Table 2.

Overview of pretreatment methods for lignocellulosic biomass

	Size reduction	Fractionation	Reduction of cellulose crystallinity	Dissolution of lignin	Dissolution/hydrolysis of hemicellulose	Dissolution/hydrolysis of cellulose	Delignification	Removal of aromatic compounds	References
Physical
Milling, etc.	+	+							Holtzapple et al. (1991), Licari et al. (2016)
Irradiation			+						Jusri et al. (2018)
Chemical
Acidic pretreatment				+	+	+			Kucharska et al. (2018),
Alkaline pretreatment			+						Rabemanolontsoa and Saka (2016), Xu et al. (2010)
Organic solvents					+	+	+		Kucharska et al. (2018), Schmetz et al. (2019)
Ionic liquids, DES						+	+		Remsing et al. (2006), Yu et al. (2019)
Oxidation processes				+	+	+			Hendriks and Zeeman (2009), M'Arimi et al. (2020)
Physicochemical
Liquid Hot Water					+				Kumar et al. (2009), Yu et al. (2016)
Steam explosion		+		+	+	+			Kim (2018)
Supercritical water		+							Akalın et al. (2017), Peterson et al. (2008)
AFEX			+						Holtzapple et al. (1991), Mes-Hartree et al. (1988)
ARP					+		+		Mes-Hartree et al. (1988), Yoon et al. (1991)
Ultrasound				+	+	+			Bussemaker et al. (2013)
Biological
Wood-rot fungi							+	+	Akin et al. (1995), Dionisi et al. (2015), Kerem et al. (1992), Sun and Cheng, (2002)
Enzymes					+	+	+	+	Bayer et al. (2004), Gutiérrez et al. (2012), Prawitwong et al. (2013), Rabemanolontsoa and Saka (2016)