Alkaline pretreatment
Alkaline pretreatment uses bases, such as NaOH, Ca(OH)2, KOH,
and NH3$H2O, to remove lignin, hemicellulose, and/or cellulose,
rendering lignocellulosic biomass more degradable to microbes
and enzymes. Alkaline treatment with NaOH has been extensively
used in the pulp and paper industry. The function of alkaline pretreatment
is believed to be the saponification and cleavage of
lignin-carbohydrate linkages [149]. By removal of crosslinks, alkaline
pretreatment leads to an increase of porosity and internal
surface area, structural swelling, a decrease in the degree of polymerization
and crystallinity, disruption of lignin structure, and a
breakdown of links between lignin and other polymers. The
effectiveness of alkaline pretreatment is associated with the lignin
content of biomass materials [150].