Page 220 - Refining Biomass Residues for Sustainable Energy and Bioproducts

190 Refining Biomass Residues for Sustainable Energy and Bioproducts

the form of adenosine triphospate. In dissimilarity metal reducing microorganisms,
the chemical compounds are involved in the electron transportation. The microorgan-
isms such as Shewanella putrefaciens, Geobacter sulfurreducens,and Geobacter
metallireducens transfer electrons to anode by similar method.

8.7 Confront/dispute in microbial fuel cell

The MFC technology has seen wide commercial applications, because they can uti-
lize the same biomass in many cases for energy productions. MFCs are able to con-

vert biomass at low temperature (20 C) and with low substrate concentrations. In
order to improve the power density output, new anodophilic microorganisms that
enormously improve the electron transport rate are much needed. It is claimed that
in MFCs, current flow could increase by four orders of magnitude if Geobacter
transports electrons to the anode at the same rate as it does to its natural electron
acceptor. In the future, it is possible that an optimized microbial consortium can be
obtained to operate an MFC without extraneous mediators while achieving superior
mass transfer and electron transfer rates.
MFCs can be used in various applications as aforementioned. When MFCs used
in wastewater treatment, a large surface area is needed for biofilm to build up on
the anode. In some cases, 80% 90% Coulombic efficiency has been achieved; it
has little effect on low reaction rate. Although some basic knowledge has been
gained in MFC research, there is still a lot to be learned in the scale-up of MFC for
large-scale applications. Besides, large-scale application of MFCs has yet to be
implemented due to low yields of power and high cost.

8.8 Utilization of microbial fuel cell

8.8.1 Electricity generation
MFCs are capable of converting the chemical energy to electrical energy with the aid
of microorganisms. In MFCs the substrates oxidization is directly converted into elec-
tricity; electricity generation with an electron yield by ferrireducens as high as 80%
was reported and higher electron yield up to 89% was also reported (Du et al., 2007).
High Coulombic efficiency of 97% was reported during the oxidation of formate
with the catalysis of platinum (Pt) black. However, MFC power generation is still
very low. To overcome this issue, one sensible method is to make storage of the pro-
duced electricity in storage devices and then distribute it to the end users.

8.8.2 Biohydrogen

MFCs can be easily modified to produce hydrogen instead of electricity. The pro-
tons and the electrons produced by the metabolism of microbes in an MFC are