Glucan Digestibility

1. Xylan Lignin ( All compositions are on the basis of untreated dry biomass) Xylan Lignin Glucan Digestibility ( All compositions are on the basis of untreated dry biomass) LL hybrid poplar HL hybrid poplar Xylan Digestibility Glucan Digestibility LL hybrid poplar HL hybrid poplar Corn Stover HL hybrid poplar LL hybrid poplar Xylan Digestibility Corn Stover LL hybrid poplar HL hybrid poplar Effect of xylanase supplementation on enzymatic digestion of ammonia treated biomass Rajesh Gupta, T H Kim & Y Y Lee Department of Chemical Engineering Auburn University Abstract Composition of biomass is one of the key factors affecting the pretreatment. To further delineate it, we have applied pretreatments based on aqueous ammonia to three different substrates with widely varying compositions, i.e., corn stover, high lignin (HL) hybrid poplar, and low lignin (LL) hybrid poplar. Pretreatments were applied by two different methods: Ammonia Recycle Percolation (ARP) and Soaking in Aqueous Ammonia (SAA). ARP and SAA are both highly efficient in delignifying the biomass. Yet they retain most of the carbohydrates in the solid after pretreatment. Since most cellulases have xylanase activity as well as cellulase activity, sugars are obtained directly from solid by enzymatic hydrolysis. This is a significant economic benefit since it eliminates the need of detoxification of hemicellulose sugars in liquid stream. For treated corn stover, the overall enzymatic digestibility was in the vicinity of 90% with 15 FPU loading of Spezyme CP. With poplar feedstocks, the digestibilities were lower than that of corn stover. In order to achieve acceptable level of enzymatic digestibility of both glucan and xylan, supplementation of external xylanase was necessary. Xylanase supplementation increases not only the digestibility of xylan but also the digestibility of glucan. With xylanase addition, the overall sugar yield from SAA/ARP treated low lignin hybrid poplar has increased from 70%/61% to 90%. Although the digestibilities of ARP or SAA treated corn stover is higher than poplar in general, the net increase of digestibility by xylanase addition was insignificant. Pretreatment by Aqueous Ammonia SAA (Soaking in Aqueous Ammonia) Treatment Optimum Conditions: • ARP • (Ammonia Recycle Percolation) • Flow through Reactor • High Temperature • Short Pretreatment time • (several min.) • SAA • (Soaking in Aqueous Ammonia) • Batch Reactor • Low Temperature • Long Pretreatment time • (several hours) Corn stover: Temperature (60°C), Reaction time (12hrs), Ammonia concentration (15%), Liquid :Solid (8:1) Hybrid Poplar: Temperature (150°C), Reaction time (24hrs), Ammonia concentration (15%), Liquid :Solid (10:1) Effect of SAA treatment on Composition ARP (Ammonia Recycle Percolation) Treatment Optimum Conditions: Corn stover: Temperature (170°C), Reaction time (20min), Ammonia concentration (15%), Liquid :Solid (3.33:1) Hybrid Poplar: Temperature (185°C), Reaction time(27.5min), Ammonia concentration(15%), Liquid :Solid(3.67:1) Effect of Xylanase supplementation on Digestibility of SAA-treated Poplar Effect of ARP treatment on Composition Effect of Xylanase supplementation on Digestibility of ARP treated Biomass Enzyme Used: Cellulase : GC220 (Supplied by Genencor Int.); Cellobiase: Novo 188 ( Sigma; cat: C-6150); Xylanase: Multifect Xylanase (Supplied by Genencor Int.) 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) (Enzyme loadings are same as shown in ARP section) Overall Sugar Yield in SAA treatment (Sugar yield from pretreatment liquor is not included here) Summary • The ratio of Lignin/Xylan (L/X) is an important factor controlling retention of sugar • in the pretreatment by aqueous ammonia. • Substrates with high L/X value are difficult to treat with ammonia. • Significant amount of the hemicellulose is dissolved into liquid during the pretreat- • ment of corn stover. The dissolved hemicellulose is difficult to utilize. • ARP and SAA treatment on LL Poplar resulted high digestibility as well as high • hemicellulose retention. • Xylanase supplementation increases the digestibility of ammonia treated biomass. • Increase of sugar yield by xylanase supplementation is proportional to the xylan • retained in solids after pretreatment. • With Xylanase supplementation, the pretreatment can be conducted under low • severity and still attain high digestibility. The low severity condition lowers the toxin • levels in fermentation, thus enhances the fermentation efficiency. Overall Sugar Yield in ARP treatment 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 (Sugar yield from pretreatment liquor is not included here)