power generated could be used as an in-situ indicator for the biodegradation rate of SMFCs.

Effects of cathode/anode electron accumulation on soil microbial fuel cell power generation and heavy metal removal.

Microbial fuel cells (MFCs) with different electrode configurations were constructed to study the mechanism of influence of multiple current paths on their electrical performance and the removal of heavy metals in soil. Three types of MFCs were constructed, namely, double anode-single cathode (DASC), single anode-dual cathode (SADC), and single anode-single cathode (SASC). The total electricity generation of the three kinds of MFC was similar: 143.44 × 10-3 mW, 114.90 × 10-3 mW, and 132.50 × 10-3 mW, respectively. However, the maximum voltage and cathode current density produced by a single current path differed significantly. The corresponding values were 0.27, 0.23, and 0.42 V and 0.130, 0.122, and 0.096 A/m 2, respectively. The SASC had the best electricity generation performance. Based on a limited reduction rate of oxygen at the cathode, the accumulation of cathode electrons was facilitated by the construction of multiple current paths in the MFC, which significantly increased the cathode electron transfer resistance and limited the electricity generation performance of the MFC. However, at the same time, the construction of multiple current paths promoted output of more electrons in the anode, reducing the retention of anode electrons and anode electron transfer resistance. The heavy metal removal efficiencies of SASC, DASC, and SADC were 2.68, 2.18, and 1.70 times that of the open circuit group, respectively. The migration of heavy metals in the soil depended mainly on the internal electric field intensity of the MFC rather than the total electricity generation. As the internal electric field intensity increased, the removal efficiency of heavy metals in the MFC increased.

Simultaneous copper migration and removal from soil and water using a three-chamber microbial fuel cell.

In this study, we constructed a three-chamber microbial fuel cell (TC-MFC) that avoided the adverse effects of H+ diffusion on anode microorganisms in the acidic catholyte and the precipitation of heavy metals in the soil near the cathode side (S4), while also achieving migration of copper from the soil and reduction of Cu2+ in the catholyte. The removal efficiency of acid-soluble Cu from the soil near the anode region reached 42.5% after 63 days of operation at an external resistance of 100â€…Ω and electrode spacing of 10 cm, and Cu2+ in the catholyte was completely removed within 21 days. Heavy metal mobility index (MF) values indicated that the bioavailability and mobility of heavy metals were reduced by the TC-MFC. We found that changing the cathode potential and external circuit current in TC-MFC would affect the type (via XRD) and morphology (via SEM) of cathode deposits and the average removal rate of heavy metals. At the meantime, it should be noted that the interaction between the electric-field-dependent soil heavy metal migration and electron-dependent copper reduction in TC-MFC occurred, which was confirmed to have a relationship with the negative correlation between voltage and current during the test.

Limitation of voltage reversal in the degradation of azo dye by a stacked double-anode microbial fuel cell and characterization of the microbial community structure.

In this study, two double-anode microbial fuel cells (MFCs) were connected in series for degradation of the azo dye reactive brilliant red X-3B. After the series connection, the electricity generation of one of the MFCs decreased, and the other was not affected too much. Due to the special structure in the double-anode MFC reduced the imbalanced performance between the MFC units, the occurrence of voltage reversal was limited. The removal efficiencies in two MFC reactors were not consistent after the series connection, the results showed that the MFC with the reduced electricity generation had the higher removal efficiencies, it was 12.90, 11.66, and 40.05% higher than in the MFC in which the power generation capacity was not affected after the series connection, the MFC without serial connection, and the control group, respectively. Meanwhile, the microbial communities related to the degradation of refractory organic compounds increased and related to electricity generation decreased in the MFC with the reduced electricity generation, the changes of the microbial communities were consistent with its electricity generation and the removal efficiencies. The degradation products in the effluent from two MFC units showed that had the products generated from the MFC with the reduced electricity generation had simpler structures comparing the other MFC unit.

Effect of soil type on heavy metals removal in bioelectrochemical system.

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

Simultaneous enhancement of heavy metal removal and electricity generation in soil microbial fuel cell.

As an environmentally sustainable bioelectrochemical technology, the microbial fuel cell (MFC) has attracted great attention. In this study, a three-chamber MFC (TC-MFC) was enhanced with different auxiliary reagents to remove heavy metals from soil. The results showed that the removal efficiency of heavy metals from soil increased with increasing auxiliary reagent concentration. When 1 mol/L citric acid, HCl, or acetic acid were used as an auxiliary reagent, the total copper (500 mg/kg) removal efficiency after 74 days of TC-MFC treatment was 3.89, 5.01 and 2.01 times that of the control group, respectively. The highest soil electrical conductivity (15.29 ms/cm), ionic heavy metal content (94.78%), electricity generation performance (363.04 mW h), and desorption stability of heavy metals were obtained when using 1 mol/L HCl as an auxiliary reagent, indicating that HCl was more suitable for the remediation of heavy metals in soil using a TC-MFC. Correlation analysis showed that the electricity generation of the TC-MFC was linearly related to the removal efficiency of heavy metals from soil (R2 = 0.9296). At the same time, higher content of ionic heavy metals in the soil led to better migration of heavy metals under the internal electric field of the TC-MFC.

The synergistic effect of biophoto anode for the enhancement of current generation and degradation.

The demand for removal of refractory organic pollutants limits the application of microbial fuel cells. In this study, the synergistic effects of bioelectrochemical and photocatalysis methods were captured by constructing a biophoto anode from a combination of WO3/TiO2 and carbon felt. This biophoto electrode was able to decrease the aniline concentration from 63.3 ± 6.2 to 9.3 ± 5.5 mg/L. The structure of the benzene ring was broken through strong oxidation by photocatalysis. Electrochemical analysis showed that photocatalysis also enhanced the extracellular electron transfer of microorganisms and reduced the resistance of the anode from 136.9â€…Ω to 69.9 Ω. In addition, the maximum current output increased by 28.5% under the composite biophoto electrode. Further analysis of the microbial community indicated that the biophoto electrode promoted the enrichment of Geobacter in the anode. This biophoto electrode provided a method for overcoming the disadvantages of anaerobic degradation of refractory organics.