Table 2 Comparison of biological pretreatment with other pretreatment methods
| Pretreatment type | Merits or advantages | Common chemicals/solvents used | Constraints/limitation | References |
|---|---|---|---|---|
| Biological | ✓ Low use of energy and chemicals ✓ Able to degrade hemicellulose and lignin ✓ Environmentally sound | – | Have lower hydrolysis rate | Dunlop 2011; Monavari et al. 2009; Dionisi et al. 2014 |
| Organosolv | Able to depolymerize lignin and hemicelluloses | Acetone, formic acid, methanol, ethylene glycol, butanol, ethanol |
➢ Needs solvent recycling and draining ➢ Expensive ➢ Inhibitors are produced | Monavari et al. 2009 |
| Steam explosion | Able to depolymerize lignin and hemicelluloses | Steam |
➢ Xylan loss ➢ Partial depolymerization of components ➢ Inhibitors are produced | Galbe and Zacchi 2002;Wyman et al. 2005 |
| Alkali treatment |
➢ Able to take out lignin and hemicelluloses ➢ Increases the accessibility of the surface | Sodium hydroxide, calcium hydroxide, ammonia |
➢ Washing is required ➢ Salt formation causing fouling problems | Alexandropoulou et al. 2017; Narra et al. 2017 |
| Ozonolysis |
➢ Able to depolymerize lignin ➢ No inhibitory production | Ozone |
➢ High amount of ozone is required ➢ Expensive | Sun and Cheng 2002 |
| Ammonium fiber explosion |
➢ Increases the accessibility of the surface ➢ Able to depolymerize lignin and hemicellulose | Ammonia, water |
➢ Efficient problem ➢ Inhibitors are produced | Gupta and Lee 2009 |
| Acid treatment |
➢ Able to hydrolyze hemicellulose ➢ Modifies lignin structure | Sulfuric acid, nitric acid |
➢ Expensive ➢ Corrosive to equipment ➢ Inhibitors are produced | Pu et al. 2013; Mohapatra et al. 2017 |