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decolorize during reduction (Mu et al., 2009a). Biohazardous toxic com-
pounds such as endocrine-disrupting estrogens can also be considered as medi-
ator molecules in the MFC (Kiran Kumar et al., 2012). A few reports are
available regarding the cathodic function in the effective removal of
pollutants. Azo dyes (Mu et al., 2009a), nitrobenzene (Mu et al., 2009b),
and nitrate (Lefebvre et al., 2008) are some of the pollutants studied in the
cathode chamber of the BET. Hypothetically, it can be assumed that in the
cathode chamber under anaerobic conditions most of the pollutants act as
TEAs for power generation. Pollutants in the anodic chamber also act as medi-
ators for electron transfer to the anode, which can increase the power gener-
ation efficiency with a simultaneous reduction of pollutants, but very little
work has been reported in the use of pollutants as mediators. Apart from sub-
strate removal, considerable reduction of toxicity, color, and TDS in waste-
water was also observed (Mohanakrishna et al., 2010a; Velvizhi and Venkata
Mohan, 2011). The application of an MFC was also extended to treat solid
waste and toxic aromatic hydrocarbons, taking advantage of the in situ biopo-
tential and by considering the anode as the electron acceptor (Venkata Mohan
and Chandrasekhar, 2011a,b). Studies related to the mechanisms of pollutant
reduction and their role in electron transfer or acceptance will give a spectrum
of practical feasibility of this technology for the removal of toxic pollutants.

6.4.3 Electrically Driven Biohydrogenesis

MEC is one of the recent advancements and a promising technology for the
production of renewable and sustainable hydrogen gas. Use of the MEC
provides a completely new approach for hydrogen generation from a wide
variety of biomass, such as biowaste and wastewater and accomplishing
waste treatment at the same time (Call and Logan, 2008; Cheng and Logan,
2007; Ditzig et al., 2007; Liu et al., 2005; Logan, 2008; Rozendal et al.,
2006, 2007). The principle of MEC is similar to the water electrolysis pro-
cess, except that microbes (biocatalyst) are used in the anodic reaction to
+

degrade organic matter into CO 2 , electrons (e ), and protons (H )
+

(Figure 6.4). The e and H travel through the external circuit and mem-
brane and are reduced to H 2 at the cathode. MEC operation is similar to the
existing MFC operation except that the cathode is sealed in the anolyte in
order to avoid oxygen, and an additional voltage is added to the circuit
(Venkata Mohan et al., 2013c). An external potential is required because
+
under standard conditions, H 2 formation is not spontaneous. The H
migrate to the cathode and get reduced to form H 2 in presence of e coming