Pretreatment of sugarcane bagasse with NH4OH-H2O2 and ionic liquid for efficient hydrolysis and bioethanol production

Two-Stage Pretreatment of Jerusalem Artichoke Stalks with Wastewater Recycling and Lignin Recovery for the Biorefinery of Lignocellulosic Biomass

Jerusalem artichoke (Helianthus tuberosus L.) is emerging as one of the energy plants considered for biofuel production. Alkali and alkali-involved pretreatment methods have been widely used for the bioconversion of cellulosic materials due to their high sugar yield and low inhibitor release. However, the recovery and treatment of wastewater (black liquor) have been poorly studied. Here, we present a novel two-stage pretreatment process design for recycling black liquor. Jerusalem artichoke stalk (JAS) was first treated with 2% (w/v) NaOH, after which lignin was recovered by H2SO4 at pH 2.0 from the black liquor. The recycled solutions were subsequently used to treat the NaOH-pretreated JAS for the second time to dissolve hemicellulose. CO-pretreated JAS, hydrolysates, and acid-insoluble lignin were obtained after the above-mentioned two-stage pretreatment. A reducing sugar yield of 809.98 mg/g Co-pretreated JAS was achieved after 48 h at 5% substrate concentration using a cellulase dosage of 25 FPU/g substrate. In addition, hydrolysates containing xylose and acid-insoluble lignin were obtained as byproducts. The pretreatment strategy described here using alkali and acid combined with wastewater recycling provides an alternative approach for cellulosic biorefinery.

Sustainable valorization of sugarcane residues: Efficient deconstruction strategies for fuels and chemicals production

The global climate crisis and the ongoing increase in fossil-based fuels have led to an alternative solution of using biomass for fuel production. Sugarcane bagasse (SCB) is an agricultural residue with a global production of more than 100 million metric tons and it has various applications in a biorefinery concept. This review brings forth the composition, life cycle assessment, and various pretreatments for the deconstruction techniques of SCB for the production of valuable products. The ongoing research in the production of biofuels, biogas, and electricity utilizing the bagasse was elucidated. SCB is used in the production of carboxymethyl cellulose, pigment, lactic acid, levulinic acid, and xylooligosaccharides and it has prospective in meeting the demand for global energy and environmental sustainability.

Xylose recovery and bioethanol production from sugarcane bagasse pretreated by mild two-stage ultrasonic assisted dilute acid

Pretreatment can improve biomass biodegradability. Here, a novel sugarcane bagasse (SCB) pretreatment process based on two-stage ultrasonic assisted dilute H₂SO₄ (TUDA) under mild conditions was reported. After optimization, the pretreatment was shown to significantly degrade hemicellulose (92.40%) and remove lignin (57.41%) of SCB, leading to reduction of inhibitors and an ethanol fermentation efficiency of 93.37% by SSCF under cellulase 10 FPU/g SCB and 30% pretreated SCB loading. Physical characterization revealed that two-stage ultrasonic could better disrupt SCB than traditional ultrasonic by amplifying the collapse effect and synergistically promoting lignin removal through dilute H₂SO₄. Furthermore, xylose was also effectively recovered from pretreatment supernatant by biochar derived from bagasse. This study established a simple and efficient pretreatment process for high value-added recycling of SCB from solid residue to pretreatment liquid.

Cost-efficient microbial electrosynthesis of hydrogen peroxide on a facile-prepared floating electrode by entrapping oxygen

Microbial electrosynthesis of hydrogen peroxide is receiving growing interest for a green substitute for anthraquinone process.However, poor oxygen transmission of electrode remains an obstacle to enhance H₂O₂ production rate without aeration. Here, a superhydrophobic natural air diffusion floating electrode (NADFE), which naturally and efficiently entraps O₂ in the air, was proposed for the first time to improve microbial electrosynthesis of H₂O₂. Furthermore, a one-step calcined electrode preparation method was developed to reduce energy consumption further. In the microbial electrolysis cell with the NADFE, a high H₂O₂ production rate of 39 mg/L/h and current efficiency of 86% were achieved without aeration. The production rate of H₂O₂ was 2.2 times that of a gas diffusion electrode. Importantly, the energy consumption was 34.3 times lower than an electrochemical system. Therefore, the high H₂O₂ production rate and current efficiency, and low energy consumption of the process provide a superior alternative for environmental remediation.

Sonoprocessing: From Concepts to Large-Scale Reactors

Intensification of ultrasonic processes for diversified applications, including environmental remediation, extractions, food processes, and synthesis of materials, has received attention from the scientific community and industry. The mechanistic pathways involved in intensification of ultrasonic processes that include the ultrasonic generation of cavitation bubbles, radical formation upon their collapse, and the possibility of fine-tuning operating parameters for specific applications are all well documented in the literature. However, the scale-up of ultrasonic processes with large-scale sonochemical reactors for industrial applications remains a challenge. In this context, this review provides a complete overview of the current understanding of the role of operating parameters and reactor configuration on the sonochemical processes. Experimental and theoretical techniques to characterize the intensity and distribution of cavitation activity within sonoreactors are compared. Classes of laboratory and large-scale sonoreactors are reviewed, highlighting recent advances in batch and flow-through reactors. Finally, examples of large-scale sonoprocessing applications have been reviewed, discussing the major scale-up and sustainability challenges.

Enhanced lignin removal and enzymolysis efficiency of grass waste by hydrogen peroxide synergized dilute alkali pretreatment

Pretreatment process plays a key role in biofuel production from lignocellulosic feedstocks. A study on dilute NaOH pretreatment supplemented with H₂O₂ under mild condition was conducted to overcome the recalcitrance of grass waste (GW). The optimized process could selectively increase lignin removal (73.2%), resulting in high overall recovery of holocellulose (73.8%) as well as high enzymolysis efficiency (83.5%) compared to H₂O₂ or NaOH pretreatment. The analyses by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) revealed that supplementary H₂O₂ disrupted the structure of GW to facilitate the removal of lignin by NaOH, and exhibited synergistic effect on lignin removal and enzymolysis with dilute NaOH. Moreover, high titer of ethanol (100.7 g/L) was achieved by SSCF on 30% (w/v) pretreated GW loading. The present study suggests that the established synergistic pretreatment is a simple, efficient, and promising process for GW biorefinery.

Acidic Ionic Liquid as Both Solvent and Catalyst for Fast Chemical Esterification of Industrial Lignins: Performances and Regioselectivity

Lignin can be considered an essential under-exploited polymer from lignocellulosic biomass representing a key for a profitable biorefinery. One method of lignin valorization could be the improvement of physico-chemical properties by esterification to enhance miscibility in apolar polyolefin matrices, thereby helping the production of bio-based composites. The present work describes for the first time a succeeded chemical esterification of industrial lignins with maleic anhydride in an acidic ionic liquid: 1-butyl-3-methyl imidazolium hydrogen sulfate without additional catalyst. This efficient strategy was applied to four industrial lignins: two softwood Kraft lignins (Indulin AT, Wayagamack), one hardwood Kraft lignin (Windsor), and one softwood organosolv lignin (Lignol), distinct in origin, extraction process and thus chemical structure. The chemical, structural, and thermal properties of modified lignins were characterized by ³¹P nuclear magnetic resonance, infrared spectroscopy and thermal analyses, then compared to those of unmodified lignins. After 4 h of reaction, between 30 to 52% of the constitutive hydroxyls were esterified depending on the type of lignin sample. The regioselectivity of the reaction was demonstrated to be preferentially orientated toward aliphatic hydroxyls for three out of four lignins (66.6, 65.5, and 83.6% for Indulin AT, Windsor and Lignol, respectively, vs. 51.7% for Wayagamack). The origin and the extraction process of the polymer would thus influence the efficiency and the regioselectivity of this reaction. Finally, we demonstrated that the covalent grafting of maleyl chain on lignins did not significantly affect thermal stability and increased significantly the solubility in polar and protic solvent probably due to additional exposed carboxylic groups resulted from mono-acylation independently of H/G/S ratio. Blending with polyolefins could then be considered in regard of compatibility with the obtained physico-chemical properties.

Bioconversion of Lignocellulosic Biomass to Fermentable Sugars by Immobilized Magnetic Cellulolytic Enzyme Cocktails

Enzyme cocktails of reusable, highly stable cellulolytic enzymes play an inevitable role in bioconversion of biomass to biofuels economically. Cellulase, xylanase and β-1,3-glucanase bound silica-amine functionalized iron oxide magnetic nanoparticles (ISN-CLEAs) were prepared and used as the biocatalyst for the depolymerization of cellulosic biomass into monomeric sugar in the present study. The Fe₃O₄-NPs and Fe₃O₄@SiO₂-NH₂-NPs and ISN-CLEAs had an average hydrodynamic size of 82.2, 86.4, and 976.9 nm, respectively, which was confirmed by dynamic light scattering (DLS). About 97% of protein binding was achieved with 135 mM glutaraldehyde at 10 h of cross-linking time and successful binding was confirmed by Fourier transform infrared spectroscopy (FTIR). The ISN-CLEAs exhibited the highest thermal stability of 95% at 50 °C for 2 h and retained extended storage stability of 97% compared to 60% of its free counterpart. Besides, cross-linking allowed ISN-CLEAs reuse for at least eight consecutive cycles retaining over 70% of its initial activity. ISN-CLEAs exhibited approximately 15% increase in carbohydrate digestibility on sugar cane bagasse and eucalyptus pulp than the free enzyme.

Enhanced bioethanol production by fed-batch simultaneous saccharification and co-fermentation at high solid loading of Fenton reaction and sodium hydroxide sequentially pretreated sugarcane bagasse

A study on the fed-batch simultaneous saccharification and co-fermentation (SSCF) of Fenton reaction combined with NaOH pretreated sugarcane bagasse (SCB) at a high solid loading of 10-30% (w/v) was investigated. Enzyme feeding mode, substrate feeding mode and combination of both were compared with the batch mode under respective solid loadings. Ethanol concentrations of above 80g/L were obtained in batch and enzyme feeding modes at a solid loading of 30% (w/v). Enzyme feeding mode was found to increase ethanol productivity and reduce enzyme loading to a value of 1.23g/L/h and 9FPU/g substrate, respectively. The present study provides an economically feasible process for high concentration bioethanol production.

Determination of kinetics and heat of hydrolysis for non-homogenous substrate by isothermal calorimetry

The competitiveness of the second-generation bioethanol by biotechnological process requires an effective and quantitative control of biochemical reactions. In this study, the potential of isothermal calorimetry technique to measure heat and kinetics of a non-homogeneous substrate enzymatic hydrolysis is intended. Using this technique, optimum temperature of the enzymes used for lignocellulosic molecules hydrolysis was determined. Thus, the amount of substrate-to-enzyme ratio was highlighted as an important parameter of the hydrolysis yield. Furthermore, a new enzymes' cocktail efficiency consisting of a mix of cellulases and cellobiose dehydrogenase (CDH) was qualified by this technique. The results showed that this cocktail allowed the production of a high amount of gluconic acid that could improve the attractiveness of these second-generation biofuels. From the set of experiments, the hydrolysis heat of wheat straw was derived and a meaningful value of -32.2 ± 3.2 J g^-1 (gram reducing sugars product) is calculated. Then, isothermal measurements were used to determine kinetic constants of the cellulases and CDH mix on wheat straw. Results showed that this enzyme cocktail has an optimal rate at 45 °C in the range of temperatures tested (40-55 °C).

Enhancing enzymolysis and fermentation efficiency of sugarcane bagasse by synergistic pretreatment of Fenton reaction and sodium hydroxide extraction

A study on the synergistic pretreatment of sugarcane bagasse (SCB) using Fenton reaction and NaOH extraction was conducted. The optimized process conditions for Fenton pretreatment were 10% (w/w) of H2O2, 20mM of Fe(2+), pH 2.5, pretreatment time 6h, and pretreatment temperature 55°C. Sequential pretreatments were performed in combination with NaOH extraction (NaOH 1% (w/w), 80°C, 5% of solid loading, 1h). Among all the pretreatments, Fenton pretreatment followed by NaOH extraction had the highest efficiency of 64.7% and 108.3% for enzymolysis and simultaneous saccharification fermentation (SSF) with an ethanol concentration of 17.44g/L. The analyses by the scanning electron microscopy, X-ray diffraction and confocal laser scanning microscopy revealed that Fenton pretreatment disrupts the structure of SCB to facilitate the degradation of lignin by NaOH. The overall data suggest that this combinatorial strategy is a promising process for SCB pretreatment.

Suitability assessment of a continuous process combining thermo-mechano-chemical and bio-catalytic action in a single pilot-scale twin-screw extruder for six different biomass sources

A process has been validated for the deconstruction of lignocellulose on a pilot scale installation using six types of biomass selected for their sustainability, accessibility, worldwide availability, and differences of chemical composition and physical structure. The process combines thermo-mechano-chemical and bio-catalytic action in a single twin-screw extruder. Three treatment phases were sequentially performed: an alkaline pretreatment, a neutralization step coupled with an extraction-separation phase and a bioextrusion treatment. Alkaline pretreatment destructured the wall polymers after just a few minutes and allowed the initial extraction of 18-54% of the hemicelluloses and 9-41% of the lignin. The bioextrusion step induced the start of enzymatic hydrolysis and increased the proportion of soluble organic matter. Extension of saccharification for 24h at high consistency (20%) and without the addition of new enzyme resulted in the production of 39-84% of the potential glucose.

Production of cellulosic ethanol from sugarcane bagasse by steam explosion: Effect of extractives content, acid catalysis and different fermentation technologies

The production of cellulosic ethanol was carried out using samples of native (NCB) and ethanol-extracted (EECB) sugarcane bagasse. Autohydrolysis (AH) exhibited the best glucose recovery from both samples, compared to the use of both H3PO4 and H2SO4 catalysis at the same pretreatment time and temperature. All water-insoluble steam-exploded materials (SEB-WI) resulted in high glucose yields by enzymatic hydrolysis. SHF (separate hydrolysis and fermentation) gave ethanol yields higher than those obtained by SSF (simultaneous hydrolysis and fermentation) and pSSF (pre-hydrolysis followed by SSF). For instance, AH gave 25, 18 and 16 g L(-1) of ethanol by SHF, SSF and pSSF, respectively. However, when the total processing time was taken into account, pSSF provided the best overall ethanol volumetric productivity of 0.58 g L(-1) h(-1). Also, the removal of ethanol-extractable materials from cane bagasse had no influence on the cellulosic ethanol production of SEB-WI, regardless of the fermentation strategy used for conversion.

Feed additive production by fermentation of herb Polygonum hydropiper L. and cassava pulp with simultaneous flavonoid dissolution

Fermentation of herb Polygonum hydropiper L. (PHL) and cassava pulp (CP) for feed additive production with simultaneous flavonoid dissolution was investigated, and a two-stage response surface methodology (RSM) based on Plackett-Burman factorial design (PB design) was used to optimize the flavonoid dissolution and protein content. Using the screening function of PB design, four different significant factors for the two response variables were acquired: factors A (CP) and B (PHL) for the flavonoid dissolution versus factors G (inoculum size) and H (fermentation time) for protein content. Then, two RSMs were used sequentially to improve the values of the two response variables separately. The mutual corroboration of the experimental results in the present study confirmed the validity of the associated experimental design. The validation experiment showed a flavonoid dissolution rate of 94.00%, and a protein content of 18.20%, gaining an increase in 21.20% and 199.10% over the control, respectively. The present study confirms the feasibility of feed additive production by Saccharomyces cerevisiae with CP and PHL and simultaneous optimization of flavonoid dissolution and protein content using a two-stage RSM.

Mechanistic study on ultrasound assisted pretreatment of sugarcane bagasse using metal salt with hydrogen peroxide for bioethanol production

This study presents the ultrasound assisted pretreatment of sugarcane bagasse (SCB) using metal salt with hydrogen peroxide for bioethanol production. Among the different metal salts used, maximum holocellulose recovery and delignification were achieved with ultrasound assisted titanium dioxide (TiO2) pretreatment (UATP) system. At optimum conditions (1% H2O2, 4 g SCB dosage, 60 min sonication time, 2:100 M ratio of metal salt and H2O2, 75°C, 50% ultrasound amplitude and 70% ultrasound duty cycle), 94.98 ± 1.11% holocellulose recovery and 78.72 ± 0.86% delignification were observed. The pretreated SCB was subjected to dilute acid hydrolysis using 0.25% H2SO4 and maximum xylose, glucose and arabinose concentration obtained were 10.94 ± 0.35 g/L, 14.86 ± 0.12 g/L and 2.52 ± 0.27 g/L, respectively. The inhibitors production was found to be very less (0.93 ± 0.11 g/L furfural and 0.76 ± 0.62 g/L acetic acid) and the maximum theoretical yield of glucose and hemicellulose conversion attained were 85.8% and 77%, respectively. The fermentation was carried out using Saccharomyces cerevisiae and at the end of 72 h, 0.468 g bioethanol/g holocellulose was achieved. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis of pretreated SCB was made and its morphology was studied using scanning electron microscopy (SEM). The compounds formed during the pretreatment were identified using gas chromatography-mass spectrometry (GC-MS) analysis.

Efficient approach for bioethanol production from red seaweed Gelidium amansii

Gelidium amansii (GA), a red seaweed species, is a popular source of food and chemicals due to its high galactose and glucose content. In this study, we investigated the potential of bioethanol production from autoclave-treated GA (ATGA). The proposed method involved autoclaving GA for 60min for hydrolysis to glucose. Separate hydrolysis and fermentation processing (SHF) achieved a maximum ethanol concentration of 3.33mg/mL, with a conversion yield of 74.7% after 6h (2% substrate loading, w/v). In contrast, simultaneous saccharification and fermentation (SSF) produced an ethanol concentration of 3.78mg/mL, with an ethanol conversion yield of 84.9% after 12h. We also recorded an ethanol concentration of 25.7mg/mL from SSF processing of 15% (w/v) dry matter from ATGA after 24h. These results indicate that autoclaving can improve the glucose and ethanol conversion yield of GA, and that SSF is superior to SHF for ethanol production.

Effects of metal ions on the hydrolysis of bamboo biomass in 1-butyl-3-methylimidazolium chloride with dilute acid as catalyst

In this study, the effects of six metal ions including Na+, K+, Mg2+, Ca2+, Cu2+ and Fe3+ on hydrolysis of bamboo biomass by diluted hydrochloride acid (HCl) in ionic liquid [C4mim]Cl under mild conditions was investigated. These metal ions as co-catalysts exhibited significant effects on accelerating the hydrolysis process and improving the yield of total reducing sugar compared to single diluted hydrochloride acid hydrolysis in [C4mim]Cl at the same conditions. The most effective ion was Cu2+ and the total reducing sugar yield of 67.1% was achieved at 100 °C with CuCl2 as co-catalyst after 4-h reaction. The total reducing sugar yield was increased by about 7% and the reaction time was decreased by 3 h. The kinetic model was also investigated to give an insight into the mechanism of hydrolysis process.

A novel anaerobic co-culture system for bio-hydrogen production from sugarcane bagasse

A novel co-culture of Clostridium thermocellum and Thermoanaerobacterium aotearoense with pretreated sugarcane bagasse (SCB) under mild alkali conditions for bio-hydrogen production was established, exhibiting a cost-effective and synergetic advantage in bio-hydrogen production over monoculture of C. thermocellum or T. aotearoense with untreated SCB. The optimized pretreatment conditions were established to be 3% NaOH, and a liquid to solid ratio of 25:1 at 80°C for 3h. A final hydrogen production of 50.05±1.51 mmol/L was achieved with 40 g/L pretreated SCB at 55°C. The established co-culture system provides a novel consolidated bio-processing strategy for bioconversion of SCB to bio-hydrogen.

Renewable Sugars Hydrolyzed from Banana Pseudo-Stem Using Different Chemical Pretreatments

Cellulose and hemicelluloses are the main building block of plant cell wall and are known as a natural polymer that usually used in the industries. Cellulose and hemicelluloses could be used as a feedstock for second generation biofuel production where it is subjected to hydrolysis into sugar after which it can be converted into bioethanol through fermentation process. In this study, the matured banana pseudo-stem is used as the source of hydrolyzing sugar from natural material. The objective of this research is to study the effects of different chemical pretreatments (sodium hydroxide, mixture of sodium hydroxide and hydrogen peroxide, sulphuric acid, mixture of sulphuric acid and hydrogen peroxide) and hydrolysis time (1-5 hours) on the sugar yield from banana pseudo-stem. Results showed that, after 3 hours hydrolysis most of the sugars from all chemical pretreatments reduced gradually. Analysis of sugar contents from acid hydrolysis process using High Pressure Liquid Chromatography (HPLC) showed that all the samples contained glucose, xylose, and arabinose where the highest glucose (16.02 mg/L) obtained from fiber treated with mixture of 1.0 M sulphuric acid and hydrogen peroxide. In addition, both highest xylose (64.23 mg/L) and arabinose (45.78 mg/L) are obtained from fiber treated with 0.5 M sodium hydroxide.

Supercritical CO2 and ionic liquids for the pretreatment of lignocellulosic biomass in bioethanol production

Owing to high petroleum prices, there has been a major push in recent years to use lignocellulosic biomass as biorefinery feedstocks. Unfortunately, by nature's design, lignocellulosic biomass is notoriously recalcitrant. Cellulose is the most abundant renewable carbon source on the planet and comprises glucan polysaccharides which self-assemble into paracrystalline microfibrils. The extent of cellulose crystallinity largely contributes to biomass recalcitrance. Additionally, cellulose microfibrils are embedded into both hemicellulose and lignin polymeric networks, making cellulose accessibility an additional obstacle. Pretreatment is necessary before enzymatic hydrolysis in order to liberate high yields of glucose and other fermentable sugars from biomass polysaccharides. This work discusses two pretreatment methods, supercritical CO2 and ionic liquids (ILs). Both methods utilize green solvents that do not emit toxic vapours. Mechanisms for destroying or weakening biomass recalcitrance have been explored. Various pretreatment operating parameters such as temperature, pressure, time, dry biomass/solvent ratio, water content, etc. have been investigated for the pretreatment of various biomass types such as corn stover, switchgrass, sugarcane bagasse, soft and hard wood. The two pretreatment methods have their pros and cons. For example, supercritical CO2 explosion pretreatment uses inexpensive CO2, but requires a high pressure. By comparison, while IL pretreatment does not require an elevated pressure, ILs are still too expensive for large-scale uses. Further research and development are needed to make the two green pretreatment methods practical.

Butyric acid production from sugarcane bagasse hydrolysate by Clostridium tyrobutyricum immobilized in a fibrous-bed bioreactor

A fermentation process using Clostridium tyrobutyricum immobilized in a fibrous-bed bioreactor (FBB) was developed for butyric acid production from sugarcane bagasse (SCB) hydrolysate. SCB was first treated with dilute acid and then hydrolyzed with cellulases. The hydrolysate containing glucose and xylose was used as carbon source for the fermentation without detoxification. The bacterium was able to grow at a specific growth rate of ∼0.06 h(-1) in media containing 15-20% (w/v) SCB in serum bottles. In batch cultures in the FBB, both glucose and xylose in the SCB hydrolysate were simultaneously converted to butyrate with a high yield (0.45-0.54 g/gsugar) and productivity (0.48-0.60 g/Lh). A final butyrate concentration of 20.9 g/L was obtained in a fed-batch culture, with an overall productivity of 0.51 g/Lh and butyrate yield of 0.48 g/g sugar consumed. This work demonstrated the feasibility of using SCB as a low-cost feedstock to produce butyric acid.

Chemical Pretreatment Methods for the Production of Cellulosic Ethanol: Technologies and Innovations

Pretreatment of lignocellulose has received considerable research globally due to its influence on the technical, economic and environmental sustainability of cellulosic ethanol production. Some of the most promising pretreatment methods require the application of chemicals such as acids, alkali, salts, oxidants, and solvents. Thus, advances in research have enabled the development and integration of chemical-based pretreatment into proprietary ethanol production technologies in several pilot and demonstration plants globally, with potential to scale-up to commercial levels. This paper reviews known and emerging chemical pretreatment methods, highlighting recent findings and process innovations developed to offset inherent challenges via a range of interventions, notably, the combination of chemical pretreatment with other methods to improve carbohydrate preservation, reduce formation of degradation products, achieve high sugar yields at mild reaction conditions, reduce solvent loads and enzyme dose, reduce waste generation, and improve recovery of biomass components in pure forms. The use of chemicals such as ionic liquids, NMMO, and sulphite are promising once challenges in solvent recovery are overcome. For developing countries, alkali-based methods are relatively easy to deploy in decentralized, low-tech systems owing to advantages such as the requirement of simple reactors and the ease of operation.