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Reorienting Waste Remediation Towards Harnessing Bioenergy 249

In particular, its application for waste remediation attracted considerable
attention along with energy harvesting in the form of bioelectricity. Broadly,
applications of MFC can be classified as a power generator, wastewater treat-
ment unit, and system for the recovery of value-added products (Venkata
Mohan et al., 2013a). Reducing equivalents get reduced in the presence
of an electron acceptor at a physically distinct cathode, which results in
power generation. When the waste/wastewater functions as an electron
donor or acceptor, its remediation is manifested either through anodic oxi-
dation or cathodic reduction. Alternatively, when oxidized metabolites act
as electron acceptors during operation, they form reduced end products hav-
ing commercial importance. The application of MFC was also extended to
the production of commercially viable end products such as organic acids,
aldehydes, and alcohols (Logan, 2010; Rabaey and Rozendal, 2010;
Srikanth et al., 2012). Apart from these, several other distinct applications
are reported that also fall in either one or all of these three categories. Micro-
algae were used as a biocatalyst in the anode chamber of a fuel cell to harness
bioelectricity through oxygenic (Subhash et al., 2013) and anoxygenic
(Chandraetal.,2012) microenvironments through a photomixotrophic mech-
anism. An ecologically engineered submerged and emergent macrophyte-
based system was studied with an integrated eco-electrogenic design for
harnessing power with simultaneous wastewater treatment (Chiranjeevi
et al., 2013). Rhizosphere-based fuel cells were also studied for harnessing
bioenergy through CO 2 sequestration (Chiranjeevietal.,2012).

6.4.1.1 Bioelectricity Production
The microbial-catalyzed oxidation of a substrate takes place at the anode,
generating reducing equivalents, while their reduction takes place at cathode
(Equations 6.6–6.8).
+
C 6 H 12 O 6 +6H 2 O!6CO 2 +24H +24e (anode) (6.6)
+

4e +4H +O 2 !2H 2 O (cathode) (6.7)
C 6 H 12 O 6 +6H 2 O+6O 2 !6CO 2 +12H 2 O (overall) (6.8)
The proton exchange membrane (PEM) between the fermentation
(anode) and respiration (cathode) mimics the function of an external mem-
brane, generating a potential gradient, while the electrodes act as redox
components of the cell, assisting in the electron flow towards TEA. Electron
transfer from its source (metabolism) to the sink (TEA; terminal electron
acceptor) will be driven by the potential difference between the redox com-
ponents of the microbe and the fuel cell. The membrane potential across the