Overall Sugar Yield in SAA treatment

1
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 (60C), Reaction time
(12hrs), Ammonia
concentration (15), Liquid Solid (81)
Hybrid Poplar Temperature (150C), Reaction time
(24hrs), Ammonia
concentration (15), Liquid Solid (101)
Effect of SAA treatment on Composition
ARP (Ammonia Recycle Percolation) Treatment
Optimum Conditions
Corn stover Temperature (170C), Reaction time
(20min), Ammonia
concentration (15), Liquid Solid (3.331)
Hybrid Poplar Temperature (185C), Reaction
time(27.5min), Ammonia
concentration(15), Liquid Solid(3.671)
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 Cß-G
Cellulase (15FPU/g glucan) Cellobiase (30CBU/g
glucan) C ß-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)