Effect of chip size on steam explosion pretreatment of softwood

Opuntia ficus indica waste as a cost effective carbon source for lactic acid production by Lactobacillus plantarum

Opuntia ficus indica (OFI) waste was evaluated as a fermentation feedstock for lactic acid production using Lactobacillus plantarum. Dilute acid pretreatment of the OFI cladodes (OFIC) was performed for extracting maximum fermentable sugars by optimizing process parameters using statistical optimization method. The best results were obtained with HCl 1% (v/v), temperature 120 °C, residence time 40 min, granulation 350 µm and substrate loading 5% (w/v), the sugar concentration reached 24 g/L with low concentration of hydroxymethylfurfural. The feasibility of producing lactic acid from OFI fruit peel (OFIFP) as a source of carbon was also investigated. Lactobacillus plantarum was shown to have a capacity for lactic acid production from OFIC₃₅₀ (granulation 350 µm) hydrolysate and OFIFP extract without detoxification. The highest lactic acid yields of 0.46 and 0.78 g/g were obtained from enzymatic hydrolysate of pretreated OFIC₃₅₀ and OFIFP extract, respectively.

Liquefaction of lignocellulosic biomass for methane production: A review

Hydrothermal pretreatment (HTP) (Hot water extraction (HWE) and steam pretreatment) and pyrolysis have the potential to liquefy lignocellulosic biomass. HTP produces hydrolysate, consisting mainly of solubilized hemicellulose, while pyrolysis produces aqueous pyrolysis liquid (APL). The liquid products, either as main products or by-product, can be used as anaerobic digestion (AD) feeds, overcoming shortcomings of solid-state AD (SS-AD). This paper reviews HWE, steam pretreatment, and pyrolysis pretreatment methods used to liquefy lignocellulosic biomass, AD of liquefied products, effects of inhibition from intermediate by-products such as furan and phenolic compounds, and pretreatment tuning to increase methane yield. HTP, focusing on methane production, produces less inhibitory compounds when carried out at moderate temperatures. APL is a challenging feed for AD due to its complexity, including various inhibitory substances. Pre-treatment of biomass before pyrolysis, adaptation of microorganism to inhibitors, and additives, such as biochar, may help the AD cultures cope with inhibitors in APL.

CO2 -Enabled Biomass Fractionation/Depolymerization: A Highly Versatile Pre-Step for Downstream Processing

Lignocellulosic biomass is inevitably subject to fractionation and depolymerization processes for enhanced selectivity toward specific products, in most cases prior to catalytic upgrading of the three main fractions-cellulose, hemicellulose, and lignin. Among the developed pretreatment techniques, CO₂ -assisted biomass processing exhibits some unique advantages such as the lowest critical temperature (31.0 °C) with moderate critical pressure, low cost, nontoxicity, nonflammability, ready availability, and the addition of acidity, alongside easy recovery by pressure release. This Review showcases progress in the study of sub- or supercritical CO₂ -mediated thermal processing of lignocellulosic biomass-the key pre-step for downstream conversion processes. The auxo-action of CO₂ in biomass pretreatment and fractionation, along with the involved variables, direct degradation of untreated biomass in CO₂ by gasification, pyrolysis, and liquefaction with relevant conversion mechanisms, and CO₂ -enabled depolymerization of lignocellulosic fractions with representative reaction pathways are summarized. Moreover, future prospects for the practical application of CO₂ -assisted up- and downstream biomass-to-bioproduct conversion are also briefly discussed.

Steam Explosion Pretreatment of Beechwood. Part 1: Comparison of the Enzymatic Hydrolysis of Washed Solids and Whole Pretreatment Slurry at Different Solid Loadings

Steam explosion is a well-known process to pretreat lignocellulosic biomass in order to enhance sugar yields in enzymatic hydrolysis, but pretreatment conditions have to be optimized individually for each material. In this study, we investigated how the results of a pretreatment optimization procedure are influenced by the chosen reaction conditions in the enzymatic hydrolysis. Beechwood was pretreated by steam explosion and the resulting biomass was subjected to enzymatic hydrolysis at glucan loadings of 1% and 5% employing either washed solids or the whole pretreatment slurry. For enzymatic hydrolysis in both reaction modes at a glucan loading of 1%, the glucose yields markedly increased with increasing severity and with increasing pretreatment temperature at identical severities and maximal values were reached at a pretreatment temperature of 230 °C. However, the optimal severity was 5.0 for washed solids enzymatic hydrolysis, but only 4.75 for whole slurry enzymatic hydrolysis. When the glucan loading was increased to 5%, glucose yields hardly increased for pretreatment temperatures between 210 and 230 °C at a given severity, and a pretreatment temperature of 220 °C was sufficient under these conditions. Consequently, it is important to precisely choose the desired conditions of the enzymatic hydrolysis reaction, when aiming to optimize the pretreatment conditions for a certain biomass.

Hydrothermal pretreatment of wood by mild steam explosion and hot water extraction

The aim of this work was to compare the two most common hydrothermal pre-treatments for wood - mild steam explosion and hot water extraction - both with the prospect of enabling extraction of hemicelluloses and facilitating further processing. Although both involve autohydrolysis of the lignocellulosic tissue, they are performed under different conditions: the most prominent difference is the rapid, disintegrating, discharge employed in the steam explosion opening up the structure. In this comparative study, the emphasis was placed on local composition of the pre-treated wood chips (of industrially relevant size). The results show that short hot water extraction treatments lead to significant variations in the local composition within the wood chips, while steam explosion accomplishes a comparably more even removal of hemicelluloses due to the advective mass transport during the explosion step.

Evaluating the effect of wood ultrastructural changes from mechanical treatment on kinetics of monomeric sugars and chemicals production in acid bisulfite treatment

Currently, various chemical-mechanical treatments were widely used in biofuel production to achieve high total sugar yields. However, the interaction between two treatments was scarcely investigated. In this study, we employed a ball milling process to create ultrastructural changes for Douglas-fir (Pseudotsuga menziesii) micronized wood powders. The 0, 30, and 60min ball milled wood powders resulted in a crystallinity index of 0.41, 0.21, and 0.10 respectively. It was found that the ultrastructural changes accelerate monomeric sugars production without influencing the yield of sugar degradation products. The optimal acid bisulfite treatment time was substantially decreased from 120min to 40min as the cellulose crystallinity decreased. Meanwhile, total sugar yield increased from 65% to 92% and had a linear relation with a decrease of the cellulose crystallinity.

Periodic peristalsis releasing constrained water in high solids enzymatic hydrolysis of steam exploded corn stover

Periodic peristalsis was used to release water constraint and increase high solids enzymatic hydrolysis efficiency. Glucan and xylan conversion in periodic peristalsis enzymatic hydrolysis (PPEH) at 21% solid loading increased by 5.2-6.4% and 6.8-8.8% compared with that in incubator shaker enzymatic hydrolysis (ISEH), respectively. Hydrolysis kinetics suggested that sugars conversion significantly increased within 24h in PPEH compared with ISEH. The peak height of main water pool increased by 7.7-43.1% within 24h in PPEH compared with ISEH. The increases in peak height of main water pool were consistent with the increases in glucan conversion. Submicroscopic particulates and macro granule residues contributed greatly to water constraint compared with glucose, xylose, ethanol, and Tween 80. Smaller particle size and longer residence time resulted in lower water constraint and facilitated the enzymatic hydrolysis performance. Periodic peristalsis was an effective method to reduce water constraint and increase high solids enzymatic hydrolysis efficiency.

Optimization of chip size and moisture content to obtain high, combined sugar recovery after sulfur dioxide-catalyzed steam pretreatment of softwood and enzymatic hydrolysis of the cellulosic component

The influence of chip size and moisture content on the combined sugar recovery after steam pretreatment of lodgepole pine and subsequent enzymatic hydrolysis of the cellulosic component were investigated using response surface methodology. Chip size had little influence on sugar recovery after both steam pretreatment and enzymatic hydrolysis. In contrast, the moisture of the chips greatly influenced the relative severity of steam pretreatment and, as a result, the combined sugar recovery from the hemicellulosic and cellulosic fractions. Irrespective of chip size and the pretreatment temperature, time, and SO2 loading that were used, the relative severity of pretreatment was highest at a moisture of 30-40w/w%. However, the predictive model indicated that an elevated moisture content of roughly 50w/w% (about the moisture content of a standard softwood mill chip) would result in the highest, combined sugar recovery (80%) over the widest range of steam pretreatment conditions.

Study on loading coefficient in steam explosion process of corn stalk

The object of this work was to evaluate the effect of loading coefficient on steam explosion process and efficacy of corn stalk. Loading coefficient's relation with loading pattern and material property was first revealed, then its effect on transfer process and pretreatment efficacy of steam explosion was assessed by established models and enzymatic hydrolysis tests, respectively, in order to propose its optimization strategy for improving the process economy. Results showed that loading coefficient was mainly determined by loading pattern, moisture content and chip size. Both compact loading pattern and low moisture content improved the energy efficiency of steam explosion pretreatment and overall sugar yield of pretreated materials, indicating that they are desirable to improve the process economy. Pretreatment of small chip size showed opposite effects in pretreatment energy efficiency and enzymatic hydrolysis performance, thus its optimization should be balanced in investigated aspects according to further techno-economical evaluation.

How chip size impacts steam pretreatment effectiveness for biological conversion of poplar wood into fermentable sugars

BACKGROUND

Woody biomass is highly recalcitrant to enzymatic sugar release and often requires significant size reduction and severe pretreatments to achieve economically viable sugar yields in biological production of sustainable fuels and chemicals. However, because mechanical size reduction of woody biomass can consume significant amounts of energy, it is desirable to minimize size reduction and instead pretreat larger wood chips prior to biological conversion. To date, however, most laboratory research has been performed on materials that are significantly smaller than applicable in a commercial setting. As a result, there is a limited understanding of the effects that larger biomass particle size has on the effectiveness of steam explosion pretreatment and subsequent enzymatic hydrolysis of wood chips.

RESULTS

To address these concerns, novel downscaled analysis and high throughput pretreatment and hydrolysis (HTPH) were applied to examine whether differences exist in the composition and digestibility within a single pretreated wood chip due to heterogeneous pretreatment across its thickness. Heat transfer modeling, Simons' stain testing, magnetic resonance imaging (MRI), and scanning electron microscopy (SEM) were applied to probe the effects of pretreatment within and between pretreated wood samples to shed light on potential causes of variation, pointing to enzyme accessibility (i.e., pore size) distribution being a key factor dictating enzyme digestibility in these samples. Application of these techniques demonstrated that the effectiveness of pretreatment of Populus tremuloides can vary substantially over the chip thickness at short pretreatment times, resulting in spatial digestibility effects and overall lower sugar yields in subsequent enzymatic hydrolysis.

CONCLUSIONS

These results indicate that rapid decompression pretreatments (e.g., steam explosion) that specifically alter accessibility at lower temperature conditions are well suited for larger wood chips due to the non-uniformity in temperature and digestibility profiles that can result from high temperature and short pretreatment times. Furthermore, this study also demonstrated that wood chips were hydrated primarily through the natural pore structure during pretreatment, suggesting that preserving the natural grain and transport systems in wood during storage and chipping processes could likely promote pretreatment efficacy and uniformity.

Particulate size of microalgal biomass affects hydrolysate properties and bioethanol concentration

Effective optimization of microalgae-to-bioethanol process systems hinges on an in-depth characterization of key process parameters relevant to the overall bioprocess engineering. One of the such important variables is the biomass particle size distribution and the effects on saccharification levels and bioethanol titres. This study examined the effects of three different microalgal biomass particle size ranges, 35 μm ≤ x ≤ 90 μm, 125 μm ≤ x ≤ 180 μm, and 295 μm ≤ x ≤ 425 μm, on the degree of enzymatic hydrolysis and bioethanol production. Two scenarios were investigated: single enzyme hydrolysis (cellulase) and double enzyme hydrolysis (cellulase and cellobiase). The glucose yield from biomass in the smallest particle size range (35 μm ≤ x ≤ 90 μm) was the highest, 134.73 mg glucose/g algae, while the yield from biomass in the larger particle size range (295 μm ≤ x ≤ 425 μm) was 75.45 mg glucose/g algae. A similar trend was observed for bioethanol yield, with the highest yield of 0.47 g EtOH/g glucose obtained from biomass in the smallest particle size range. The results have shown that the microalgal biomass particle size has a significant effect on enzymatic hydrolysis and bioethanol yield.

Ethanol production from glucose and xylose obtained from steam exploded water-extracted olive tree pruning using phosphoric acid as catalyst

In this work, the effect of phosphoric acid (1% w/w) in steam explosion pretreatment of water extracted olive tree pruning at 175°C and 195°C was evaluated. The objective is to produce ethanol from all sugars (mainly glucose and xylose) contained in the pretreated material. The water insoluble fraction obtained after pretreatment was used as substrate in a simultaneous saccharification and fermentation (SSF) process by a commercial strain of Saccharomyces cerevisiae. The liquid fraction, containing mainly xylose, was detoxified by alkali and ion-exchange resin and then fermented by the xylose fermenting yeast Scheffersomyces stipitis. Ethanol yields reached in a SSF process were close to 80% when using 15% (w/w) substrate consistency and about 70% of theoretical when using prehydrolysates detoxified by ion-exchange resins. Considering sugars recovery and ethanol yields about 160g of ethanol from kg of water extracted olive tree pruning could be obtained.

Specific effects of fiber size and fiber swelling on biomass substrate surface area and enzymatic digestibility

To clarify the specific effect of biomass substrate surface area on its enzymatic digestibility, factors of fiber size reduction and swelling changes were investigated by using poplar substrates with controlled morphological and chemical properties after modified chemical pulping. Results showed that fiber size changes had insignificant influence on enzymatic hydrolysis, although the external surface area increased up to 41% with the reduction of fiber size. Swelling changes caused by increased biomass fiber porosities after PFI refining showed a significant influence on the efficiency of enzymatic hydrolysis. It is also found that chemical properties such as xylan and lignin content can influence the swelling effect. Xylan is confirmed to facilitate substrate hydrolysability by swelling, while lignin restricts swelling effect and thus minimizes the enzyme accessibility to substrates.

Efficient fractionation of spruce by SO(2)-ethanol-water treatment: closed mass balances for carbohydrates and sulfur

SO(2)-ethanol-water (SEW) lignocellulosic fractionation has the potential to overcome the present techno-economic barriers that hinder the commercial implementation of renewable transportation fuel production. In this study, SEW fractionation of spruce wood chips is examined for its ability to separate the main wood components, hemicelluloses, lignin, and cellulose, and the potential to recover SO(2) and ethanol from the spent fractionation liquid. Therefore, overall sulfur and carbohydrate mass balances are established. 95-97 % of the charged SO(2) remains in the liquid and can be fully recovered by distillation. During fractionation, hemicelluloses and lignin are effectively dissolved, whereas cellulose is preserved in the solid (fibre) phase. Hemicelluloses are hydrolysed, producing up to 50 % monomeric sugars, whereas dehydration and oxidation of carbohydrates are insignificant. The latter is proven by the closed carbohydrate material balances as well as by the near absence of corresponding by-products (furfural, hydroxymethylfurfural (HMF) and aldonic acids). In addition, acid methanolysis/GC and acid hydrolysis/high performance anion exchange chromatography (HPAEC) methods for the carbohydrate determination are compared.

Bio-ethanol production from non-food parts of cassava (Manihot esculenta Crantz)

Global climate issues and a looming energy crisis put agriculture under pressure in Sub-Saharan Africa. Climate adaptation measures must entail sustainable development benefits, and growing crops for food as well as energy may be a solution, removing people from hunger and poverty without compromising the environment. The present study investigated the feasibility of using non-food parts of cassava for energy production and the promising results revealed that at least 28% of peels and stems comprise dry matter, and 10 g feedstock yields >8.5 g sugar, which in turn produced >60% ethanol, with pH ≈ 2.85, 74-84% light transmittance and a conductivity of 368 mV, indicating a potential use of cassava feedstock for ethanol production. Thus, harnessing cassava for food as well as ethanol production is deemed feasible. Such a system would, however, require supportive policies to acquire a balance between food security and fuel.

Steam refining as an alternative to steam explosion

In steam pretreatment the defibration is usually achieved by an explosion at the end of the treatment, but can also be carried out in a subsequent refiner step. A steam explosion and a steam refining unit were compared by using the same raw material and pretreatment conditions, i.e. temperature and time. Smaller particle size was needed for the steam explosion unit to obtain homogenous slurries without considerable amounts of solid chips. A higher amount of volatiles could be condensed from the vapour phase after steam refining. The results from enzymatic hydrolysis showed no significant differences. It could be shown that, beside the chemical changes in the cell wall, the decrease of the particle size is the decisive factor to enhance the enzymatic accessibility while the explosion effect is not required.

Biohydrogen production from lignocellulosic feedstock

Due to the recent energy crisis and rising concern over climate change, the development of clean alternative energy sources is of significant interest. Biohydrogen produced from cellulosic feedstock, such as second generation feedstock (lignocellulosic biomass) and third generation feedstock (carbohydrate-rich microalgae), is a promising candidate as a clean, CO2-neutral, non-polluting and high efficiency energy carrier to meet the future needs. This article reviews state-of-the-art technology on lignocellulosic biohydrogen production in terms of feedstock pretreatment, saccharification strategy, and fermentation technology. Future developments of integrated biohydrogen processes leading to efficient waste reduction, low CO2 emission and high overall hydrogen yield is discussed.

Influence of feedstock particle size on lignocellulose conversion--a review

Feedstock particle sizing can impact the economics of cellulosic ethanol commercialization through its effects on conversion yield and energy cost. Past studies demonstrated that particle size influences biomass enzyme digestibility to a limited extent. Physical size reduction was able to increase conversion rates to maximum of ≈ 50%, whereas chemical modification achieved conversions of >70% regardless of biomass particle size. This suggests that (1) mechanical pretreatment by itself is insufficient to attain economically feasible biomass conversion, and, therefore, (2) necessary particle sizing needs to be determined in the context of thermochemical pretreatment employed for lignocellulose conversion. Studies of thermochemical pretreatments that have taken into account particle size as a factor have exhibited a wide range of maximal sizes (i.e., particle sizes below which no increase in pretreatment effectiveness, measured in terms of the enzymatic conversion resulting from the pretreatment, were observed) from <0.15 to 50 mm. Maximal sizes as defined above were dependent on the pretreatment employed, with maximal size range decreasing as follows: steam explosion > liquid hot water > dilute acid and base pretreatments. Maximal sizes also appeared dependent on feedstock, with herbaceous or grassy biomass exhibiting lower maximal size range (<3 mm) than woody biomass (>3 mm). Such trends, considered alongside the intensive energy requirement of size reduction processes, warrant a more systematic study of particle size effects across different pretreatment technologies and feedstock, as a requisite for optimizing the feedstock supply system.

Optimized delignification of wood-derived lignocellulosics for improved enzymatic hydrolysis

One of the major bottlenecks in the bioconversion of lignocelluosic feedstocks to liquid ethanol is the recalcitrance of residue following pretreatment, specifically softwood derived residues. Peroxide delignification has previously been shown to effectively aid in the removal of condensed lignaceous moieties from substrates following pretreatment, and thereby improve the hydrolyzability of the polymeric carbohydrates to their monomeric constituents. Despite the effectiveness of peroxide, drawbacks in this system still remain, as the concentration of peroxide required for adequate hydrolysis performance is currently uneconomical. In an attempt to improve the efficacy of the delignification process, we evaluated other post-treatment operations and concurrently attempted to limit the decomposition of peroxide loading; with the over arching aim to improve the efficiency of the bioconversion process. By employing several peroxide stabilizers and pre-chelating the steam exploded recalcitrant substrates, we were able to substantially improve the delignification treatment of Douglas-fir wood chips, and to reduce peroxide loading by more than 50% without negative effects on the hydrolysis rates and yield.

Impact of dual temperature profile in dilute acid hydrolysis of spruce for ethanol production

BACKGROUND

The two-step dilute acid hydrolysis (DAH) of softwood is costly in energy demands and capital costs. However, it has the advantage that hydrolysis and subsequent removal of hemicellulose-derived sugars can be carried out under conditions of low severity, resulting in a reduction in the level of sugar degradation products during the more severe subsequent steps of cellulose hydrolysis. In this paper, we discuss a single-step DAH method that incorporates a temperature profile at two levels. This profile should simulate the two-step process while removing its major disadvantage, that is, the washing step between the runs, which leads to increased energy demand.

RESULTS

The experiments were conducted in a reactor with a controlled temperature profile. The total dry matter content of the hydrolysate was up to 21.1% w/w, corresponding to a content of 15.5% w/w of water insoluble solids. The highest measured glucose yield, (18.3 g glucose per 100 g dry raw material), was obtained after DAH cycles of 3 min at 209 degrees C and 6 min at 211 degrees C with 1% H2SO4, which resulted in a total of 26.3 g solubilized C6 sugars per 100 g dry raw material. To estimate the remaining sugar potential, enzymatic hydrolysis (EH) of the solid fraction was also performed. EH of the solid residue increased the total level of solubilized C6 sugars to a maximum of 35.5 g per 100 g dry raw material when DAH was performed as described above (3 min at 210 degrees C and 2 min at 211 degrees C with 1% H2SO4).

CONCLUSION

The dual-temperature DAH method did not yield decisively better results than the single-temperature, one-step DAH. When we compared the results with those of earlier studies, the hydrolysis performance was better than with the one-step DAH but not as well as that of the two-step, single-temperature DAH. Additional enzymatic hydrolysis resulted in lower levels of solubilized sugars compared with other studies on one-step DAH and two-step DAH followed by enzymatic hydrolysis. A two-step steam pretreatment with EH gave rise to a considerably higher sugar yield in this study.

Impact of impregnation time and chip size on sugar yield in pretreatment of softwood for ethanol production

Efficient pretreatment is necessary to make the wood-to-ethanol process more feasible. In this study, chips of different sizes were impregnated with SO(2) and steam-pretreated. Dilute-acid pretreatment together with subsequent enzymatic hydrolysis resulted in solubilization of between 69% and 73% of the fermentable sugars (glucose and mannose) in the raw material for the combinations of impregnation times and chip sizes investigated. Shorter impregnation times resulted in slightly lower mannose yields for the larger chips, probably due to poor diffusion of the catalyst. Small differences in glucose yield after enzymatic hydrolysis showed that the overall glucose yield was slightly higher for the smaller chips, however, whether the increased energy demand and cost of size reduction is compensated for by the higher yield, requires techno-economical evaluations.

Pretreatment of lignocellulosic wastes to improve ethanol and biogas production: a review

Lignocelluloses are often a major or sometimes the sole components of different waste streams from various industries, forestry, agriculture and municipalities. Hydrolysis of these materials is the first step for either digestion to biogas (methane) or fermentation to ethanol. However, enzymatic hydrolysis of lignocelluloses with no pretreatment is usually not so effective because of high stability of the materials to enzymatic or bacterial attacks. The present work is dedicated to reviewing the methods that have been studied for pretreatment of lignocellulosic wastes for conversion to ethanol or biogas. Effective parameters in pretreatment of lignocelluloses, such as crystallinity, accessible surface area, and protection by lignin and hemicellulose are described first. Then, several pretreatment methods are discussed and their effects on improvement in ethanol and/or biogas production are described. They include milling, irradiation, microwave, steam explosion, ammonia fiber explosion (AFEX), supercritical CO(2) and its explosion, alkaline hydrolysis, liquid hot-water pretreatment, organosolv processes, wet oxidation, ozonolysis, dilute-and concentrated-acid hydrolyses, and biological pretreatments.

Substrate pretreatment: the key to effective enzymatic hydrolysis of lignocellulosics?

Although the structure and function of cellulase systems continue to be the subject of intense research, it is widely acknowledged that the rate and extent of the cellulolytic hydrolysis of lignocellulosic substrates is influenced not only by the effectiveness of the enzymes but also by the chemical, physical and morphological characteristics of the heterogeneous lignocellulosic substrates. Although strategies such as site-directed mutagenesis or directed evolution have been successfully employed to improve cellulase properties such as binding affinity, catalytic activity and thermostability, complementary goals that we and other groups have studied have been the determination of which substrate characteristics are responsible for limiting hydrolysis and the development of pretreatment methods that maximize substrate accessibility to the cellulase complex. Over the last few years we have looked at the various lignocellulosic substrate characteristics at the fiber, fibril and microfibril level that have been modified during pretreatment and subsequent hydrolysis. The initial characteristics of the woody biomass and the effect of subsequent pretreatment play a significant role on the development of substrate properties, which in turn govern the efficacy of enzymatic hydrolysis. Focusing particularly on steam pretreatment, this review examines the influence that pretreatment conditions have on substrate characteristics such as lignin and hemicellulose content, crystallinity, degree of polymerization and specific surface, and the resulting implications for effective hydrolysis by cellulases.

Optimization of enzyme complexes for lignocellulose hydrolysis

The ability of a commercial Trichoderma reesei cellulase preparation (Celluclast 1.5L), to hydrolyze the cellulose and xylan components of pretreated corn stover (PCS) was significantly improved by supplementation with three types of crude commercial enzyme preparations nominally enriched in xylanase, pectinase, and beta-glucosidase activity. Although the well-documented relief of product inhibition by beta-glucosidase contributed to the observed improvement in cellulase performance, significant benefits could also be attributed to enzymes components that hydrolyze non-cellulosic polysaccharides. It is suggested that so-called "accessory" enzymes such as xylanase and pectinase stimulate cellulose hydrolysis by removing non-cellulosic polysaccharides that coat cellulose fibers. A high-throughput microassay, in combination with response surface methodology, enabled production of an optimally supplemented enzyme mixture. This mixture allowed for a approximately twofold reduction in the total protein required to reach glucan to glucose and xylan to xylose hydrolysis targets (99% and 88% conversion, respectively), thereby validating this approach towards enzyme improvement and process cost reduction for lignocellulose hydrolysis.

Characteristics of degraded cellulose obtained from steam-exploded wheat straw

The isolation of cellulose from wheat straw was studied using a two-stage process based on steam explosion pre-treatment followed by alkaline peroxide post-treatment. Straw was steamed at 200 degrees C, 15 bar for 10 and 33 min, and 220 degrees C, 22 bar for 3, 5 and 8 min with a solid to liquid ratio of 2:1 (w/w) and 220 degrees C, 22 bar for 5 min with a solid to liquid ratio of 10:1, respectively. The steamed straw was washed with hot water to yield a solution rich in hemicelluloses-derived mono- and oligosaccharides and gave 61.3%, 60.2%, 66.2%, 63.1%, 60.3% and 61.3% of the straw residue, respectively. The washed fibre was delignified and bleached by 2% H2O2 at 50 degrees C for 5 h under pH 11.5, which yielded 34.9%, 32.6%, 40.0%, 36.9%, 30.9% and 36.1% (% dry wheat straw) of the cellulose preparation, respectively. The optimum cellulose yield (40.0%) was obtained when the steam explosion pre-treatment was performed at 220 degrees C, 22 bar for 3 min with a solid to liquid ratio of 2:1, in which the cellulose fraction obtained had a viscosity average degree of polymerisation of 587 and contained 14.6% hemicelluloses and 1.2% klason lignin. The steam explosion pre-treatment led to a significant loss in hemicelluloses and alkaline peroxide post-treatment resulted in substantial dissolution of lignin and an increase in cellulose crystallinity. The six isolated cellulose samples were further characterised by FT-IR and 13C-CP/MAS NMR spectroscopy and thermal analysis.

Effect of initial moisture content and chip size on the bioconversion efficiency of softwood lignocellulosics

Previous optimization strategies for the bioconversion of lignocellulosics by steam explosion technologies have focused on the effects of temperature, pH, and treatment time, but have not accounted for changes in severity brought about by properties inherent in the starting feedstock. Consequently, this study evaluated the effects of chip properties, feedstock size (40-mesh, 1.5 x 1.5 cm, 5 x 5 cm), and moisture content (12% and 30%) on the overall bioconversion process, and more specifically on the efficacy of removal of recalcitrant lignin from the lignocellulosic substrates following steam explosion. Increasing chip size resulted in an improvement in the solids recovery, with concurrent increases in the water soluble, hemicellulose-derived sugar recovery (7.5%). This increased recovery is a result of a decrease in the "relative severity" of the pretreatment as chip size increases. Additionally, the decreased relative severity minimized the condensation of the recalcitrant residual lignin and therefore increased the efficacy of peroxide fractionation, where a 60% improvement in lignin removal was possible with chips of larger initial size. Similarly, increased initial moisture content reduced the relative severity of the pretreatment, generating improved solids and hemicellulose-derived carbohydrate recovery. Both increased chip size and higher initial moisture content results in a substrate that performs better during peroxide delignification, and consequently enzymatic hydrolysis. Furthermore, a post steam-explosion refining step increased hemicellulose-derived sugar recovery and was most effectively delignified (to as low as 6.5%). The refined substrate could be enzymatically hydrolyzed to very high levels (98%) and relatively fast rates (1.23 g/L/h).