1. Abstract NaOH and its derivatives are used as pulping reagents, wherein the spent NaOH is recovered in salt form and reused. In this study, low concentration of NaOH (approx. 1-5%) was used for pretreatment of corn stover and high lignin (HL) hybrid poplar. It was done with the understanding that NaOH can be recovered. In alkaline pretreatments, it is technically feasible to retain most of carbohydrates while removing large fraction of lignin in the biomass. The enhancement of digestibility is caused primarily by lignin removal. Retention of hemicellulose after pretreatment gives a significant economic benefit since it eliminates the need of detoxifying hemicellulose sugars. The main objective of this study is to see if NaOH treatment can achieve that goal. From the results, the optimum process conditions were identified for each of the feedstocks on the basis of carbohydrate retention and digestibility of treated solid. Among the noteworthy findings was that corn stover, after treated with NaOH under moderate conditions, attains near 100% glucan digestibility. On the other hand, hybrid poplar required treatment with much higher severity, in terms of temperature and NaOH concentration, in order to attain acceptable digestibility. It is found that hydrogen peroxide supplementation in pretreatment of hybrid poplar helps in retaining the sugar in solids and further enhances the delignification thus digestibility of solids. Xylanase supplementation during the enzymatic digestibility of treated hybrid poplar drastically improves the sugars yields. Corn Stover Untreated corn stoverTreated with 15% ammoniaTreated with 1.5% NaOH SEM Pictures of Untreated and treated Corn stover High Lignin Hybrid Poplar Effect of NaOH treatment on composition and Digestibility Treatment Conditions: Temperature ( 60°C); Time (24hrs); Solid:Liq.(1:10) NaOH treatment at very mild conditions Treatment Conditions: Concentration (1%); Temperature ( 60°C) Time (24hrs); Solid : Liquid (1:10) Glucan Digestibility Xylan Digestibility Enzyme Loading: C+β-G : Cellulase (15FPU/g glucan) + Cellobiase (30CBU/g glucan) Enzyme Loading: C+β-G : Cellulase (15FPU/g glucan) + Cellobiase (30CBU/g glucan) C+ β-G +X : Cellulase (15FPU/g glucan) + Cellobiase (30CBU/g glucan) + Xylanase (31.3mg protein/g glucan) Glucan Digestibility Xylan Digestibility Composition Composition and Digestibility( With and Without Xylanase add.) of NaOH treated Corn stover Overall Sugar Yield Effect of NaOH treatment on composition and Digestibility Treatment Conditions: Temperature ( 80°C); Time (24hrs); Solid:Liq.(1:10) (Sugar yield from pretreatment liquor is not included here) Without Hydrogen Peroxide With Hydrogen Peroxide (5% conc. In Liquid) Glucan Digestibility Xylan Digestibility Effect of Xylanase supplementation Enzyme Loading: C+β-G : Cellulase (15FPU/g glucan) + Cellobiase (30CBU/g glucan) Treatment Conditions: Temperature ( 80°C); NaOH Conc. (5%) H2O2 Conc. (5%); Time (24hrs); Solid:Liq.(1:10) Glucan DigestibilityXylan Digestibility Enzyme Loading: C+β-G : Cellulase (15FPU/g glucan) + Cellobiase (30CBU/g glucan) C+ β-G +X : Cellulase (15FPU/g glucan) + Cellobiase (30CBU/g glucan) + Xylanase (31.3mg protein/g glucan) Overall Sugar Yield (Sugar yield from pretreatment liquor is not included here) Enzymes Used: Cellulase : GC220 (Supplied by Genencor Int.) Cellobiase: Novo 188 ( Sigma; cat: C-6150) Xylanase: Multifect Xylanase (Supplied by Genencor Int.) Summary NaOH is very effective in delignification of corn stover. Treated under moderate conditions of 60°C temp. and 1.5% concentration, the glucan digestibility above 90% is obtained. Treated at 25°C and 1%NaOH, corn stover retains more carbohydrates in solids, and still gives 73% of overall sugar yield if enzymatic hydrolysis is done with xylanase addition. Summary (Contd.) HL hybrid poplar is more difficult to delignify, thus requires treatment conditions with high severity. Addition of 5% hydrogen peroxide in NaOH treatment increases the delignification, helps retaining the carbohydrates, and significantly improves the glucan digestibility. Hydrogen peroxide addition also reduces the Na + conc. in pretreatment liquor. It appears that hydrogen peroxide promotes NaOH induced lignin degradation. As an oxidizing agent, hydrogen peroxide helps in stabilizing the reducing end in polysaccharide thus lowering the sugar degradation. Summary (Contd.) The effect of hydrogen peroxide is higher with higher conc. of NaOH. The overall sugar yield in enzymatic digestion of NaOH/H 2 O 2 treated poplar is drastically improved by xylanase supplementation. Acknowledgement US Department of Energy for funding the project (US/DOE No. DE-PS36-00GO10482) Members of CAFI-II team Genencor International Inc. for supplying enzyme