Pretreatment of Leucaena leucocephala wood by acidified glycerol: optimization, severity index and correlation analysis

In this study, Leucaena leucocephala wood was pretreated with aqueous glycerol having H₂SO₄ as the catalyst. Response surface methodology (RSM) and artificial neural network (ANN) were used to optimize the process parameters, catalyst concentration (1-3%), duration (120-300 min) and temperature (100-150 °C). ANN gave more accurate predictions for total reducing sugar yield than RSM. ANN also had lower values for error functions. Severity index (SI) was calculated based on the temperature, duration and catalyst concentration. Increase in SI from 0.21 * 10³ to 2.06 * 10³ increased total reducing sugar (TRS) production from 39.97 g/kg to 321.8 g/kg. Further increase in SI reduced the TRS and this change positively correlates with the loss of cellulose content. Correlation analysis showed that severity index can also be used to describe pretreatment process.

A Biorefinery Cascade Conversion of Hemicellulose-Free Eucalyptus Globulus Wood: Production of Concentrated Levulinic Acid Solutions for γ-Valerolactone Sustainable Preparation

Eucalyptus globulus wood samples were subjected to preliminary aqueous processing to remove water-soluble extractives and hemicelluloses, and the resulting solid (mainly made up of cellulose and lignin) was employed as a substrate for converting the cellulosic fraction into mixtures of levulinic and formic acid through a sulfuric acid-catalyzed reaction. These runs were carried out in a microwave-heated reactor at different temperatures and reaction times, operating in single-batch or cross-flow modes, in order to identify the most favorable operational conditions. Selected liquid phases deriving from these experiments, which resulted in concentrated levulinic acid up to 408 mmol/L, were then employed for γ-valerolactone production by levulinc acid hydrogenation in the presence of the commercial 5% Ru/C catalyst. In order to assess the effects of the main reaction parameters, hydrogenation experiments were performed at different temperatures, reaction times, amounts of ruthenium catalyst and hydrogen pressure. Yields of γ-valerolactone in the range of 85–90 mol % were obtained from the hydrogenation of the wood-derived solutions containing levulinic acid, obtained by single-batch operation or by the cross-flow process. The negative effect of co-produced formic acid present in crude levulinic acid solutions was evidenced and counteracted efficiently by allowing the preliminary thermal decomposition of formic acid itself.

A novel hybrid organosolv: steam explosion method for the efficient fractionation and pretreatment of birch biomass

BACKGROUND

The main role of pretreatment is to reduce the natural biomass recalcitrance and thus enhance saccharification yield. A further prerequisite for efficient utilization of all biomass components is their efficient fractionation into well-defined process streams. Currently available pretreatment methods only partially fulfill these criteria. Steam explosion, for example, excels as a pretreatment method but has limited potential for fractionation, whereas organosolv is excellent for delignification but offers poor biomass deconstruction.

RESULTS

In this article, a hybrid method combining the cooking and fractionation of conventional organosolv pretreatment with the implementation of an explosive discharge of the cooking mixture at the end of pretreatment was developed. The effects of various pretreatment parameters (ethanol content, duration, and addition of sulfuric acid) were evaluated. Pretreatment of birch at 200 °C with 60% v/v ethanol and 1% w/w_biomass H₂SO₄ was proven to be the most efficient pretreatment condition yielding pretreated solids with 77.9% w/w cellulose, 8.9% w/w hemicellulose, and 7.0 w/w lignin content. Under these conditions, high delignification of 86.2% was demonstrated. The recovered lignin was of high purity, with cellulose and hemicellulose contents not exceeding 0.31 and 3.25% w/w, respectively, and ash to be < 0.17% w/w in all cases, making it suitable for various applications. The pretreated solids presented high saccharification yields, reaching 68% at low enzyme load (6 FPU/g) and complete saccharification at high enzyme load (22.5 FPU/g). Finally, simultaneous saccharification and fermentation (SSF) at 20% w/w solids yielded an ethanol titer of 80 g/L after 192 h, corresponding to 90% of the theoretical maximum.

CONCLUSIONS

The novel hybrid method developed in this study allowed for the efficient fractionation of birch biomass and production of pretreated solids with high cellulose and low lignin contents. Moreover, the explosive discharge at the end of pretreatment had a positive effect on enzymatic saccharification, resulting in high hydrolyzability of the pretreated solids and elevated ethanol titers in the following high-gravity SSF. To the best of our knowledge, the ethanol concentration obtained with this method is the highest so far for birch biomass.

Impact and significance of alkaline-oxidant pretreatment on the enzymatic digestibility of Sphenoclea zeylanica for bioethanol production

Gooseweed (Sphenoclea zeylanica Gaertn.) is a pest on the rice field that has a potential to be a promising substrate for bioethanol production. Dry powdered gooseweed was firstly pretreated with 1% NaOH, following 1% H₂O₂ at variety conditions. The hydrolysis process was set at 50°C for 24-72h with enzyme cellulase (β-glucosidase) while the fermentation process was carried using Saccharomyces cerevisiae TISTR 5020 at 33°C for nine days. The ethanol concentration was recorded for three, five, seven, and nine days using an ebulliometer. The results showed that the treatment with only 1% NaOH for 24h has the highest sugar performance. In regard with hydrolysis, the optimum retention time was at 24h. Lastly, the highest ethanol concentration was achieved at 11.84g/L after five days and a rapid decreasing after seven to nine days was also observed.

Comparison of red microalgae (Porphyridium cruentum) culture conditions for bioethanol production

Microalgae biomass are useful resources in biofuel production. The objective of this study was to evaluate bioethanol production in response to Porphyridium cruemtum culture conditions. Enzymatic hydrolysis of seawater P. cruemtum (SPC) and freshwater P. cruemtum (FPC, 1% substrate loading, w/v) resulted in glucose conversion yields of 89.8 and 85.3%, respectively, without any pretreatment. However, FPC hydrolysate was more efficiently converted to ethanol about 7.1% than SPC hydrolysate. The comparison of separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) showed that SSF processing is a superior method for bioethanol production from both SPC and FPC. Though SSF processing (5% substrate loading, w/v) in a 500-mL twin-neck round bottom flask, we achieved ethanol conversion yields of 65.4 and 70.3% from SPC and FPC, respectively, after 9h. These findings indicate that P. cruemtum can grow in freshwater conditions and is an efficient candidate for bioethanol production.

Effective depolymerization of concentrated acid hydrolysis lignin using a carbon-supported ruthenium catalyst in ethanol/formic acid media

Lignin isolated by two-step concentrated acid hydrolysis of empty fruit bunch (EFB) was effectively depolymerized into a high-quality bio-oil using formic acid (FA) as an in-situ hydrogen source and Ru/C as a catalyst in supercritical ethanol. A bio-oil yield of 66.3wt% with an average molecular weight of 822g/mol and an aromatic monomer content of 6.1wt% was achieved at 350°C and a FA-to-lignin mass ratio of 3 after a reaction time of 60min. The combination of Ru/C and FA also resulted in a significant reduction in the oxygen content of the bio-oil by ∼60% and a corresponding increase in the higher heating value (HHV) to 32.7MJ/kg due to the enhanced hydrodeoxygenation activity. An examination of the FA decomposition characteristics revealed that Ru/C provides a greater increase in the rate of hydrogen production from FA, explaining the efficient depolymerization of lignin in a combined system.

Effects of acidified aqueous glycerol and glycerol carbonate pretreatment of rice husk on the enzymatic digestibility, structural characteristics, and bioethanol production

Rice husk as an abundant biomass was used in this study, and it contained 30.1% glucan and 13.5% xylan, 22.4% lignin. The pretreated rice husk with glycerol carbonate and acidified aqueous glycerol (10% water) at 90°C and 130°C for 60min had the maximum yield of glucan digestibility which was 78.2% and 69.7% respectively, using cellulase for 72h. The simultaneous saccharification and fermentation was conducted anaerobically at 37°C with Saccharomyces cerevisiae, 5% w/v glucan and 10FPU/g glucan of cellulase. 11.58 and 8.84g/L was the highest ethanol concentration after 3days of incubation form pretreated rice husk with glycerol carbonate and acidified aqueous glycerol respectively.

Production and characterization of enzymatic cocktail produced by Aspergillus niger using green macroalgae as nitrogen source and its application in the pre-treatment for biogas production from Ulva rigida

Marine macroalgae are gaining more and more importance as a renewable feedstock for durable bioenergy production, but polysaccharides of this macroalgae are structurally complex in its chemical composition. The use of enzymatic hydrolysis may provide new pathways in the conversion of complex polysaccharides to fermentable sugars. In this study, an enzymatic cocktail with high specificity was first isolated from Aspergillus niger using the green macroalgae Ulva rigida as nitrogen source. The cocktail is rich on β-glucosidase, pectinase and carboxy-methyl-cellulase (CMCase). The highest activity was obtained with β-glucosidase (109IUmL(-1)) and pectinase (76IUmL(-1)), while CMCase present the lowest activity 4.6IUmL(-1). The U. rigida pre-treatment with this enzymatic cocktail showed high rate of reduced sugar release, and could bring promising prospects for enzymatic pre-treatment of the biogas production from U. rigida biomass which reached 1175mLgCODint(-1).

Combined Detoxification and In-situ Product Removal by a Single Resin During Lignocellulosic Butanol Production

Phragmites australis (an invasive plant in North America) was used as feedstock for ABE (acetone-butanol-ethanol) fermentation by Clostridium saccharobutylicum. Sulphuric acid pretreated phragmites hydrolysate (SAEH) without detoxification inhibited butanol production (0.73 g/L butanol from 30 g/L sugars). The treatment of SAEH with resin L-493 prior the fermentation resulted in no inhibitory effects and an ABE titer of 14.44 g/L, including 5.49 g/L butanol was obtained, corresponding to an ABE yield and productivity of 0.49 g/g and 0.60 g/L/h, respectively. Dual functionality of the resin was realized by also using it as an in-situ product removal agent. Integrating in-situ product removal allowed for the use of high substrate concentrations without the typical product inhibition. Resin-detoxified SAEH was supplemented with neat glucose and an effective ABE titer of 33 g/L (including 13.7 g/L acetone, 16.4 g/L butanol and 1.9 g/L ethanol) was achieved with resin-based in-situ product removal, corresponding to an ABE yield and productivity of 0.41 g/g and 0.69 g/L/h, respectively. Both detoxification of the substrate and the products was achieved by the same resin, which was added prior the fermentation. Integrating hydrolysate detoxification and in-situ butanol removal in a batch process through single resin can potentially simplify cellulosic butanol production.

Characterization and biotechnological application of recombinant xylanases from Aspergillus nidulans

Two xylanases from Aspergillus nidulans, XlnB and XlnC, were expressed in Pichia pastoris, purified and characterized. XlnB and XlnC achieved maximal activities at 60°C and pH 7.5 and at 50°C and pH 6.0, respectively. XlnB showed to be very thermostable by maintaining 50% of its original activity after 49h incubated at 50°C. XlnB had its highest activity against wheat arabinoxylan while XlnC had the best activity against beechwood xylan. Both enzymes were completely inhibited by SDS and HgCl2. Xylotriose at 1mg/ml also totally inibited XlnB activity. TLC analysis showed that the main product of beechwood xylan hydrolysis by XlnB and XlnC was xylotetraose. An additive effect was shown between XlnB and XlnC and the xylanases of two tested commercial cocktails. Sugarcane bagasse saccharification results showed that these two commercial enzymatic cocktails were able to release more glucose and xylose after supplementation with XlnB and XlnC.

Surface Modification of Naturally Available Biomass for Enhancement of Heavy Metal Removal Efficiency, Upscaling Prospects, and Management Aspects of Spent Biosorbents: A Review

Heavy metal pollution in water emerges as a severe socio-environmental problem originating primarily from the discharge of industrial wastewater. In view of the toxic, non-biodegradable, and persistent nature of most of the heavy metal ions, remediation of such components becomes an absolute necessity. Biosorption is an emerging tool for bioremediation that has gained momentum for employing low-cost biological materials with effective metal binding capacities. Even though biological materials possess excellent metal adsorption abilities, they show poor mechanical strength and low rigidity. Other disadvantages include solid-liquid separation problems, possible biomass swelling, lower efficiency for regeneration or reuse, and frequent development of high pressure drop in the column mode that limits its applications under real conditions. To improve the biosorption efficiency, biomasses need to be modified with a simple technique for selective/multi-metal adsorption. This review is intended to cover discussion on biomass modification for enhanced biosorption efficiency, mechanism studies using various instrumental/analytical techniques, and future direction for research and development including the fate of spent biosorbent. In most of the previously published researches, difficulty of the process in scaling up has not been addressed. The current article outlines the application potential of biosorbents in the development of hybrid technology integrated with membrane processes for water and wastewater treatment in industrial scale.

Phosphoric acid pretreatment of Achyranthes aspera and Sida acuta weed biomass to improve enzymatic hydrolysis

Achyranthes aspera and Sida acuta, two types of weed biomass are abundant and waste in Thailand. We focus on them as novel feedstock for bio-ethanol production because they contain high-cellulose content (45.9% and 46.9%, respectively) and unutilized material. Phosphoric acid (70%, 75%, and 80%) was employed for the pretreatment to improve by enzymatic hydrolysis. The pretreatment process removed most of the xylan and a part of the lignin from the weeds, while most of the glucan remained. The cellulose conversion to glucose was greater for pretreated A. aspera (86.2 ± 0.3%) than that of the pretreated S. acuta (82.2 ± 1.1%). Thus, the removal of hemicellulose significantly affected the efficiency of the enzymatic hydrolysis. The scanning electron microscopy images showed the exposed fibrous cellulose on the cell wall surface, and this substantial change of the surface structure contributed to improving the enzyme accessibility.

A perspective on bioethanol production from biomass as alternative fuel for spark ignition engine

The increasing fuel consumption of fossil fuels has led to the development of alternative fuels for the future.

Utilization of Ionic Liquids in Lignocellulose Biorefineries as Agents for Separation, Derivatization, Fractionation, or Pretreatment

Ionic liquids (ILs) can play multiple roles in lignocellulose biorefineries, including utilization as agents for the separation of selected compounds or as reaction media for processing lignocellulosic materials (LCM). Imidazolium-based ILs have been proposed for separating target components from LCM biorefinery streams, for example, the dehydration of ethanol-water mixtures or the extractive separation of biofuels (ethanol, butanol) or lactic acid from the respective fermentation broths. As in other industries, ILs are potentially suitable for removing volatile organic compounds or carbon dioxide from gaseous biorefinery effluents. On the other hand, cellulose dissolution in ILs allows homogeneous derivatization reactions to be carried out, opening new ways for product design or for improving the quality of the products. Imidazolium-based ILs are also suitable for processing native LCM, allowing the integral benefit of the feedstocks via separation of polysaccharides and lignin. Even strongly lignified materials can yield cellulose-enriched substrates highly susceptible to enzymatic hydrolysis upon ILs processing. Recent developments in enzymatic hydrolysis include the identification of ILs causing limited enzyme inhibition and the utilization of enzymes with improved performance in the presence of ILs.

Effects of pre-treatment technologies on dark fermentative biohydrogen production: A review

Biohydrogen production from dark fermentation of lignocellulosic materials represents a huge potential in terms of renewable energy exploitation. However, the low hydrogen yield is currently hindering its development on industrial scale. This study reviewed various technologies that have been investigated for enhancing dark fermentative biohydrogen production. The pre-treatment technologies can be classified based on their applications as inoculum or substrates pre-treatment or they can be categorised into physical, chemical, physicochemical and biological based on the techniques used. From the different technologies reviewed, heat and acid pre-treatments are the most commonly studied technologies for both substrates and inoculum pre-treatment. Nevertheless, these two technologies need not necessarily be the most suitable since across different studies, a wide array of other emerging techniques as well as combined technologies have yielded positive findings. To date, there exists no perfect technology for either inoculum or substrate pre-treatment. Although the aim of inoculum pre-treatment is to suppress H2-consumers and enrich H2-producers, many sporulating H2-consumers survive the pre-treatment while some non-spore H2-producers are inhibited. Besides, several inoculum pre-treatment techniques are not effective in the long run and repeated pre-treatment may be required for continuous suppression of H2-consumers and sustained biohydrogen production. Furthermore, many technologies employed for substrates pre-treatment may yield inhibitory compounds that can eventually decrease biohydrogen production. Consequently, much research needs to be done to find out the best technology for both substrates and inoculum pre-treatment while also taking into consideration the energetic, economic and technical feasibility of implementing such a process on an industrial scale.

Effects of extrusion pretreatment parameters on sweet sorghum bagasse enzymatic hydrolysis and its subsequent conversion into bioethanol

Second-generation bioethanol production from sweet sorghum bagasse first extruded at different conditions and then treated with cell wall degrading enzymes and fermented with I. orientalis was determined. The twin extruder parameters tested were barrel temperature, screws speed, and feedstock moisture content using surface response methodology. The best extrusion conditions were 100°C, 200 rpm, and 30% conditioning moisture content. This nonchemical and continuous pretreatment did not generate inhibitory compounds. The extruded feedstocks were saccharified varying the biocatalysis time and solids loading. The best conditions were 20% solids loading and 72 h of enzymatic treatment. These particular conditions converted 70% of the total fibrous carbohydrates into total fermentable C5 and C6 sugars. The extruded enzymatically hydrolyzed sweet sorghum bagasse was fermented with the strain I. orientalis at 12% solids obtaining a yield of 198.1 mL of ethanol per kilogram of bagasse (dw).

Thermochemical pretreatment of lignocellulose residues: assessment of the effect on operational conditions and their interactions on the characteristics of leachable fraction

Annually, large amounts of agricultural residues are produced in Chile, which can be turned into a good opportunity to diversify the energy matrix. These residues have a slow hydrolysis stage during anaerobic digestion; therefore, the application of a pretreatment seems to be an alternative to improve the process. This work focused on applying a thermochemical pretreatment with NaOH on two lignocellulosic residues. The experiments were performed according to a 2(4) factorial design. The factors studied in a 2(4) factorial design were: temperature (60 and 120 °C), pretreatment time (10 and 30 minutes), NaOH dose (2 and 4%), and residue size (<1 and 1-3 mm for wheat straw; 1-5 and 5-10 mm for corn stover). The analyzed response variables were the solubilization of organic matter, and the biodegradability of the lignocellulose hydrolysate. The statistical analysis of the data allowed the identification of the experimental conditions that maximized solubilization of organic matter and biodegradability. The main results showed that more aggressive experimental conditions could increase the breaking down of the structure; in addition, the time of pretreatment was not significant. Conversely, the less aggressive experimental conditions, regarding regent dosage and downsizing, favored the release of biodegradable organic matter. The main conclusion of this study was the identification of the operational conditions of the thermochemical pretreatment that promote maximum biogas production, which was caused due to the solubilization of a large amount of organic matter, but not because of the increase in biodegradability of the released organic matter.

Evaluation of ultrasonic, acid, thermo-alkaline and enzymatic pre-treatments on anaerobic digestion of Ulva rigida for biogas production

Pre-treatment of macroalgae has received considerable research globally due to its influence on the technical, economic and environmental sustainability of algae biogas production. Some of the most promising pre-treatment methods require the application of chemicals, enzymatic, and mechanical. This study focused on these pre-treatments of Ulva rigida for biogas production. The evaluation of different pre-treatment in terms of reducing sugar yields demonstrates that 3.62, 2.88, 2.53 and 7.3g/L of reducing sugar was obtained in acid catalysis, thermoalkaline, ultrasonication and enzymatic pre-treatment, respectively. However in crude macroalgae only 0.6g/L of reducing sugar was given. After anaerobic digestion, the enzymatic hydrolysis was demonstrated the best biogas yield than other pre-treatment which reached 626.5mL/gCODint with 62.65% of biodegradability. The best demonstrated method which uses crude broth of Aspergillus niger showed an effective and environmentally friendly strategy for enhancing the biogas production yields after the anaerobic digestion.

Complete chemical hydrolysis of cellulose into fermentable sugars through ionic liquids and antisolvent pretreatments

This work describes a relatively simple methodology for efficiently deconstructing cellulose into monomeric glucose, which is more easily transformed into a variety of platform molecules for the production of chemicals and fuels. The approach undertaken herein first involves the dissolution of cellulose in an ionic liquid (IL), followed by a second reconstruction step aided by an antisolvent. The regenerated cellulose exhibited strong structural and morphological changes, as revealed by XRD and SEM analyses. These changes dramatically affect the hydrolytic reactivity of cellulose with dilute mineral acids. As a consequence, the glucose yield obtained from the deconstructed-reconstructed cellulose was substantially higher than that achieved through hydrolysis of the starting cellulose. Factors that affect the hydrolysis reaction include the type of cellulose substrate, the type of IL used in pretreatment, and the type of acid used in the hydrolysis step. The best results were obtained by treating cellulose with IL and using phosphotungstic acid (0.067 mol L(-1) ) as a catalyst at 413 K. Under these conditions, the conversion of cellulose was almost complete (>99%), with a glucose yield of 87% after only 5 h of reaction.

Acid-catalyzed autohydrolysis of wheat straw to improve sugar recovery

A comparison study of autohydrolysis and acid-catalyzed autohydrolysis of wheat straw was performed to understand the impact of acid addition on overall sugar recovery. Autohydrolysis combined with refining is capable of achieving sugar recoveries in the mid 70s. If the addition of a small amount of acid is capable of increasing the sugar recovery even higher it may be economically attractive. Acetic, sulfuric, hydrochloric and sulfurous acids were selected for acid-catalyzed autohydrolysis pretreatments. Autohydrolysis with no acid at 190 °C showed the highest total sugar in the prehydrolyzate. Enzymatic hydrolysis was performed for all the post-treated solids with and without refining at enzyme loadings of 4 and 10 FPU/g for 96 h. Acid-catalyzed autohydrolysis at 190 °C with sulfurous acid showed the highest total sugar recovery of 81.2% at 4 FPU/g enzyme charge compared with 64.3% at 190 °C autohydrolysis without acid.

Current challenges in commercially producing biofuels from lignocellulosic biomass

Biofuels that are produced from biobased materials are a good alternative to petroleum based fuels. They offer several benefits to society and the environment. Producing second generation biofuels is even more challenging than producing first generation biofuels due the complexity of the biomass and issues related to producing, harvesting, and transporting less dense biomass to centralized biorefineries. In addition to this logistic challenge, other challenges with respect to processing steps in converting biomass to liquid transportation fuel like pretreatment, hydrolysis, microbial fermentation, and fuel separation still exist and are discussed in this review. The possible coproducts that could be produced in the biorefinery and their importance to reduce the processing cost of biofuel are discussed. About $1 billion was spent in the year 2012 by the government agencies in US to meet the mandate to replace 30% existing liquid transportation fuels by 2022 which is 36 billion gallons/year. Other countries in the world have set their own targets to replace petroleum fuel by biofuels. Because of the challenges listed in this review and lack of government policies to create the demand for biofuels, it may take more time for the lignocellulosic biofuels to hit the market place than previously projected.