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318 Refining Biomass Residues for Sustainable Energy and Bioproducts
depletion (Bellido et al., 2013). The maximum ethanol concentration was enhanced
by the oxygen supply in ozonated wheat straw hydrolysates by increasing ethanol
production by 29.1%, and additionally the metabolism of xylose also improved.
Kaur et al. (2012) compared the alkali-treated with ozone-treated cotton stalks
for the ethanol production using thermotolerant Pichia kudriavzevii HOP-1. The
ethanol obtained 19.82 g/L from alkali-treated cotton stalks and 10.96 g/L from
ozone-treated cotton stalk (Kaur et al., 2012). The glucose obtained from alkali-
treated biomass and ozone-treated biomass in 48 g was around 65% and 53%,
respectively. This is because the alkali treatment causes the structural linkages
between lignin and carbohydrates to be separated as well as degrading the lignin
structure (Kaur et al., 2012). Meanwhile, the ozone treatment degraded lignin and
hemicellulose without affecting the cellulose content. Other than that, the ozonoly-
sis process has the advantage in that the reaction is carried out at atmospheric pres-
sure and temperature, which does not lead to any degradation and formation of
other products that might interfere the hydrolysis and fermentation process by Vidal
and Molinier (1988).
Other than that ozone pretreatment method, Papa et al. (2015) compared the
mild ionic liquid and pressurized hot water treatment method on switchgrass and
corn stover for the bioethanol production. The results indicated that ionic liquid pre-
treatment obtained higher bioethanol yield than the pressurized hot water treated
and untreated biomasses (Papa et al., 2015). Schultz-Jensen et al. (2013) did a com-
parison of five pretreatment technologies including hydrothermal pretreatment, wet
oxidation, steam explosion, PAP, and ball milling method for bioethanol production
and found that the ball milling method resulted in 64% higher raw material con-
sumption compared to untreated biomass for ethanol yield (Schultz-Jensen et al.,
2013). Moreover, the wet oxidation and ball milling obtained 42% higher raw
glucan-based ethanol yield compared to the untreated biomass and yielded around
77% ethanol yield. The hydrothermal pretreatment produced less formic acid and
extracted less sugar compared to wet oxidation and steam explosion. The steam
explosion method obtained the lowest ethanol yield due to high loss of glucan dur-
ing its pretreatment, while other pretreatments including hydrothermal, wet oxida-
tion, PAP, and ball milling increased the ethanol yield.
The ethanol production from lignocellulosic biomass could be significantly
improved by applying pretreatment method. The reaction parameter of each pre-
treatment depends on the type of biomass used, which would affect delignification
efficiency and sugar release yield.
14.3.2 Biohydrogen
Biohydrogen or biogas could also be better synthesized by applying pretreatment
method on the lignocellulosic biomass feedstock. The biohydrogen production is
generally conducted through the pretreatment, hydrolysis, and fermentation steps
(Wu et al., 2013a). The rate of enzyme hydrolysis could be improved, and fermenta-
tion yields can be increased by applying a suitable pretreatment method to compro-
mise the structure and composition of the biomass (Hendriks and Zeeman, 2009).