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226 Refining Biomass Residues for Sustainable Energy and Bioproducts

white-rot fungi have been applied for the pretreatment purpose, which include
genus such as Phanerochaete, Fusarium, Ganoderma, Tricholoma, Trametes,
Pleurotus, Schizophyllum, Cerrena, Cerporiopsis, and Coprinopsis (Gahlout et al.,
2017; Prom et al., 2003; Rudakiya and Gupte, 2019; Rudakiya et al., 2018;
Shirkavand et al., 2016). Mishra et al. (2017a,b) observed that fungal pretreatment
(Coriolus versicolor) on sweet sorghum bagasse increased the lignin removal and
retained cellulose content, and the addition of gallic and syringic acid enhanced the
lignin removal by 1.56-folds more than the control, whereas the addition of CuSO 4
and syringic acid enhanced the lignin removal by 1.86-folds.
10.3.4 Combinatorial

This type of method is used to overcome the disadvantages of different methods.
The mixture of physical chemical, physical biological, chemical biological, and
thermal biological pretreatments are applied, and later on, the treated biomass is
enzymatically hydrolyzed to produce ethanol, acetone, butanol, and other value-
added chemicals from sorghum (Jafari et al., 2016; Kumari and Singh, 2018;
Rabemanolontsoa and Saka, 2016; Shirkavand et al., 2016). Li et al. (2016b)
adopted the two-stage pretreatment method, that is, acid (H 2 SO 4 ) followed by alkali
(NaOH) and vice versa on sweet sorghum bagasse and observed that acid alkali
treatment improved the cellulose hydrolysis effectively, whereas the solids recovery
was found better in alkali acid treatment and single-stage pretreatments using

alkali or acid. Optimal hydrothermal (170 C for 30 min) treatment followed by
alkali (2% NaOH) treatment on sweet sorghum stalks helped to decrease the recal-
citrance and improved its hydrolysis yield (Sun et al., 2015).
10.3.5 Emerging technologies

Nonthermal technologies, such as microwave irradiation, high hydrostatic pressure,
electron beam, homogenization under high pressure, ultrasound, and gamma ray,
have been utilized for food processing at large scale. These technologies play a sub-
stantial role in pretreatment of lignocellulosic biomass content (Hassan et al., 2018).
Microwave, an electromagnetic radiation, ranging from 300 to 300,000 MHz on
the electromagnetic spectrum is a nonionizing radiation which transmits energy to
the material in specific manner. In addition, various chemicals in combination with
microwave irradiation are also being used to enhance degradation of lignocellulose
components. In recent times, microwave-assisted pretreatments have been utilized
to produce value-added chemicals, biooil, biochar, and other by-products. It is clas-
sified based on temperature; where mild-temperature reaction occurs at less than

200 C and high-temperature reaction occurs at more than 400 C. Microwave-

assisted method has various advantages when compared to the conventional heating
method: (1) reaction time is less, however, heat transfer rate is higher; (2) it can
save energy as compared to conventional methods; (3) uniform heating performance
observed during operation; and (4) by-products are also produced during the reac-
tion (Hassan et al., 2018; Huang et al., 2016). Recently, various researchers have
opted for microwave-assisted approaches to produce bioethanol from sweet