Pretreatment of yellow poplar sawdust by pressure cooking in water

Effects of Inhibitors Generated by Dilute Phosphoric Acid Plus Steam-Exploded Poplar on Saccharomyces cerevisiae Growth

The pretreatment of lignocellulosic biomass is important for efficient bioethanol conversion, but causes undesirable by-products that inhibit microbial growth, conversely affecting the bioconversion efficiency. In this study, the main inhibitors derived from dilute phosphoric acid plus steam-exploded poplar wood were identified as 0.22 g/L furfural, 3.63 g/L acetic acid, 0.08 g/L syringaldehyde, etc., indicating the green nature and low toxicity of the pretreatment process. The effects of the three typical inhibitors (furfural, acetic acid, and syringaldehyde) on Saccharomyces cerevisiae 1517RM growth were analyzed and shown to prolong the lag phase of microbial growth to different degrees. In all the inhibitor groups, the ergosterol secretion was boosted, indicating low cell membrane fluidity and robustness of the strain to an adverse environment. The cell electronegativity and morphology of S. cerevisiae 1517RM also changed under different growth conditions, which was helpful for monitoring the physicochemical properties of cells. Furfural, acetic acid, and syringaldehyde had a synergistic effect on each other, providing an important reference to improving the subsequent ethanol fermentation process.

Liquid hot water as sustainable biomass pretreatment technique for bioenergy production: A review

In recent years, lignocellulosic biomass has emerged as one of the most versatile energy sources among the research community for the production of biofuels and value-added chemicals. However, biomass pretreatment plays an important role in reducing the recalcitrant properties of lignocellulose, leading to superior quality of target products in bioenergy production. Among existing pretreatment techniques, liquid hot water (LHW) pretreatment has several outstanding advantages compared to others including minimum formation of monomeric sugars, significant removal of hemicellulose, and positive environmental impacts; however, several constraints of LHW pretreatment should be clarified. This contribution aims to provide a comprehensive analysis of reaction mechanism, reactor characteristics, influencing factors, techno-economic aspects, challenges, and prospects for LHW-based biomass pretreatment. Generally, LHW pretreatment could be widely employed in bioenergy processing from biomass, but circular economy-based advanced pretreatment techniques should be further studied in the future to achieve maximum efficiency, and minimum cost and drawbacks.

Liquid Hot Water Pretreatment of Lignocellulosic Biomass at Lab and Pilot Scale

Liquid hot water pretreatment is considered to be a promising method for increasing biomass digestibility due to the moderate operational conditions without chemical additions. A necessary step towards the scalability of this pretreatment process is performing pilot plant trials. Upscaling was evaluated with a scaling factor of 500, by using 50 mL in the laboratory and 25 L in a pilot plant batch reactor. Pretreatment times were varied from 30 to 240 min, and temperatures used were 180–188 °C, while applying similar heating profiles at both scales. The initial mass fraction of poplar wood chips ranged from 10% to 16%. Liquid hot water pretreatment at laboratory and pilot scale led to analogous results. The acetic acid analysis of the liquid and solid fractions obtained after pretreatment indicated that complete deacetylation of poplar biomass can be achieved.

Steam explosion (SE) and instant controlled pressure drop (DIC) as thermo-hydro-mechanical pretreatment methods for bioethanol production

Lignocellulosic biomass can be considered as one of the largest sources for the production of renewable biofuels (bioethanol). It involves an enzymatic treatment capable of ensuring the depolymerization of cellulose into fermentable sugars, followed by the production of ethanol by appropriate bacteriological fermentation. Proper destruction of the compact natural structure of the biomass would allow an interesting intensification of the operation. Among the most prominent technical approaches, the steam explosion (SE) is the most famous. However, this high pressure-high temperature process implies too high energy consumption while leading to the generation of many non-fermentable molecules. In recent years, many studies have proposed the use of the Instant Controlled Pressure-Drop (DIC) texturing pretreatment as an effective alternative to SE for ethanol production. Therefore, in this manuscript, we propose to compare and discuss the fundamental principles and experimental results of these two operations, as presented in the relevant literature.

Pretreatment of agricultural biomass for anaerobic digestion: Current state and challenges

The anaerobic digestion (AD) of agricultural biomass is an attractive second generation biofuel with potential environmental and economic benefits. Most agricultural biomass contains lignocellulose which requires pretreatment prior to AD. For optimization, the pretreatment methods need to be specific to the characteristics of the biomass feedstock. In this review, cereal residue, fruit and vegetable wastes, grasses and animal manure were selected as the agricultural biomass candidates, and the fundamentals and current state of various pretreatment methods used for AD of these feedstocks were investigated. Several nonconventional methods (electrical, ionic liquid-based chemicals, ruminant biological pretreatment) offer potential as targeted pretreatments of lignocellulosic biomass, but each comes with its own challenges. Pursuing an energy-intensive route, a combined bioethanol-biogas production could be a promising a second biofuel refinery option, further emphasizing the importance of pretreatment when lignocellulosic feedstock is used.

An integrated process to produce bio-ethanol and xylooligosaccharides rich in xylobiose and xylotriose from high ash content waste wheat straw

A bio-refinery process of wheat straw pulping solid residue (waste wheat straw, WWS) was established by combining prewashing and liquid hot water pretreatment (LHWP). The results showed that employing a prewashing step prior to the LHWP remarkably improved enzymatic glucose yields from 39.7% to 76.6%. Moreover, after 96h simultaneous saccharification and fermentation (SSF), identical ethanol yields of 0.41g/g-cellulose were obtained despite varied solid loadings (5-30%). Beyond ethanol, enzymatic post-hydrolysis of the prehydrolyzate effectively increased xylobiose and xylotriose yields from 15mg/g-WWS and 14mg/g-WWS to 53mg/g-WWS and 20mg/g-WWS, respectively. For mass balance, about 10.9tons raw WWS will be consumed to produce 1ton ethanol, in addition to producing 614.8kg xylooligosaccharides (XOS) containing 334.3kg xylobiose and 124.8kg xylotriose. The results demonstrated that the integrated process for the WWS bio-refinery is promising, based on value-adding co-production in addition to robust ethanol yields.

Green methods of lignocellulose pretreatment for biorefinery development

Lignocellulosic biomass is the most abundant, low-cost, bio-renewable resource that holds enormous importance as alternative source for production of biofuels and other biochemicals that can be utilized as building blocks for production of new materials. Enzymatic hydrolysis is an essential step involved in the bioconversion of lignocellulose to produce fermentable monosaccharides. However, to allow the enzymatic hydrolysis, a pretreatment step is needed in order to remove the lignin barrier and break down the crystalline structure of cellulose. The present manuscript is dedicated to reviewing the most commonly applied "green" pretreatment processes used in bioconversion of lignocellulosic biomasses within the "biorefinery" concept. In this frame, the effects of different pretreatment methods on lignocellulosic biomass are described along with an in-depth discussion on the benefits and drawbacks of each method, including generation of potentially inhibitory compounds for enzymatic hydrolysis, effect on cellulose digestibility, and generation of compounds toxic for the environment, and energy and economic demand.

Changes on structural properties of biomass pretreated by combined deacetylation with liquid hot water and its effect on enzymatic hydrolysis

A novel combined pretreatment of deacetylation and liquid hot water (LHW) was invented which has been proved to be effective in increasing enzymatic hydrolysis yield of biomass. In order to further understand the effect of this new pretreatment process on biomass, the variation on structural properties including cellulose crystallinity index (CrI), specific surface area (SSA) and degree of polymerization (DP) before/after pretreatment and how these properties affected the enzymatic hydrolysis of biomass were explored. The improvement of pretreatment severity (PS) could increase CrI, SSA and reduce DP. Whereas the enhancement of degree of deacetylation could decrease SSA and DP. An optimal formula (E12Y=0.347(100-CrI)(-0.375)×(SSA)(0.203)×(1700-DP)(0.281)) was achieved to express the correlation between structural properties and enzymatic hydrolysis after 12h. The enzymatic yield was more sensitive to CrI than to SSA and DP.

Current Pretreatment Technologies for the Development of Cellulosic Ethanol and Biorefineries

Lignocellulosic materials, such as forest, agriculture, and agroindustrial residues, are among the most important resources for biorefineries to provide fuels, chemicals, and materials in such a way to substitute for, at least in part, the role of petrochemistry in modern society. Most of these sustainable biorefinery products can be produced from plant polysaccharides (glucans, hemicelluloses, starch, and pectic materials) and lignin. In this scenario, cellulosic ethanol has been considered for decades as one of the most promising alternatives to mitigate fossil fuel dependence and carbon dioxide accumulation in the atmosphere. However, a pretreatment method is required to overcome the physical and chemical barriers that exist in the lignin-carbohydrate composite and to render most, if not all, of the plant cell wall components easily available for conversion into valuable products, including the fuel ethanol. Hence, pretreatment is a key step for an economically viable biorefinery. Successful pretreatment method must lead to partial or total separation of the lignocellulosic components, increasing the accessibility of holocellulose to enzymatic hydrolysis with the least inhibitory compounds being released for subsequent steps of enzymatic hydrolysis and fermentation. Each pretreatment technology has a different specificity against both carbohydrates and lignin and may or may not be efficient for different types of biomasses. Furthermore, it is also desirable to develop pretreatment methods with chemicals that are greener and effluent streams that have a lower impact on the environment. This paper provides an overview of the most important pretreatment methods available, including those that are based on the use of green solvents (supercritical fluids and ionic liquids).

The effect of a combined biological and thermo-mechanical pretreatment of wheat straw on energy yields in coupled ethanol and methane generation

Ethanol and biogas are energy carriers that could contribute to a future energy system independent of fossil fuels. Straw is a favorable bioenergy substrate as it does not compete with food or feed production. As straw is very resistant to microbial degradation, it requires a pretreatment to insure efficient conversion to ethanol and/or methane. This study investigates the effect of combining biological pretreatment and steam explosion on ethanol and methane yields in order to improve the coupled generation process. Results show that the temperature of the steam explosion pretreatment has a particularly strong effect on possible ethanol yields, whereas combination with the biological pretreatment showed no difference in overall energy yield. The highest overall energy output was found to be 10.86 MJ kg VS(-1) using a combined biological and steam explosion pretreatment at a temperature of 200°C.

Augmented digestion of lignocellulose by steam explosion, acid and alkaline pretreatment methods: a review

Lignocellulosic materials can be explored as one of the sustainable substrates for bioethanol production through microbial intervention as they are abundant, cheap and renewable. But at the same time, their recalcitrant structure makes the conversion process more cumbersome owing to their chemical composition which adversely affects the efficiency of bioethanol production. Therefore, the technical approaches to overcome recalcitrance of biomass feedstock has been developed to remove the barriers with the help of pretreatment methods which make cellulose more accessible to the hydrolytic enzymes, secreted by the microorganisms, for its conversion to glucose. Pretreatment of lignocellulosic biomass in cost effective manner is a major challenge to bioethanol technology research and development. Hence, in this review, we have discussed various aspects of three commonly used pretreatment methods, viz., steam explosion, acid and alkaline, applied on various lignocellulosic biomasses to augment their digestibility alongwith the challenges associated with their processing.

Pretreatment methods for bioethanol production

Lignocellulosic biomass, such as wood, grass, agricultural, and forest residues, are potential resources for the production of bioethanol. The current biochemical process of converting biomass to bioethanol typically consists of three main steps: pretreatment, enzymatic hydrolysis, and fermentation. For this process, pretreatment is probably the most crucial step since it has a large impact on the efficiency of the overall bioconversion. The aim of pretreatment is to disrupt recalcitrant structures of cellulosic biomass to make cellulose more accessible to the enzymes that convert carbohydrate polymers into fermentable sugars. This paper reviews several leading acidic, neutral, and alkaline pretreatments technologies. Different pretreatment methods, including dilute acid pretreatment (DAP), steam explosion pretreatment (SEP), organosolv, liquid hot water (LHW), ammonia fiber expansion (AFEX), soaking in aqueous ammonia (SAA), sodium hydroxide/lime pretreatments, and ozonolysis are intensively introduced and discussed. In this minireview, the key points are focused on the structural changes primarily in cellulose, hemicellulose, and lignin during the above leading pretreatment technologies.

Use of Empty Fruit Bunches from the oil palm for bioethanol production: a thorough comparison between dilute acid and dilute alkali pretreatment

In the present work, two pretreatment techniques using either dilute acid (H2SO4) or dilute alkali (NaOH) have been compared for producing bioethanol from Empty Fruit Bunches (EFBs) from oil palm tree, a relevant feedstock for tropical countries. Treatments' performances under different conditions have been assessed and statistically optimized with respect to the response upon standardized enzymatic saccharification. The dilute acid treatment performed at optimal conditions (161.5°C, 9.44 min and 1.51% acid loading) gave 85.5% glucose yield, comparable to those of other commonly investigated feedstocks. Besides, the possibility of using fibers instead of finely ground biomass may be of economic interest. Oppositely, treatment with dilute alkali has shown lower performances under the conditions explored, most likely given the relatively significant lignin content, suggesting that the use of stronger alkali regime (with the associated drawbacks) is unavoidable to improve the performance of this treatment.

Enhancement of total sugar and lignin yields through dissolution of poplar wood by hot water and dilute acid flowthrough pretreatment

BACKGROUND

Pretreatment is a vital but expensive step in biomass biofuel production. Overall, most of this past effort has been directed at maximizing sugar yields from hemicellulose and cellulose through trials with different chemicals, operating conditions, and equipment configurations. Flowthrough pretreatment provides a promising platform to dissolution of lignocellulosic biomass to generate high yields of fermentable sugars and lignin for biofuels productions.

RESULTS

Dissolution of xylan, lignin, and cellulose from poplar wood were significantly enhanced by water-only and dilute acid (0.05% w/w, H2SO4) flowthrough pretreatment when the temperature was raised from 200°C to 280°C over a range of flow rates 10-62.5 mL/min, resulting in more than 98% solid removal. Up to 40% of original xylan was converted to xylose in the hydrolyzate and the rest xylan was solubilized into xylooligomers with negligible furfural formation. Up to 100% cellulose was removed into hydrolyzate with the highest glucose yield of 60% and low 5-hydroxymethylfurfural (5-HMF) formation. The maximal recovered insoluble lignin and soluble lignin were 98% and 15% of original lignin, respectively. In addition, enzymatic hydrolysis of pretreated whole slurries was characterized under various enzyme loadings with or without Bovine serum albumin (BSA) treatment. More than 90% glucose yield and 95% xylose yield were obtained from enzymatic hydrolysis of dilute acid pretreated whole slurries with 10 mg protein Ctec 2 with 2 mg Htec2/g glucan + xylan.

CONCLUSIONS

Nearly complete dissolution of whole biomass was realized through water-only and dilute acid flowthrough pretreatment under tested conditions. Temperature was considered as the most significant factor for cellulose degradation. The cellulose removal significantly increased as temperature reached 240°C for water-only and 220°C for dilute acid. Dilute acid pretreatment resulted in higher yields of recovered xylan and cellulose as monomeric sugars in the hydrolyzate than that for water-only pretreatment. Enzymes readily hydrolyzed the degraded cellulose and xylooligomers in pretreatment hydrolysate. Results suggested that kinetics controlled the flowthrough pretreatment of biomass dissolution, which was also affected by flow rate to certain extent.

Production of Trametes pubescens laccase under submerged and semi-solid culture conditions on agro-industrial wastes

Laccases are copper-containing enzymes involved in the degradation of lignocellulosic materials and used in the treatment of phenol-containing wastewater. In this study we investigated the effect of culture conditions, i.e. submerged or semi-solid, and copper supplementation on laccase production by Trametespubescens grown on coffee husk, soybean pod husk, or cedar sawdust. The highest specific laccase activity was achieved when the culture was conducted under submerged conditions supplemented with copper (5 mM), and using coffee husk as substrate. The crude extracts presented two laccase isoforms with molecular mass of 120 (Lac1) and 60 kDa (Lac2). Regardless of the substrate, enzymatic crude extract and purified fractions behaved similarly at different temperatures and pHs, most of them presented the maximum activity at 55 °C and a pH range between 2 and 3. In addition, they showed similar stability and electro-chemical properties. At optimal culture conditions laccase activity was 7.69 ± 0.28 U mg(-1) of protein for the crude extract, and 0.08 ± 0.001 and 2.86 ± 0.05 U mg(-1) of protein for Lac1 and Lac2, respectively. In summary, these results show the potential of coffee husk as an important and economical growth medium to produce laccase, offering a new alternative use for this common agro-industrial byproduct.

Severity factor coefficients for subcritical liquid hot water pretreatment of hardwood chips

Single stage and multi-stage liquid hot water pretreatments of mixed hardwood pinchips were investigated at various severities (log R0  = 3.65-4.81) to assess the efficiencies of the pretreatments with respect to achieving high pentose sugar yields and improved enzymatic digestibility of pretreated cellulose. We investigate the effect of pretreatment parameters that is, temperature, and time, as expressed in the severity factor, on the recovery of sugars and hydrolyzability of pretreated cellulose. We find the severity factor, in its widely used form, is an incomplete measure for evaluating the pretreatment efficiencies and predicting overall sugar yields when pretreatment temperatures above 200°C are used. Corrections to the severity factor and its correlation to the measured pretreatment responses (% xylan solubilization, xylan recovery as fermentable sugars, cellulose enzymatic digestibility) indicate a greater influence of temperature on the pretreatment efficiencies than predicted by the commonly used severity factor. A low temperature, long residence time is preferred for hemicellulose dissolution during the pretreatment since the condition favors oligosaccharide and monomeric sugar formation over sugar degradation. On the contrary, high cellulose hydrolyzability is achieved with a high temperature (>200°C), high severity pretreatment when pretreatment is followed by enzyme hydrolysis. In multi-stage pretreatment, the first low-severity pretreatment is optimized for solubilizing fast-hydrolyzing hemicellulose while minimizing formation of furans. The subsequent pretreatment is carried out at over 200°C to recover the difficult-to-hydrolyze hemicellulose fraction as well as to increase susceptibility of pretreated cellulose to enzymes. High recovery (>92%) of hemicellulose-derived pentose sugars and enhanced enzymatic hydrolysis of pretreated cellulose (where >80% glucose yield results with 20 FPU = 32 mg protein/g glucan or 10-13 mg/g initial hardwood) are achieved by applying a multi-stage pretreatment. This work shows how the severity equation may be used to obtain a single characteristic curve that correlate xylan solubilization and enzymatic cellulose hydrolysis as a function of severity at pretreatment temperatures up to 230°C.

Comparative data on effects of leading pretreatments and enzyme loadings and formulations on sugar yields from different switchgrass sources

Dilute sulfuric acid (DA), sulfur dioxide (SO(2)), liquid hot water (LHW), soaking in aqueous ammonia (SAA), ammonia fiber expansion (AFEX), and lime pretreatments were applied to Alamo, Dacotah, and Shawnee switchgrass. Application of the same analytical methods and material balance approaches facilitated meaningful comparisons of glucose and xylose yields from combined pretreatment and enzymatic hydrolysis. Use of a common supply of cellulase, beta-glucosidase, and xylanase also eased comparisons. All pretreatments enhanced sugar recovery from pretreatment and subsequent enzymatic hydrolysis substantially compared to untreated switchgrass. Adding beta-glucosidase was effective early in enzymatic hydrolysis while cellobiose levels were high but had limited effect on longer term yields at the enzyme loadings applied. Adding xylanase improved yields most for higher pH pretreatments where more xylan was left in the solids. Harvest time had more impact on performance than switchgrass variety, and microscopy showed changes in different features could impact performance by different pretreatments.

Enzymatic digestion of liquid hot water pretreated hybrid poplar

Liquid hot (LHW) water pretreatment (LHW) of lignocellulosic material enhances enzymatic conversion of cellulose to glucose by solubilizing hemicellulose fraction of the biomass, while leaving the cellulose more reactive and accessible to cellulase enzymes. Within the range of pretreatment conditions tested in this study, the optimized LHW pretreatment conditions for a 15% (wt/vol) slurry of hybrid poplar were found to be 200(o)C, 10 min, which resulted in the highest fermentable sugar yield with minimal formation of sugar decomposition products during the pretreatment. The LHW pretreatment solubilized 62% of hemicellulose as soluble oligomers. Hot-washing of the pretreated poplar slurry increased the efficiency of hydrolysis by doubling the yield of glucose for a given enzyme dose. The 15% (wt/vol) slurry of hybrid poplar, pretreated at the optimal conditions and hot-washed, resulted in 54% glucose yield by 15 FPU cellulase per gram glucan after 120 h. The hydrolysate contained 56 g/L glucose and 12 g/L xylose. The effect of cellulase loading on the enzymatic digestibility of the pretreated poplar is also reported. Total monomeric sugar yield (glucose and xylose) reached 67% after 72 h of hydrolysis when 40 FPU cellulase per gram glucan were used. An overall mass balance of the poplar-to-ethanol process was established based on the experimentally determined composition and hydrolysis efficiencies of the liquid hot water pretreated poplar.

Extraction and separation of carbohydrates and phenolic compounds in flax shives with pH-controlled pressurized low polarity water

A bench-scale pressurized low polarity water (PLPW) extractor was used for the extraction and separation of hemicellulose, cellulose, lignin, and other phenolic compounds in flax shives. In the first part of this research, the key PLPW extraction process variables of temperature, pH, and flow rate, were optimized using central composite design (CCD). Temperature and pH of water had a significant affect on the fractionation of carbohydrates (cellulose and hemicellulose), lignin, and other phenolics. The optimal extraction conditions for the separation of hemicellulose and lignin, determined by the optimization using CCD, were 170 degrees C, pH 3.0, and a flow rate of 2.5 mL/min. Under these extraction conditions, 39.3% of the initial biomass or feed, 70.1% of the hemicellulose, 35.3% of the lignin, and 5.3% of the cellulose were extracted from the flax shives. In order to improve the purity and yield of the cellulose, a two-stage PLPW extraction was examined. The first stage was designed to remove hemicellulose by water at 170 degrees C and the second stage was intended for delignification by a pH 12 buffer at 220 degrees C. The two-stage PLPW extraction effectively removed 63.2% of the feed, 97.3% of hemicellulose, and 86.3% of lignin, while solubilizing 23.9% of cellulose; resulting in a solid residue containing 0.7 g of hemicellulose, 3.5 g of lignin, and 27.3 g of cellulose/100 g of DFS. The PLPW extraction is able to extract and separate components in flax shives by changing pH and temperature. The best case occurs between pH 9.5 and 12, resulting in maximum solubilization of hemicellulose and lignin.

Liquid hot water pretreatment of cellulosic biomass

Lignocellulosic biomass is an abundant and renewable resource for fuel ethanol production. However, the lignocellulose is recalcitrant to enzymatic hydrolysis because of its structural complexity. Controlled-pH liquid hot water (LHW) pretreatment of cellulosic feedstock improves its enzymatic digestibility by removing hemicellulose and making the cellulose more accessible to cellulase enzymes. The removed hemicellulose is solubilized in the liquid phase of the pretreated feedstock as oligosaccharides. Formation of monomeric sugars during the LHW pretreatment is minimal. The LHW pretreatment is carried out by cooking the feedstock in process water at temperatures between 160 and 190 degrees C and at a pH of 4-7. No additional chemicals are needed. This chapter presents the detailed procedure of the LHW pretreatment of lignocellulosic biomass.

Pretreatments to enhance the digestibility of lignocellulosic biomass

Lignocellulosic biomass represents a rather unused source for biogas and ethanol production. Many factors, like lignin content, crystallinity of cellulose, and particle size, limit the digestibility of the hemicellulose and cellulose present in the lignocellulosic biomass. Pretreatments have as a goal to improve the digestibility of the lignocellulosic biomass. Each pretreatment has its own effect(s) on the cellulose, hemicellulose and lignin; the three main components of lignocellulosic biomass. This paper reviews the different effect(s) of several pretreatments on the three main parts of the lignocellulosic biomass to improve its digestibility. Steam pretreatment, lime pretreatment, liquid hot water pretreatments and ammonia based pretreatments are concluded to be pretreatments with high potentials. The main effects are dissolving hemicellulose and alteration of lignin structure, providing an improved accessibility of the cellulose for hydrolytic enzymes.

Water solubilization of DDGS via derivatization with phosphite esters

Ethanol production from corn starch in the corn dry milling process leaves Distillers' Dry Grains and Solubles (DDGS) as a major by-product from which additional ethanol may be economically obtained from its glucan content. A challenge in processing the cellulose content of this material lies in its extensive inter-cellulose chain hydrogen bonding, which inhibits access of enzymes capable of cleaving glycosidic bonds, a transformation required for providing fermentable sugars. The phosphitylation of cellulosic OH groups using a reactive bicyclic phosphite ester is utilized to disrupt cellulosic hydrogen bonds, thus providing access to cellulose chains for further processing. We describe a method of pretreating DDGS with commercially available trimethylolpropane phosphite [P(OCH2)3CEt] in the presence of a slight molar excess of water to afford greater than 90% DDGS solubility in the reaction mixture in methanol and in water. Preliminary results using a model compound [D-(+)-permethylated cellobiose] indicate that glycosidic bonds are cleaved as a consequence of this pretreatment.

Enzyme hydrolysis and ethanol fermentation of liquid hot water and AFEX pretreated distillers' grains at high-solids loadings

The dry milling ethanol industry produces distiller's grains as major co-products, which are composed of unhydrolyzed and unfermented polymeric sugars. Utilization of the distiller's grains as an additional source of fermentable sugars has the potential to increase overall ethanol yields in current dry grind processes. In this study, controlled pH liquid hot water pretreatment (LHW) and ammonia fiber expansion (AFEX) treatment have been applied to enhance enzymatic digestibility of the distiller's grains. Both pretreatment methods significantly increased the hydrolysis rate of distiller's dried grains with solubles (DDGS) over unpretreated material, resulting in 90% cellulose conversion to glucose within 24h of hydrolysis at an enzyme loading of 15FPU cellulase and 40 IU beta-glucosidase per gram of glucan and a solids loading of 5% DDGS. Hydrolysis of the pretreated wet distiller's grains at 13-15% (wt of dry distiller's grains per wt of total mixture) solids loading at the same enzyme reduced cellulose conversion to 70% and increased conversion time to 72h for both LHW and AFEX pretreatments. However, when the cellulase was supplemented with xylanase and feruloyl esterase, the pretreated wet distiller's grains at 15% or 20% solids (w/w) gave 80% glucose and 50% xylose yields. The rationale for supplementation of cellulases with non-cellulolytic enzymes is given by Dien et al., later in this journal volume. Fermentation of the hydrolyzed wet distiller's grains by glucose fermenting Saccharomyces cerevisiae ATCC 4124 strain resulted in 100% theoretical ethanol yields for both LHW and AFEX pretreated wet distiller's grains. The solids remaining after fermentation had significantly higher protein content and are representative of a protein-enhanced wet DG that would result in enhanced DDGS. Enhanced DDGS refers to the solid product of a modified dry grind process in which the distiller's grains are recycled and processed further to extract the unutilized polymeric sugars. Compositional changes of the laboratory generated enhanced DDGS are also presented and discussed.

Combining hot-compressed water and ball milling pretreatments to improve the efficiency of the enzymatic hydrolysis of eucalyptus

BACKGROUND

Lignocellulosic biomass such as wood is an attractive material for fuel ethanol production. Pretreatment technologies that increase the digestibility of cellulose and hemicellulose in the lignocellulosic biomass have a major influence on the cost of the subsequent enzymatic hydrolysis and ethanol fermentation processes. Pretreatments without chemicals such as acids, bases or organic solvents are less effective for an enzymatic hydrolysis process than those with chemicals, but they have a less negative effect on the environment.

RESULTS

The enzymatic digestibility of eucalyptus was examined following a combined pretreatment without chemicals comprising a ball milling (BM) and hot-compressed water (HCW) treatment. The BM treatment simultaneously improved the digestibility of both glucan and xylan, and was effective in lowering the enzyme loading compared with the HCW treatment. The combination of HCW and BM treatment reduced the BM time. The eucalyptus treated with HCW (160 degrees C, 30 minutes) followed by BM (20 minutes) had an approximately 70% yield of total sugar with a cellulase loading of 4 FPU/g substrate. This yield was comparable to the yields from samples treated with HCW (200 degrees C, 30 minutes) or BM (40 minutes) hydrolyzed with 40 FPU/g substrate.

CONCLUSION

The HCW treatment is useful in improving the milling efficiency. The combined HCW-BM treatment can save energy and enzyme loading.

Coordinated development of leading biomass pretreatment technologies

For the first time, a single source of cellulosic biomass was pretreated by leading technologies using identical analytical methods to provide comparative performance data. In particular, ammonia explosion, aqueous ammonia recycle, controlled pH, dilute acid, flowthrough, and lime approaches were applied to prepare corn stover for subsequent biological conversion to sugars through a Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI) among Auburn University, Dartmouth College, Michigan State University, the National Renewable Energy Laboratory, Purdue University, and Texas A&M University. An Agricultural and Industrial Advisory Board provided guidance to the project. Pretreatment conditions were selected based on the extensive experience of the team with each of the technologies, and the resulting fluid and solid streams were characterized using standard methods. The data were used to close material balances, and energy balances were estimated for all processes. The digestibilities of the solids by a controlled supply of cellulase enzyme and the fermentability of the liquids were also assessed and used to guide selection of optimum pretreatment conditions. Economic assessments were applied based on the performance data to estimate each pretreatment cost on a consistent basis. Through this approach, comparative data were developed on sugar recovery from hemicellulose and cellulose by the combined pretreatment and enzymatic hydrolysis operations when applied to corn stover. This paper introduces the project and summarizes the shared methods for papers reporting results of this research in this special edition of Bioresource Technology.

Optimization of pH controlled liquid hot water pretreatment of corn stover

Controlled pH, liquid hot water pretreatment of corn stover has been optimized for enzyme digestibility with respect to processing temperature and time. This processing technology does not require the addition of chemicals such as sulfuric acid, lime, or ammonia that add cost to the process because these chemicals must be neutralized or recovered in addition to the significant expense of the chemicals themselves. Second, an optimized controlled pH, liquid hot water pretreatment process maximizes the solubilization of the hemicellulose fraction as liquid soluble oligosaccharides while minimizing the formation of monomeric sugars. The optimized conditions for controlled pH, liquid hot water pretreatment of a 16% slurry of corn stover in water was found to be 190 degrees C for 15 min. At the optimal conditions, 90% of the cellulose was hydrolyzed to glucose by 15FPU of cellulase per gram of glucan. When the resulting pretreated slurry, in undiluted form, was hydrolyzed by 11FPU of cellulase per gram of glucan, a hydrolyzate containing 32.5 g/L glucose and 18 g/L xylose was formed. Both the xylose and the glucose in this undiluted hydrolyzate were shown to be fermented by recombinant yeast 424A(LNH-ST) to ethanol at 88% of theoretical yield.