Various Types of Pretreatment
- • Numerous pretreatment technologies can be used to accomplish the abovemen- tioned objectives of pretreatment. These include physical, chemical, physicochemical, and biological pretreatment.
- • Physical pretreatment: These are energy-intense processes that include grinding and milling, microwave and extrusion, etc., that physically break the plant cell wall to improve their digestibility for the further conversion into biofuels (Yang and Wyman 2008).
- • Chemical pretreatment: These pretreatments include the action of chemicals, e.g., acidic, alkaline, oxidizing agents, ammonia, SO2, solvents, etc. Chemical pretreatment includes dilute acid pretreatment, steam explosion, ammonia fiber explosion (AFEX), sulfite processing, organosolv pretreatment, CO2 explosion, ionic liquid, and wet oxidation, etc. (Yang and Wyman 2008).
- • Physicochemical pretreatment: Physicochemical pretreatment is the combination of physical and chemical pretreatments and is the most commonly applied pretreatment process to break down the lignocellulosic biomass.
- • Biological pretreatment: This type of pretreatment uses microorganisms to degrade lignin, hemicellulose, and cellulose. Brown-, white-, and soft-rot fungi are used to treat biomass and to enhance enzymatic hydrolysis (Kumar et al. 2009). White-rot fungi are recognized to be one of the most effective microorganisms for lignocellulosic biomass degradation (Vares et al. 1993; Kumar et al. 2009).