Table 5.
Different pre-treatment strategies used for biomass processing and sugar recovery.
| Pre-Treatment Strategies | Operating Conditions |
Mechanism | References |
|---|---|---|---|
| Physical | |||
| Milling and grinding | Drying, milling to fine or coarse powder | More surface area, improve flow properties, increase the bulk density and porosity | [68,69] |
| Irradiation | γ-radiation and electron beam | Scission of glycosidic bonds in polysaccharides and destruction of the cell wall | [70,71] |
| Physico-chemical treatment | |||
| Autohydrolysis and steam explosion | 160–260 °C and 5–50 atm pressure 1% acid may be added |
The complex structure of LCB is disrupted due to the expansion of steam | [72,73] |
| Microwave radiation (MWR) | MWR/water, MWR/alkali, MWR/acid, MWR/ionic liquid, MWR/salt |
Accelerates cellulose dissolution in ionic liquids, removes hemicellulose and lignin | [74] |
| Chemical treatment | |||
| Acid | CH3COOH, HCl and H2SO4 (Dilute or concentrated acid) |
Disruption of the hydrogen bonds and covalent bonds, solubilization of hemicellulose and reduction of cellulose complexity | [75] |
| Alkali | KOH, NaOH, Ca(OH)2, Ammonia (ammonia fiber expansion) | Destruction of lignin, reduction of the degree of polymerization of hemicellulose, lower crystallinity of cellulose | [76,77,78] |
| Ionic liquids | 1-butyl-3-methyl-imidazolium acetate, cholinium ionic liquid, etc. | Attachment of hydrogen bonds to dissociate the lignocellulose complex | [79] |
| Biological treatment | |||
| Microbiological treatment | Yeast, fungi, micro-algae, bacteria | Enzymes break respective bonds and depolymerize/solubilize polymers | [79,80,81] |
| Enzymatic hydrolysis | Xylanases and cellulases | ||
| Nanotechnology in biomass pretreatment | |||
| Nanoparticles of metal/biopolymers | Acid/base/enzymes/microbes | Nanoparticles improve the delivery of agents and enhance the activity | [79,82,83] |