The technologies for biomass
pretreatment can be divided into five main categories, including 1)
physical (e.g., milling/grinding and extrusion); 2) thermal (e.g.,
torrefaction, steam explosion/liquid hot water pretreatment and
ultrasound/microwave irradiation); 3) chemical (e.g., treatment
with acids, bases and ionic liquids); 4) biological (e.g., fungal,
microbial consortium and enzymatic); and 5) above combined
pretreatments [174]