Page 543 - Refining Biomass Residues for Sustainable Energy and Bioproducts

492 Refining Biomass Residues for Sustainable Energy and Bioproducts

22.3.2 Thermal pretreatment

The hydrolyzing organic constituents present in the organic wastes is used to
enhance the AD method (Banu et al., 2018a, 2019; Kavitha et al., 2014a). Thermal
pretreatment results in elevated disintegration of organic waste components that
endorse transfer of the disintegrated components in absence of oxygen to biogas
during the production of volatile organic acid and also it is an easy and fastest
method of pretreatment (Agyeman and Tao, 2014). Thermal pretreatment methods
are categorized into wet and dry types. In wet temperature the waste can be
hydrolyzed through high temperature and pressure and gives better solubilization.
The change of pH also additionally progresses the efficiency of thermal pretreat-

ment. During high temperature (150 C), the recalcitrant compounds can be
formed, and at the same time, low temperature affects the recovery of product
(Ariunbaatar et al., 2014).

22.3.3 Chemical pretreatment
Chemical pretreatment is a valuable technique in which the disintegration of
organic constituents is done by strong to mild chemical agents (acids, alkali, and
oxidants) (Banu et al., 2012; Packyam et al., 2015; Kannah et al., 2017a). From
these methods, oxidation was considered as an effective method that results in high-
er sludge solubilization with negotiated biogas production (Cabrol et al., 2017).
However, these chemicals alter the characteristics of waste. Disadvantages of chem-
ical pretreatment are the presence of amassing inhibitors such as eight furanic or
phenolic compounds. The alkali disintegration entails greater reaction time than
acid pretreatment with the drawback of salt formation (Chakraborty et al., 2018).

22.3.4 Combined pretreatment

Combined pretreatment process is the combination of one or two pretreatment
methods, which results in enhanced sludge solubilization and ended up in higher
biogas production (Banu et al., 2018b,c; Kavitha et al., 2015; Kannah et al., 2017b,
2019). Numerous researches reveal that the grouping of thermal and mechanical
into physical and grouping of alkali and acid into chemical had been done to attain
a higher methane production (Fisgativa et al., 2017).

22.3.5 Biological pretreatment

Biological pretreatment advocates for the development and maintenance of ecologi-
cal sustainability (Banu et al., 2018c; Kavitha et al., 2013, 2014b; Lakshmi et al.,
2014). AD has been improved by the disintegration of organic components by
diverse microbial systems (Kiran et al., 2014). This is a typically deliberate method
that involves greater time and controlled environmental conditions for microbial
growth. Development and isolation of new microorganism for the improvement of