The use of alkaline pretreatments is effective depending on the lignin content of the biomass. Alkali pretreatments increase cellulose digestibility and they are more effective for lignin solubilization, exhibiting minor cellulose and hemicellulose solubilization than acid or hydro-thermal processes [24]. Alkali pretreatment can be performed at room temperature and times ranging from seconds to days. It is described to cause less sugar degradation than acid pretreatment and it was shown to be more effective on agricultural residues than on wood materials [100]. In alkali hydrolysis possible loss of fermentable sugars and production of inhibitory compounds must be taken into consideration to optimize the pretreatment condi­tions. Sodium, potassium, calcium, and ammonium hydroxides are suitable alka­line pretreatments. NaOH causes swelling, increasing the internal surface of cellulose and decreasing the degree of polymerization and crystallinity, which provokes lignin structure disruption from 24-55% to 20% [101, 182]. The example of alkali hydrolysis cited below by using Lime pretreatment Ca(OH)2 removes amorphous substances such as lignin, which increases the crystallinity index. Lignin removal increases enzyme effectiveness by reducing non-productive adsorption sites for enzymes and by increasing cellulose accessibility [96]. Lime also removes acetyl groups from hemicellulose reducing steric hindrance of enzymes and enhancing cellulose digestibility [126]. Lime has been proven suc­cessfully at temperatures ranging from 85 to 150°C and for 3-13 h with corn stover or poplar wood [27]. Pretreatment with lime has lower cost and less safety requirements compared to NaOH or KOH pretreatments and can be easily recovered from hydrolysate by reaction with CO2 [126].