Biofilms in… Microbial Fuel Cells

Microbial fuel cells (MFCs) are devices in which bioelectrochemical reactions and biocatalytic transformations lead to the conversion of organic matter to electricity via microbial or enzymatic participation. MFCs principle of operation lies on electron transfer processes from viable microbial cells—which can be forming biofilms—or enzymes from an anode to a cathode (placed in an electrochemical cell functioning as a bioreactor) through an external conductor, due to the potential difference created between them.

One of the multiple alternatives of new developments for building up the upcoming world’s energy portfolio are these bio-devices, as long as they are properly optimized for producing important amounts of energy and requiring minimal maintenance processes, which ensures competitiveness against the current and the forecoming energy sources.

How do MFCs work? Usually, MFCs comprise two chambers (or a single chamber comprising two conditions) which have aerobic and anaerobic (free of oxygen) environments, respectively. Microorganisms are placed in the anaerobic chamber attaching to an electrode as biofilms—in this chamber the electrode acts as an anode—to which they transfer the electrons derived from their metabolic activity; the electrons flow from the anode to the cathode (placed in the aerobic chamber), where they combine with oxygen and protons to form water as product. The occurrence of this process implies that a potential difference is generated between the anode and the cathode, as it happens in a regular battery or in a fuel cell (depending on a batch or continuous processes), from which electric energy is obtained.

Microbial fuel cell principle of operation.
Click on the image below to view it full size.

(Image edited from Lovley D. R. (2006). Microbial fuel cells: novel microbial physiologies and engineering approaches, Current Opinion in Biotechnology, 7:327–332.)

The first MFCs produced between 1 and 40 milliwatts per square meter (mW/m²) of an electrode surface area, while in the past years some laboratories have been able to generate power in the range of up to 500 mW/m² using domestic water and 1500 to 3600 mW/m² using glucose in the feedstock [1]. However, the achieved understanding of the processes involved in this matter has not yet produced practical applications due to the significant optimization that is required to transform these devices into a highly efficient energy source.

Some of the current actors in MFCs Science and Engineering are (alphabetical listing):

AECG (University of Greifswald, Germany)
AEMC (University of Queensland, Australia)
ATL (Helsinki University of Technology, Finland)
E&R (DTU, Denmark)
EBL (Gwangju Institute of Science and Technology, Korea)
ET (Wageningen University, The Netherlands)
IAS (UWE Bristol, United Kindgom)
LabMET (Ghent University, Belgium) **
The Angenent Lab (Washington University in St. Louis, USA)
The Laboratoire Ampère-EMGG (Ecole Centrale de Lyon, France)
The Logan Group (PSU, USA) **
The Lovley Lab (UMass, USA) **
Wetsus (The Netherlands)

** Currently the most popular ones.

References:

[1] Holzman D. (2005). Microbe Power, Environmental Health Perspectives, Vol. 113, No. 11, p. p. A754-A757.

~ by koxinelle on February 23, 2007.