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energy sources. Recovering energy from treatment benefits the effluent treat-
ment plant (ETP) operators by recouping revenue, simultaneously reducing
the overall effluent treatment cost. Recent energy and environment scenarios
visualize a paradigm shift from waste remediation to energy generation in
order to combine both aspects into a unified and biorefinery approach that
is environmentally sustainable. Biological processes are preferred to treat waste
because of their simple, economical, and eco-friendly nature. These processes
facilitate the conversion of negatively valued waste to useful forms of energy.
Simultaneously, they achieve the objective of pollution control. Using waste
as a potential source for value addition through biological routes has instigated
considerable interest because of its sustainable nature and has further opened
up a new avenue for the use of renewable and inexhaustible energy sources.
The integration of bioenergy generation and the ETP is the futuristic goal
envisioned, with wastewater as the primary feedstock. A comprehensive
attempt is made in this chapter to illustrate various routes employed for gen-
erating diverse forms of value addition from negative-valued wastewater/
waste such as biohydrogen, bioelectricity, bioplastics and algal-based lipids
(Figure 6.1).

6.2 ANAEROBIC FERMENTATION
Anaerobic metabolism is a favored process for harnessing bioenergy
(Venkata Mohan et al., 2013c). If oxygen is not available as an electron
acceptor, bacteria use other terminal electron acceptors (TEAs) such as oxi-
dized organic compounds or pollutants resulting in the generation of
reduced energy-rich compounds with simultaneous treatment. However,
based on thermodynamic hierarchy of the reactions, the microbes will
switch over to other biochemical pathways. Anaerobic fermentation helps
in generating energy-rich metabolic intermediates and maintains the carbon
flow for longer periods of time without releasing the end products (Venkata
Mohan et al., 2013c). Complete degradation of certain persistent chemicals
cannot be catalyzed by a single microbe but a syntrophic association of phys-
iologically distinctive organisms is required for organic carbon-driven
reduction of iron, manganese, sulfate etc, along with acetogenesis and
methanogenesis. Microbial fermentation helps to generate energy-rich
reducing factors (e.g., NADH, FADH) that subsequently are reoxidized
during respiration with simultaneous generation of biological energy mol-
ecules (ATP) in the presence of a terminal electron acceptor (TEA). Both
aerobic and anaerobic metabolisms have a common glycolytic pathway.