Exoelectrogenic bacteria

Parra E, Lin L (2009) Microbial fuel cell based on electrode-exoelectrogenic bacteria interface. Proc. of 19th IEEE Int. Conf. on Micro Electro Mechanical Systems (MEMS) 31-34... 

Logan, B.E. (2009) Exoelectrogenic bacteria that power microbial fuel cells. Nat. Rev. Microbiol, 7 (5), 375-381. 

Metals and metal coatings. The use of various metals and metal coatings on carbon materials has not been well-examined for MFCs. In one study, it was shown that addition of vapor-deposited iron oxide to a carbon paper cathode decreased acclimation time of a reactor but did not affect maximum power Kim et al. 2005). A two-chamber reactor was used, and thus power production was limited by high internal resistance so it is not known if the iron oxide would have resulted in an increase in power production in a reactor with less internal resistance. Over time the iron oxide coating dissolved into solution, leaving only the carbon paper electrode. However, the use of iron to enrich iron-reducing bacteria on the electrode may be a beneficial approach for acclimation of an electrode with exoelectrogenic bacteria. 

Figure 8.1. Illustration of a typical two-chamber microbial fuel cell (MFC) specific bacteria species in the anode chamber, named exoelectrogenic or anode-respiring bacteria (ARB), break down organic substrates, i.e., acetate, to produce electrons, protons, and CO2. The electrons pass through an external resistor to be reduced at the cathode while protons pass through the proton exchange membrane (PEM) from the anode to the cathode chamber.

EET mechanisms are nearly as diverse as the bacteria that perform them. Some bacteria transfer electrons to electrodes efficiently on their own while others need help in the form of exogenous redox molecules. Some of the most proficient exoelectrogens likely employ some combination of the mechanisms discussed here (Fig. 9.2). Understanding these mechanisms and how they interplay is integral to future engineering efforts of MFCs along with other bioelectrochemical systems. 

In 2005, two research groups independendy found that bacteria could produce hydrogen in an electrolysis process based on a microbial fuel cell (MFC) (Logan et al., 2008). The device is called a microbial electrolysis cell (MEC), and the microbes are exoelectrogens because they release electrons instead of hydrogen. The half reactions at anode and cathode of MFCs for conversion of hydrogen from acetate are ... 

Hybrid system Organic compound, light or electricity Fermentative bacteria plus photosynthetic bacteria or exoelectrogens CO2 High production yield More complicated reactor design... 

Numerous bacteria that can generate electricity have been isolated and investigated. Studies on these pure cultures provide us valuable knowledge about the properties of exoelectrogens, as well as the exocellular electron transfer mechanisms. Some examples of exoelectrogenic active bacteria are listed in... 

Polyaniline was tested as a method to increase power Schroder et al. 2003), but studies were only conducted on anodes containing Pt where power was generated via hydrogen produced by bacteria fermenting a sugar, and not by exoelectrogens. These types of hydrogen MFC (HMFC) reactors are further discussed in the next chapter. 

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