Enzymatic Hydrolysis Of Pretreated Biomass Research Articles

Synthesis of lignin-based biosurfactant derived from kraft black liquor and its effect on enzymatic hydrolysis of pretreated biomass

Lignin, the main constituent in black liquor of up to 40%, can be converted into a value-added commodity such as a biosurfactant. In this study, lignin was extracted from the Acacia mangium black liquor kraft by acid precipitation (L1S) and ethanol fractionation (L2S). Subsequently, dried lignin was characterized physically and chemically. Biosurfactant was obtained by reacting lignin with polyvinyl alcohol (PVA). To evaluate the fruitfulness of biosurfactants on enzymatic hydrolysis, some optimizations have been conducted: volume ratio PVA: lignin, concentration PVA: lignin, different lignin source, substrate variation, and the effect of an initiator (potassium peroxodisulfate). Lignin by ethanol fractionation resulted in higher lignin content, methoxyl, molecular weight, and syringil but lower particle size and ash content. However, the thermal stability of these two lignins is similar. The ratio of PVA: lignin gave a positive effect on boosting reducing sugar yield (RSY) while the high concentration of PVA: lignin had the opposite effect. The best volume of PVA: lignin was 250 μL with a concentration of biosurfactant 0.4% to get the highest RSY per biomass about 80%. Meanwhile, biosurfactant-based L2S released more RSY than L1S and lignin sigma Aldrich. Kraft process of sweet sorghum bagasse (SSB) obtained more sugar than other substrates such as an alkaline autoclave SSB, jabon soda pulp, and microwave-assisted sulfuric acid pretreated of oil palm empty fruit bunch (EFB). The initiator addition during synthesizing of biosurfactant was predicted to contribute to achieving higher RSY compared to that of that non-initiator addition. This study demonstrates the ability of lignin-based biosurfactants to improve enzymatic hydrolysis yet the best condition was depending on the ratio, concentration, and volume of PVA: lignin, lignin types, substrates, and initiator.

Assessment of the effectiveness of liquid hot water and steam explosion pretreatments of fast-growing poplar (Populus trichocarpa) wood

In this paper, the influence of physicochemical pretreatment methods on the chemical composition, enzymatic hydrolysis efficiency and porosity of fast-growing Populus trichocarpa wood was compared. Among the pretreatment methods, the liquid hot water (LHW) and steam explosion (SE) were used, which were performed at three different temperatures (160 °C, 175 °C and 190 °C) and two residence times (15 min and 1 h). The chemical composition, enzymatic hydrolysis and porosity analysis were done for native wood and solid fraction obtained after LHW and SE pretreatments. The porosity analysis was performed by inverse size exclusion chromatography method. Additionally, inhibitors of hydrolysis and fermentation processes in the liquid and solid fractions obtained after pretreatments were examined. Based on the results, it was found that the tested pretreatments caused the greatest changes in the chemical content of hemicelluloses. It was found that after LHW and SE pretreatments up to 99.1% or 94.0%, respectively, of hemicelluloses were removed from the obtained solid fraction. Moreover, the LHW and SE processes greatly enhanced the enzymatic digestibility of fast-growing poplar wood. The highest glucose yield was achieved after 15 min of SE pretreatment at 190 °C and was 676.4 mg/g pretreated biomass, while in the case of xylose the highest value (119.3 mg/g pretreated biomass) was obtained after 15 min of LHW pretreatment at 160 °C. Generally, after SE pretreatment process, more inhibitors were formed, and a greater effect of porous structure development was noticed than after LHW pretreatment. Despite this difference, the average glucose contents and yields after enzymatic hydrolysis of pretreated biomass were generally similar regardless of the pretreatment used.

Curtailing citrate buffer inhibition effect on S. cerevisiae to enhance the fermentability of cellulosic hydrolysate

The current investigation emphasizes the effect of different citrate buffer strengths on cellulose conversion efficiency during the enzymatic hydrolysis of pretreated sorghum stalks, and the subsequent fermentation of enzymatic hydrolysates to achieve the industrial titer of bioethanol. A set of enzymatic hydrolysis experiments were conducted in 50 mM, 5 mM and 0.5 mM citrate buffer mediums which contain dilute sulfuric acid pretreatment derived biomass as substrate. As a result, similar cellulose conversion efficiencies such as 68.7%, 68.8% and 69% were observed during enzymatic hydrolysis of pretreated biomass at 50 mM, 5 mM and 0.5 mM citrate buffer strengths, respectively. Enzymatic hydrolysates derived from 50 mM, 5 mM and 0.5 mM citrate buffer mediums has been fermented by S. cerevisiae, which resulted in ethanol yield of 0.38 gp/gs, 0.47 gp/gs, and 0.47 gp/gs, respectively. As per the fermentation results, it has been observed that, metabolic growth of S. cerevisiae has been hindered due to the presence of high concentration of citric acid (50 mM) in the enzymatic hydrolysate.

Column reactors in fluidized bed configuration as intensification system for xylitol and ethanol production from napier grass (Pennisetum Purpureum)

Currently, the modern concept biorefinery industries require a consolidated, robust and cost-effective bioprocess applied to multi-products manufacturing. In alignment, this work presents biomass pretreatment of Pennisetum purpureum grass and integrated developments for carbohydrates portions utilization as carbon source for xylitol and ethanol production in intensified process conducted in column reactor with fluidized bed configuration, homogenized simply by air insertion. Primarily, by using hemicellulosic portion from acid hydrolysis, xylitol production was evaluated in column fluidized bed reactor by using the novel-wild Brazilian yeast Candida Tropicalis UFMGBX12-a verifying YP/S and Qp of 0.26 g/g and 0.06 g/L.h, respectively. Forwardly, the remaining celulignin from the acid hydrolysis was subjected to alkaline pretreatment, followed by Semi-Simultaneous saccharification and Fermentation process, in an intensification approach performed in column fluidized bed reactor, applied to ethanol production by Scheffersomyces Shehatae UFMG-HM 52.2. Enzymatic hydrolysis of pretreated biomass comprised 90% of glucose yield in 72h of saccharification, while ethanol productivity of 0.21 g/L.h, was found in 24 h of fermentation process. These new developments conferred potential use of Pennisetum purpureum grass as carbon source for xylitol and ethanol production in column reactor towards sustainable intensification process implementation.

Two Nonnegligible Factors Influencing Lignocellulosic Biomass Valorization: Filtration Method after Pretreatment and Solid Loading during Enzymatic Hydrolysis

Valorization of lignocellulosic biomass into biofuels has received considerable attention for decades with tremendous thermochemical pretreatments proposed. However, inconsistencies among studies in lignin removal can often be misleading and even violate the chemical mechanism, which might be attributed to the variation in the filtration method used after pretreatment. A phenomenon, promoting pretreatment strategies based on sugar conversion efficiency or yield only from single and random low-solid enzymatic hydrolysis, was also observed. Herein, the effects of filtration methods using a slow drip metal filter (SDMF) with an aperture of 0.2 mm and Whatman grade 4 filter paper (WGFP) with an aperture of 20–25 μm under vacuum filtration after liquid hot water (LHW), acid, and alkali pretreatments on the chemical composition of the solid and liquid, sugar recoveries, and lignin removal and solid loading (2–15%) on enzymatic hydrolysis of corn stover and poplar wood were investigated. Results showed that SDMF increased the glucan content (1.1–3.0%) in pretreated biomass and induced solid loss (3.8–12.6%) into the filtrates, resulting in lower sugar recoveries and overestimated lignin removal compared to WGFP. 5-Hydroxymethylfurfural (HMF) and furfural derived from sugar degradation triggered pseudolignin formation, inducing a negative lignin removal for both LHW and acid pretreated biomass. In comparison, alkali pretreatment neutralized the weak acids released from sugar decomposition and achieved a robust delignification (67.8–90.8%). Solid loading used for enzymatic hydrolysis of pretreated biomass determined sugar concentration, conversion efficiency, and yield. This result indicates that promoting pretreatment technologies based on sugar conversion efficiency or yield of enzymatic hydrolysis at low solid loading may be misleading. This work demonstrates that the filtration method used for solid and liquid separations after pretreatment and solid loading for enzymatic hydrolysis should be cautiously selected and implemented when valorizing biomass into biofuels.

Enzymatic Hydrolysis Performance of Biomass by the Addition of a Lignin Based Biosurfactant

Hydrolysis of biomass for the production of fermentable sugar can be improved by the addition of surfactants. In pulp and paper mills, lignin, which is a by-product of the pulping process, can be utilized as a fine chemical. In the hydrolysis process, lignin is one of the major inhibitors of the enzymatic breakdown cellulose into sugar monomer. Therefore, the conversion of lignin into a biosurfactant offers the opportunity to solve the waste problem and improve hydrolysis efficiency. In this study, lignin derivatives, a biosurfactant, was applied to enzymatic hydrolysis of various lignocellulosic biomass. This Biosurfactant can be prepared by reacting lignin with a hydrophilic polymer such as polyethylene glycol diglycidylethers (PEDGE). In this study, the effect of biosurfactants on the enzymatic hydrolysis of pretreated sweet sorghum bagasse (SSB), oil palm empty fruit bunch, and sugarcane trash with different lignin contents was investigated. The results show that lignin derivatives improve the enzymatic hydrolysis of the pretreated biomass with low lignin content, however, it has less influence on the enzymatic hydrolysis of other pretreated biomass with lignin content higher than 10% (w/w). The use of biosurfactant on SSB kraft pulp can increase the sugar yield from 45.57% to 81.49%.

Enhancement of alkaline-oxidative delignification of wheat straw by semi-batch operation in a stirred tank reactor

This paper compares a semi-batch operation and a conventional one of an alkaline oxidative pretreatment of wheat straw carried out in a stirred tank reactor. For the pretreatment, different concentrations of biomass (6% up to 12% w/v) and two different particle sizes (mesh #40–60 and #>60) were experimented. The performance of processes was evaluated through the analysis of lignocellulosic composition of the biomass, and the enzymatic hydrolysis of pretreated biomass using the Cellic® CTec2 enzyme complex by Novozymes®. The process time of semi-batch operation is significantly lower than the batch one and enables a higher load of biomass, showing a delignification yield between 55 and 60%. In the first 5 h of reaction time, the enzymatic hydrolysis experiments reached their maximum yields of 72 and 66% according to reducing sugars conversion when using the mesh #>60 mesh and #40–60, respectively.

Evaluation of efficient glucose release using sodium hydroxide and phosphoric acid as pretreating agents from the biomass of Sesbania grandiflora (L.) Pers.: A fast growing tree legume

Sesbania grandiflora (L.) Pers. is one of the fast growing tree legumes having the efficiency to produce around 50tha−1 above ground dry matters in a year. In this study, biomass of 2years old S. grandiflora was selected for the chemical composition, pretreatments and enzymatic hydrolysis studies. The stem biomass with a wood density of 3.89±0.01gmcm−3 contains about 38% cellulose, 12% hemicellulose and 28% lignin. Enzymatic hydrolysis of pretreated biomass revealed that phosphoric acid (H3PO4) pretreated samples even at lower cellulase loadings [1 Filter Paper Units (FPU)], could efficiently convert about 86% glucose, while, even at higher cellulase loadings (60FPU) alkali pretreated biomass could convert only about 58% glucose. The effectiveness of phosphoric acid pretreatment was also supported by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FTIR) analysis.

Enzymatic hydrolysis of thermochemically pretreated biomass using a mixture of cellulolytic enzymes produced from different fungal sources

Enzymatic hydrolysis of pretreated lignocellulosic raw material is one of the major steps in the biofuel production. In this study, sorghum straw was pretreated under previously optimized conditions (using 0.5 M sodium hydroxide, 8% substrate concentration, 120 °C temperature and 20 min of incubation time). Cellulase enzymes were produced using three different fungal sources (Aspergillus niger, Fusarium oxysporum and Trichoderma harzianum). Enzymatic hydrolysis of pretreated biomass was carried out using individual and different mixture of cellulases. Maximum reducing sugar yield was obtained when an equal mixture of three different cellulases was used. The enzymatic hydrolysis process was optimized through central composite design based on response surface methodology using an equal mixture of three different cellulases (1:1:1). The data showed that maximum reducing sugar yield of 464.2 mg/g dry substrate was obtained at 10% substrate concentration, 55 °C and after 48 h of incubation. Further, batch (a process where all the substrates were fed into the bioreactor at the beginning of the reaction) and fed-batch (a process where substrates were fed into the bioreactor at specific time intervals) process of enzymatic hydrolysis were compared at high substrate concentration (20%). The results showed that an increase in reducing sugar yield (355.6 mg/g dry substrate) was obtained in case of fed-batch enzymatic hydrolysis as compared to batch enzymatic hydrolysis (285.3 mg/g dry substrate) process. The above results can be useful for efficient hydrolysis of lignocellulosic biomass and cost-effective biofuel production.

에탄올 유기용매 전처리를 이용한 옥수수대의 효소당화

새로운 수송용 에너지자원으로 각광받는 바이오매스의 효율적인 당화를 위한 전처리방법이 연구되고 있다. 최근 바이오매스의 에너지 전환 공정 중 전처리 비용이 높은 비중을 차지하고 있으며 이중 폐수처리가 커다란 문제점으로 지적되고 있다. 따라서 폐수발생을 줄이고 재사용이 용이한 유기용매(Organosolv)를 이용한 전처리를 수행하였으며, 전처리 바이오매스의 잔류 고형물의 양과 제거된 성분의 양을 이용하여 바이오매스의 전처리 효과를 효소당화를 통해 알아보았다. 전처리에 사용한 유기용매로는 99.5 wt% 에탄올을 사용하였고, 초본계 바이오매스인 옥수수대(corn stover)를 이용하여 전처리 하였다. 전처리 효과는 <TEX>$130{\sim}190^{\circ}C$</TEX> 조건에서 시간대별로 진행하여 전처리된 바이오매스의 효소당화를 통하여 확인하였다. 효소당화결과로 가장 높은 글루코오스 당화율을 보였던 전처리 온도는 <TEX>$190^{\circ}C$</TEX>에서 반응시간 70분 이상의 조건 이였으며, 이 때 68% 이상의 당화율을 얻을 수 있었다. 또한 전처리 바이오매스의 잔류 고형물(Solid remaining)은 70% 이상이었고, 대부분의 셀룰로오스(Cellulose)와 헤미셀룰로오스(Hemicellulose)의 손실이 미비하여 대부분의 당 성분을 회수할 수 있다는 장점을 보였다. This study is for the effective pretreatment and saccharification of lignocellulosic biomass for a transport fuel receiving attention. The waste water during the pretreatment of biomass is major factor for determining the price of biofuel. Therefore, we conducted high concentration of organosolv pretreatment for decline waste water and reusing the solvent. We confirmed effect of organosolv pretreatment by components analysis and enzymatic hydrolysis of pretreated biomass. The corn stover was used for and 99.5 wt% of ethanol as a organosolv pretreatment. The pretreatment condition was varied 130 to <TEX>$190^{\circ}C$</TEX> during the designated reaction times and the effect of pretreatment was investigated by enzymatic hydrolysis. The highest glucose conversion was more than 68% the pretreatment condition of <TEX>$190^{\circ}C$</TEX> for 70 min or more. The solid remaining was more than 70% and almost of cellulose and hemicellulose were survived.

Pretreatment of fibrous biomass and growth of biosurfactant-producing Bacillus subtilis on biomass-derived fermentable sugars.

Pretreatment of six fibrous biomasses (switchgrass, alfalfa, soy hulls, soy fiber, DDGS and Baggase) and subsequent hydrolysis using cellulolytic enzymes at a 2.5% (v/v) and 5% (v/v) loading 2.5 (v/v) and 5% (v/v) loading was compared for higher amounts of sugars released. Soaking of biomasses of switchgrass, alfalfa, soy hulls and bagasse in 15% w/w ammonia was optimal at 60 °C for 12 h, followed by enzymatic hydrolysis, yielding 72, 70, 80 and 75% carbohydrate conversions, respectively. However, soaking in ammonia was not needed for soy fiber and DDGS as these contained very little lignin. Ultrasonication for 3 min @ 100% amplitude (170 µM) was found to be optimal for soy fiber and DDGS from which 77 and 83% carbohydrate conversion, respectively, was obtained following enzyme treatment at 5% (w/v) enzyme. The sugars released by enzymatic hydrolysis of pretreated biomass were utilized as an energy source by Bacillus subtilis in fermentation media at 2% (w/v) of concentration. In shake flask trials, cell growth was 15-20% higher on hydrolysates of ammonia-treated switchgrass and alfalfa vs. glucose-based control media due to the presence of a wider range of monomeric sugars (glucose, xylose, arabinose, mannose and galactose). In contrast, growth was less on soy hull hydrolysates prepared with ammonia pretreatment.

Enhancement of fungal delignification of rice straw by Trichoderma viride sp. to improve its saccharification

Fungal delignification can be considered as a feasible process to pre-treat lignocellulosic biomass in biofuel production, if its performance is improved in terms of efficiency thorough a few modifications. In this study, Trichoderma viride was utilized to investigate the effect of wet-milling, addition of surfactant (Tween 80) and optimization of operating factors such as temperature, biomass to liquid medium ratio and glucose concentration on biodelignification of rice straw. Next, the enzymatic hydrolysis of pretreated biomass was studied at various pretreatment times. Results revealed that the wet milling and addition of surfactant increases the lignin removal about 15% and 11%, respectively. The optimization of operating factors resulted in high lignin removal efficiency equal to 74% in a 30 day pretreatment. The maximum enzymatic saccharification of pretreated biomass at optimum conditions was obtained equal to 56%. Conversion of cellulose to reducing sugars during the pretreatment stage was 21% which suggests that higher saccharification efficiency could be achieved in a simultaneous pretreatment and saccharification process.

Hemp hurds biorefining: A path to green l-(+)-lactic acid production

Sugars streams generated by organosolv pretreatment of hemp hurds, cellulose (C6) and hemicellulose (C5) fractions, were fermented to lactic acid (LA) by Bacillus coagulans strains XZL4 and DSM1. Pretreatment conditions and enzymatic hydrolysis were optimized and B. coagulans aptness to use lignocellulosic-derived sugars as a carbon source was evaluated. Methanolic organosolv pretreatment with 2.5% (w/w) H2SO4 gave the best results in terms of glucan recovery (98%), enzymatic hydrolysis of pretreated biomass (70%) and hemicellulosic sugars recovery (61%). C6 and C5 sugars fermentation by strain XZL4 gave, high LA yields (0.90 and 0.84g/g), high titers (141 and 109g/L), and high enantiomeric excess (>99%). Overall, 42g of l-LA were obtained from 100g of raw hemp hurds. These results can be considered promising for lignocellulosic feedstock valorization toward the production of polymer-grade LA.

Design and optimization of a sono-hybrid process for bioethanol production from Parthenium hysterophorus

This paper presents a laboratory scale process for production of bioethanol from Parthenium hysterophorus. This process consists of three steps, viz. biomass pretreatment, enzymatic hydrolysis of pretreated biomass and fermentation of pentose and hexose hydrolyzates obtained from acid pretreatment and enzyme hydrolysis, respectively. The step of enzyme hydrolysis has been optimized using response surface methodology for concentrations of the enzymes and the concentration of biomass. The optimum parameters were: biomass concentration = 4.212% (w/v), cellulase concentration = 135.86 FPU/g substrate and cellobiase concentration = 75 U/g substrate. Use of ultrasound during enzymatic hydrolysis at optimized conditions resulted in a marked 18-fold enhancement in the kinetics of hydrolysis. Fermentation of the pentose hydrolyzate with Candida shehatae NCIM 3500 resulted to ethanol yield of 0.069 g/g raw biomass, while fermentation of the enzymatic hydrolyzate with Saccharomyces cerevisiae MTCC 170 resulted to an ethanol yield of 0.187 g/g raw biomass. The total ethanol yield from fermentation of pentose and hexose hydrolyzates was 0.26 g/g raw biomass. This process also provides a potential solution to effective utilization of the noxious waste biomass of P. hysterophorus.

Screening and optimization of pretreatments for Parthenium hysterophorus as feedstock for alcoholic biofuels

Parthenium hysterophorus world’s seven most devastating and hazardous weeds, and is abundantly available in several parts of the world. This study treats the subject of effective utilization of this waste biomass (which has cellulose content of 45.2±1.81% w/w) for biofuels production. We have presented a comprehensive and comparative assessment of numerous pretreatment strategies for P. hysterophorus, comprising of all major physical, chemical and physicochemical methods. The yardstick of assessment has been amount of fermentable sugars released during the pretreatment and the post-treatment enzymatic hydrolysis of pretreated biomass. Carboxymethylcellulase (1.0U/mg, 1.7mg/mL) produced by an isolate Bacillus amyloliquefaciens SS35 and β-glucosidase (Novozyme 188), have been used for enzymatic hydrolysis of pretreated biomass. Among the different methods employed for pretreatment, the most efficient treatment has been revealed to be autoclaving of biomass at 121°C and 15psi pressure for 30min in acidic (1% v/v, H2SO4) environment. Total reducing sugar (TRS) yield during this pretreatment, mainly due to hydrolysis of hemicellulosic fraction of biomass, has been 285.3mg/g of raw biomass. Further enzymatic hydrolysis resulted in reducing sugar yield of 187.4mg/g of pretreated biomass (9.37g/L). The total fermentable sugar (TFS) yield from the optimized pretreatment was 397.7mg/g raw biomass (39.77g/100g raw biomass). The effects of different pretreatment methods on biomass structure and complexity were investigated by field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) techniques. Comparative assessment of the results with pretreatment and hydrolysis of other conventional agro- and forest residues shows that P. hysterophorus has same potential for being the feedstock for biofuels. These results conclusively demonstrate the utility of P. hysterophorus for sustainable biofuels production.

Swollenin aids in the amorphogenesis step during the enzymatic hydrolysis of pretreated biomass

A key limitation in the overall hydrolysis process is the restricted access that the hydrolytic enzymes have due to the macro-and-micro structure of cellulose and its association with hemicellulose and lignin. Previous work has shown that several non-hydrolytic proteins can disrupt cellulose structure and boost the activity of hydrolytic enzymes when purer forms of cellulose are used. In the work reported here, Swollenin primarily disrupted the hemicellulosic fraction of pretreated corn stover, resulting in the solubilisation of monomeric and oligomeric sugars. Although Swollenin showed little synergism when combined with the cellulase monocomponents exoglucanase (CEL7A) and endoglucanase (CEL5A), it showed pronounced synergism with xylanase monocomponents Xylanase GH10 and Xylanase GH11, resulting in the release of significantly more xylose (>300%). It appears that Swollenin plays a role in amorphogenesis and that its primary action is enhancing access to the hemicellulose fraction that limits or masks accessibility to the cellulose component of lignocellulosic substrates.

Temperature sensitivity of cellulase adsorption on lignin and its impact on enzymatic hydrolysis of lignocellulosic biomass

Unproductive enzyme adsorption is an important factor in addition to steric hindrance of lignin that limits the enzymatic hydrolysis of lignocellulosic biomass. While both are important factors, enzymatic hydrolysis of pretreated biomass is most likely conducted in the presence of certain amount of lignin residues that may not necessarily present accessibility hindrance, but can competitively absorb the enzyme. This paper presents a study with purified lignin samples to elucidate the role of unproductive enzyme adsorption. It appeared that lignin adsorbed cellulase quickly at 4°C with adsorption equilibrium reached within 1h, similar to that observed for crystalline cellulose. Increasing temperature to 50°C (typical hydrolytic reaction condition) facilitated the rate of cellulase adsorption on cellulose with a peak of adsorption reached at 0.25h; however, adsorption on lignin was surprisingly slower and took over 12h to reach equilibrium, which was accompanied with a 10-fold increase in adsorption capacity. Despite the high adsorption capacity of lignin (which is comparable to that of cellulose) at 50°C, the presence of added lignin imposed only minimal impact on the enzyme apparent activity, most likely due to the slow adsorption kinetics of lignin.

Hydrogen peroxide and lime based oxidative pretreatment of wood waste to enhance enzymatic hydrolysis for a biorefinery: Process parameters optimization using response surface methodology

Response surface methodology (RSM) was adopted for the optimization of process variables in the alkaline peroxide oxidation (APO) pretreatment of Vitellaria paradoxa sawdust based on central composite design (CCD) experiments. A 23 five level CCD with central and axial points was used to develop a statistical model for the optimization of process variables. Maximum response for the pretreatment was obtained when applying the optimum values for temperature (150°C), time (45min), and 1% (v/v) H2O2. At the optimum conditions, up to 70% of the initial hemicellulose was removed in treatments, which also caused some delignification (up to 11% of the initial lignin was removed), whereas cellulose was almost quantitatively retained in the solid phase. Alkaline peroxide assisted wet air oxidation (APAWAO) pretreatment at the optimum conditions resulted in enrichment up to 60% cellulose content along with solubilization of 80% hemicellulose and 17% of lignin initially present in the raw sawdust. Reducing sugars yield after 72h enzymatic hydrolysis of pretreated biomass at optimized APO conditions was 177.89mgequivalent glucoseg−1 dry biomass. Addition of 10bar air pressure at the optimized pretreatment conditions increased the sugars yield to 263.49mgequivalent glucoseg−1 dry biomass.

Different ionic liquids favor different lignocellulosic biomass particle sizes during pretreatment to function efficiently

Cotton stalks at four different particles sizes (<0.15 mm, 0.15–0.5 mm, 0.5–1.0 mm and 1.0–2.0 mm) were subjected to ionic liquid pretreatment via 1-ethyl-3-methylimidazolium acetate (EMIMAc) and 1-ethyl-3-methylimidazolium chloride (EMIMCl) followed by the enzymatic hydrolysis of pretreated biomass. The changes in crystalline structure, lignin content and digestibility of the pretreated samples were investigated in addition to the glucose yield obtained from cotton stalks. For EMIMAc pretreatment, the lowest glucose yield (57%) was obtained upon the pretreatment of cotton stalks having the smallest particle size prior to pretreatment (<0.15 mm) while cotton stalks with larger particle sizes gave higher glucose yields of which were at least 71%. On the contrary, EMIMCl pretreatment functioned more efficiently with cotton stalks having smaller particle sizes (<0.15 mm and 0.15–0.5 mm) where increasing the biomass particle size further caused a decrease in the glucose yield from approximately 49% to 33%, unlike the EMIMAc pretreatment. These differences in the glucose yields obtained for different ionic liquids suggest that the ideal particle size of biomass prior to pretreatment may change from one ionic liquid to another.

Comparison of mechanistic models in the initial rate enzymatic hydrolysis of AFEX-treated wheat straw

BackgroundDifferent mechanistic models have been used in the literature to describe the enzymatic hydrolysis of pretreated biomass. Although these different models have been applied to different substrates, most of these mechanistic models fit into two- and three-parameter mechanistic models. The purpose of this study is to compare the models and determine the activation energy and the enthalpy of adsorption of Trichoderma reesei enzymes on ammonia fibre explosion (AFEX)-treated wheat straw. Experimental enzymatic hydrolysis data from AFEX-treated wheat straw were modelled with two- and three-parameter mechanistic models from the literature. In order to discriminate between the models, initial rate data at 49°C were subjected to statistical analysis (analysis of variance and scatter plots).ResultsFor three-parameter models, the HCH-1 model best fitted the experimental data; for two-parameter models Michaelis-Menten (M-M) best fitted the experimental data. All the three-parameter models fitted the data better than the two-parameter models. The best three models at 49°C (HCH-1, Huang and M-M) were compared using initial rate data at three temperatures (35°, 42° and 49°C). The HCH-1 model provided the best fit based on the F values, the scatter plot and the residual sum of squares. Also, its kinetic parameters were linear in Arrhenius/van't Hoff's plots, unlike the other models. The activation energy (Ea) is 47.6 kJ/mol and the enthalpy change of adsorption (ΔH) is -118 kJ/mol for T. reesei enzymes on AFEX-treated wheat straw.ConclusionAmong the two-parameter models, Michaelis-Menten model provided the best fit compared to models proposed by Humphrey and Wald. For the three-parameter models, HCH-1 provided the best fit because the model includes a fractional coverage parameter (ϕ) which accounts for the number of reactive sites covered by the enzymes.