Page 221 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Generation of bioenergy from industrial waste using microbial fuel cell technology 191

thermodynamically unfavorable. It applied an external potential to amplify the cath-
ode potential in a MFC circuit and thus overcame the thermodynamic barrier.
Protons and electrons produced by the anolyte reaction are combined at the cathode
chamber to form hydrogen. The external potential for an MFC theoretically requires
100 mV, much lower than the 1110 mV required for direct electrolysis of water at
neutral pH. This may be due to the fact that some energy comes from the biomass
oxidation process in the anodic chamber. In biohydrogen production using MFCs,
oxygen is no longer needed in the cathodic chamber. Thus oxygen leak to the
anodic chamber is no longer an issue in improved efficiency of MFCs. The main
advantage is that hydrogen can be accumulated and stored for future usage.
Therefore MFCs provide a renewable hydrogen source that can contribute to the
overall hydrogen demand in a hydrogen economy.

8.8.3 Wastewater treatment
The important applications of MFCs are treating domestic as well as industrial
wastewater. Municipal wastewater contains a multitude of organic compounds that
can fuel MFCs. The amount of electric power generated by MFCs during the waste-
water treatment process can potentially halve the electricity needed in a conven-
tional treatment process. A hybrid incorporating both electrophiles and anodophilies
is especially suitable for wastewater treatment, because more organics can be biode-
graded by a variety of organic substances. MFCs using certain microbes have a spe-
cial ability to remove sulfides as required in wastewater treatment. MFCs can
enhance the growth of bioelectrochemically active microbes during wastewater
treatment. Continuous flow and single-compartment MFCs and membrane-less
MFCs are favored for wastewater treatment due to concerns in scale-up. Sanitary
wastes, food-processing wastewater, swine wastewater, and corn stover are all great
biomass sources for MFCs because they are rich in organic matters. Up to 80% of
the chemical oxygen demand (COD) can be removed in some cases, and a
Coulombic efficiency as high as 80% has been reported.

8.8.4 Biosensor

Another potential application of the MFC technology is to use it as a sensor for pol-
lutant analysis and in situ process monitoring and control, apart from the aforemen-
tioned applications. The correlation between the Coulombic yield of MFCs and the
strength of the wastewater makes MFCs possible to serve biological oxygen
demand (BOD). A number of works showed a good linear relationship between the
Coulombic yield and the strength of the wastewater in a quite wide BOD concentra-
tion range. MFC-type of BOD sensors is advantageous over other types of BOD
sensor, because they have excellent operational stability, good reproducibility, and
accuracy. An MFC-type BOD sensor constructed with the microbes enriched with
MFC can be kept operational for over 5 years without extra maintenance.