Consortium of Bacteria with Natural Nanowires Power Improved Microbial Fuel Cell

Microbial fuel cells (MFCs) are fuel cells which operate by using microorganisms that possess the ability to donate electrons to the anode of the fuel cell in order to produce electricity. Such microorganisms are known as exoelectrogenic organisms. Exoelectrogenic organisms can donate electrons to the anode in either of two ways: via mediators (e.g., the numerous dyes used in the art for this purpose) or in the absence of mediators (i.e. a mediator-less MFC). 

Oak Ridge National Laboratory Bioscientist Abhijeet P Borole  (Knoxville, TN) developed a method for preparing an inexpensive microbial fuel cell (MFC) that can produce electricity and hydrogen from waste water or industrial waste.  The MFC features improved electrical efficiency and reduced power fluctuation. 

FIG. 1A: Schematic of the MFC recirculation set up with an air-cathode.

 A significant benefit of MFCs is their ability to produce electricity by environmentally-friendly and renewable means. Furthermore, MFCs can be fueled by waste products (e.g., waste water from sewage treatment or industrial waste), which are typically valueless and in need of degradation. MFCs can also be configured to produce hydrogen gas by, for example, providing an assistive anodic potential and eliminating oxygen from the cathode such that hydrogen can be produced at the cathode.

Further, there is great interest in hydrogen as a particularly environmentally clean fuel, such as used in ordinary hydrogen fuel cells. There is particular interest in producing hydrogen by environmentally-friendly means. Additionally, MFCs can also be configured to provide electrons to any reductive process requiring electrons, for example, by using a suitable electrode material for the cathode and passing the substrate requiring reduction through the cathode chamber

Borole’s method of making an improved MFC includes: (i) inoculating an anodic liquid medium in contact with an anode of the microbial fuel cell with one or more types of microorganisms capable of functioning by an exoelectrogenic mechanism; (ii) establishing a biofilm of the microorganisms on and/or within the anode along with a substantial absence of planktonic forms of the microorganisms by substantial removal of the planktonic microorganisms during forced flow and recirculation conditions of the anodic liquid medium; and (iii) subjecting the microorganisms of the biofilm to a growth stage by incorporating one or more carbon-containing nutritive compounds in the anodic liquid medium during biofilm formation or after biofilm formation on the anode has been established.

FIG. 3 is an image of the microbial consortium inhabiting anode electrode (carbon felt) of the mixed carbon source MFC. The sample was stained with Syto9 (Molecular Probes). The community is seen to be dominated by biofilm-forming organisms.  Carbon nanotubes may be substituted for the carbon felt. 

Microorganisms with a strong propensity for forming biofilms are more likely to contain pili (nanowires) on their external membrane which can also be used by the microorganisms for direct electron transfer to the anode. Therefore, the forced flow and recirculation conditions of the anodic medium can also serve to further enrich the biofilm with exoelectrogenic microorganisms capable of direct electron transfer.

The advantage of enriching the biofilm with exoelectrogenic microorganisms capable of direct electron transfer is that mediators (e.g., ferric oxides, neutral red, anthraquinone dyes, 1,4-napthoquinone, thionine, methyl viologen, methyl blue, humic acid, and the like) are not needed to permit the electron transfer. Not only are mediators typically expensive, toxic, and require replenishment, but mediated electron transfer is much less efficient than direct (mediator-less) electron transfer. 

The exoelectrogenic microorganisms that form the biofilm can be any suitable microorganism. Without wishing to be bound by any theory, it is believed that nearly any type (e.g., domain, kingdom, phylum, class, order, family, genus, or species) of microorganism will contain, in some portion of its population, microorganisms capable of exhibiting exoelectrogenic behavior and capable of forming a biofilm. 

FIG. 4 Pie charts showing distribution of microbial consortium from MFC anode. Clockwise from top left: a) Consortium from MFC-A sampled on day 113, b) Consortium from MFC-A sampled on day 126, c) Consortium from MFC-A sampled on day 136, d) Consortium from MFC-C sampled on day 162. The longer the fuel cell operates the more beneficial microbes are produced and non-productive bacteria are eliminated. 

UT-Battelle, LLC holds the rights to the patent pending technology (U.S. Patent Application 20100092804).

Oak Ridge National Laboratory 

Bioconversion Science & Technology
BioSciences Division
 Oak Ridge, TN 37831-6341
Phone: (865) 576-7421
Fax: (865) 241-1555
borolea@ornl.gov