Microbial Fuel Cells for Wastewater Treatment - Biotechnologies and Biomimetics for Civil Engineering - page 407

Recent investigations have shown that during the last 10 years, the current
density of MFCs has been improved by 10,000-fold (Debabov 2008 ). Power
densities of MFCs have increased from less than 1 W/m 3 to over 4000 W/m 3 ,
which is the highest MFC power density reported up to date (Logan 2008 ;
Biffinger et al. 2009 ). Despite their potential applications and continuously
improved power, limited maximum power production by these systems impedes
commercial applications of bioelectrochemical wastewater treatment, primarily
because of high internal resistance including anode limitations and electrochem-
ical losses. Improvements of power generation are also dependent on the materials
and design of MFCs and capabilities of the microorganisms. Analysis of the
community profiles of exoelectrogenic microbial consortia shows great diversity,
ranging from primarily d-Proteobacteria that dominate in sediment MFCs to
communities composed of a-, b-, c-ord-Proteobacteria, Firmicutes, and
uncharacterized clones in other types of MFCs. Much remains to be discovered
about the physiology of these bacteria (collectively referred to as exoelectrogens)
capable of exocellular electron transfer.
This chapter is intended to provide an overview of recent development and
challenges in MFCs with a special focus on the materials, design, and microbi-
ology of MFC research. Since microorganisms play a crucial role in the MFCs,
comprehensive reviews focused on isolated exoelectrogens that have been iden-
tified to produce electricity, their mechanisms of exocellular electron transfer, and
the microbial communities found in MFCs. In the end, the prospects for this
emerging bioelectrochemical technology were discussed.
18.2 History of MFCs
Currently, MFCs have been recognized as a promising green technology for the
generation of electricity through the microbial oxidation of biodegradable organic
matters. The concept of generating electricity by bacteria was introduced more
than 100 years ago. The electricity generated by microorganisms was firstly
demonstrated in 1911 by Potter, a Professor of Botany Department at the Uni-
versity of Durham (Potter 1911 ). To examine the electricity producing capability
of microorganism, he conducted his experiment using yeast and certain other
bacteria in an apparatus consisted of a glass jar containing a porous cylinder. He
observed that Saccharomyces cerevisiae and Bacillus coli communis (now called
Escherichia coli) produced electric current when glucose was used as substrate.
After that there was no important research on MFCs up to 1966 (Lewis 1966 ) and
most studies on MFCs did not appear until the late twentieth century. However,
experiments carried out by researchers used artificial electrochemical mediators to
facilitate electron transfer between microbes and electrodes. Thurston and his
colleagues used thionine as a redox mediator and Proteus vulgaris culture as
catalyst in a two-chamber MFC to evaluate coulombic yield from glucose oxi-
dation (Thurston et al. 1985 ). These chemicals were considered important for