Effect of particle size, moisture content, and supplements on selective pretreatment of cotton stalks by Daedalea flavida and enzymatic saccharification

A large amount of cotton stalk waste biomass with high cellulose content are incinerated by the farmers causing air pollution. The high cellulose content of cotton stalks can be converted to fermentable sugars by fungal delignification pretreatment of lignocellulosic biomass and enzymatic saccharification. The effect of particle size, moisture content, and media supplements was studied for delignification of cotton stalks by Daedalea flavida MTCC 145 (DF-2) in solid-state fermentation. The highest lignolytic enzyme activities, optimal lignin degradation 29.88 ± 0.97% (w/w) with cellulose loss 11.70 ± 1.30% (w/w), were observed in cotton stalks at particle size 5 mm with 75% moisture content after 20 days. Cellulolytic enzyme activity increased with decrease in particle size and increased moisture content. The addition of Cu2+, gallic acid, and veratryl alcohol enhanced the lignolytic enzyme production and the lignin degradation. In addition to increased laccase activity, Cu2+ inhibited the cellulolytic activity. Supplements Cu2+ at 0.5 mM/g gave the best results of lignin degradation 33.74 ± 1.17% (w/w) and highest selectivity value (SV) 3.15 after pretreatment. The glucose yield increased to 127.44 ± 4.56 mg/g from 20 day pretreated cotton stalks with Cu2+ supplements, ~threefolds higher than untreated cotton stalks. The study is important for the production of fermentable sugars from cotton stalks residues which can further be utilized in production of bioethanol and other applications.