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Microbial Electrochemical Technology Drives Metal Recovery
Published in Sonia M. Tiquia-Arashiro, Deepak Pant, Microbial Electrochemical Technologies, 2020
Xochitl Dominguez-Benetton, Jeet Chandrakant Varia, Guillermo Pozo
In a pioneering investigation, which opened the gate to extensive research that is now dedicated to unraveling the principles and applications of biocathodic MET, Gregory and Lovley used Geobacter sulfurreducens for U6+ reduction on a biocathode. Uranium removal was effectively achieved by reducing soluble hexavalent uranium U6+ to the relatively insoluble tetravalent uranium U4+ oxide precipitate (Table 3 R1) (Gregory and Lovley 2005). The cathode served as an electron donor to Geobacter sulfurreducens. U4+ remained as a stable precipitate on the electrode in the absence of O2. In the absence of microbes, uranium could not be reduced. With the MET, 87% of the total U6+ was removed, achieving a 97% current efficiency. Reports of metals recovered in biocathodes are summarized in Table 3.
Fundamentals of Photosynthetic Microbial Fuel Cell
Published in Lakhveer Singh, Durga Madhab Mahapatra, Waste to Sustainable Energy, 2019
Indirect electron transfer has emerged as a secondary way to carry out electrons to the anode in a PhFC. Whereas few microbes can achieve a direct electron transport, other microorganisms excrete redox-active molecules to accomplish an indirect electron transport with electrodes. This process is carried out without physical contact between the bacterial cell membrane and the cathode electrode surface. Exoelectrogenic bacteria, capable of transferring electrons extracellularly, have been well studied due to their biotechnological relevance and are ubiquitous in anoxic sediments and other anaerobic environmental systems (Logan 2009). The most prominent of these are Geobacter sulfurreducens and Shewanella oneidensis, which are used as model systems for electron transfer, and are recognized for their ability to conduct electrons through specialized appendages, such as microbial nanowires and c-type cytochromes (Eaktasang et al. 2016, Li et al. 2016).
Microorganisms Involved in Biofuel Production Processes
Published in Debabrata Das, Jhansi L. Varanasi, Fundamentals of Biofuel Production Processes, 2019
Debabrata Das, Jhansi L. Varanasi
With the discovery of certain bacteria capable of generating electricity (Potter 1911), several attempts have been made to use these bacteria for direct power generation. These organisms often are used in different applications such as microbial fuel cells and microbial electrolysis to harness electricity and fuel (hydrogen), respectively (Varanasi and Das 2017a). The electron-generating bacteria, known as exoelectrogens or simply electrogens, can interact and shuttle electrons outside their cell to the solid metal surfaces. Depending upon the organism, this electron transfer can either be mediated (with the aid of exogenous or endogenous shuttles) or a direct electron transfer. Early reports focused on exogenous mediated electron transfer using organisms such as Enterobacter aerogenes and E.coli. Later on, organisms such as Pseudomonas aeruginosa (shuttle: pyocyanin) and certain Shewanella sp. (shuttle: flavins) were discovered which had innate capabilities to produce endogeneous shuttles (Varanasi and Das 2017b). Direct electron transfer is reported in organisms like Geobacter sulfurreducens, which rely on c-Cyts and/or pili for the biofilm formation and electron transfer to solid electrodes (Kumar et al. 2016). Direct electron transfer is expected to be much efficient than the mediated electron transfer because of minimal mass transfer losses in the former. So far, maximum current is produced using Geobacter sp. However, the ongoing research has brought about several new species whose efficiency still remains to be examined. Furthermore, recent studies have shown the potential of these organisms to convert CO2 to fuels, thereby, providing nexus of applications in the coming years (Nevin et al. 2010).
Biofilm formation and electron transfer in bioelectrochemical systems
Published in Environmental Technology Reviews, 2018
Surajbhan Sevda, Swati Sharma, Chetan Joshi, Lalit Pandey, Namrata Tyagi, Ibrahim Abu-Reesh, T.R. Sreekrishnan
Geobacter species plays a vital role in the BES for the electron transfer; the basic mechanism of the electron transfer is direct electron transfer. BESs are campaign that harness the electroactivity of microorganisms as power for the processing of, and energy recovery from organic wastes. BES performance is at the end of the day dependent on the capability of microorganisms to catalyse redox reactions using electrodes. Not unexpectedly, any parameter that influences the augmentation of BES microorganisms also affects liveliness outputs. The best-studied BESs are those single-minded by anode-reducing bacteria in the genus Geobacter. The group contains some of the most resourceful exoelectrogens presented in pure culture, and their growth and electroactivity are what in due course drive the catalytic activity of mixed-species anode biofilms in BESs. The theory and practice of Geobacter-driven BESs focuses on the model representative Geobacter sulfurreducens.
A review of design, operational conditions and applications of microbial fuel cells
Published in Biofuels, 2018
Rachna Goswami, Vijay Kumar Mishra
Geobacter is a genus of proteobacteria. Geobacter are anaerobic respiration bacterial species and found to be the first organism with the skill to oxidize organic compounds and metals, including iron, radioactive metals and petroleum compounds, into environmentally benign carbon dioxide while using iron oxide or other available metals as electron acceptor [82]. Bond and Lovley [69] used Geobacter sulfurreducens in MFC chambers, graphite electrode as the sole electron acceptor, and acetate or hydrogen as the electron donor. Holmes et al. [52] studied the potential role of Geobacteraceae, Geopsychrobacter electrodiphilus gen. nov., sp. nov., in electricity generation through a marine sediment fuel cell. Two unique marine isolates were found, strains A1T and A2. They are gram-negative, non-motile rods with copious c-type cytochromes. Phylogenetic assessment of the 16S rRNA, recA, gyrB, fusA, rpoB and nifD genes inferred that strains A1T and A2 represented a distinctive phylogenetic cluster in the Geobacteraceae. Both strains were capable to grow with an electrode providing the sole electron acceptor. These organisms were the first psychrotolerant members of Geobacteraceae reported and grown at temperatures of 4–30◦C, with an optimal temperature of 22◦C. Marine sediment microorganisms were evaluated by Bond et al. to harvest energy [1]. A specific enrichment of microorganisms of the family Geobacteraceae on an energy harvesting anode displayed that these microorganisms conserved energy to sustain their growth by oxidizing organic compounds with an electrode helping as the sole electron acceptor. This was valuable in encouraging the bioremediation of organic contaminants in subsurface environments.