Table 4.

Purposes of the pretreatment strategies and their advantages and disadvantages.

Pretreatments	Preferred Natural Fibres	Purposes	Advantages	Disadvantages
Physical	Hardwoods and agricultural residues	Enhance the digestibility of lignocellulosic biomass by increase the available specific surface area, and reduce both the degree of polymerisation and cellulose crystallinity	(1) No recycling cost (2) No chemical usage (3) Increase biogas, bioethanol and biohydrogen yields	(1) Excessive size reduction decreases biofuel production (2) Formation of fermentation inhibitors at high temperature (3) Incomplete digestion of lignin-carbohydrate matrix (4) The need to wash the hydrolysate decreases sugar yield (5) High energy requirement
Biological	Hardwoods, softwoods, and agricultural residues	Leverage the action of fungi capable of producing enzymes that can degrade lignin, hemicellulose, and polyphenols	(1) The depolymerisation is very selective and efficient (2) Low-capital cost (3) Low energy requirement (4) No chemicals requirement (5) Mild process conditions	(1) The rate of biological pretreatment is too slow for industrial purposes (10–14 days) (2) Require careful growth conditions and a large amount of space (3) A fraction of carbohydrate is consumed by the microbes, thus reduces the sugar yield