Microbial fuel cell

The idea of using microbes to produce electricity was conceived in the early twentieth century. Michael Cressé Potter initiated the subject in 1911.{{cite journal |doi=10.1098/rspb.1911.0073 |jstor=80609 |title=Electrical Effects Accompanying the Decomposition of Organic Compounds |journal=Proceedings of the Royal Society B: Biological Sciences |volume=84 |issue=571 |pages=260–76 |year=1911 |last1=Potter |first1=M. C.|bibcode=1911RSPSB..84..260P |doi-access=free }} Potter managed to generate electricity from Saccharomyces cerevisiae, but the work received little coverage. In 1931, Barnett Cohen created microbial half fuel cells that, when connected in series, were capable of producing over 35 volts with only a current of 2 milliamps.{{cite journal |last1= Cohen |first1= B. |year= 1931 |title= The Bacterial Culture as an Electrical Half-Cell |journal= Journal of Bacteriology |volume= 21 |pages= 18–19}}

A study by DelDuca et al. used hydrogen produced by the fermentation of glucose by Clostridium butyricum as the reactant at the anode of a hydrogen and air fuel cell. Though the cell functioned, it was unreliable owing to the unstable nature of hydrogen production by the micro-organisms.DelDuca, M. G., Friscoe, J. M. and Zurilla, R. W. (1963). Developments in Industrial Microbiology. American Institute of Biological Sciences, 4, pp81–84. This issue was resolved by Suzuki et al. in 1976,{{cite journal |last1= Karube |first1= I. |last2= Matasunga |first2= T. |last3= Suzuki |first3= S. |last4= Tsuru |first4= S. |year= 1976 |title= Continuous hydrogen production by immobilized whole cels of Clostridium butyricum |journal= Biochimica et Biophysica Acta (BBA) - General Subjects |volume= 24 |issue= 2 |pages= 338–343 |doi=10.1016/0304-4165(76)90376-7|pmid= 9145 }} who produced a successful MFC design a year later.{{cite journal |first1=Isao |last1=Karube |first2=Tadashi |last2=Matsunaga |first3=Shinya |last3=Tsuru |first4=Shuichi |last4=Suzuki |date=November 1977 |title=Biochemical cells utilizing immobilized cells of Clostridium butyricum |journal=Biotechnology and Bioengineering |volume=19 |issue=11 |pages=1727–1733 |doi=10.1002/bit.260191112|doi-access=free }}

In the late 1970s, little was understood about how microbial fuel cells functioned. The concept was studied by Robin M. Allen and later by H. Peter Bennetto. People saw the fuel cell as a possible method for the generation of electricity for developing countries. Bennetto's work, starting in the early 1980s, helped build an understanding of how fuel cells operate and he was seen by many{{Who|date=April 2011}} as the topic's foremost authority.

In May 2007, the University of Queensland, Australia completed a prototype MFC as a cooperative effort with Foster's Brewing. The prototype, a 10 L design, converted brewery wastewater into carbon dioxide, clean water and electricity. The group had plans to create a pilot-scale model for an upcoming international bio-energy conference.{{cite web|title=Brewing a sustainable energy solution|url=http://www.uq.edu.au/news/article/2007/05/brewing-sustainable-energy-solution|website=The University of Queensland Australia|access-date=26 August 2014}}

A microbial fuel cell (MFC) is a device that converts chemical energy to electrical energy by the action of microorganisms.{{cite journal |last1=Allen |first1=R.M. |last2=Bennetto |first2=H.P. |year=1993 |title=Microbial fuel cells: Electricity production from carbohydrates |journal=Applied Biochemistry and Biotechnology |volume=39–40 |pages=27–40 |doi=10.1007/bf02918975|s2cid=84142118 }} These electrochemical cells are constructed using either a bioanode and/or a biocathode. Most MFCs contain a membrane to separate the compartments of the anode (where oxidation takes place) and the cathode (where reduction takes place). The electrons produced during oxidation are transferred directly to an electrode or to a redox mediator species. The electron flux is moved to the cathode. The charge balance of the system is maintained by ionic movement inside the cell, usually across an ionic membrane. Most MFCs use an organic electron donor that is oxidized to produce CO₂, protons, and electrons. Other electron donors have been reported, such as sulfur compounds or hydrogen.{{cite journal |last1= Pant |first1= D. |last2= Van Bogaert |first2= G. |last3= Diels |first3= L. |last4= Vanbroekhoven |first4= K. |year= 2010 |title= A review of the substrates used in microbial fuel cells (MFCs) for sustainable energy production |journal= Bioresource Technology |volume= 101 |issue= 6 |pages= 1533–43 |doi= 10.1016/j.biortech.2009.10.017 |pmid=19892549|bibcode= 2010BiTec.101.1533P }} The cathode reaction uses a variety of electron acceptors, most often oxygen (O₂). Other electron acceptors studied include metal recovery by reduction,{{cite journal |last1= Lu |first1= Z. |last2= Chang |first2= D. |last3= Ma |first3= J. |last4= Huang |first4= G. |last5= Cai |first5= L. |last6= Zhang |first6= L. |year= 2015 |title= Behavior of metal ions in bioelectrochemical systems: A review |journal= Journal of Power Sources |volume= 275 |pages= 243–260 |doi= 10.1016/j.jpowsour.2014.10.168|bibcode= 2015JPS...275..243L }} water to hydrogen,{{cite journal |last1= Oh |first1= S. |last2= Logan |first2= B. E. |year= 2005 |title= Hydrogen and electricity production from a food processing wastewater using fermentation and microbial fuel cell technologies |journal= Water Research |volume= 39 |issue= 19 |pages= 4673–4682 |doi= 10.1016/j.watres.2005.09.019 |pmid= 16289673|bibcode= 2005WatRe..39.4673O }} nitrate reduction,{{Cite journal|date=2021-08-01|title=Denitrifying bio-cathodes developed from constructed wetland sediments exhibit electroactive nitrate reducing biofilms dominated by the genera Azoarcus and Pontibacter|journal=Bioelectrochemistry|language=en|volume=140|pages=107819|doi=10.1016/j.bioelechem.2021.107819|issn=1567-5394|last1=Philippon|first1=Timothé|last2=Tian|first2=Jianghao|last3=Bureau|first3=Chrystelle|last4=Chaumont|first4=Cédric|last5=Midoux|first5=Cédric|last6=Tournebize|first6=Julien|last7=Bouchez|first7=Théodore|last8=Barrière|first8=Frédéric|pmid=33894567|s2cid=233390050 |doi-access=free}}{{Cite journal|date=2014-12-01|title=Extracellular electron transfer of biocathodes: Revealing the potentials for nitrate and nitrite reduction of denitrifying microbiomes dominated by Thiobacillus sp.|url=https://www.sciencedirect.com/science/article/pii/S1388248114003294|journal=Electrochemistry Communications|language=en|volume=49|pages=93–97|doi=10.1016/j.elecom.2014.10.011|issn=1388-2481|hdl=10256/10827|hdl-access=free|last1=Pous|first1=Narcís|last2=Koch|first2=Christin|last3=Colprim|first3=Jesús|last4=Puig|first4=Sebastià|last5=Harnisch|first5=Falk}} and sulfate reduction.

MFCs are attractive for power generation applications that require only low power, but where replacing batteries may be impractical, such as wireless sensor networks.{{cite book|title=Wireless Sensor Networks and Ecological Monitoring|volume=3|publisher=Springer link|year=2013|isbn=978-3-642-36365-8|pages=151–178|author1=Subhas C Mukhopadhyay|author2=Joe-Air Jiang|doi=10.1007/978-3-642-36365-8_6|chapter=Application of Microbial Fuel Cells to Power Sensor Networks for Ecological Monitoring|series=Smart Sensors, Measurement and Instrumentation}}{{cite journal |doi=10.1016/j.biortech.2013.12.078 |pmid=24434696 |title=A stable synergistic microbial consortium for simultaneous azo dye removal and bioelectricity generation |journal=Bioresource Technology |volume=155 |pages=71–6 |year=2014 |last1=Wang |first1=Victor Bochuan |last2=Chua |first2=Song-Lin |last3=Cai |first3=Zhao |last4=Sivakumar |first4=Krishnakumar |last5=Zhang |first5=Qichun |last6=Kjelleberg |first6=Staffan |last7=Cao |first7=Bin |last8=Loo |first8=Say Chye Joachim |last9=Yang |first9=Liang|bibcode=2014BiTec.155...71W }}{{cite journal |doi=10.1371/journal.pone.0063129 |pmid=23700414 |pmc=3659106 |title=Engineering PQS Biosynthesis Pathway for Enhancement of Bioelectricity Production in Pseudomonas aeruginosa Microbial Fuel Cells |journal=PLOS ONE |volume=8 |issue=5 |pages=e63129 |year=2013 |last1=Wang |first1=Victor Bochuan |last2=Chua |first2=Song-Lin |last3=Cao |first3=Bin |last4=Seviour |first4=Thomas |last5=Nesatyy |first5=Victor J |last6=Marsili |first6=Enrico |last7=Kjelleberg |first7=Staffan |last8=Givskov |first8=Michael |last9=Tolker-Nielsen |first9=Tim |last10=Song |first10=Hao |last11=Loo |first11=Joachim Say Chye |last12=Yang |first12=Liang|bibcode=2013PLoSO...863129W |doi-access=free }}

Wireless sensors powered by microbial fuel cells can then for example be used for remote monitoring (conservation).{{Cite web|url=https://www.zsl.org/zsl-london-zoo/news/zsl-london-zoo-trials-world%E2%80%99s-first-plant-selfie|title=ZSL London Zoo trials world's first plant selfie|website=Zoological Society of London (ZSL)}}

Virtually any organic material could be used to feed the fuel cell, including coupling cells to wastewater treatment plants. Chemical process wastewater{{cite journal |doi=10.1016/j.fuel.2008.03.002 |title=Harnessing of bioelectricity in microbial fuel cell (MFC) employing aerated cathode through anaerobic treatment of chemical wastewater using selectively enriched hydrogen producing mixed consortia |journal=Fuel |volume=87 |issue=12 |pages=2667–76 |year=2008 |last1=Venkata Mohan |first1=S |last2=Mohanakrishna |first2=G |last3=Srikanth |first3=S |last4=Sarma |first4=P.N|bibcode=2008Fuel...87.2667V }}{{cite journal |doi=10.1016/j.bej.2007.08.023 |title=Bioelectricity generation from chemical wastewater treatment in mediatorless (anode) microbial fuel cell (MFC) using selectively enriched hydrogen producing mixed culture under acidophilic microenvironment |journal=Biochemical Engineering Journal |volume=39 |pages=121–30 |year=2008 |last1=Venkata Mohan |first1=S |last2=Mohanakrishna |first2=G |last3=Reddy |first3=B. Purushotham |last4=Saravanan |first4=R |last5=Sarma |first5=P.N|issue=1 |bibcode=2008BioEJ..39..121V }} and synthetic wastewater{{cite journal |first1=S. Venkata |last1=Mohan |first2=S. |last2=Veer Raghavulu |first3=S. |last3=Srikanth |first4=P. N. |last4=Sarma |title=Bioelectricity production by mediatorless microbial fuel cell under acidophilic condition using wastewater as substrate: Influence of substrate loading rate |journal=Current Science |volume=92 |issue=12 |date=25 June 2007 |pages=1720–6 |jstor=24107621}}{{cite journal |doi=10.1016/j.biortech.2006.12.026 |pmid=17321135 |title=Bioelectricity production from wastewater treatment in dual chambered microbial fuel cell (MFC) using selectively enriched mixed microflora: Effect of catholyte |journal=Bioresource Technology |volume=99 |issue=3 |pages=596–603 |year=2008 |last1=Venkata Mohan |first1=S |last2=Saravanan |first2=R |last3=Raghavulu |first3=S. Veer |last4=Mohanakrishna |first4=G |last5=Sarma |first5=P.N|bibcode=2008BiTec..99..596V }} have been used to produce bioelectricity in dual- and single-chamber mediator less MFCs (uncoated graphite electrodes).

Higher power production was observed with a biofilm-covered graphite anode.{{cite journal |doi=10.1016/j.bios.2007.11.016 |pmid=18248978 |title=Biochemical evaluation of bioelectricity production process from anaerobic wastewater treatment in a single chambered microbial fuel cell (MFC) employing glass wool membrane |journal=Biosensors and Bioelectronics |volume=23 |issue=9 |pages=1326–32 |year=2008 |last1=Venkata Mohan |first1=S |last2=Veer Raghavulu |first2=S |last3=Sarma |first3=P.N}}{{cite journal |doi=10.1016/j.bios.2008.03.010 |pmid=18440217 |title=Influence of anodic biofilm growth on bioelectricity production in single chambered mediatorless microbial fuel cell using mixed anaerobic consortia |journal=Biosensors and Bioelectronics |volume=24 |issue=1 |pages=41–7 |year=2008 |last1=Venkata Mohan |first1=S |last2=Veer Raghavulu |first2=S |last3=Sarma |first3=P.N}} Fuel cell emissions are well under regulatory limits.{{cite journal |last1=Choi |first1=Y. |last2=Jung |first2=S. |last3=Kim |first3=S. |year=2000 |title=Development of Microbial Fuel Cells Using Proteus Vulgaris Bulletin of the Korean Chemical Society |volume=21 |issue=1 |pages=44–8}} MFCs convert energy more efficiently than standard internal combustion engines, which are limited by the Carnot efficiency. In theory, an MFC is capable of energy efficiency far beyond 50%.Yue & Lowther, 1986 Rozendal produced hydrogen with 8 times less energy input than conventional hydrogen production technologies.

Moreover, MFCs can also work at a smaller scale. Electrodes in some cases need only be 7 μm thick by 2 cm long,{{cite journal|last2=Barton|first2=S.C.|last3=Binyamin|first3=G.|last4=Gao|first4=Z.|last5=Zhang|first5=Y.|last6=Kim|first6=H.-H.|last7=Heller|first7=A.|date=Sep 2001|title=A miniature biofuel cell.|journal=J Am Chem Soc|volume=123|issue=35|pages=8630–1|doi=10.1021/ja0163164|pmid=11525685|last1=Chen|first1=T.}} such that an MFC can replace a battery. It provides a renewable form of energy and does not need to be recharged.

MFCs operate well in mild conditions, 20 °C to 40 °C and at pH of around 7{{cite journal|year=2006|title=Biofuel cells and their development.|journal=Biosensors & Bioelectronics|volume=21|issue=11|pages=2015–45|doi=10.1016/j.bios.2006.01.030|pmid=16569499|vauthors=Bullen RA, Arnot TC, Lakeman JB, Walsh FC|url=https://eprints.soton.ac.uk/49019/1/Biofuel_cells_and_their_development.pdf}} but lack the stability required for long-term medical applications such as in pacemakers.

Power stations can be based on aquatic plants such as algae. If sited adjacent to an existing power system, the MFC system can share its electricity lines.Eos magazine, Waterstof uit het riool, June 2008

Soil-based microbial fuel cells serve as educational tools, as they encompass multiple scientific disciplines (microbiology, geochemistry, electrical engineering, etc.) and can be made using commonly available materials, such as soils and items from the refrigerator. Kits for home science projects and classrooms are available. One example of microbial fuel cells being used in the classroom is in the IBET (Integrated Biology, English, and Technology) curriculum for Thomas Jefferson High School for Science and Technology. Several educational videos and articles are also available on the International Society for Microbial Electrochemistry and Technology (ISMET Society)"{{Cite web|url=https://is-met.org/|title=ISMET – The International Society for Microbial Electrochemistry and Technology|date=September 4, 2023}}".

{{main|Biosensor}}

The current generated from a microbial fuel cell is directly proportional to the organic-matter content of wastewater used as the fuel. MFCs can measure the solute concentration of wastewater (i.e., as a biosensor).{{cite journal|last2=Chang|first2=IS.|last3=Gil|first3=GC.|last4=Park|first4=HS.|last5=Kim|first5=HJ.|date=April 2003|title=Novel BOD (biological oxygen demand) sensor using mediator-less microbial fuel cell|journal=Biotechnology Letters|volume=25|issue=7|pages=541–545|doi=10.1023/A:1022891231369|last1=Kim|first1=BH.|pmid=12882142|s2cid=5980362}}

Wastewater is commonly assessed for its biochemical oxygen demand (BOD) values.{{Clarify|date=April 2011}} BOD values are determined by incubating samples for 5 days with proper source of microbes, usually activated sludge collected from wastewater plants.

An MFC-type BOD sensor can provide real-time BOD values. Oxygen and nitrate are interfering preferred electron acceptors over the anode, reducing current generation from an MFC. Therefore, MFC BOD sensors underestimate BOD values in the presence of these electron acceptors. This can be avoided by inhibiting aerobic and nitrate respiration in the MFC using terminal oxidase inhibitors such as cyanide and azide.{{cite journal |doi=10.1016/j.bios.2004.06.003 |pmid=15681205 |title=Improvement of a microbial fuel cell performance as a BOD sensor using respiratory inhibitors |journal=Biosensors and Bioelectronics |volume=20 |issue=9 |pages=1856–9 |year=2005 |last1=Chang |first1=In Seop |last2=Moon |first2=Hyunsoo |last3=Jang |first3=Jae Kyung |last4=Kim |first4=Byung Hong}} Such BOD sensors are commercially available.

The United States Navy is considering microbial fuel cells for environmental sensors. The use of microbial fuel cells to power environmental sensors could provide power for longer periods and enable the collection and retrieval of undersea data without a wired infrastructure. The energy created by these fuel cells is enough to sustain the sensors after an initial startup time.{{cite journal|year=2011|title=Benthic Microbial Fuel Cell as Direct Power Source for an Acoustic Modem and Seawater Oxygen/Temperature Sensor System|journal=Environmental Science and Technology|volume=45|issue=11|pages=5047–53|doi=10.1021/es104383q|pmid=21545151|author1=Gong, Y. |author2=Radachowsky, S. E.|author3=Wolf, M.|author4=Nielsen, M. E.|author5-link=Peter Girguis|author5=Girguis, P. R.|author6=Reimers, C. E.|author-link6=Clare Reimers|bibcode=2011EnST...45.5047G}} Due to undersea conditions (high salt concentrations, fluctuating temperatures and limited nutrient supply), the Navy may deploy MFCs with a mixture of salt-tolerant microorganisms that would allow for a more complete utilization of available nutrients. Shewanella oneidensis is their primary candidate, but other heat- and cold-tolerant Shewanella spp may also be included.{{cite journal|year=2008|title=Aerobic Miniature Microbial Fuel Cells|journal=NRL Review|pages=141–42|author=Biffinger, J.C., Little, B., Pietron, J., Ray, R., Ringeisen, B.R.}}

A first self-powered and autonomous BOD/COD biosensor has been developed and enables detection of organic contaminants in freshwater. The sensor relies only on power produced by MFCs and operates continuously without maintenance. It turns on the alarm to inform about contamination level: the increased frequency of the signal warns about a higher contamination level, while a low frequency informs about a low contamination level.{{cite journal|date=2017-06-01|title=Self-powered, autonomous Biological Oxygen Demand biosensor for online water quality monitoring|journal=Sensors and Actuators B: Chemical|language=en|volume=244|pages=815–822|doi=10.1016/j.snb.2017.01.019|pmid=28579695|pmc=5362149|issn=0925-4005|last1=Pasternak|first1=Grzegorz|last2=Greenman|first2=John|last3=Ieropoulos|first3=Ioannis|bibcode=2017SeAcB.244..815P }}

In 2010, A. ter Heijne et al.{{cite journal |doi=10.1021/es100526g |pmid=20462261 |title=Copper Recovery Combined with Electricity Production in a Microbial Fuel Cell |journal=Environmental Science & Technology |volume=44 |issue=11 |pages=4376–81 |year=2010 |last1=Heijne |first1=Annemiek Ter |last2=Liu |first2=Fei |last3=Weijden |first3=Renata van der |last4=Weijma |first4=Jan |last5=Buisman |first5=Cees J.N |last6=Hamelers |first6=Hubertus V.M|bibcode=2010EnST...44.4376H }} constructed a device capable of producing electricity and reducing Cu²⁺ ions to copper metal.

Microbial electrolysis cells have been demonstrated to produce hydrogen.{{cite journal |doi=10.1007/s00253-012-4456-7 |pmid=23053105 |title=Production of hydrogen from domestic wastewater in a pilot-scale microbial electrolysis cell |journal=Applied Microbiology and Biotechnology |volume=97 |issue=15 |pages=6979–89 |year=2012 |last1=Heidrich |first1=E. S |last2=Dolfing |first2=J |last3=Scott |first3=K |last4=Edwards |first4=S. R |last5=Jones |first5=C |last6=Curtis |first6=T. P|s2cid=15306503 }}

MFCs are used in water treatment to harvest energy utilizing anaerobic digestion. The process can also reduce pathogens. However, it requires temperatures upwards of 30 degrees C and requires an extra step in order to convert biogas to electricity. Spiral spacers may be used to increase electricity generation by creating a helical flow in the MFC. Scaling MFCs is a challenge because of the power output challenges of a larger surface area.{{cite journal|year=2013|title=Using Microbial Fuel Cells to Treat Raw Sludge and Primary Effluent for Bioelectricity Generation|journal=Department of Civil Engineering and Mechanics; University of Wisconsin – Milwaukee|author=Zhang, Fei, He, Zhen, Ge, Zheng}}

Most microbial cells are electrochemically inactive. Electron transfer from microbial cells to the electrode is facilitated by mediators such as thionine, pyocyanin,K. Rabaey et al.: Biofuel cells select for microbial consortia that self-mediate electron transfer. In: Appl. Environ. Microbiol., Volume 70, Nr. 9, 2004, S. 5373–5382. methyl viologen, methyl blue, humic acid, and neutral red.{{cite journal

|last1= Delaney |first1= G. M.

|last2= Bennetto |first2= H. P.

|last3= Mason |first3= J. R.

|last4= Roller |first4= S. D.

|last5= Stirling |first5= J. L.

|last6= Thurston |first6= C. F.

|doi= 10.1002/jctb.280340104

|title= Electron-transfer coupling in microbial fuel cells. 2. Performance of fuel cells containing selected microorganism-mediator-substrate combinations

|journal= Journal of Chemical Technology and Biotechnology. Biotechnology

|volume= 34

|pages= 13–27

|year= 2008

}}Lithgow, A.M., Romero, L., Sanchez, I.C., Souto, F.A., and Vega, C.A. (1986). Interception of electron-transport chain in bacteria with hydrophilic redox mediators. J. Chem. Research, (S):178–179. Most available mediators are expensive and toxic.

file:plant Microbial Fuel Cell.png

Mediator-free microbial fuel cells use electrochemically active bacteria such as Shewanella putrefaciens{{cite journal|last1=Kim|first1=B.H.|last2=Kim|first2=H.J.|last3=Hyun|first3=M.S.|last4=Park|first4=D.H.|year=1999a|title=Direct electrode reaction of Fe (III) reducing bacterium, Shewanella putrefacience|url=http://bioelectrochemistry.kist.re.kr/downloads/pdf/1-5.pdf|url-status=dead|journal=J Microbiol Biotechnol|volume=9|pages=127–131|archive-url=https://web.archive.org/web/20040908164327/http://bioelectrochemistry.kist.re.kr/downloads/pdf/1-5.pdf|archive-date=2004-09-08}} and Aeromonas hydrophila{{cite journal|last1=Pham|first1=C. A.|last2=Jung|first2=S. J.|last3=Phung|first3=N. T.|last4=Lee|first4=J.|last5=Chang|first5=I. S.|last6=Kim|first6=B. H.|last7=Yi|first7=H.|last8=Chun|first8=J.|year=2003|title=A novel electrochemically active and Fe(III)-reducing bacterium phylogenetically related to Aeromonas hydrophila, isolated from a microbial fuel cell|journal=FEMS Microbiology Letters|volume=223|issue=1|pages=129–134|doi=10.1016/S0378-1097(03)00354-9|pmid=12799011|doi-access=free}} to transfer electrons directly from the bacterial respiratory enzyme to the electrode. Some bacteria are able to transfer their electron production via the pili on their external membrane. Mediator-free MFCs are less well characterized, such as the strain of bacteria used in the system, type of ion-exchange membrane and system conditions (temperature, pH, etc.)

Mediator-free microbial fuel cells can run on wastewater and derive energy directly from certain plants and O₂. This configuration is known as a plant microbial fuel cell. Possible plants include reed sweetgrass, cordgrass, rice, tomatoes, lupines and algae.{{Cite web|url=https://plantpower.eu/gesundheit-und-schoenheit/rasierapparate/|archiveurl=https://web.archive.org/web/20110310220311/http://www.plantpower.eu/index.php?option=com_content&view=article&id=3&Itemid=4|url-status=dead|title=Rasierapparate • plantpower.eu • 2021|archivedate=March 10, 2011|website=plantpower.eu}}{{cite web|url=http://www.ete.wur.nl/UK/Research/Renewable+Energy/Green+electricity+production+by+living+plants+in+a+microbial+fuel+cell/|title=Environmental Technology|work=Wageningen UR|date=2012-06-06}}{{cite journal |doi=10.1002/er.1397 |title=Green electricity production with living plants and bacteria in a fuel cell |journal=International Journal of Energy Research |volume=32 |issue=9 |pages=870–6 |year=2008 |last1=Strik |first1=David P. B. T. B |last2=Hamelers (Bert) |first2=H. V. M |last3=Snel |first3=Jan F. H |last4=Buisman |first4=Cees J. N|bibcode=2008IJER...32..870S |s2cid=96849691 }} Given that the power is obtained using living plants (in situ-energy production), this variant can provide ecological advantages.

{{main|Microbial electrolysis cell}}

One variation of the mediator-less MFC is the microbial electrolysis cell (MEC). While MFCs produce electric current by the bacterial decomposition of organic compounds in water, MECs partially reverse the process to generate hydrogen or methane by applying a voltage to bacteria. This supplements the voltage generated by the microbial decomposition of organics, leading to the electrolysis of water or methane production.{{Cite web|url=http://www.awmc.uq.edu.au/|title=Advanced Water Management Centre|website=Advanced Water Management Centre}}{{cite web|url=http://www.dailytech.com/Microbial+Hydrogen+Production+Threatens+Extinction+for+the+Ethanol+Dinosaur/article9278.htm|title=DailyTech – Microbial Hydrogen Production Threatens Extinction for the Ethanol Dinosaur}} A complete reversal of the MFC principle is found in microbial electrosynthesis, in which carbon dioxide is reduced by bacteria using an external electric current to form multi-carbon organic compounds.{{cite journal |title=Microbial Electrosynthesis: Feeding Microbes Electricity To Convert Carbon Dioxide and Water to Multicarbon Extracellular Organic Compounds |doi=10.1128/mBio.00103-10 |date=May–June 2010 |author1=Nevin Kelly P. |author2=Woodard Trevor L. |author3=Franks Ashley E. |journal=mBio |volume=1 |issue=2|display-authors=etal |pages=e00103–10 |pmid=20714445 |pmc=2921159}}

file:soilMFC.png

Soil-based microbial fuel cells adhere to the basic MFC principles, whereby soil acts as the nutrient-rich anodic media, the inoculum and the proton exchange membrane (PEM). The anode is placed at a particular depth within the soil, while the cathode rests on top the soil and is exposed to air.

Soils naturally teem with diverse microbes, including electrogenic bacteria needed for MFCs, and are full of complex sugars and other nutrients that have accumulated from plant and animal material decay. Moreover, the aerobic (oxygen consuming) microbes present in the soil act as an oxygen filter, much like the expensive PEM materials used in laboratory MFC systems, which cause the redox potential of the soil to decrease with greater depth. Soil-based MFCs are becoming popular educational tools for science classrooms.{{cite web|url=https://www.magicalmicrobes.com/collections/kits/products/mudwatt-clean-energy-from-mud|title=MudWatt Science Kit|author=MudWatt|work=MudWatt}}

Sediment microbial fuel cells (SMFCs) have been applied for wastewater treatment. Simple SMFCs can generate energy while decontaminating wastewater. Most such SMFCs contain plants to mimic constructed wetlands. By 2015 SMFC tests had reached more than 150 L.{{cite journal |doi=10.1039/C5EW00020C |title=Sediment microbial fuel cells for wastewater treatment: Challenges and opportunities |journal=Environmental Science: Water Research & Technology |volume=1 |issue=3 |pages=279–84 |year=2015 |last1=Xu |first1=Bojun |last2=Ge |first2=Zheng |last3=He |first3=Zhen |hdl=10919/64969 |doi-access=free |hdl-access=free }}

In 2015 researchers announced an SMFC application that extracts energy and charges a battery. Salts dissociate into positively and negatively charged ions in water and move and adhere to the respective negative and positive electrodes, charging the battery and making it possible to remove the salt effecting microbial capacitive desalination. The microbes produce more energy than is required for the desalination process.{{cite news |title=Cleaning up wastewater from oil and gas operations using a microbe-powered battery |first= Helen |last=Clark |date=March 2, 2015 |publisher=Gizmag}} In 2020, a European research project achieved the treatment of seawater into fresh water for human consumption with an energy consumption around 0.5 kWh/m3, which represents an 85% reduction in current energy consumption respect state of the art desalination technologies. Furthermore, the biological process from which the energy is obtained simultaneously purifies residual water for its discharge in the environment or reuse in agricultural/industrial uses. This has been achieved in the desalination innovation center that Aqualia has opened in Denia, Spain early 2020.{{cite web |last1=Borras |first1=Eduard |title=New Technologies for Microbial Desalination Ready for Market Entry |url=https://projects.leitat.org/new-technologies-for-microbial-desalination-ready-for-market-entry/ |website=Leitat's Projects Blog |date=8 October 2020 |access-date=9 October 2020}}

Phototrophic biofilm MFCs (ner) use a phototrophic biofilm anode containing photosynthetic microorganism such as chlorophyta and candyanophyta. They carry out photosynthesis and thus produce organic metabolites and donate electrons.{{cite journal

|last1= Elizabeth

|first1= Elmy

|url= http://www.biosaints.com/archives/vol1/vol1_3/microbial_fuelcells.html

|title= GENERATING ELECTRICITY BY "NATURE'S WAY"

|journal= SALT 'B' Online Magazine

|volume= 1

|year= 2012

|url-status= dead

|archive-url= https://archive.today/20130118060508/http://www.biosaints.com/archives/vol1/vol1_3/microbial_fuelcells.html

|archive-date= 2013-01-18

}}

One study found that PBMFCs display a power density sufficient for practical applications.{{cite journal |doi=10.1016/j.tibtech.2010.10.001 |pmid=21067833 |title=Microbial solar cells: Applying photosynthetic and electrochemically active organisms |journal=Trends in Biotechnology |volume=29 |issue=1 |pages=41–9 |year=2011 |last1=Strik |first1=David P.B.T.B |last2=Timmers |first2=Ruud A |last3=Helder |first3=Marjolein |last4=Steinbusch |first4=Kirsten J.J |last5=Hamelers |first5=Hubertus V.M |last6=Buisman |first6=Cees J.N |url=https://zenodo.org/record/812}}

The sub-category of phototrophic MFCs that use purely oxygenic photosynthetic material at the anode are sometimes called biological photovoltaic systems.{{cite journal |doi=10.1039/c1ee02531g |title=Quantitative analysis of the factors limiting solar power transduction by Synechocystis sp. PCC 6803 in biological photovoltaic devices |journal=Energy & Environmental Science |volume=4 |issue=11 |pages=4690–8 |year=2011 |last1=Bombelli |first1=Paolo |last2=Bradley |first2=Robert W |last3=Scott |first3=Amanda M |last4=Philips |first4=Alexander J |last5=McCormick |first5=Alistair J |last6=Cruz |first6=Sonia M |last7=Anderson |first7=Alexander |last8=Yunus |first8=Kamran |last9=Bendall |first9=Derek S |last10=Cameron |first10=Petra J |last11=Davies |first11=Julia M |last12=Smith |first12=Alison G |last13=Howe |first13=Christopher J |last14=Fisher |first14=Adrian C}}

The United States Naval Research Laboratory developed nanoporous membrane microbial fuel cells that use a non-PEM to generate passive diffusion within the cell.{{cite web |url=https://techlinkcenter.org/labs/nrl/d9edc424-c771-4826-b58f-f55e2b88f66f |title=Miniature Microbial Fuel Cells |website=Technology Transfer Office |access-date=30 November 2014}} The membrane is a nonporous polymer filter (nylon, cellulose, or polycarbonate). It offers comparable power densities to Nafion (a well-known PEM) with greater durability. Porous membranes allow passive diffusion thereby reducing the necessary power supplied to the MFC in order to keep the PEM active and increasing the total energy output.{{cite journal |last1=Biffinger |first1=Justin C. |last2=Ray |first2=Ricky |last3=Little |first3=Brenda |last4=Ringeisen |first4=Bradley R. |year=2007 |title=Diversifying Biological Fuel Cell Design by Use of Nanoporous Filters |journal=Environmental Science and Technology |volume=41 |issue=4 |pages=1444–49 |doi=10.1021/es061634u |pmid=17593755 |bibcode=2007EnST...41.1444B |url=https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1017&context=usnavyresearch}}

MFCs that do not use a membrane can deploy anaerobic bacteria in aerobic environments. However, membrane-less MFCs experience cathode contamination by the indigenous bacteria and the power-supplying microbe. The novel passive diffusion of nanoporous membranes can achieve the benefits of a membrane-less MFC without worry of cathode contamination.Nanoporous membranes are also 11 times cheaper than Nafion (Nafion-117, $0.22/cm² vs. polycarbonate, <$0.02/cm²).{{cite web|url=http://www.slideshare.net/ShabeebaVAnthru/seminar-2-56681944|title=Seminar 2|last=Shabeeba|first=Anthru|date=5 Jan 2016|website=Slide Share}}

PEM membranes can be replaced with ceramic materials. Ceramic membrane costs can be as low as $5.66/m². The macroporous structure of ceramic membranes allows for good transport of ionic species.{{cite journal |doi=10.1002/cssc.201501320 |pmid=26692569 |pmc=4744959 |title=Comprehensive Study on Ceramic Membranes for Low-Cost Microbial Fuel Cells |journal=ChemSusChem |volume=9 |issue=1 |pages=88–96 |year=2016 |last1=Pasternak |first1=Grzegorz |last2=Greenman |first2=John |last3=Ieropoulos |first3=Ioannis|bibcode=2016ChSCh...9...88P }}

The materials that have been successfully employed in ceramic MFCs are earthenware, alumina, mullite, pyrophyllite, and terracotta.{{cite journal |doi=10.1016/j.biortech.2009.07.089 |pmid=19800223 |title=Performance evaluation of low cost microbial fuel cell fabricated using earthen pot with biotic and abiotic cathode |journal=Bioresource Technology |volume=101 |issue=4 |pages=1183–9 |year=2010 |last1=Behera |first1=Manaswini |last2=Jana |first2=Partha S |last3=Ghangrekar |first3=M.M|bibcode=2010BiTec.101.1183B }}{{cite journal |doi=10.1007/s00449-013-0967-6 |pmid=23728836 |title=Comparing terracotta and earthenware for multiple functionalities in microbial fuel cells |journal=Bioprocess and Biosystems Engineering |volume=36 |issue=12 |pages=1913–21 |year=2013 |last1=Winfield |first1=Jonathan |last2=Greenman |first2=John |last3=Huson |first3=David |last4=Ieropoulos |first4=Ioannis|s2cid=206992845 |url=http://eprints.uwe.ac.uk/20792/ }}

When microorganisms consume a substance such as sugar in aerobic conditions, they produce carbon dioxide and water. However, when oxygen is not present, they may produce carbon dioxide, hydrons (hydrogen ions), and electrons, as described below for sucrose:{{cite journal |url=http://www.ncbe.reading.ac.uk/ncbe/protocols/PRACBIOTECH/PDF/bennetto.pdf |last=Bennetto |first=H. P. |year=1990 |title=Electricity Generation by Micro-organisms |journal=Biotechnology Education |volume=1 |number=4 |pages=163–168}}

{{NumBlk|:|C₁₂H₂₂O₁₁ + 13H₂O → 12CO₂ + 48H⁺ + 48e⁻ |{{EquationRef|Eqt. 1}}}}

Microbial fuel cells use inorganic mediators to tap into the electron transport chain of cells and channel electrons produced. The mediator crosses the outer cell lipid membranes and bacterial outer membrane; then, it begins to liberate electrons from the electron transport chain that normally would be taken up by oxygen or other intermediates.

The now-reduced mediator exits the cell laden with electrons that it transfers to an electrode; this electrode becomes the anode. The release of the electrons recycles the mediator to its original oxidized state, ready to repeat the process. This can happen only under anaerobic conditions; if oxygen is present, it will collect the electrons, as it has more free energy to release.

Certain bacteria can circumvent the use of inorganic mediators by making use of special electron transport pathways known collectively as extracellular electron transfer (EET). EET pathways allow the microbe to directly reduce compounds outside of the cell, and can be used to enable direct electrochemical communication with the anode.{{Cite journal |last=Aiyer |first=Kartik S. |date=2020-01-18 |title=How does electron transfer occur in microbial fuel cells? |url=https://pubmed.ncbi.nlm.nih.gov/31955250/ |journal=World Journal of Microbiology & Biotechnology |volume=36 |issue=2 |pages=19 |doi=10.1007/s11274-020-2801-z |issn=1573-0972 |pmid=31955250}}

In MFC operation, the anode is the terminal electron acceptor recognized by bacteria in the anodic chamber. Therefore, the microbial activity is strongly dependent on the anode's redox potential. A Michaelis–Menten curve was obtained between the anodic potential and the power output of an acetate-driven MFC. A critical anodic potential seems to provide maximum power output.{{cite journal |doi=10.1021/es8003969 |pmid=18546730 |title=Affinity of Microbial Fuel Cell Biofilm for the Anodic Potential |journal=Environmental Science & Technology |volume=42 |issue=10 |pages=3828–34 |year=2008 |last1=Cheng |first1=Ka Yu |last2=Ho |first2=Goen |last3=Cord-Ruwisch |first3=Ralf|bibcode=2008EnST...42.3828C }}

Potential mediators include natural red, methylene blue, thionine, and resorufin.{{cite journal |doi=10.1002/bit.260250219 |pmid=18548670 |title=Anodic reactions in microbial fuel cells |journal=Biotechnology and Bioengineering |volume=25 |issue=2 |pages=559–68 |year=1983 |last1=Bennetto |first1=H. Peter |last2=Stirling |first2=John L |last3=Tanaka |first3=Kazuko |last4=Vega |first4=Carmen A|s2cid=33986929 }}

Organisms capable of producing an electric current are termed exoelectrogens. In order to turn this current into usable electricity, exoelectrogens have to be accommodated in a fuel cell.

The mediator and a micro-organism such as yeast, are mixed together in a solution to which is added a substrate such as glucose. This mixture is placed in a sealed chamber to prevent oxygen from entering, thus forcing the micro-organism to undertake anaerobic respiration. An electrode is placed in the solution to act as the anode.

In the second chamber of the MFC is another solution and the positively charged cathode. It is the equivalent of the oxygen sink at the end of the electron transport chain, external to the biological cell. The solution is an oxidizing agent that picks up the electrons at the cathode. As with the electron chain in the yeast cell, this could be a variety of molecules such as oxygen, although a more convenient option is a solid oxidizing agent, which requires less volume.

Connecting the two electrodes is a wire (or other electrically conductive path). Completing the circuit and connecting the two chambers is a salt bridge or ion-exchange membrane. This last feature allows the protons produced, as described in {{EquationNote|Eqt. 1}}, to pass from the anode chamber to the cathode chamber.

The reduced mediator carries electrons from the cell to the electrode. Here the mediator is oxidized as it deposits the electrons. These then flow across the wire to the second electrode, which acts as an electron sink. From here they pass to an oxidizing material. Also the hydrogen ions/protons are moved from the anode to the cathode via a proton exchange membrane such as Nafion. They will move across to the lower concentration gradient and be combined with the oxygen but to do this they need an electron. This generates current and the hydrogen is used sustaining the concentration gradient.

Algal biomass has been observed to give high energy when used as the substrate in microbial fuel cell.{{cite journal |doi=10.1016/j.scitotenv.2013.03.067 |pmid=23584037 |title=Enhanced electricity generation by using algae biomass and activated sludge in microbial fuel cell |journal=Science of the Total Environment |volume=456-457 |pages=91–4 |year=2013 |last1=Rashid |first1=Naim |last2=Cui |first2=Yu-Feng |last3=Saif Ur Rehman |first3=Muhammad |last4=Han |first4=Jong-In|bibcode=2013ScTEn.456...91R }}

Microbial fuel cells (MFCs) have emerged as promising tools for environmental remediation due to their unique ability to utilize the metabolic activities of microorganisms for both electricity generation and pollutant degradation.{{cite journal |last1=Bankefa |first1=Olufemi Emmanuel |last2=Oladeji |first2=Seye Julius |last3=Ayilara-Akande |first3=Simbiat Olufunke |last4=Lasisi |first4=Modupe Mariam |title=Microbial redemption of "evil" days: a global appraisal to food security |journal=Journal of Food Science and Technology |date=June 2021 |volume=58 |issue=6 |pages=2041–2053 |doi=10.1007/s13197-020-04725-7|pmid=33967303 |pmc=8076430 }} MFCs find applications across diverse contexts in environmental remediation. One primary application is in bioremediation, where the electroactive microorganisms on the MFC anode actively participate in the breakdown of organic pollutants, providing a sustainable and efficient method for pollutant removal. Moreover, MFCs play a significant role in wastewater treatment by simultaneously generating electricity and enhancing water quality through the microbial degradation of contaminants. These fuel cells can be deployed in situ, allowing for continuous and autonomous remediation in contaminated sites. Furthermore, their versatility extends to sediment microbial fuel cells (SMFCs), which are capable of removing heavy metals and nutrients from sediments.{{cite journal |last1=Shabangu |first1=Khaya |last2=Bakare |first2=Babatunde |last3=Bwapwa |first3=Joseph |title=Microbial Fuel Cells for Electrical Energy: Outlook on Scaling-Up and Application Possibilities towards South African Energy Grid |journal=Sustainability |date=1 November 2022 |volume=14 |issue=21 |pages=14268 |doi=10.3390/su142114268|doi-access=free }} By integrating MFCs with sensors, they enable remote environmental monitoring in challenging locations. The applications of microbial fuel cells in environmental remediation highlight their potential to convert pollutants into a renewable energy source while actively contributing to the restoration and preservation of ecosystems.

Microbial fuel cells (MFCs) offer significant potential as sustainable and innovative technologies, but they are not without their challenges. One major obstacle lies in the optimization of MFC performance, which remains a complex task due to various factors including microbial diversity, electrode materials, and reactor design.{{cite journal |last1=Choi |first1=Seokheun |title=Microscale microbial fuel cells: Advances and challenges |journal=Biosensors and Bioelectronics |date=July 2015 |volume=69 |pages=8–25 |doi=10.1016/j.bios.2015.02.021|pmid=25703724 }} The development of cost-effective and long-lasting electrode materials presents another hurdle, as it directly affects the economic viability of MFCs on a larger scale. Furthermore, the scaling up of MFCs for practical applications poses engineering and logistical challenges. Nonetheless, ongoing research in microbial fuel cell technology continues to address these obstacles. Scientists are actively exploring new electrode materials, enhancing microbial communities to improve efficiency, and optimizing reactor configurations. Moreover, advancements in synthetic biology and genetic engineering have opened up possibilities for designing custom microbes with enhanced electron transfer capabilities, pushing the boundaries of MFC performance.{{cite journal |last1=He |first1=Li |last2=Du |first2=Peng |last3=Chen |first3=Yizhong |last4=Lu |first4=Hongwei |last5=Cheng |first5=Xi |last6=Chang |first6=Bei |last7=Wang |first7=Zheng |title=Advances in microbial fuel cells for wastewater treatment |journal=Renewable and Sustainable Energy Reviews |date=May 2017 |volume=71 |pages=388–403 |doi=10.1016/j.rser.2016.12.069|bibcode=2017RSERv..71..388H }} Collaborative efforts between multidisciplinary fields are also contributing to a deeper understanding of MFC mechanisms and expanding their potential applications in areas such as wastewater treatment, environmental remediation, and sustainable energy production.

{{portal|Energy|Renewable energy}}

• Bacterial nanowires
• Biobattery
• Cable bacteria
• Dark fermentation
• Electrohydrogenesis
• Electromethanogenesis
• Fermentative hydrogen production
• Glossary of fuel cell terms
• Hydrogen hypothesis
• Hydrogen technologies
• Photofermentation

{{Reflist|2}}

{{Refbegin}}

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• Yue P.L. and Lowther K. (1986). Enzymatic Oxidation of C1 compounds in a Biochemical Fuel Cell. The Chemical Engineering Journal, 33B, p 69-77

{{Refend}}

• {{cite journal |doi=10.1038/ismej.2007.4 |pmid=18043609 |title=Microbial ecology meets electrochemistry: Electricity-driven and driving communities |journal=The ISME Journal |volume=1 |issue=1 |pages=9–18 |year=2007 |last1=Rabaey |first1=Korneel |last2=Rodríguez |first2=Jorge |last3=Blackall |first3=Linda L|author3-link= Linda Blackall |last4=Keller |first4=Jurg |last5=Gross |first5=Pamela |last6=Batstone |first6=Damien |last7=Verstraete |first7=Willy |last8=Nealson |first8=Kenneth H|doi-access=free |bibcode=2007ISMEJ...1....9R }}
• {{cite journal |doi=10.1016/j.biortech.2009.10.017 |pmid=19892549 |title=A review of the substrates used in microbial fuel cells (MFCs) for sustainable energy production |journal=Bioresource Technology |volume=101 |issue=6 |pages=1533–43 |year=2010 |last1=Pant |first1=Deepak |last2=Van Bogaert |first2=Gilbert |last3=Diels |first3=Ludo |last4=Vanbroekhoven |first4=Karolien|bibcode=2010BiTec.101.1533P }}

• [https://magicalmicrobes.com/collections/kits/products/mudwatt-clean-energy-from-mud DIY MFC Kit]
• [https://biomarmicrobialtechnologies.com/en/bio-energy/biofuels.html BioFuel from Microalgae]
• [https://pnas.org/content/104/47/18871.abstract Sustainable and efficient biohydrogen production via electrohydrogenesis – November 2007]
• [https://web.archive.org/web/20060903112234/http://microbialfuelcell.wordpress.com Microbial Fuel Cell blog] A research-type blog on common techniques used in MFC research.
• [https://microbialfuelcell.org Microbial Fuel Cells] This website is originating from a few of the research groups currently active in the MFC research domain.
• [https://scq.ubc.ca/microbial-fuel-cells-from-rhodopherax-ferrireducens Microbial Fuel Cells from Rhodopherax Ferrireducens] An overview from the Science Creative Quarterly.
• [https://web.archive.org/web/20110419104018/http://microbialfuelcell.org/MFC/index2.htm Building a Two-Chamber Microbial Fuel Cell]
• [https://groups.yahoo.com/neo/groups/MicrobialFuelCells/info Discussion group on Microbial Fuel Cells]
• [https://cambrianinnovation.com Innovation company developing MFC technology]

{{fuel cells}}

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