Table 1.

Application based pretreatment methods and related pros as well as cons.

Application	Pretreatment Methods		Pros	Cons	Refs.
Agriculture sector Biofuels and manure Enzymatic digestibility Ethanol production Bio-oil and biochar formation Food sector Bioactive compounds Nutraceuticals Ethanol and enzyme production	Physical	Grinding	From biomass, a fine powder with a crystallinity of up to 0.2 mm is produced.	Lack of long-term viability in technique calls for a lot of energy.	[27,28,29,30,31,32]
		Ultrasonic	Easing the process of breaking down a variety of lignocellulosic materials.	Collisions between particles during prolonged sonication could result in an antagonistic effect.
		Steaming explosion	Minimal need for energy.	Incomplete lignin-carbohydrate matrix cleavage, xylan fraction destruction, creation of hydrolysis, and fermentation inhibitors.
		Microwave	Easily functional, and with efficiency in handling large agro-waste with fewer inhibitors being formed.	This causes both a rise in temperature and an increase in the amount of electricity used.
		Pyrolysis	The highest possible rate of cellulose sugar conversion.	High-cost technique.
		Irradiations	The surface area was increased, crystallinity was reduced, hemicelluloses were hydrolyzed, and the structure of lignin was altered.	Expensive method.
Pharma sectorSugars (glucose, xylose, mannose, and galactose) and organic acids (formic, acetic acid) production Agriculture sector Enzymes production, organic acids, and hydrolysis of agro-waste to increase glucose yield Biorefinery Biomass saccharification, bioethanol and biogas production Food sector Extraction of phenolic compounds and acids productions	Chemical	Acid hydrolysis (HCl, CH3COOH, H2SO4)	Change the structure of lignin, and hydrolyze hemicellulose to xylose and other sugars.	Corrosion of expensive equipment and the production of harmful byproducts are additional costs.	[2,29,33,34,35]
		Alkaline hydrolysis (KOH, NaOH, NH4OH, Mg(OH)2, Ca(OH)2	Pretreatment under milder conditions. Removing lignin and hemicelluloses raises the available surface area.	High alkalinity concentrations and lengthy residence durations are necessary.
		Ozonolysis	Decreases lignin content. Does not indicate the production of hazardous substances.	Method that is both expensive and demanding of a substantial quantity of ozone.
		Organosolv	Hydrolyzes lignin and hemicellulose; helpful for lignin extraction.	Due to their high volatility, costly solvents are unsuitable for industrial use.
		Wet oxidation	Effectively eliminated lignin and low formation inhibitors.	Expensive because of the utilization of oxygen and acid catalyst.
Agriculture sector Animal manure and biofertilizers Biorefinery and animal feed Pharma sector Antibiotics production Food sector Single cell protein	Biological	Enzyme	Moderate circumstances are present, and minimal effort is necessary.	Low hydrolysis rate and a large sterile space requirement.	[13,23,36,37]
		Bacteria	Economical and requiring only mild reaction conditions.
		Fungi	Inexpensive, destroys lignin and hemicelluloses, minimal energy needs.
Food and pharma sectors Antibiotic production Antioxidant properties Antibacterial and anticancer properties	Green solvents	Ionic liquids	Effective at dissolving copious amounts of cellulose and recovering usable cellulose from lignin.	Possible toxicity, prohibitively expensive method, and a lack of practicality for mass production.	[38,39,40]
		Deep eutectic solvents	Conditions are modest but environmentally friendly and safe.	Creates undesirable contaminants and higher viscosity on occasion.
		Natural deep eutectic solvents	Low-cost, readily available, highly modifiable, and less hazardous.