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Reorienting Waste Remediation Towards Harnessing Bioenergy 245

feasible for the mass production of H 2 . Municipal and industrial wastewaters
along with the waste generated from agriculture and food-processing indus-
tries contains enough organic load that can be appropriately tapped (Venkata
Mohan et al., 2013b). Biologically derived organic material and their resi-
due, such as agricultural crops and their waste by-products, wood and wood
waste, food-processing waste, aquatic plants, and algae constitute a large
source of biomass, which can also be used as a fermentable substrate
(Saratale et al., 2008). Cellulosic material or solid waste require an initial
pretreatment step to make the organic fraction soluble and bioavailable to
the microorganism for metabolic reactions. Its highly crystalline and water
insoluble nature makes cellulose recalcitrant to hydrolysis (Saratale et al.,
2008). Table 6.2 illustrates the details of wastewater used as substrate to gen-
erate H 2 . Fermentative H 2 production is relatively less energy-intensive and
more environmentally sustainable due to utilization of waste material as
substrate.

6.3.3 Thermochemical Process
Thermochemical treatment of biomass is a nonbiological biohydrogen
production processes that produces a H 2 rich stream of gas known as syngas
(a blend of hydrogen and carbon monoxide) by gasification and pyrolysis
(heating biomass in the absence of oxygen) (Lipman, 2011). These processes
involve a series of thermally assisted chemical reactions that release H 2 from a
broad range of feedstocks (Yildiz and Kazimi, 2006). Gasification is a process
operated at temperatures above 1000 K in the presence of oxygen and/or
steam where the feedstock undergoes partial oxidation and/or steam-
reforming reactions yielding gas and char product ( Jong, 2009; Navarro

et al., 2009). Low-temperature (<1000 C) gasification yields a significant
amount of hydrocarbon while at higher temperature the syngas is without
any hydrocarbons (Navarro et al., 2009). Pyrolysis facilitates thermal decom-
position of biomass at a temperature of 650–800 K (1–5 bar) in the absence
of air to yield oils, charcoal, and gaseous compounds (Navarro et al., 2009).
Hydrogen can be produced directly through both slow and fast flash
pyrolysis if both high temperature and sufficient volatile phase residence
time are provided (Agarwal et al., 2013; Navarro et al., 2009). Pyrolysis
followed by reforming of bio-oil and gasification of char has received
significant interest as this provides an improved quality fuel product
(Saxena et al., 2008). Gasification followed by reformation of the syngas
and fast pyrolysis, in turn followed by the reformation of the carbohydrate