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Reorienting Waste Remediation Towards Harnessing Bioenergy 253

Lee et al., 2008; Liu et al., 2005; Luo et al., 2010; Mohanakrishna et al.,
2010a; Rabaey et al., 2003; Sun et al., 2009; Velvizhi and Venkata Mohan,
2011, 2013a,b; Venkata Mohan and Chandrasekhar, 2011b; Venkata
Mohan and Srikanth, 2011; Venkata Mohan et al., 2008h,i, 2009a). Hence,
MFC can also be termed as a bioelectrochemical treatment system (BET).
Enhanced treatment efficiency along with simultaneous electrogenesis has
made BET an effective process particularly for complex wastewater treat-
+

ment. Protons (H ) and electrons (e ) released during substrate metabolism
by electrochemically active microorganisms through various redox reactions
travel from a reduced electron donor to an electrode and finally to an oxi-
dized electron acceptor before generating power. This is the basis for the
function of an MFC or a BET. BET operation triggers multiple reactions
such as biochemical, physical, physicochemical, electrochemical and oxida-
tive, which cohesively are denoted as bioelectrochemical reactions. The
potential difference between anodic oxidation and cathodic reduction reac-
tions can have a positive influence on the pollutant removal in MFCs.
Anodic oxidation generates in situ biopotential by which potential reactive

species like OH ,O , and others are generated at the anode surface. These
reactive species help to break the complex chemical structures present in
wastewater and also aid in the degradation of different pollutants. The anode
chamber of the MFC resembles a conventional anaerobic bioreactor and
mimics the functions of a conventional electrochemical cell used for waste-
water treatment, where the redox reactions help in the degradation of
organic matter and toxic/xenobiotic pollutants (Mohanakrishna et al.,
2010a; Venkata Mohan et al., 2009a). Pollutant removal during BET oper-
ation is possible mainly due to direct anodic oxidation (DAO) and indirect
anodic oxidation (IAO) mechanisms. The pollutants are adsorbed on the
anode surface and get destroyed by the anodic electron transfer reactions
in the DAO. During the IAO, pollutants will be oxidized by the oxidants
formed electrochemically on the anode surface under in situ biopotential.
DAO allows the formation of primary oxidants that further react with the
anode, yielding secondary oxidants such as chlorine dioxide and ozone, both
of which might have significant positive effects on the color removal effi-
ciency throughout the oxidation process.
In some reports pollutants present in the wastewater themselves act as
mediators in electron transfer. For example, elemental sulfur present in
the wastewater acts as a mediator for electron transfer to the anode and con-
verts itself to sulfate in the MFC, which is easier for degradation (Dutta et al.,
2009). Azo dyes also act as mediators for the electron transfer in the MFC and