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Introduction to Wikipedia

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+<noinclude>{{pp-semi-indef|small=yes}}</noinclude>{{intro to single|background=yes|padbottom=20px
+| title = '''Introduction to Wikipedia'''
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+<big>'''Wikipedia is made by [[Special:RecentChanges|people like <strong>you</strong>]].'''</big>
+This page takes you through a set of tutorials aimed at '''complete newcomers''' interested in contributing. It covers all the basics<noinclude>, and each tutorial takes only a few minutes, so you could become a proficient [[Wikipedia:Wikipedians|Wikipedian]] in no time!</noinclude>
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-'''Microbial electrochemical technologies (METs)''' use microorganisms as electrochemical catalyst, merging the microbial metabolism with electrochemical processes for the production of bioelectricity, biofuels, H<sub>2</sub> and other valuable chemicals<ref>Logan, B.E., et al., ''Electroactive microorganisms in bioelectrochemical systems.'' Nature Reviews Microbiology, 2019. '''17'''(5): p. 307-319. </ref>. Microbial fuel cells (MFC) and microbial electrolysis cells (MEC) are prominent examples of METs. While MFC is used to generate electricity from organic matter typically associated with wastewater treatment, MEC use electricity to drive chemical reactions such as the production of H<sub>2</sub> or methane. Recently, microbial electrosynthesis cells (MES) have also emerged as a promising MET, where valuable chemicals can be produced in the cathode compartment <ref> Nevin, K.P., et al., ''Microbial Electrosynthesis: Feeding Microbes Electricity To Convert Carbon Dioxide and Water to Multicarbon Extracellular Organic Compounds.'' mBio, 2010. '''1'''(2): p. e00103-10.</ref><ref>Logan, B.E., ''Exoelectrogenic bacteria that power microbial fuel cells.'' Nature Reviews Microbiology, 2009. '''7'''(5): p. 375-381.</ref><ref>Rozendal, R.A., et al., ''Efficient hydrogen peroxide generation from organic matter in a bioelectrochemical system.'' Electrochemistry Communications, 2009.'''11'''(9): p. 1752-175</ref>. Other MET applications include microbial remediation cell, microbial desalination cell, microbial solar cell, microbial chemical cell, etc., <ref>Harnisch, F. and U. Schroder, ''From MFC to MXC: chemical and biological cathodes and their potential for microbial bioelectrochemical systems.'' Chem Soc Rev, 2010. '''39'''(11): p. 4433-48.</ref><ref>Kumar, P., et al., ''Electro-Fermentation in Aid of Bioenergy and Biopolymers.'' Energies, 2018. '''11'''(2): p. 343-343.</ref><ref>Bajracharya, S., et al., ''An overview on emerging bioelectrochemical systems (BESs): Technology for sustainable electricity, waste remediation, resource recovery, chemical production and beyond.'' Renewable Energy, 2016. '''98''': p. 153-170.</ref>.
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-== History ==
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-The use of microbial cells to produce electricity was perceived by M.C. Potter in 1911 with the finding that “''The disintegration of organic compounds by microorganisms is accompanied by the liberation of electrical energy''” <ref>Potter, M.C. and A.D. Waller, ''Electrical effects accompanying the decomposition of organic compounds.'' Proceedings of the Royal Society of London. Series B, Containing Papers of a Biological Character, 1911. '''84'''(571): p. 260-276.</ref>. Noteworthy, addition in MFC research was made by B. Cohen in 1931 <ref>Cohen, B., ''The bacterial culture as an electrical half-cell.'' J. Bacteriol, 1931. '''21'''(1): p. 18-19.</ref>, when microbial half fuel cells stack connected in series was created, capable of producing over 35 V with 0.2 mA. Two breakthrough in late 80’s was made when two of the first known bacteria capable of transporting electron from the cell interior to the extracellular metal oxides without artificial redox mediators: ''Shewanella'' (formerly ''Alteromonas'') ''oneidensis'' MR-1 <ref>Myers, C.R. and K.H. Nealson, ''Bacterial Manganese Reduction and Growth with Manganese Oxide as the Sole Electron-Acceptor.'' Science, 1988. '''240'''(4857): p. 1319-1321.</ref> and ''Geobacter sulfurreducens'' PCA were isolated. In late 90s, Kim ''et al''. <ref>Kim, H.J., et al., ''A mediator-less microbial fuel cell using a metal reducing bacterium, Shewanella putrefaciens.'' Enzyme and Microbial Technology, 2002. '''30'''(2): p. 145-152.</ref> showed that the Fe(III)-reducing bacterium, ''S. oneidensis'' MR-1 was electrochemically active and can generate electricity in a MFC without any added electron mediators. These findings set basis for the development of electromicrobiology, and the field of MFC started. However, due to low power generation, it was also doubtful whether the MFC can be practical application on wastewater organics reduction. This view was changed when it was established that domestic wastewater could be treated to practical limits while simultaneously producing power <ref>Liu, H., R. Ramnarayanan, and B.E. Logan, ''Production of electricity during wastewater treatment using a single chamber microbial fuel cell.'' Environ Sci Technol, 2004. '''38'''(7): p. 2281-5.</ref>. Furthermore, power densities two orders of magnitude higher was demonstrated in an MFC using glucose, without the need for exogenous chemical mediators <ref>Rabaey, K., et al., ''A microbial fuel cell capable of converting glucose to electricity at high rate and efficiency.'' Biotechnology Letters, 2003. '''25'''(18): p. 1531-1535.</ref>. Building upon these works, a race to develop practical applications of MFCs initiated to emerge at a very fast pace, with the major goals being development of a large scale technology for the treatment of domestic, industrial, and other types of wastewaters <ref>Logan, B.E., et al., ''Microbial Fuel Cells:  Methodology and Technology.'' Environmental Science & Technology, 2006. '''40'''(17): p. 5181-5192.</ref>.
+{{clickable button 2|Help:Introduction to policies and guidelines/1       |Policies and Guidelines |style=width:16em; margin-bottom:10px;}}<br>
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-In 2004, extracellular electron uptake (EEU) from cathodes to microbes (Geobacter spp.) was established with attached biofilm, where fumarate was reduced to succinate <ref>Gregory, K.B., D.R. Bond, and D.R. Lovley, ''Graphite electrodes as electron donors for anaerobic respiration.'' Environ Microbiol, 2004. 6(6): p. 596-604.</ref>. This reverse reaction for electron transport generated the research field of MES. In 2010, Nevin et al. discovered that the acetogenic microorganism ''Sporomusa ovata'' can convert CO<sub>2</sub> to acetic acid in MES cells by uptaking electrons from the cathode electrode <ref>Nevin, K.P., et al., ''Microbial Electrosynthesis: Feeding Microbes Electricity To Convert Carbon Dioxide and Water to Multicarbon Extracellular Organic Compounds.'' Mbio, 2010. '''1'''(2).</ref>. In the next years, also due to the growing concerns on greenhouse gas emissions, the field of CO<sub>2</sub> bioelectroconversion in MES cell flourished. Several autotrophic microorganisms showed ability of capturing electrons from the cathode, either directly or through mediators<ref>Logan, B.E., et al., ''Electroactive microorganisms in bioelectrochemical systems.'' Nat Rev Microbiol, 2019. '''17'''(5): p. 307-319.</ref>. Besides specific microbial species, it was shown that CO<sub>2</sub> reducing communities can be enriched in MES cells from inoculum sources such as sewage sludge, digester sludge  or marine/river sediments<ref>Izadi, P., et al., ''Parameters influencing the development of highly conductive and efficient biofilm during microbial electrosynthesis: the importance of applied potential and inorganic carbon source.'' NPJ Biofilms Microbiomes, 2020. '''6'''(1): p. 40.</ref><ref>Bian, B., et al., ''Resistance assessment of microbial electrosynthesis for biochemical production to changes in delivery methods and CO2 flow rates.'' Bioresour Technol, 2021. '''319''': p. 124177.</ref><ref>Alqahtani, M.F., et al., ''Enrichment of salt-tolerant CO2-fixing communities in microbial electrosynthesis systems using porous ceramic hollow tube wrapped with carbon cloth as cathode and for CO2 supply.'' Sci Total Environ, 2021. '''766''': p. 142668.</ref>. In the following decade, technical improvements led to an increase of acetate production rate from few to hundreds g/m<sup>2</sup><sub>cathode</sub>/d <ref>Jourdin, L., et al., ''Bringing High-Rate, CO2-Based Microbial Electrosynthesis Closer to Practical Implementation through Improved Electrode Design and Operating Conditions.'' Environ Sci Technol, 2016. '''50'''(4): p. 1982-9.</ref>. MES cells demonstrated also a promising technology for converting CO<sub>2</sub> into biomethane, with production rates up to 200 L CH<sub>4</sub>/m<sup>2</sup><sub>cathode</sub>/d <ref>Zhou, H., et al., ''Optimization of a newly developed electromethanogenesis for the highest record of methane production.'' J Hazard Mater, 2021. '''407''': p. 124363.</ref>. Furthermore, the MES scope was expanded to target more valuable products, including ethanol and caproate.<ref>Srikanth, S., et al., ''Electro-biocatalytic conversion of carbon dioxide to alcohols using gas diffusion electrode.'' Bioresour Technol, 2018. '''265''': p. 45-51.</ref>.
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-=== '''Microbial extracellular electron transfer''' ===
+{{clickable button 2|Help:Introduction to talk pages/1                    |Talk pages              |style=width:12em; margin-bottom:10px;}}<br>
-There are various mechanisms for bacteria to electrons with an electrode. These include a “direct” process, where redox components located on the cell surface, that can be multiheme cytochromes or nanofilaments, contact directly with the solid surfaces '''(Figure 1A, C and D)''' <ref>Rosenbaum, M., et al., ''Cathodes as electron donors for microbial metabolism: which extracellular electron transfer mechanisms are involved?'' Bioresour Technol, 2011. '''102'''(1): p. 324-33.</ref><ref>Myers, C.R. and J.M. Myers, ''Localization of cytochromes to the outer membrane of anaerobically grown Shewanella putrefaciens MR-1.'' J Bacteriol, 1992. '''174'''(11): p. 3429-38.</ref><ref>Tang, H.Y., et al., ''Iron Corrosion via Direct Metal-Microbe Electron Transfer.'' mBio, 2019. '''10'''(3).</ref><ref>Okamoto, A., et al., ''Bound Flavin Model Suggests Similar Electron-Transfer Mechanisms in Shewanella and Geobacter.'' ChemElectroChem, 2014. '''1'''(11): p. 1808-1812.</ref>, and an “indirect” process that is mediated by soluble redox mediators that cyclically shuttle electrons between cells and electrodes [28-30]<ref>Newman, D.K. and R. Kolter, ''A role for excreted quinones in extracellular electron transfer.'' Nature, 2000. '''405'''(6782): p. 94-7.</ref><ref>Derek R. Lovley, J.D.C., Elizabeth L. Blunt-Harris, Elizabeth J. P. Phillips, Joan C. Woodward ''Humic substances as electron acceptors for microbial respiration.'' Nature, 1996(382): p. 445–448.</ref><ref>You, L.X., et al., ''Flavins mediate extracellular electron transfer in Gram-positive Bacillus megaterium strain LLD-1.'' Bioelectrochemistry, 2018. '''119''': p. 196-202.</ref> '''(Figure 1B)'''. Electron shuttles can be humic substances that are not produced by the cells<ref>Holmes, D.E., D.R. Bond, and D.R. Lovley, ''Electron transfer by Desulfobulbus propionicus to Fe(III) and graphite electrodes.'' Applied and environmental microbiology, 2004. '''70'''(2): p. 1234-1237.</ref>, or secondary metabolites that are produced by the organisms including phenazines [32, 33]<ref>Rabaey, K., et al., ''Microbial Phenazine Production Enhances Electron Transfer in Biofuel Cells.'' Environmental Science & Technology, 2005. '''39'''(9): p. 3401-3408.</ref><ref>Rabaey, K., et al., Biofuel Cells Select for Microbial Consortia That Self-Mediate Electron Transfer. Applied and Environmental Microbiology, 2004. 70(9): p. 5373.</ref> and flavins [34, 35]<ref>Marsili, E., et al., ''&#x26;lt;em&#x26;gt;Shewanella&#x26;lt;/em&#x26;gt; secretes flavins that mediate extracellular electron transfer.'' Proceedings of the National Academy of Sciences, 2008. '''105'''(10): p. 3968.</ref><ref>von Canstein, H., et al., ''Secretion of Flavins by &#x26;lt;em&#x26;gt;Shewanella&#x26;lt;/em&#x26;gt; Species and Their Role in Extracellular Electron Transfer.'' Applied and Environmental Microbiology, 2008. '''74'''(3): p. 615.</ref>. In addition, some primary metabolites of bacteria, such as sulphur species and H<sub>2</sub>, can convey electrons towards extracellular electrn acceptors. In addition to heme cofactors in multiheme cytochromes, flavin mononucleotide also were shown to enhance the rate of electron transfer in some outer membrane cytochrome as redox cofactors [27]<ref>Okamoto, A., et al., Bound Flavin Model Suggests Similar Electron-Transfer Mechanisms in Shewanella and Geobacter. ChemElectroChem, 2014. 1(11): p. 1808-1812</ref>. Because electrons are transferred from the interior to the exterior of microbial cells across the cellular membrane during EET, ions with positive charge need to simultaneously move in the same direction as the electron flow to maintain charge neutrality ('''Figure 1A''')<ref>Okamoto, A., et al., ''Proton Transport in the Outer-Membrane Flavocytochrome Complex Limits the Rate of Extracellular Electron Transport.'' Angewandte Chemie International Edition, 2017. '''56'''(31): p. 9082-9086.</ref>.
+{{clickable button 2|Help:Introduction to navigating Wikipedia/1          |Navigating Wikipedia    |style=width:12em; margin-bottom:10px;
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+clickable button 2|Help:Introduction/Conclusion                           |Conclusion              |style=width:12em; margin-bottom:10px;
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-=== '''Bioelectrochemical systems''' (principles, components, configurations) ===
-A bioelectrochemical system (BES) the device used in METs. A classic BES, such as the MFC,is typically composed by two sections ('''Figure 2'''): An anodic and a cathodic section separated by a selectively permeable, proton/cation exchange membrane or a salt-bridge. In a MFC, the anodic section contains microbes that work as biocatalysts under anaerobic conditions in the anolyte, where the cathodic section contains the electron acceptor (e.g. oxygen). Electrons generated from the oxidation of organic compounds are conveyed to the anode. Electrons produced by the microbes are transferred to the anode directly<ref>Bond, D.R. and D.R. Lovley, Electricity production by Geobacter sulfurreducens attached to electrodes. Appl Environ Microbiol, 2003. 69(3): p. 1548-55.</ref> via ‘nanowires’ <ref>Reguera, G., et al., ''Extracellular electron transfer via microbial nanowires.'' Nature, 2005. '''435'''(7045): p. 1098-1101.</ref> or outer-membrane proteins, or indirectly using electron shuttling agents. These electrons reach the cathode across an external circuit and for every electron conducted, protons react at the cathode for completing the reaction and sustaining the electric current<ref>Logan, B.E. and J.M. Regan, ''Electricity-producing bacterial communities in microbial fuel cells.'' Trends in Microbiology, 2006. '''14'''(12): p. 512-518.</ref>
-.There are numerous types of BES reactors but broadly they all share the same operating principles. Various designs and conﬁgurations have been established to optimize the assembly of the three basic elements (anode, cathode and separator) in a functioning system <ref>Osman, M.H., A.A. Shah, and F.C. Walsh, ''Recent progress and continuing challenges in bio-fuel cells. Part I: Enzymatic cells.'' Biosensors and Bioelectronics, 2011. '''26'''(7): p. 3087-3102.</ref>. The performance of BESs is significantly changed with their design. '''Table 1'''. shows a summary of the major BES components and associated materials for their construction.
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-'''Table 1. Major components of MFC'''
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-== Applications ==
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-=== '''Energy recovery and generation''' ===
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-==== '''Wastewater treatment with MFC''' ====
+}}
-It is well-known that pumping, aeration, and solids handling are the major energy consuming process in wastewater treatments. Aeration alone can account for 50% of the operation costs at a typical wastewater treatment plant. Eliminating these costs can save a large amount of energy. MFCs in wastewater treatment, besides electricity generation, also help in energy savings linked to these mentioned processes which add a great advantage. The MFC process is an anaerobic process and sludge production for an anaerobic process is approximately 1/5 of that for an aerobic process. Thus, using MFCs could reduce solids production at a wastewater treatment plant, ultimately reducing significant operating costs for solids handling. Moreover, this technology has seen a nearly exponential increase in power production from the start of this century. This evolution echoes a mounting appreciation by engineers that this technology is ready to emerge as practical applications and associated technologies will be in limelight very soon.
-The treatment of wastewater by MFC technologies is a promising and yet unique methodology as the process of wastewater treatment can become an approach of producing energy in the form of electricity, rather than energy expenditure. MFCs were used for the determination of lactate in water by Kim and coworkers <ref>Hyung-Joo, K.I.M., H. Moon-Sik, and C. In-Seop, ''A Microbial Fuel Cell Type Lactate Biosensor Using a Metal - Reducing Bacterium , Shewanella putrefaciens.'' Journal of Microbiology and Biotechnology, 1999. '''9'''(3): p. 365-367.</ref>, and later showed that electricity production in an MFC could be sustained by starch using an industrial wastewater. A great variety of substrates have been used in MFCs for electricity production varying from pure compounds to complex mixtures of organic matter present in wastewater. The application of MFC for biotreatment of wastewater has also recorded effective conversion of organic matter in wastewater into electricity with about 40-90% COD and BOD reduction <ref>A. Oji, C.C.O.a.M.K.O., ''Fundamentals and Field Application of Microbial Fuel cells (MFCs).'' Euro. J. Appl. Eng. Sci. Res, 2012. '''1'''(4): p. 185-189.</ref>.Obviously, the energy that could be captured from wastewater is not enough to power a city, but it could be large enough to run a treatment plant. With the continuous advances, bagging this power could lead to energy sustainability of the wastewater infrastructure.
-=== '''Benthic MFC''' ===
-Benthic MFCs generate power through the microbial oxidation of organic substrates in anoxic marine sediments coupled to reduction of oxygen in the overlying water column. Electrons are generated from the metabolism of the naturally occurring microorganism in the various sediments. As such, benthic MFCs do not require the addition of any exogenous microorganisms or electron shuttles <ref>Bond, D.R., et al., ''Electrode-reducing microorganisms that harvest energy from marine sediments.'' Science, 2002. '''295'''(5554): p. 483-5.</ref><ref>Tender, L.M., et al., ''Harnessing microbially generated power on the seafloor.'' Nature Biotechnology, 2002. '''20'''(8): p. 821-825.</ref>. The wether buoys obtained their entire power from the benthic MFC allowing them to operate continuously and independently from the need to replace batteries. Benthic MFCs can be operated for several years with no decrease in power output. The researchers estimated that a benthic MFC could provide power indefinitely at the same power levels and the same cost as a deep-sea power and light enclosed lead acid battery could deliver for one year.
-=== '''Nutrients recovery''' ===
-Nitrogen and phosphorous are considered as major pollutants in the wastewater whose removal and recovery are required for sustainable treatment systems. Nitrogen is conventionally removed by biological nitrification and denitrification processes which involves a very high energy and cost in wastewater treatment. BESs has a good potential for the recovery of ammonium nitrogen with good profits from waste streams rich in nitrogen such as urine, swine liquor, digester liquor and landfill leachate, etc<ref>Nancharaiah, Y.V., S. Venkata Mohan, and P.N.L. Lens, ''Recent advances in nutrient removal and recovery in biological and bioelectrochemical systems.'' Bioresour Technol, 2016. '''215''': p. 173-185.</ref>
-. Phosphorus from the wastewaters is conventionally recovered as polyphosphate granules, Fe-P or struvite by bacteria. Cusick ''et al.'' achieved struvite production in a BES by employing single-chamber MEC, where up to 40% soluble phosphate was recovered by struvite precipitation at a rate of 0.3–0.9 g/m<sup>2</sup>/h
-<ref>Cusick, R.D. and B.E. Logan, ''Phosphate recovery as struvite within a single chamber microbial electrolysis cell.'' Bioresource Technology, 2012. '''107''': p. 110-115.</ref>. Other phosphorus recovery in BES involved exchange of hydroxide ions generated by the cathode reaction with phosphate ions from wastewater which resulted in removing 52.4 ± 9.8% of phosphate<ref>Zhang, F., J. Li, and Z. He, ''A new method for nutrients removal and recovery from wastewater using a bioelectrochemical system.'' Bioresource Technology, 2014. '''166''': p. 630-634.</ref>.
-=== '''Microbial Electrochemical Remediation''' ===
-BESs are known for both the oxidation and reduction-based processes for remediation of underground contaminants. In comparison to conventional biological treatment or chemical processes, BESs employ a single or multiple electrodes which are not closed reactors for pollutants’ remediation. Solid electrodes in this system work as non-exhaustible electron acceptors/donors for stimulating microbial transformation of pollutants into non-toxic or less toxic forms. For example, enhancing the biodegradation of toxins with concomitant bioelectricity can be production <ref>Mohan, S.V. and K. Chandrasekhar, ''Self-induced bio-potential and graphite electron accepting conditions enhances petroleum sludge degradation in bio-electrochemical system with simultaneous power generation.'' Bioresource Technology, 2011. '''102'''(20): p. 9532-9541.</ref>. The complex petroleum organics, such as BTEX complexes (benzene, toluene, xylenes, and ethylbenzenes, etc.) can be bioremediated using BES systems. Morris et al reported that diesel (C8–C25) degradation was improved by 164 % by introducing electrodes without power input<ref>Morris, J.M., et al., ''Microbial fuel cell in enhancing anaerobic biodegradation of diesel.'' Chemical Engineering Journal, 2009. '''146'''(2): p. 161-167.</ref>. Investigations on biodiesel, phenol, total petroleum hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), 1,2-dichloroethane, pyridine, etc., have been also stated, validating BES can be used as a practical technology for degrading petroleum hydrocarbon with simultaneous current generation <ref>Lovley, D.R. and K.P. Nevin, ''A shift in the current: new applications and concepts for microbe-electrode electron exchange.'' Curr Opin Biotechnol, 2011. '''22'''(3): p. 441-8.</ref><ref>Chandrasekhar, K. and S. Venkata Mohan, ''Bio-electrochemical remediation of real field petroleum sludge as an electron donor with simultaneous power generation facilitates biotransformation of PAH: Effect of substrate concentration.'' Bioresource Technology, 2012. '''110''': p. 517-525.</ref>
-. Chlorinated solvents like trichloroethene and perchloroethene, known for high toxicity or carcinogenic nature have been reported to degrade by using negatively polarized solid-state electrode which donate electrons with and without electron shuttles <ref>Aulenta, F., et al., ''Trichloroethene dechlorination and H2 evolution are alternative biological pathways of electric charge utilization by a dechlorinating culture in a bioelectrochemical system.'' Environ Sci Technol, 2008. '''42'''(16): p. 6185-90.</ref>
-. The removal of nitrate, a common groundwater contaminant, have also been demonstrated either alone {Cecconet, 2018 #9} or in combination with other co-contaminants such as arsenite <ref>Ceballos-Escalera, A., et al., ''Electro-bioremediation of nitrate and arsenite polluted groundwater.'' Water Res, 2021. '''190''': p. 116748.</ref>. In comparison to traditional denitrification which involves heterotrophic denitrifying bacteria, denitrification by BES involves autotrophic denitrifying bacteria which have the electrons uptake ability from the electrodes. Consequently, biocathodes in BES have been developed for denitrification which results in an efficient reduction of nitrate/nitrite at low energy costs in either groundwater and wastewater<ref>Zhao, H., et al., ''Performance of Denitrifying Microbial Fuel Cell with Biocathode over Nitrite.'' Frontiers in Microbiology, 2016. '''7'''(344).</ref><ref>Virdis, B., et al., ''Electron fluxes in a microbial fuel cell performing carbon and nitrogen removal.'' Environ Sci Technol, 2009. '''43'''(13): p. 5144-9.</ref>. In other studies, reduction of perchlorate <ref>Butler, C.S., et al., ''Bioelectrochemical Perchlorate Reduction in a Microbial Fuel Cell.'' Environmental Science & Technology, 2010. '''44'''(12): p. 4685-4691.</ref>, Cr(VI)<ref>Wang, G., L.P. Huang, and Y.F. Zhang, ''Cathodic reduction of hexavalent chromium [Cr(VI)] coupled with electricity generation in microbial fuel cells.'' Biotechnology Letters, 2008. '''30'''(11): p. 1959-1966.</ref>, Cu(II), and radioactive uranium<ref>Gregory, K.B. and D.R. Lovley, ''Remediation and recovery of uranium from contaminated subsurface environments with electrodes.'' Environmental Science & Technology, 2005. '''39'''(22): p. 8943-8947.</ref> have also been achieved in BESs with cathode as electron donors. The major benefit associated with the use of a solid electrodes as an electron donor instead of soluble electron donor is the reduction of contaminant (e.g., U(VI) to U(IV)) which is a stable precipitate at the electrode. Not only groundwater but also soil bioremediation have been explored using BES. For example, it has been demonstrated successful cleaning of herbicides and antibiotics in soil (Ref) <ref>Dominguez-Garay, A., et al., ''Bioelectroventing: an electrochemical-assisted bioremediation strategy for cleaning-up atrazine-polluted soils.'' Microb Biotechnol, 2018. '''11'''(1): p. 50-62.</ref><ref>Rodrigo Quejigo, J., et al., ''Stimulating soil microorganisms for mineralizing the herbicide isoproturon by means of microbial electroremediating cells.'' Microb Biotechnol, 2016. '''9'''(3): p. 369-80.</ref>.
-=== '''Microbial electrochemical production of chemicals''' ===
-MES, a type of BES, can employ electricity for driving the synthesis of fuels and high value chemicals by employing microbes as cathodic catalysts which also results in the treatment of waste streams (Fig. 3) <ref>Rabaey, K. and R.A. Rozendal, ''Microbial electrosynthesis — revisiting the electrical route for microbial production.'' Nature Reviews Microbiology, 2010. '''8'''(10): p. 706-716.</ref>. The dual benefits associated with this system are carbon sequestration and value added chemicals production <ref>Irfan, M., et al., ''Direct microbial transformation of carbon dioxide to value-added chemicals: A comprehensive analysis and application potentials.'' Bioresource Technology, 2019. '''288''': p. 121401.</ref>. A wide range of valuable compounds have been produced by MES, such as H<sub>2</sub>, acetate, CH<sub>4</sub>, ethanol, butanol, H<sub>2</sub>O<sub>2</sub>, etc <ref>Miran, W., et al., ''Chlorinated phenol treatment and in situ hydrogen peroxide production in a sulfate-reducing bacteria enriched bioelectrochemical system.'' Water Research, 2017. '''117''': p. 198-206.</ref><ref>Marshall, C.W., et al., ''Long-term Operation of Microbial Electrosynthesis Systems Improves Acetate Production by Autotrophic Microbiomes.'' Environmental Science & Technology, 2013. '''47'''(11): p. 6023-6029.</ref><ref>van Eerten-Jansen, M.C.A.A., et al., ''Analysis of the mechanisms of bioelectrochemical methane production by mixed cultures.'' Journal of Chemical Technology & Biotechnology, 2015. '''90'''(5): p. 963-970.</ref><ref>Bajracharya, S., et al., ''Carbon dioxide reduction by mixed and pure cultures in microbial electrosynthesis using an assembly of graphite felt and stainless steel as a cathode.'' Bioresource Technology, 2015. '''195''': p. 14-24.</ref>. The product spectrum in MES is largely governed by biocathodes materials (carbon- or metal-based), microorganisms involved, reduction potentials, and redox mediators activity, and operation conditions including pH, temperature and pressure<ref>Kumar, G., et al., ''A review on bio-electrochemical systems (BESs) for the syngas and value added biochemicals production.'' Chemosphere, 2017. '''177''': p. 84-92.</ref> <ref>Kumar, A., et al., ''The ins and outs of microorganism–electrode electron transfer reactions.'' Nature Reviews Chemistry, 2017. '''1'''(3).</ref>. Potentials between -0.6 and -1.0 V ''vs'' SHE are typically applied to MES inoculated with mixed cultures to ensure production of hydrogen at the cathode, which is then uptake by acetogenic and methanogenic microorganisms to reduce CO<sub>2</sub><ref>Philips, J., ''Extracellular Electron Uptake by Acetogenic Bacteria: Does H2 Consumption Favor the H2 Evolution Reaction on a Cathode or Metallic Iron?'' Front Microbiol, 2019. '''10''': p. 2997.</ref>. CO<sub>2</sub> reduction at less negative potentials, even above the theoretical potential of -0.4 V ''vs'' SHE, ha been demonstrated for specific microorganisms such as ''Sporomusa'', although is still debated whether this it to be attributed to direct electron uptake from the cathode or to favourable thermodynamics at the electrode surface<ref>Philips, J., Extracellular Electron Uptake by Acetogenic Bacteria: Does H2 Consumption Favor the H2 Evolution Reaction on a Cathode or Metallic Iron? Front Microbiol, 2019. 10: p. 2997.</ref>. Most studies on MES has been performed under ambient (around 20°C) or mesophilic (around 35°C), but the process was demonstrated feasible under thermophilic conditions (50-70°C)<ref>Dessi, P., et al., ''Carboxylic acids production and electrosynthetic microbial community evolution under different CO2 feeding regimens.'' Bioelectrochemistry, 2021. '''137''': p. 107686.</ref>. Neutral or slightly acidic pH (5.5-7.0) was shown optimal for CO<sub>2</sub> conversion to acetic acid, although lower pH, or use of inhibitors such as bromoethanesulphonic acid (BESA), is required to avoid the onset of methanogenesis<ref>Dessì, P., et al., ''Microbial electrosynthesis: Towards sustainable biorefineries for production of green chemicals from CO(2) emissions.'' Biotechnol Adv, 2021. '''46''': p. 107675.</ref> .The chemical compounds obtained from MES can be used as precursors for the production of downstream industrial products such as polymeric products, diesel or kerosene resembling products, plasticizers, and as lubricating agents in many industries<ref>van Eerten-Jansen, M.C.A.A., et al., Analysis of the mechanisms of bioelectrochemical methane production by mixed cultures. Journal of Chemical Technology & Biotechnology, 2015. 90(5): p. 963-970.</ref>.
-'''Figure. 3.''' Schematics of MES showing treatment of waste streams and formation of high value products.
-Many organic compounds such as acetate, butyrate, and lactate, largely exists in effluents of wastewater plants and fermentation units. These organics are valued products, but due to their low concentrations, extraction is not a cost-effective option. Therefore, MES has been employed for the conversion of these short-chain carboxylic acids to longer chain acids and other useful products<ref>Steinbusch, K.J.J., et al., ''Bioelectrochemical Ethanol Production through Mediated Acetate Reduction by Mixed Cultures.'' Environmental Science & Technology, 2010. '''44'''(1): p. 513-517.</ref><ref>Raes, S.M.T., et al., ''Continuous Long-Term Bioelectrochemical Chain Elongation to Butyrate.'' ChemElectroChem, 2017. '''4'''(2): p. 386-395.</ref>. Although higher value compounds can be obtained from low resource cost feeds, studies are required to compare if controlling the redox potential and supplying current to cathodes is economically feasible in comparison to current technologies. Nevertheless, further improvements in this technology platform can help in overcoming many of the fundamental challenges of a future bioeconomy.
-=== '''Microbial electrolysis for production of H<sub>2</sub>''' ===
-When used for hydrogen production, the MEC needs to be supplemented by an external power source to get over the energy barrier of turning all organic material into carbon dioxide and hydrogen gas. A standard MFC is converted to a hydrogen producing MEC by supplementing > 0.14 V <ref>Kim, I.S., et al., ''Microbial Fuel Cells: Recent Advances, Bacterial Communities and Application Beyond Electricity Generation.'' Environmental Engineering Research, 2008. '''13'''(2): p. 51-65.</ref>. Hydrogen bubbles form at the cathode and are collected to be used as fuel source<ref>Logan, B.E., ''MECs for Hydrogen Production'', in ''Microbial Fuel Cells''. 2007, Wiley, 2008. p. 125-145.</ref>. Although electricity is used instead of generated as in normal MFCs, this method of producing hydrogen is efficient because more than 90% of the protons and electrons generated by the bacteria at the anode are turned into hydrogen gas <ref>Rabaey, K. and W. Verstraete, ''Microbial fuel cells: novel biotechnology for energy generation.'' Trends in Biotechnology, 2005. '''23'''(6): p. 291-298.</ref>. Hydrogen can be accumulated and stored for later usage to overcome the inherent low power feature of the MFCs<ref>Du, Z., H. Li, and T. Gu, ''A state of the art review on microbial fuel cells: A promising technology for wastewater treatment and bioenergy.'' Biotechnology Advances, 2007. '''25'''(5): p. 464-482.</ref>.
-=== '''Microbial electrochemical biogas upgrading to CH<sub>4</sub>''' ===
-The concept of microbial electrochemical reduction involves the conversion of carbon dioxide which is the non-energy-rich component of the biogas produced in the anaerobic digester to the energy-rich component of methane. This reduction is possible through the chemical reaction between carbon dioxide, protons and electrons (from electricity) in a MES <ref>Nelabhotla, A.B.T. and C. Dinamarca, ''Electrochemically mediated CO2 reduction for bio-methane production: a review.'' Reviews in Environmental Science and Bio/Technology, 2018. '''17'''(3): p. 531-551.</ref>. This is otherwise known as Power-to-Gas technology, which allows electrochemical units to act as carbon sinks for industrial waste and more importantly industrial CO<sub>2</sub> emissions<ref>Sánchez, O.G., et al., ''Recent advances in industrial CO2 electroreduction.'' Current Opinion in Green and Sustainable Chemistry, 2019. '''16''': p. 47-56.</ref>. Power-to-Gas technology potentially generates biogas with a similar grade to natural gas without the need to remove CO<sub>2</sub> using expensive techniques, such as amine scrubbing or pressure swing adsorption<ref>Angenent, L.T., et al., ''Integrating electrochemical, biological, physical, and thermochemical process units to expand the applicability of anaerobic digestion.'' Bioresource Technology, 2018. '''247''': p. 1085-1094.</ref>.
-=== '''Water desalination''' ===
-Desalination of sea water and brackish water used for drinking water has always presented significant problems because of the amount of energy required to remove the dissolved salts from the water. By using an adapted MFC, this process could proceed with no external electrical energy input. When adding a third chamber in between the two electrodes of a standard MFC and filling it with sea water, the cell’s positive and negative electrodes attract the positive and negative salt ions, respectively, and the salt can be filtered out from the sea water using semi-permeable membranes<ref>Kim, Y. and B.E. Logan, ''Microbial desalination cells for energy production and desalination.'' Desalination, 2013. '''308''': p. 122-130.</ref>. Salt removal efficiencies of up to 90% have been recorded in laboratory work<ref>Cao, X., et al., ''A New Method for Water Desalination Using Microbial Desalination Cells.'' Environmental Science & Technology, 2009. '''43'''(18): p. 7148-7152.</ref>.
-=== '''Biosensors''' ===
-MFCs have application in monitoring and control of biological waste treatment unit due to correlation of coulombic yield of MFC and strength of organic matter in wastewater which serves as reading for biosensor<ref>Di Lorenzo, M., et al., ''A single-chamber microbial fuel cell as a biosensor for wastewaters.'' Water Research, 2009. '''43'''(13): p. 3145-3154.</ref>. Systems based on the microorganism Shewanella show promise as sensors for quantifying the biological oxygen demand in sewage <ref>Kim, B.H., et al., ''Novel BOD (biological oxygen demand) sensor using mediator-less microbial fuel cell.'' Biotechnology Letters, 2003. '''25'''(7): p. 541-545.</ref><ref>Chang, I.S., et al., ''Improvement of a microbial fuel cell performance as a BOD sensor using respiratory inhibitors.'' Biosensors and Bioelectronics, 2005. '''20'''(9): p. 1856-1859.</ref>. This concept can readily be expanded to detect other compounds that can act as electron donors for electricity production, such as hydrogen or aromatic contaminants<ref>Lovley, D.R., ''Microbial fuel cells: novel microbial physiologies and engineering approaches.'' Current Opinion in Biotechnology, 2006. '''17'''(3): p. 327-332.</ref>. Also, such sensors could be extremely useful as indicators of toxicants in rivers, at the entrance of wastewater treatment plants, to detect pollution or illegal dumping, or to perform research on polluted sites<ref>Chang, I.S., et al., ''Continuous determination of biochemical oxygen demand using microbial fuel cell type biosensor.'' Biosensors and Bioelectronics, 2004. '''19'''(6): p. 607-613.</ref><ref>Meyer, R.L., L.H. Larsen, and N.P. Revsbech, ''Microscale Biosensor for Measurement of Volatile Fatty Acids in Anoxic Environments.'' Applied and Environmental Microbiology, 2002. '''68'''(3): p. 1204.</ref>.
-With the development of micro-electronics and related disciplines the power requirement for electronic devices has drastically reduced. MFCs can run low-power sensors that collect data from remote areas. Anaerobic bacteria that naturally grow in the sediment produce the small current that can be used to charge a capacitor to store energy for the sensor. One major advantage of using a MFC in remote sensing rather than a traditional battery is that the bacteria reproduce, giving the MFC a significantly longer lifetime than traditional batteries<ref>Wrighton, K. and J. Coates, ''Microbial Fuel Cells: Plug-in and Power-on Microbiology.'' Microbe Magazine, 2009. '''4''': p. 281-287.</ref>. The sensor can thus be left alone in a remote area for many years without maintenance. Extensive research toward developing reliable MFCs to this effect, is focused mostly on selecting suitable organic and inorganic substances that could be used as sources of energy <ref>Shantaram, A., et al., ''Wireless Sensors Powered by Microbial Fuel Cells.'' Environmental Science & Technology, 2005. '''39'''(13): p. 5037-5042.</ref>. Microbial current production is also applicable to bioelectrochemical sensors for drug screening to biofilm <ref>Miran, W., D. Naradasu, and A. Okamoto, ''Pathogens electrogenicity as a tool for in-situ metabolic activity monitoring and drug assessment in biofilms.'' iScience, 2021. '''24'''(2): p. 102068.</ref><ref>Naradasu, D., et al., ''Microbial current production from Streptococcus mutans correlates with biofilm metabolic activity.'' Biosens Bioelectron, 2020. '''162''': p. 112236.</ref> or wastewater-based epidemiology<ref>94.Miran, W., et al., ''Current Production Capability of Drug-Resistant Pathogen Enables Its Rapid Label-Free Detection Applicable to Wastewater-Based Epidemiology.'' Microorganisms, 2022. '''10'''(2).</ref>.
-== See also ==
-(''contains links to other relevant Wikipedia pages'')
-- [[:ja:Microbial fuel cell|microbial fuel cell]]
-- [[:ja:Microbial electrolysis cell|microbial electrolysis cell]]
-- [[:ja:Shewanella|Shewanella]]
-- [[Geobacter]]
-- [[Bacterial nanowires]]
-- [[Exoelectrogen]]
--[[Bioelectrochemical reactor]]
-== References ==
-{{Reflist|2}}