Introduction: There are two general mechanisms for electron transfer in MFC: 1. Direct transfer electron or DET. 2. Mediated electron transfer or MET (11).
One of the fields of research in MFC is power generation from wastewater along with the oxidation of organic or inorganic compounds. Any compound that can be destroyed by bacteria can be converted to electricity. The range of compounds includes acetate, glucose, starch, cellulose, wheat straw, pyridine, phenol, nitrophenol, and complex solutions such as household wastewater, desalination waste, waste leachate, chocolate industry waste, mixed fatty acids, and petroleum products (1). The MFC greatly reduces the amount of COD in the treated effluent. The highest percentage of carbon removal from wastewater with the help of the MFC is about 90% (12). Nitrogen removal from the wastewater is also possible by MFC. For example, the use of MFC for domestic wastewater treatment has reduced COD by 94% and nitrogen removal by 85% (13). Ieropoulos et al. (2012) identified urine as an excellent source of electricity generation in the MFC. In addition, Struvite crystals are extracted from the urine with the help of an MFC, and electricity is also generated (14). Recently, MFC has been used to remove sulfide by simultaneously generating electricity in wastewater treatment. In the anode chamber, sulfide was first produced with the help of sulfate-reducing bacteria and the sulfide is then converted to sulfur with the help of sulfide oxidizing bacteria (8). Provides oxidation/reduction conditions in MFC for the elimination of drugs, especially antibiotics (Sulfonamides, Penicillin, Sulfadimidine, aureomycin, Norfloxacin, Chloramphenicol) (15-16). MFCs have shown great potential for the reduction of heavy metals, which are used both at the anode as an electron donor and at the cathode chamber as an electron receiver (17). Yangpin et al. (2017), a single-chamber bio-photoelectrochemical system (BPES) that receives high-performance destruction for azo dye (methyl orange (MO)) and energy recovery (2).
To improve wastewater treatment, technologies are added to the MFC, such as aerobic decomposition (AD), struvite deposition, algae treatment, and membrane filtration. In the first step, we have a settling tank to remove large particles. Then, depending on the characteristics of the wastewater, we have it through three different treatment ways: 1- Low organic load wastewater can be fed directly to the MFC system. 2- High organic load wastewater must be pre-fermented in an anaerobic reactor before entering the MFC system to produce biogas and the optimal composition for wastewater. 3. Phosphate-rich wastewater can undergo Struvite recovery before MFC treatment (18-19).
Methods: 1 .Franks AE, Nevin KP. Microbial fuel cells, a current review. Energies. 2010;3(5):899-919.
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3. Richter H, McCarthy K, Nevin KP, Johnson JP, Rotello VM, Lovley DR. Electricity generation by Geobacter sulfurreducens attached to gold electrodes. Langmuir. 2008;24(8):4376-9.
4. Park Y, Cho H, Yu J, Min B, Kim HS, Kim BG, et al. Response of microbial community structure to pre-acclimation strategies in microbial fuel cells for domestic wastewater treatment. Bioresource technology. 2017;233:176-83.
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6 .Wang Z, Lim B, Choi C. Removal of Hg2+ as an electron acceptor coupled with power generation using a microbial fuel cell. Bioresource Technology. 2011;102(10):6304-7.
7 .Kumar R, Singh L, Zularisam A, Hai FI. Microbial fuel cell is emerging as a versatile technology: a review on its possible applications, challenges and strategies to improve the performances. International Journal of Energy Research. 2018;42(2):369-94.
8 .Palanisamy G, Jung H-Y, Sadhasivam T, Kurkuri MD, Kim SC, Roh S-H. A comprehensive review on microbial fuel cell technologies: Processes, utilization, and advanced developments in electrodes and membranes. Journal of cleaner production. 2019;221:598-621.
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10 .Rathour R, Kalola V, Johnson J, Jain K, Madamwar D, Desai C. Treatment of various types of wastewaters using microbial fuel cell systems. Microbial Electrochemical Technology: Elsevier; 2019. p. 665-92.
11. Torgal FP, Labrincha JA, Diamanti MV, Yu C-P, Lee H-K. Biotechnologies and biomimetics for civil engineering: Springer; 2015.
12. Lu M, Chen S, Babanova S, Phadke S, Salvacion M, Mirhosseini A, et al. Long-term performance of a 20-L continuous flow microbial fuel cell for treatment of brewery wastewater. Journal of Power Sources. 2017;356:274-87.
13. Palanisamy G, Jung H-Y, Sadhasivam T, Kurkuri MD, Kim SC, Roh S-H. A comprehensive review on microbial fuel cell technologies: Processes, utilization, and advanced developments in electrodes and membranes. Journal of cleaner production. 2019;221:598-621.
14. Ieropoulos I, Greenman J, Melhuish C. Urine utilisation by microbial fuel cells; energy fuel for the future. Physical Chemistry Chemical Physics. 2012;14(1):94-8.
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16. Wu D, Sun F, Zhou Y. Degradation of chloramphenicol with novel metal foam electrodes in bioelectrochemical systems. Electrochimica Acta. 2017;240:136-45
17. Wang Z, Lim B, Choi C. Removal of Hg2+ as an electron acceptor coupled with power generation using a microbial fuel cell. Bioresource Technology. 2011;102(10):6304-7.
18. Li W-W, Yu H-Q, He Z. Towards sustainable wastewater treatment by using microbial fuel cells-centered technologies. Energy & Environmental Science. 2014;7(3):911-24.
19. .Fischer F, Bastian C, Happe M, Mabillard E, Schmidt N. Microbial fuel cell enables phosphate recovery from digested sewage sludge as struvite. Bioresource Technology. 2011;102(10):5824-30.
Results: MFC (Microbial Fuel Cell) is a system in which microbes oxidize organic matter and minerals, then transfer the generated electrons to the anode electrode, and then these electrons are transferred by wire to the cathode electrode, which generates electricity. Electron transfer from microbes to electrodes occurs in two direct and indirect ways (1). MFC has different types such as single-chamber and double-chamber and batch MFC (2). Of course, MFC has a variety of applications, such as generating electricity, treating wastewater, removing certain chemicals, biosensors, producing hydrogen, and using rumen bacteria (3-4-5-6-7-8-9). As the world's population grows, the need for energy has increased. The need for renewable energy and the reduction of environmental pollution in this system has received much attention. Water scarcity has led to many efforts to treat and use wastewater, and MFC is a suitable system for this. Reducing pollution is the most important task of wastewater treatment, but unfortunately, wastewater treatment processes are generally energy-intensive. During treatment, large amounts of greenhouse gases (GHG) such as carbon dioxide (CO2) and nitrous oxide (N2O) are released and disposal of activated sludge produced during the effluent treatment process is very difficult. In addition, many valuable resources such as phosphate (P4O3), ammonia (NH4+), and some metals in wastewater are not recovered, which is reduced by the MFC system.
Conclusion: MFC is a promising technology for sustainable wastewater treatment (WWT) combined with power generation. Investigation of complex interactions at the electrode and microbial interface increases the output power for practical applications in the MFC device. The description of the electrochemical mechanism in microbes has made considerable progress. However, more collaborative interaction in different disciplines is needed to make this technology more practical. Of course, there are currently many problems for this technology, such as low Colombic efficiency and internal resistance, etc., which should be further studied and researched.