Page 277 - Industrial Wastewater Treatment, Recycling and Reuse

Reorienting Waste Remediation Towards Harnessing Bioenergy 251

studied (Srikanth et al., 2011). Initial studies with MFC were carried out with
a salt-bridge and later the research was extended to use PEM. The presence of
negatively charged sulfonate groups facilitates good proton conductivity.
However, the use of PEM increases the cost of MFC construction.
The extracellular electron transfer is influenced by the potential differ-
ence between the final electron carrier and the anode (Lee et al., 2009;
Marsili et al., 2008; Newman and Kolter, 2000). The cell compartmental-
ization and the highly complicated architecture of cell respiratory chains
facilitate energy harvesting from biocatalysts. Biocatalysts play an important
role in generating the reducing powers as well as transferring them to elec-
trodes. Initial research on MFCs was specific to pure cultures, but later
shifted to the use of mixed consortia that facilitates a synergistic interaction
between the individual strains, resulting in a higher power output. Electro-
chemically active microbes are facultative and metal-reducing in nature.
These organisms have an outer membrane cytochrome oxidase type c pro-

tein that allows e to be transferred from the interior of the bacterial cell
membrane to the exterior of the cell membrane. The operational factors,
such as organic load, retention time, redox condition (pH), surface area
of electrode, and anode and cathode microenvironment, also influence
MFC performance (Lenin Babu and Venkata Mohan, 2012; Mohanakrishna
et al., 2012; Raghavulu et al., 2011, 2012; Srikanth and Venkata Mohan,
2012b,c; Srikanth et al., 2010b; Velvizhi and Venkata Mohan, 2013a;
Velvizhi et al., 2012; Venkata Mohan et al., 2008e-h; Venkateswar Reddy
et al., 2010). Biofilm formation on the surface of the anode will significantly
influence the current generation in MFC irrespective of the nature of the
microbe (Venkata Mohan et al., 2008i).
Wastewater (anolyte fuel) acts as an electron donor to generate reducing
equivalents. Various types of waste/wastewater from simple domestic sew-
age to complex industrial wastewater have been considered as an anodic fuel
in MFC (Srikanth and Venkata Mohan, 2012b,c; Venkata Mohan et al.,
2013a). Highly biodegradable waste can be loaded at higher loading rates,
while low biodegradable waste will interfere with the metabolism of
microbes at higher loading rates. Higher loadings can continue the genera-
tion of reducing equivalents for longer periods, while lower loading rates can
retain the electrogenesis for less time (Velvizhi and Venkata Mohan, 2011;
Venkata Mohan and Srikanth, 2011). Neutral pH is the optimum condition
for bacterial growth and metabolic activities. Most of the enzymes function
near a neutral pH, and biomolecules of the cell become unstable at an
extreme pH. Hence, the internal pH of the microbe is maintained at a