Softwood residues are the most abundant feedstock available for bioconversion in many northern countries. However, the high costs for delig-nification and enzymatic hydrolysis currently deter commercialization of softwood bioconversion processes. This study evaluates the abilities of two novel fungal preparations (MSUBCl and MSUBC2) and two commercial cellulase preparations (TRl and TR2) to hydrolyze cellulose in Douglas-fir pretreated by steam explosion or ethanol organosolv process. MSUBCI showed significantly better performance than the other preparations on both lignocellulosic substrates. In particular, MSUBCI achieved> 76% cellulose conversion for hydrolysis of steam-exploded Douglas-fir (~ 44% lignin) after 72 h at low enzyme loading (10 filter paper units/g of cellulose) and without B-glucosidase supplementation.

Softwoods are generally considered to be one of the most difficult lignocellulosic feedstocks to hydrolyze to sugars for fermentation, primarily owing to the nature and amount of lignin. If the inhibitory effect of lignin can be significantly reduced, softwoods may become a more useful feedstock for the bioconversion processes. Moreover, strategies developed to reduce problems with softwood lignin may also provide a means to enhance the processing of other lignocellulosic substrates. The Forest Products Biotechnology Group at the University of British Columbia has been developing softwood-to-ethanol processes with SO2-catalyzed steam explosion and ethanol organosolv pretreatments. Lignin from the steam explosion process has relatively low reactivity and, consequently, low product value, compared with the highvalue coproduct that can be obtained through organosolv. The technical and economic challenges of both processes are presented, together with suggestions for future process development.

An organosolv process involving extraction with hot aqueous ethanol has been evaluated for bioconversion of hybrid poplar to ethanol. The process resulted in fractionation of poplar chips into a cellulose-rich solids fraction, an ethanol organosolv lignin (EOL) fraction, and a water-soluble fraction containing hemicellulosic sugars, sugar breakdown products, degraded lignin, and other components. The influence of four independent process variables (temperature, time, catalyst dose, and ethanol concentration) on product yields was analyzed over a broad range using a small composite design and response surface methodology. Center point conditions for the composite design (180°C, 60 min, 1.25% H 2 SO 4 , and 60% ethanol), yielded a solids fraction containing ∼88% of the cellulose present in the untreated poplar. Approximately 82% of the total cellulose in the untreated poplar was recovered as monomeric glucose after hydrolysis of the solids fraction for 24 h using a low enzyme loading (20 filter paper units of cellulase/g cellulose); ∼85% was recovered after 48 h hydrolysis. Total recovery of xylose (soluble and insoluble) was equivalent to ∼72% of the xylose present in untreated wood. Approximately 74% of the lignin in untreated wood was recovered as EOL. Other cooking conditions resulted in either similar or inferior product yields although the distribution of components between the various fractions differed markedly. Data analysis generated regression models that describe process responses for any combination of the four variables. © 2006 Wiley Periodicals, Inc.

Seven fungal cellulase preparations from Trichoderma and Penicillium spp. were evaluated for their ability to hydrolyze the cellulose component of lignocellulose samples prepared from softwoods by steam explosion or organosolv pretreatment. Hydrolysis was quantified using two indices: mean specific rate and specific conversion. The activities of the cellulase preparations on model cellulosic substrates (filter paper, carboxymethylcellulose and Avicel) were also determined, together with their β-glucosidase, xylanase, pectinase, galactomannanase and β-glucanase activities. The ability of a cellulase preparation to hydrolyze pretreated softwood showed little correlation with its activity on filter paper, carboxymethylcellulose and Avicel; however, there was a significant correlation with its level of endogenous β-glucosidase and xylanase activity. Differences in the performance of the various cellulase preparations were substantially reduced following supplementation with a commercial β-glucosidase preparation from Aspergillus niger. In addition to β-glucosidase, this preparation was shown to contain significant levels of endogenous xylanase activity. It appears that the levels of endogenous β-glucosidase and xylanase are important factors in determining the ability of a cellulase preparation to hydrolyze pretreated softwood and that deficiencies in the levels of both enzymes can be compensated by supplementation with corresponding activities present in the β-glucosidase preparation. Presumably, β-glucosidase improves cellulose hydrolysis by reducing end-product inhibition by cellobiose, while xylanase activity increases the accessibility of cellulose to cellulases.

Pulps with residual lignin ranging from 6.4-27.4% (w/w) were prepared from mixed softwoods using a proprietary biorefining technology (the Lignol process) based on aqueous ethanol organosolv extraction. The pulps were evaluated for bioconversion using enzymatic hydrolysis of the cellulose fraction to glucose and subsequent fermentation to ethanol. All pulps were readily hydrolyzed without further delignification. More than 90% of the cellulose in low lignin pulps (< or =18.4% residual lignin) was hydrolyzed to glucose in 48 h using an enzyme loading of 20 filter paper units/g cellulose. Cellulose in a high lignin pulp (27.4% residual lignin) was hydrolyzed to >90% conversion within 48 h using 40 filter paper units/g. The pulps performed well in both sequential and simultaneous saccharification and fermentation trials indicating an absence of metabolic inhibitors. Chemical and physical analyses showed that lignin extracted during organosolv pulping of softwood is a suitable feedstock for production of lignin-based adhesives and other products due to its high purity, low molecular weight, and abundance of reactive groups. Additional co-products may be derived from the hemicellulose sugars and furfural recovered from the water-soluble stream.

Pretreatment of Douglas-fir by steam explosion produces a substrate containing approx 43% lignin. Two strategies were investigated for reducing the effect of this residual lignin on enzymatic hydrolysis of cellulose: mild alkali extraction and protein addition. Extraction with cold 1% NaOH reduced the lignin content by only approx 7%, but cellulose to glucose conversion was enhanced by about 30%. Before alkali extraction, addition of exogenous protein resulted in a significant improvement in cellulose hydrolysis, but this protein effect was substantially diminished after alkali treatment. Lignin appears to reduce cellulose hydrolysis by two distinct mechanisms: by forming a physical barrier that prevents enzyme access and by non-productively binding cellulolytic enzymes. Cold alkali appears to selectively remove a fraction of lignin from steam-exploded Douglas-fir with high affinity for protein. Corresponding data for mixed softwood pretreated by organosolv extraction indicates that the relative importance of the two mechanisms by which residual lignin affects hydrolysis is different according to the pre- and post-treatment method used.

Softwood residues are the most abundant feedstock available for bioconversion in many northern countries. However, the high costs for delignification and enzymatic hydrolysis currently deter commercialization of softwood bioconversion processes. This study evaluates the abilities of two novel fungal preparations (MSUBC1 and MSUBC2) and two commercial cellulase preparations (TR1 and TR2) to hydrolyze cellulose in Douglas-fir pretreated by steam explosion or ethanol organosolv process. MSUBC1 showed significantly better performance than the other preparations on both lignocellulosic substrates. In particular, MSUBC1 achieved >76% cellulose conversion for hydrolysis of steam-exploded Douglas-fir (∼44% lignin) after 72 h at low enzyme loading (10 filter paper units/g of cellulose) and without β-glucosidase supplementation.

The biorefinery is a key concept used in the strategies and visions of many industrial countries. The potential for Canadian biorefineries based on lignocellulosic forest and agricultural residues is examined. The sector is described in terms of research interests, emerging companies, and established corporate interests. It is found that the Canadian biorefining sector currently has an emphasis on specific bioproduct generation, and the process elements required for a true sugar-based process are in the research phase. A Canadian national strategy should focus on increasing forest industry participation, and increasing collaboration with the provinces, particularly in western Canada.

The International Energy Agency (IEA) was founded in 1974 as an autonomous body within the Organization for Economic Co-operation and Development to implement an international energy program in response to the oil shocks. IEA Bioenergy was created in 1978 by the parent organization with the aim of improving cooperation and information exchange between countries that have national programs in bioenergy research, development, and deployment. The goal of IEA Bioenergy Task 39, “Liquid Biofuels,” is to successfully introduce biofuels for transportation into the marketplace. To meet this objective, the members of Task 39 have taken on the job of reviewing both technical and policy or regulatory issues that are related to commercializing the technology for fuel ethanol production. It is our belief that these issues are strongly related, and that successful commercialization of the technology will require advances in both areas. In this session, the Task 39 group worked to create a forum in which the interrelated issues of policy and technology could be reviewed and explored.

A quantitative approach was taken to determine the inhibition effects of glucose and other sugar monomers during cellulase and β-Glucosidase hydrolysis of two types of cellulosic material: Avicel and acetic acid-pretreated softwood. The increased glucose content in the hydrolysate resulted in a dramatic increase in the degrees of inhibition on both β-Glucosidase and cellulase activities. Supplementation of mannose, xylose, and galactose during cellobiose hydrolysis did not show any inhibitory effects on β-Glucosidase activity. However, these sugars were shown to have significant inhibitory effects on cellulase activity during cellulose hydrolysis. Our study suggests that high-substrate consistency hydrolysis with supplementation of hemicellulose is likely to be a practical solution to minimizing end-product inhibition effects while producing hydrolysate with high glucose concentration.

Good enzymatic hydrolysis of steam-exploded Douglas fir wood (SEDW) cannot be achieved owing to the very high lignin content (>40%) that remains associated with this substrate. Thus, in this study, we investigated the use of alkali-oxygen treatment as a posttreatment to delignify SEDW and also considered the enzymatic hydrolyzability of the delignified SEDW. The results showed that under optimized conditions of 15% NaOH, 5% consistency, 110°C, and 3 h, approx 84% of the lignin in SEDW could be removed. The resulting delignified SEDW had good hydrolyzability, and cellulose-to-glucose conversion yields of over 90 and 100% could be achieved within 48 h with 20 and 40 filter paper units / g of cellulose enzyme loadings, respectively. It was also indicated that severe conditions, such as high NaOH concentration and high temperature, should not be utilized in oxygen delignification of SEDW in order to avoid extensive condensation of lignin and significant degradation of cellulose.

The impetus for this paper is Canada's commitment under the United Nations Framework Convention on Climate Change to reduce national greenhouse gas emissions as well as reducing our dependency on fossil fuels. Wood-based ethanol offers an excellent opportunity for greenhouse gas mitigation due to market potential, an ability to offset significant emissions from the transportation sector, a reduction of emissions from CO2-intensive waste-management systems, and carbon sequestration in afforested plantations. While there are technological and economic barriers to overcome, using wood-biomass as a source of ethanol can be an economically viable tool for reducing greenhouse gas levels in the atmosphere. This paper examines the costs and mitigation potential of the production of ethanol from biomass supplied from industrial wood waste as well as from trees harvested from afforested land.

The enzymatic digestibility of steam-exploded Douglas-fir wood chips (steam exploded at 195 degrees C, 4.5 min, and 4.5% (w/w) SO(2)) was significantly improved using an optimized alkaline peroxide treatment. Best hydrolysis yields were attained when the steam-exploded material was post-treated with 1% hydrogen peroxide at pH 11.5 and 80 degrees C for 45 min. This alkaline peroxide treatment was applied directly to the water-washed, steam-exploded material eliminating the need for independent alkali treatment with 0.4% NaOH, which has been traditionally used to post-treat wood samples to try to remove residual lignin. Approximately 90% of the lignin in the original wood was solubilized by this novel procedure, leaving a cellulose-rich residue that was completely hydrolyzed within 48 h, using an enzyme loading of 10 FPU/g cellulose. About 82% of the originally available polysaccharide components of the wood could be recovered. The 18% of the carbohydrate that was not recovered was lost primarily to sugar degradation during steam explosion.

The sugar yield and enzyme adsorption profile obtained during the hydrolysis of SO 2 -catalyzed steam-exploded Douglas-fir and posttreated steamexploded Douglas-fir substrates were determined. After hot alkali peroxide posttreatment, the rates and yield of hydrolysis attained from the posttreated Douglas-fir were significantly higher, even at lower enzyme loadings, than those obtained with the corresponding steam-exploded Douglas-fir. The enzymatic adsorption profiles observed during hydrolysis of the two substrates were significantly different. Ultrafiltration was employed to recover enzyme in solution (supernatant) and reused in subsequent hydrolysis reactions with added, fresh substrate. These recycle findings suggested that the enzyme remained relatively active for three rounds of recycle. It is likely that enzyme recovery and reuse during the hydrolysis of posttreated softwood substrates could lead to reductions in the need for the addition of fresh enzyme during softwood-based bioconversion processes.

Douglas-fir sapwood and heartwood were impregnated with SO2 and steam exploded at three severity levels, and the cellulose-rich, water-insoluble component was enzymatically hydrolyzed. The high-severity conditions resulted in near complete solubilization and some degradation of hemicelluloses and a significant improvement in the efficiency of enzymatic digestibility of the cell ulose component. At lower severity, some of the hemicellulose remained un hydrolyzed, and the cellulose present in the pretreated solids was not readily hydrolyzed. The medium-severity pretreatment conditions proved to be a good compromise because they improved the enzymatic hydrolyzability of the solids and resulted in the recovery of the majority of hemicellulose in a monomeric form within the water-soluble stream. Sapwood-derived wood chips exhibited a higher susceptibility to both pretreatment and hydrolysis and, on steam explosion, formed smaller particles as compared to heartwood-derived wood chips.

A combination of Douglas fir heartwood and sapwood chips were steam pretreated under three conditions as measured by the Severity Factor (log R o ), which incorporated the time, temperature/pressure of pretreatment. By adjusting the steam pretreatment conditions, it was hoped to recover the majority of the hemicellulose component as monomers in the water-soluble stream, while providing a cellulosic-rich, water-insoluble fraction that could be readily hydrolyzed by cellulases. These three conditions were chosen to represent either high hemicellulose sugar recovery (low severity [L], log R o =3.08), high-enzyme hydrolyzability of the cellulosic component (high severity [H], log R o =4.21), and a compromise between the two conditions (medium severity [M], log R o =3.45). The medium-severity pretreatment conditions (195°C, 4.5 min, 4.5% SO 2 logR o =3.45) gave the best compromise in terms of relatively high hemicellulose recovery after stream pretreatment and the subsequent efficiency of enzymatic hydrolysis of the water-insoluble cellulosic fraction. The percent recovery of the original hemicellulose in the water-soluble fraction dropped significantly when the severity was increased (L-76.8%, M-64.7%, and H-37.5%). However, the ease of enzymatic hydrolysis of the cellulose-rich, water-insoluble fraction increased with increasing severity (L-24%, M-86.6%, and H-97.9%). Although more severe pretreatment conditions provided optimum hydrolysis of the cellulosic component, less severe conditions resulted in better recovery of the combined hemicellulose and cellulosic components.

Techno-economic modeling has been a valuable tool in directing and assessing the research and development efforts for biomass-to-ethanol processes. In developing a techno-economic model of a “generic” wood-to-ethanol process, we decided to follow a three-pronged design approach. This initially consisted of a detailed review of the current definition and technical maturity of the process, which concluded that the process remains complex and immature. More recently, we have critically assessed/compared two inherited models, and examined the historical and current trends in modeling design. We confirmed that process complexity and immaturity, in association with the capabilities of the available modeling tools and the ease with which they can be used, influenced the design and implementation of past models. We have discussed these influences with reference to our own model development decisions. For example, on review of two inherited techno-economic models, we decided that our new model would require a greater degree of flexibility in its structure and user interface.