Page 322 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Potentials of postharvest rice crop residues as a source of biofuel 291

enzymes mediated catalysis takes place during hydrolysis. The presence of
Humicola sp. during the process of cellulose hydrolysis is promising (Kumar
et al., 2008). The use of fungal species especially the white rot fungi has been
found to be most effective in the generation of biogas from lignocellulosic residue
(Take et al., 2006).

13.7.2 Production of bioethanol
13.7.2.1 Fermentation

The fermentation is required for the bioconversion of monomers such as reducing
sugars to ethanol. Fermentation of hydrolysis products requires optimal operating
conditions. The bacterial species such as Bacillus polymyxa (Singh and Mishra,
1993), Klebsiella aerogenes (Ingram et al., 1998), Clostridium thermocellum
(Herrero and Gomez, 1980), Escherichia coli (Yomano et al., 1998) are possible
species to be involved during the production of bioethanol from the products of
hydrolysis by fermentation. The fungal species such as Saccharomyces cerevisiae
(Kuhad et al., 2010) and Pichia stipitis (Gupta et al., 2009) are promising species
for production of bioethanol.

13.7.2.2 Distillation and production of bioethanol
Distillation is essential for separation of bioethanol from crude products on the
basis of its physical properties. It is one of the most predominant forms of purifica-
tion technique of ethanol being followed by the industries worldwide. During pro-
duction of bioethanol, a distillation tower separates water from ethanol in an
effective manner. Water is removed from the bottom of the tower, whereas the etha-
nol is collected from the top (Onuki et al., 2008). The product of distillation is an
azeotropic mixture of ethanol with insignificant amount of water. The vaporization

of ethanol at a low temperature of 78 C helps it during separation from crude pro-
ducts. On the basis of the utility and quality requirement of ethanol, the water could
be separated from the azeotropic mixture by azeotropic or extractive distillation
(Kumar et al., 2010).

13.7.3 Production of biogas
The lignocellulosic biomass from rice residues can also be used to produce biogas.
After the enzymatic hydrolysis the treated biomass can also be directly subjected to
the process of acidification followed by methanogenesis, respectively. The posthy-
drolysis processes requires the interaction between different types of microorgan-
isms (Kopsahelis et al., 2018; Sun et al., 2019).

13.7.3.1 Acidification

Acidification also known as biological acidification is a vital step in the production
of biogas. Higher rates of acidification will lead to higher methane production and