Energy Fuels 2010, 24, 4454–4458 Published on Web 08/02/2010
: DOI:10.1021/ef1002155
Suitability of Canola Residue for Cellulosic Ethanol Production Nicholas George,*,† Ying Yang,‡ Ziyu Wang,‡ Ratna Sharma-Shivappa,‡ and Kim Tungate† †
North Carolina Solar Center, North Carolina State University, and ‡Department of Biological and Agricultural Engineering, North Carolina State University Received June 29, 2009. Revised Manuscript Received July 21, 2010
The acreage of winter canola in the Southeastern United States is presently limited but is expected to increase in the future as demand for biodiesel grows. The residue production of canola is known to be relatively high in comparison to other grain crops. Only the seed of canola is currently harvested and utilized, but if canola is to be grown more widely the crop residue could potentially be used for biofuel production. This proof of concept study investigated the value of canola crop residue as a feedstock for cellulosic ethanol production. The mean dry yield of residue for canola was found to be approximately 9 Mg/ha, which is higher than for other common winter crops produced in the Southeast. Cellulosic ethanol production from the residue was investigated through acid (H2SO4) and alkali (NaOH) pretreatment followed by enzymatic hydrolysis with cellulase and cellobiase and hexose fermentation with Saccharomyces cerevisiae. The ethanol yield from the biomass was relatively low, at around 95 L per dry tonne, suggesting the potential of canola residue for cellulosic ethanol production is poor. However, given the high residue productivity of canola, its use for cellulosic ethanol production clearly needs to be studied further.
could be considered. Crop wastes are being investigated as a potential feedstock for biofuel production.5 The residue production of canola is known to be high compared to other grain crops, so depending on its composition, the residue of canola could be valuable for ethanol production and provide growers with an alternative revenue stream. The potential of canola biomass as a biofuel feedstock has not been previously investigated. The objective of this study was therefore to make an initial proof of concept investigation of the value of canola crop residue as a feedstock for cellulosic ethanol production.
Introduction Demand for biodiesel is growing rapidly in the United States, with a 150-fold increase in production capacity from 23 million to 3.3 billion gallons per year between 2004 and 2008.1 The need for vegetable oil feedstock to produce biodiesel is currently met largely by soybeans, but to satisfy this rapidly growing demand, alternative crops are also being examined, with winter canola (Brassica napus) currently considered to be a good-prospect species. The high value of canola as a biodiesel feedstock crop is well established; biodiesel manufactured from canola oil has superior cold flow and combustion properties compared to biodiesel produced from soy oil.2 In addition, work shows that canola has considerable potential to be grown successfully throughout much of the Eastern and Southeastern U.S.3 This work focuses on the Southeastern U.S. The area of canola planted in the Southeast is presently limited but is expected to increase in the future as demand for biodiesel grows. The area that will finally be cultivated is unknown, but given that winter canola is an alternative to winter wheat, some portion of the wheat cropping land in the Southeast, which was approximately 500 000 ha in 2007,4 could potentially be converted to canola production. Only the seed of canola is harvested and utilized, but if canola is to be grown more widely, other uses for the crop
Experimental Section Canola biomass was obtained from 28 canola varieties grown as part of a Kansas State University National Winter Canola Variety trial at the North Carolina State University Central Crops Research Station, Clayton, North Carolina. The trial was planted in October 2006 and harvested in June 2007. A 1.7 m2 area of each variety was harvested. Plants were cut 10 cm above ground level, the biomass was removed, and the material dried at 45 °C for 24 h before being stored in cloth bags. Material was threshed to remove seeds, and then the remaining biomass, comprising stems and seedpods, was weighed. A separate subsample of both the stem and pod material was taken from each bag, and material from all the varieties was bulked. The bulked material was ground to pass through a 1 mm sieve and stored at room temperature. The mean yield of residue for winter wheat and barley in the Southeastern United States was estimated using the mean grain yield for both crops between 1997 and 20074 and the straw/grainratio reported for these crops.6 Pretreatment of Canola Pods and Stem. Both acid and alkali pretreatments were applied to pod and stem samples. The biomass (5 g) was mixed with 0.5% or 1.5% (w/v) sulfuric acid
*To whom correspondence should be addressed. The Department of Horticultural Science, 214 Kilgore Hall, Campus Box 7609, Raleigh, NC 27695. Phone: 919-515-5958. E-mail:
[email protected]. (1) EMO Biodiesel 2020: Global market survey, case studies and forecasts; Emerging Markets Online (EMO): Houston, TX, 2008. (2) Gerpen, J. V. In Quality characteristics of brassica-based biodiesel, 2006 U.S. Canola Research Conference, In conjuction with the international annual meetings of the American Society of Agronomy (ASA), Crop Science Society of America (CSSA) and Soil Science Society of America (SSSA), Indianapolis, IN, U.S. Canola Association: Indianapolis, IN, 2006. (3) Stamm, M.; La Barge, C. 2006 National Winter Canola Variety Trial; Kansas State University: Manhattan, KS, 2007. (4) The United States Department of Agriculture National Agricultural Statistics Service (USDA NASS), 2008, www.nass.usda.gov. r 2010 American Chemical Society
(5) Perlack, R. D.; Wright, L. L.; Turhollow, A. F.; Graham, R. L.; Stokes, B. J.; Erbach, D. C. Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply; U.S. Department of Energy, U.S. Department of Agriculture: Oak Ridge, TN, 2005; p 78. (6) Klass, D. L. Biomass for Renewable Energy. In Fuels and Chemicals; Academic Press: Sydney, Australia, 1998; p 651.
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was modified to determine monomeric sugars using a high-performance liquid chromatograph (HPLC) (Shimadzu, Kyoto, Japan) equipped with a refractive index detector (Shimadzu RID-10A). Samples were filtered through 0.2 μm syringe filters before being injected into a Biorad Aminex HPX-87H column maintained at a working temperature of 65 °C with a corresponding guard column. The mobile phase used was 5 mM H2SO4 at a flow rate of 0.6 mL/min. Liquid samples obtained from acid insoluble lignin analysis of the unpretreated biomass were neutralized, to a pH between 5 and 6, with calcium carbonate prior to HPLC analysis. Reducing sugars (represented by glucose, xylose, arabinose, and cellobiose) in the hydrolysates and the ethanol content of fermentation broths were also measured using the same HPLC procedure but by including cellobiose or ethanol as a standard during calibration. Ethanol yield was calculated by dividing the total amount of ethanol produced (grams of ethanol) in the fermentation broth by initial weight of sample processed (grams of unpretreated biomass). The fermentation efficiency was calculated using eq 1:13,14 E 100% ð1Þ fermentation efficiency ð%Þ ¼ 0:511G
(H2SO4) or sodium hydroxide (NaOH) solutions at 10% solid loading and pretreated by autoclaving at standard liquid cycle conditions of 121 °C and 15 psi (103.4 kPa) for 60 min. Selection of treatment agent concentrations for this study was based on previous work on various lignocellulosic feedstocks.7,8 The pretreatment temperature was maintained at low levels in this study to potentially reduce sugar degradation, formation of inhibitors like furfurals, and also operating costs in scaled up operations. Room cooled, pretreated slurries were filtered through a porcelain Buchner funnel, and residual chemicals on the surface of pretreated biomass were washed with 250 mL of hot deionized water. A portion of the washed and filtered pretreated biomass was dried in a 105 °C convection oven to determine the solid recovery. The remaining wet pretreated samples were stored in zip-lock bags at room temperature for subsequent hydrolysis and fermentation within 28-30 h. The filtrate was not analyzed or used in this study. Enzymatic Hydrolysis. Enzymatic hydrolysis was performed on unpretreated and pretreated biomass samples equivalent to 0.5 g of dry matter in 0.05 M citrate buffer (pH 4.8) at 5% solid loading (on dry matter basis)9 with cellulase (Novozymes NS 50013 cellulase complex, activity 75.5 FPU (filter paper units)/mL) at 30 FPU/ g of dry biomass. Cellobiase (Novozymes NS 50010 β-glucosidase, activity 634.2 CBU (cellobiase units)/mL) was added to the cellulase complex at an activity ratio of 1 FPU-4 CBU to avoid end-product inhibition due to cellobiose accumulation. Hydrolysis was conducted in a water bath at 55 °C and 150 rpm for 72 h. Upon completion of hydrolysis, 0.5 mL of the 10 mL hydrolyzate was taken for reducing sugar (cellobiose, glucose, xylose) analysis using HPLC. The unhydrolyzed residue was not analyzed. Fermentation. The hydrolyzate (9.5 mL) was fermented by adding 125 μL of Saccharomyces cerevisiae (ATCC 24859) culture inoculum at an initial yeast cell concentration of 11 g/L. The inoculum was prepared by adding 1.0 mL of a 30% glycerol yeast stock, maintained at -80 °C, to 100 mL medium containing 20 g of glucose, 8.5 g of yeast extract, 1.32 g of NH4Cl, 0.11 g of MgSO4, and 0.06 g of CaCl2 per 1 L of deionized water7 and culturing aerobically in a water bath at 30 °C and 150 rpm for 48-72 h. Yeast cells were harvested from the culture by centrifugation (model 5810R, Eppendorf ) at 4000 rpm and 4 °C for 10 min, washed twice with 50 mL of 0.1% sterilized peptone water to remove residual media and resuspended in peptone water before use. Fermentation was conducted in airtight centrifuge bottles in an incubator at 30 °C for 48 h. At the end of the fermentation period, an aliquot of the fermentation broth was analyzed for residual glucose and ethanol contents. Composition Analyses. Biomass characteristics, namely, total solids, ash, acid insoluble lignin (AIL), acid soluble lignin (ASL), and structural carbohydrates (represented by glucose, xylose, and arabinose), were measured according to Laboratory Analytical Procedures (LAPs)10-12 released by the National Renewable Energy Laboratory (NREL). The LAP for carbohydrate analysis
where 0.511 is the theoretical ethanol yield (in grams) generated per 1 g of glucose; E=concentration of ethanol after fermentation (g/L); G=glucose concentration in hydrolysate before fermentation (g/L). Statistical Analyses. In this study, a 95% confidence level was used for the analysis of variance (ANOVA) through SAS (version 9.1.3, Cary, NC) to determine the effects of various pretreatment methods on the final ethanol yield.
Results and Discussion The yield of cellulosic biomass obtained from the canola plots is presented in Table 1. It was shown that the production of residue by canola is relatively high compared to winter wheat and barely, which are the other major winter crops produced in the Southeastern United States. The mean residue yield of canola was found to be 9.3 Mg/ha, with a maximum value of 16 Mg/ha, compared to 3.9 and 5.2 Mg/ha for winter wheat and barley, respectively. Furthermore, although the potential yield of Switchgrass (Panicum virgatum) in the Southeast could be as high as 25 Mg/ha,15 the long-term average biomass production of Switchgrass in the region is still estimated to be approximately only 15 T/ha.16 So biomass production potential of winter canola is comparatively high. The proportion of harvested biomass comprising stem material was found to be 83% and pods 17% (5% standard deviation for each). Composition of Canola Stem and Pod Residue. Canola pod and stem samples were analyzed for carbohydrate (glucan, xylan, and arabinan), lignin (both acid-insoluble and acidsoluble), and ash content (Figure 1). The moisture content in pod and stem samples was found to be 5.5% and 5.3%, respectively. Canola stems had higher carbohydrates and lower lignin content compared to pods. The lignin content of stem and pod samples used in this study was higher while the cellulose and
(7) Chen, Y.; Sharma-Shivappa, R. R.; Keshwani, D.; Chen, C. Potential of agricultural residues and hay for bioethanol production. Appl. Biochem. Biotechnol. 2007, 142, 276–290. (8) Yang, Y.; Sharma-Shivappa, R. R.; Burns, J. C.; Cheng, J. J. Dilute acid pretreatment of oven-dried switchgrass germplasms for bioethanol production. Energy Fuels 2009, 23, 3759–3766. (9) Rosgaard, L; Andric, P.; Dam-Johansen, K.; Pedersen, S.; Meyer, A. S. Effects of Substrate Loading on Enzymatic Hydrolysis and Viscosity of Pretreated Barley Straw. Appl. Biochem. Biotechnol. 2007, 143, 27–40. (10) Sluiter, A.; Hames, B.; Ruiz, R.; Scarlata, C.; Sluiter, J.; Templeton, D. Determination of Total Solids in Biomass. In Laboratory Analytical Procedures; National Renewable Energy Laboratory: Golden, CO, 2005. (11) Sluiter, A.; Hames, B.; Ruiz, R.; Scarlata, C.; Sluiter, J.; Templeton, D. Determination of Ash in Biomass. In Laboratory Analytical Procedures; National Renewable Energy Laboratory: Golden, CO, 2005. (12) Sluiter, A.; Hames, B.; Ruiz, R.; Scarlata, C.; Sluiter, J.; Templeton, D.; Crocker, D. Determination of Structural Carbohydrates and Lignin in Biomass. In Laboratory Analytical Procedures; National Renewable Energy Laboratory: Golden, CO, 2006.
(13) Mande, B. A.; Andreasen, A. A.; Sreenivasaya, R. I.; Kolachov, P. Fermentation of Bassia Flowers. Ind. Eng. Chem. 1949, 41, 1451– 1454. (14) Thomas, K. C.; Hynes, S. H.; Ingledew, W. M. Practical andtheoretical considerations in the production of high concentrations of alcohol by fermentation. Proc. Biochem. 1996, 31, 321–331. (15) Gunderson, C. A.; Davis, E. B.; Jager, H. I.; West, T. O.; Perlack, R. D.; Brandt, C. C.; Wullschleger, S. D.; Baskaran, L. M.; Wilkerson, E. G.; Downing, M. E. Exploring Potential U.S. Switchgrass Production for Lignocellulosic Ethanol, ORNL/TM-2007/183; Oak Ridge National Laboratory: Oak Ridge, TN, 2008. (16) Parrish, D. J.; Wolf, D. D.; Fike, J. H.; Daniels, W. L. Switchgrass as a biofuels crop for the upper southeast: variety trials and cultural improvements. Final Report for 1997 to 2001; Oak Ridge National Laboratory: Oak Ridge, TN, 2003; p 157.
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Figure 1. Percent composition of untreated canola stems and pods (on % dry matter basis).
comparison to other potential lignocellulosic feedstocks, such as switchgrass, barley, and wheat straw.7,20 Significantly low carbohydrate values result in low fermentable sugar generation per ton of biomass, thus requiring large amounts of biomass to produce the biofuel and higher capital costs for equipment to handle the biomass. The significant variation in data compared to other reports may be attributed to the presence of components like proteins and elemental salts besides impact of cultivation conditions, harvest time, and geography. Studies have shown that canola stalks and other herbaceous Brassica species contain more than 18% extractives and form a significant portion of the composition.17,19 Hydrolysis and Fermentation of Canola Pods and Stem. Solids recovered after pretreatment were hydrolyzed and the glucose yields from enzymatic hydrolysis and ethanol yields from fermentation of canola stems and pods are summarized in Tables 2 and 3. Higher enzyme loadings used in this study ensured that there was no enzyme limitation, which can reduce hydrolysis efficiency. In depth studies will be needed however to determine the level of enzyme loading that is sufficient for optimal cellulose and hemicellulose conversion. Additionally, considering that a significant amount of biomass is solublized during pretreatment, for lignocelluloses based biorefineries to be feasible it may be important to recover cellulosic and/or hemicellulosic sugars and the pretreatment reagent from the pretreatment filtrate as well as enzyme catalyst(s) from the hydrolysate to improve process economics. Immobilization of the enzymes is an option, but mass transfer issues need to be studied and addressed. The treatment agent used, its concentration and the interaction term (treatment agent concentration) significantly (P < 0.05) affected glucose and xylose yield during hydrolysis of canola stem and ethanol yield during fermentation. Glucose generated by canola stems pretreated with acid pretreatment at 0.5% was not significantly different from unpretreated stems; however, both alkali concentrations and 1.5% acid increased glucose yield significantly. All pretreatments resulted in higher
Table 1. Estimated Yield of Cellulosic Biomass Obtained from the Canola Varieties canola variety
companya
typeb
stem (Mg/ha)
pod (Mg/ha)
total biomass (Mg/ha)
Plainsman TCI.06.M1 Trabant DSV06202 Satori TCI.06.m3 Npz0404 Gospel Abilene KS9135 Wichita Falstaff Kronos Taurus Hybristar Ovation KS3074 Kalif Baldur DSV05100 NPZ0591rr Viking SLM0402 DSV05101 TCI.06.M2 DSV05102 DSV06200 DSV06201
2 6 4 1 3 6 4 5 2 2 2 5 4 4 3 3 2 3 4 1 4 4 4 1 6 1 1 1
OP OP H H OP OP H OP OP OP OP OP H H H OP OP OP H H H H H H OP H H H
4.1 4.7 5.9 6.0 6.0 6.1 6.2 6.2 6.4 6.8 7.0 7.0 7.0 7.3 7.5 7.6 7.6 7.7 8.0 8.5 8.5 8.9 8.9 9.3 9.5 11.5 12.1 13.7
0.9 1.0 1.2 1.2 1.3 1.3 1.3 1.3 1.3 1.4 1.5 1.5 1.5 1.5 1.6 1.6 1.6 1.6 1.7 1.8 1.8 1.9 1.9 1.9 2.0 2.4 2.5 2.9
5.0 5.6 7.1 7.2 7.3 7.4 7.5 7.5 7.8 8.2 8.4 8.4 8.5 8.8 9.1 9.1 9.2 9.3 9.6 10.3 10.3 10.7 10.8 11.3 11.5 13.9 14.6 16.6
7.7 2.1
1.6 0.4
9.3 2.6
mean standard deviation
a 1, Deutsche Saatveredelung AG (DSV); 2, Kansas State University; 3, Momont; 4, Norddeutche Pflanzenucht (NPZ); 5, Sval€ ov Weibull; 6, Technology Crops International. b H, hybrid; OP, open pollinated. All varieties are nontransgenic with the exception of NPZ0591rr, which is glyphosate resistant.
hemicellulose content was lower than that reported by Enayati et al. and Carnelley and Tiwari.17,18 The carbohydrate yield from a given quantity of canola residue was relatively low in
(19) Ballestersos, I.; Oliva, J. M.; Negro, M. J.; Manzanares, P.; Ballesteros, M. Enzymic hydrolysis of steam exploded herbaceous agricultural waste (Brassica carinata) at different particule sizes. Process Biochem. 2002, 38, 187–192. (20) Kumar, P.; Barrett, D. M.; Delwiche, M. J.; Stroeve, P. Methods for pretreatment of lignocellulosic biomass for efficiency hydrolysis and biofuel production. Ind. Eng. Chem. Res. 2009, 48, 3713–3729.
(17) Enayati, A. A.; Hamzeh, Y.; Mirshokraie, S. A.; Molaii, M. Papermaking potential of canola stalks. Bioresources 2009, 4, 245–256. (18) Carnelley, T. C. S.; Tewari, J. P. Decomposition of canola stubble by solid state fermentation with Cyathus olla. Phytoprotection 2000, 81, 87–94.
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Table 2. Solid Recovery, Hydrolysate Composition, and Ethanol Yield for Canola Stem Samples acid (H2SO4) pretreated unpretreated
avg solids recovered (%) avg solids recovered (g)
100 5
solids hydrolyzed (g) glucose (g/L) glucose (g/g)a xylose (g/L) xylose (g/g)a
0.50 3.57 (0.14) 0.071 (0.003) 0.45 (0.04) 0.009 (0.001)
ethanol (g/g)a fermentation efficiency (%)b
0.033 (0.002) 96.49 (2.87)
0.5%
1.5%
Pretreatment 73.82 3.69
65.92 3.30
Hydrolysis (at 30 FPU/g of Dry Biomass) 0.50 0.50 4.93 (0.19) 7.07 (0.78) 0.073 (0.003) 0.093 (0.010) 0.41 (0.040) 1.68 (0.13) 0.006 (0.001) 0.025 (0.002) Fermentation 0.033 (0.001) 93.92 (2.41)
0.048 (0.001) 101.75 (9.16)
alkali (NaOH) pretreated 0.5%
1.5%
78.16 3.91
61.09 3.05
0.50 10.16 (0.11) 0.159 (0.002) 1.53 (0.04) 0.024 (0.001)
0.50 9.65 (0.18) 0.118 (0.002) 4.22 (0.08) 0.066 (0.001)
0.076 (0.004) 98.94 (4.71)
0.056 (0.002) 93.35 (3.44)
a Results are presented as grams of glucose, xylose, or ethanol produced per gram of raw material. Standard deviation in parentheses. b Values over 100% may be attributed to inexact measurements during the various experimental analyses and have also been reported in other studies7,23
Table 3. Solid Recovery, Hydrolysate Composition, and Ethanol Yield for Canola Pod Samples acid (H2SO4) pretreated unpretreated
avg solids recovered (%) avg solids recovered (g)
100 5
solids hydrolyzed (g) glucose (g/L) glucose (g/g)a xylose (g/L) xylose (g/g)a
0.50 4.43 (0.07) 0.089 (0.001) 0.58 (0.00) 0.012 (0.00)
ethanol (g/g)a fermentation efficiency (%)b
0.042 (0.001) 96.76 (2.78)
0.5%
1.5%
Pretreatment 67.68 3.38
60.31 3.02
Hydrolysis (at 30 FPU/g Dry Biomass) 0.50 0.50 5.83 (0.17) 10.65 (0.17) 0.079 (0.002) 0.128 (0.007) 0.50 (0.00) 2.57 (0.03) 0.007 (0.00) 0.035 (0.00) Fermentation 0.037 (0.001) 95.78 (3.59)
0.049 (0.003) 75.28 (5.37)
alkali (NaOH) pretreated 0.5%
1.5%
76.12 3.81
55.69 2.78
0.50 9.47 (0.21) 0.144 (0.003) 1.44 (0.00) 0.022 (0.00)
0.50 6.52 (3.49) 0.073 (0.039) 2.33 (1.37) 0.036 (0.21)
0.071 (0.001) 101.33 (0.89)
0.052 (0.004) 106.40 (12.57)
a Results are presented as grams of glucose, xylose, or ethanol produced per gram of raw material. Standard deviation in parentheses. b Value over 100% may be attributed to inexact measurements during the various experimental analyses and have also been reported in other studies7,23
xylose content in the hydrolysate compared to unpretreated stems. Overall, sugars generated during hydrolysis were higher for alkali pretreated stems possibly because NaOH reduces cellulose crystallinity and enhances disruption of lignin carbohydrate linkages as a result of biomass swelling.20 No significant difference (P < 0.05) in ethanol yield was observed between canola stems from 0.5% acid pretreatment and corresponding unpretreated samples but other pretreatments significantly increased ethanol yield. The increase in acid concentration increased (p < 0.05) the ethanol yield by 45%, but the increase in alkali concentration during pretreatment resulted in a 26% lower ethanol yield possibly due to loss of sugar in the prehydrolysate. Glucose released per gram of canola pods increased (P < 0.05) when the acid concentration was increased but decreased when the alkali concentration was increased, thus resulting in a lower ethanol yield from 1.5% pretreated pods. At the same pretreatment agent concentration, acid pretreated samples generated lower glucose per gram of biomass compared to sodium hydroxide pretreated samples but no significant difference was observed for xylose generation. Ethanol yield was significantly (P < 0.05) higher from samples pretreated with 0.5% sodium hydroxide. No significant difference was observed between ethanol yield from other pretreatments and unpretreated pods. The fermentation efficiency was significantly lower in pods pretreated with acid at 1.5%.
This may have been due to generation of fermentation inhibitors during pretreatment but needs further investigation. Although the unpretreated pods were richer in glucose than unpretreated stem, the final ethanol yields from alkali pretreated stems and pods were similar. Compared to the unpretreated feedstock, 0.5% alkali pretreated stems and pods released approximately double the amount of glucose during hydrolysis and resulted in significantly higher ethanol yield of over 0.07 g/g of initial biomass. It must be noted that the yeast culture used in this study was not effective in utilizing pentose sugars. The results obtained in this study show that, in comparison to the ethanol yield from other potential cellulosic ethanol feedstocks, the ethanol yield from the canola residue is low. The estimated optimized ethanol yields from C6 sugars of switchgrass, wheat, and barley straw are approximately 230, 250, and 280 L per dry tonne of biomass, respectively.7,21 The mean nonoptimized ethanol yield for canola residue is estimated to be approximately 95 L per dry tonne, and the optimized yield would be approximately 110 L per dry tonne.21 This is due largely to the low percentage of glucan in the biomass. The value of using canola residue for ethanol production will therefore need to be weighed against the cost of collecting and transporting the material. (21) U.S. DOE. Theoretical Ethanol Yield Calculator, http://www1. eere.energy.gov/biomass/ethanol_yield_calculator.html.
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Despite these findings, further investigation of the potential of canola for cellulosic ethanol production may be worthwhile given the crop’s high residue productivity. For example, the carbohydrate composition of individual cultivars should be examined to determine whether cultivars with higher glucan content exist. It may also be worth considering alternative uses for this biomass. The use of canola residue as a feedstock for thermochemical conversion to biofuels is one avenue that could be investigated. As is the case with all crop residues, the removal of the residue for use as a biofuel could
be detrimental to long-term soil quality and further investigation is warranted.22 Acknowledgment. Enzymes for this study were provided by Novozymes North America, Inc., Franklinton, NC. (22) Wilhelm, W. W.; Johnson, J. M. F.; Karlen, D. L.; Lightle, D. T. Corn stover to sustain organic carbon further constrains biomass supply. Agron. J. 2007, 99, 1665–1667. (23) Saha, B. C.; Iten, L. B.; Cotta, M. A.; Wu, Y. V. Dilute acid pretreatment, enzymatic saccharification and fermentation of wheat straw to ethanol. Proc. Biochem 2005, 40, 3693–3700.
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