Ethanol Production from Cashew Apple Bagasse: Improvement of Enzymatic Hydrolysis by Microwave-Assisted Alkali Pretreatment

In this work, the potential of microwave-assisted alkali pretreatment in order to improve the rupture of the recalcitrant structures of the cashew able bagasse (CAB), lignocellulosic by-product in Brazil with no commercial value, is obtained from cashew apple process to juice production, was studied. First, biomass composition of CAB was determined, and the percentage of glucan and lignin was 20.54 ± 0.70% and 33.80 ± 1.30%, respectively. CAB content in terms of cellulose, hemicelluloses, and lignin, 19.21 ± 0.35%, 12.05 ± 0.37%, and 38.11 ± 0.08%, respectively, was also determined. Results showed that, after enzymatic hydrolysis, alkali concentration exerted influence on glucose formation, after pretreatment with 0.2 and 1.0 mo L⁻¹ of NaOH (372 ± 12 and 355 ± 37 mg g_glucan⁻¹) when 2% (w/v) of cashew apple bagasse pretreated by microwave-assisted alkali pretreatment (CAB-M) was used. On the other hand, pretreatment time (15–30 min) and microwave power (600–900 W) exerted no significant effect on hydrolysis. On enzymatic hydrolysis step, improvement on solid percentage (16% w/v) and enzyme load (30 FPU g_CAB-M⁻¹) increased glucose concentration to 15 g L⁻¹. The fermentation of the hydrolyzate by Saccharomyces cerevesiae resulted in ethanol concentration and productivity of 5.6 g L⁻¹ and 1.41 g L⁻¹ h⁻¹, respectively.     

Production of Bio-Ethanol by Integrating Microwave-Assisted Dilute Sulfuric Acid Pretreated Sugarcane Bagasse Slurry with Molasses

Sugarcane bagasse (SCB) and molasses, known as carbohydrate-rich biomass derived from sugar production, can serve as feedstock for bio-ethanol production. To establish a simple process, the production of bio-ethanol through integration of whole pretreated slurry (WPS) of SCB with molasses was investigated. The results showed that microwave-assisted dilute sulfuric acid pretreatment reduced the formation of toxic compounds compared to a pretreatment process involving “conventional heating”. Pretreatment at 180 ^oC with 10% w v^?1 solid loading and 0.5% w v^?1 H₂SO₄ was sufficient to achieve efficient enzymatic saccharification of WPS. By conducting separate hydrolysis and fermentation (SHF), an ethanol yield of 90.12% was obtained from the mixture of WPS and molasses, but the ethanol concentration of 33.48 g L^?1 was relatively low. By adopting fed-batch SHF, the ethanol concentration reached 41.49 g L^?1. Assuming that the molasses were converted to ethanol at an efficiency of 87.21% (i.e., ethanol was obtained from fermentation of molasses alone), the ethanol yield from WPS when a mixture of WPS and molasses was fermented was 78.30%, which was higher than that of enzymatic saccharification of WPS (73.53%). These findings suggest that the production of bio-ethanol via integration of WPS with molasses is a superior method.

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Ethanol Production by Fermentation Using Immobilized Cells of Saccharomyces cerevisiae in Cashew Apple Bagasse

In this work, cashew apple bagasse (CAB) was used for Saccharomyces cerevisiae immobilization. The support was prepared through a treatment with a solution of 3% HCl, and delignification with 2% NaOH was also conducted. Optical micrographs showed that high populations of yeast cells adhered to pre-treated CAB surface. Ten consecutive fermentations of cashew apple juice for ethanol production were carried out using immobilized yeasts. High ethanol productivity was observed from the third fermentation assay until the tenth fermentation. Ethanol concentrations (about 19.82–37.83 g L^?1 in average value) and ethanol productivities (about 3.30–6.31 g L^?1 h^?1) were high and stable, and residual sugar concentrations were low in almost all fermentations (around 3.00 g L^?1) with conversions ranging from 44.80% to 96.50%, showing efficiency (85.30–98.52%) and operational stability of the biocatalyst for ethanol fermentation. Results showed that cashew apple bagasse is an efficient support for cell immobilization aiming at ethanol production.     

Evaluation and Optimization of Organic Acid Pretreatment of Cotton Gin Waste for Enzymatic Hydrolysis and Bioethanol Production

This paper investigates the efficiency of the organic acids on the pretreatment of an industrially generated cotton gin waste for the removal of lignin, thereby releasing cellulose and hemicellulose as fermentable sugar components. Cotton gin waste was pretreated with various organic acids namely lactic acid, oxalic acid, citric acid, and maleic acid. Among these, maleic acid was found to be the most efficient producing maximum xylose sugar (126.05?±?0.74 g/g) at the optimum pretreatment condition of 150 °C, 500 mM, and 45 min. The pretreatment efficiency was comparable to the conventional dilute sulfuric acid pretreatment. A lignin removal of 88% was achieved by treating maleic acid pretreated biomass in a mixture of sodium sulfite and sodium chlorite. The pretreated biomass was further evaluated for the release of sugar by enzymatic hydrolysis and subsequently bioethanol production from hydrolysates. The maximum 686.13 g/g saccharification yield was achieved with maleic acid pretreated biomass which was slightly higher than the sulfuric acid (675.26 g/g) pretreated waste. The fermentation of mixed hydrolysates(41.75 g/l) produced 18.74 g/l bioethanol concentration with 2.25 g/l/h ethanol productivity and 0.48 g/g ethanol yield using sequential use of Saccharomyces cerevisiae and Pichia stipitis yeast strains. The production of bioethanol was higher than the ethanol produced using co-culture in comparison to sequential culture. Thus, it has been demonstrated that the maleic acid pretreatment and fermentation using sequential use of yeast strains are efficient for bioethanol production from cotton gin waste.     

Bioethanol Production from Soybean Residue via Separate Hydrolysis and Fermentation

Bioethanol was produced using polysaccharide from soybean residue as biomass by separate hydrolysis and fermentation (SHF). This study focused on pretreatment, enzyme saccharification, and fermentation. Pretreatment to obtain monosaccharide was carried out with 20% (w/v) soybean residue slurry and 270 mmol/L H₂SO₄ at 121 °C for 60 min. More monosaccharide was obtained from enzymatic hydrolysis with a 16 U/mL mixture of commercial enzymes C-Tec 2 and Viscozyme L at 45 °C for 48 h. Ethanol fermentation with 20% (w/v) soybean residue hydrolysate was performed using wild-type and Saccharomyces cerevisiae KCCM 1129 adapted to high concentrations of galactose, using a flask and 5-L fermenter. When the wild type of S. cerevisiae was used, an ethanol production of 20.8 g/L with an ethanol yield of 0.31 g/g consumed glucose was obtained. Ethanol productions of 33.9 and 31.6 g/L with ethanol yield of 0.49 g/g consumed glucose and 0.47 g/g consumed glucose were obtained in a flask and a 5-L fermenter, respectively, using S. cerevisiae adapted to a high concentration of galactose. Therefore, adapted S. cerevisiae to galactose could enhance the overall ethanol fermentation yields compared to the wild-type one.     

Lime Pretreatment of Sugarcane Bagasse for Bioethanol Production

The pretreatment of sugarcane bagasse with lime (calcium hydroxide) is evaluated. The effect of lime pretreatment on digestibility was studied through analyses using central composite design (response surface), considering pretreatment time, temperature, and lime loading as factors. The responses evaluated were the yield of glucose from pretreated bagasse after enzymatic hydrolysis. Experiments were performed using the bagasse as it comes from an alcohol/sugar factory (non-screened bagasse) and bagasse in the size range from 0.248 to 1.397 mm (screened bagasse) (12-60 mesh). It was observed that the particle size presented influence in the release of fermentable sugars after enzymatic hydrolysis using low loading of cellulase and β-glucosidase (3.5 FPU/g dry pretreated biomass and 1.0 IU/g dry pretreated biomass, respectively).     

Addition of Surfactants and Non-Hydrolytic Proteins and Their Influence on Enzymatic Hydrolysis of Pretreated Sugarcane Bagasse

Poly(ethylene glycol) (PEG 4000) and bovine serum albumin (BSA) were investigated with the purpose of evaluating their influence on enzymatic hydrolysis of sugarcane bagasse. Effects of these supplements were assayed for different enzymatic cocktails (Trichoderma harzianum and Penicillium funiculosum) that acted on lignocellulosic material submitted to different pretreatment methods with varying solid (25 and 100 g/L) and protein (7.5 and 20 mg/g cellulose) loadings. The highest levels of glucose release were achieved using partially delignified cellulignin as substrate, along with the T. harzianum cocktail: increases of 14 and 18 % for 25 g/L solid loadings and of 33 and 43 % for 100 g/L solid loadings were reached for BSA and PEG supplementation, respectively. Addition of these supplements could maintain hydrolysis yield even for higher solid loadings, but for higher enzymatic cocktail protein loadings, increases in glucose release were not observed. Results indicate that synergism might occur among these additives and cellulase and xylanases. The use of these supplements, besides depending on factors such as pretreatment method of sugarcane bagasse, enzymatic cocktails composition, and solid and protein loadings, may not always lead to positive effects on the hydrolysis of lignocellulosic material, making it necessary further statistical studies, according to process conditions.     

Sweet Sorghum as Feedstock for Ethanol Production: Enzymatic Hydrolysis of Steam-Pretreated Bagasse

Sweet sorghum is an attractive feedstock for ethanol production. The juice extracted from the fresh stem is composed of sucrose, glucose, and fructose and can therefore be readily fermented to alcohol. The solid fraction left behind, the so-called bagasse, is a lignocellulosic residue which can also be processed to ethanol. The objective of our work was to test sweet sorghum, the whole crop, as a potential raw material of ethanol production, i.e., both the extracted sugar juice and the residual bagasse were tested. The juice was investigated at different harvesting dates for sugar content. Fermentability of juices extracted from the stem with and without leaves was compared. Sweet sorghum bagasse was steam-pretreated using various pretreatment conditions (temperatures and residence times). Efficiency of pretreatments was characterized by the degree of cellulose hydrolysis of the whole pretreated slurry and the separated fiber fraction. Two settings of the studied conditions (190 °C, 10 min and 200 °C, 5 min) were found to be efficient to reach conversion of 85–90%.     

复合酶耦合酶解酸处理后玉米秸秆的研究

以玉米秸秆为研究对象,经过2%硫酸预处理后,利用果胶酶、β-葡萄糖苷酶、纤维素酶三种酶协同酶解,以提高玉米秸秆的酶解产糖量。结果表明:当酶解时间为48h,果胶酶、β-葡萄糖苷酶、纤维素酶分别为45U/mL、30U/mL、60U/mL时,葡萄糖、木糖和酶水解得率分别为67.83%、3.25%、73.65%,相比纤维素酶单一酶解的葡萄糖、木糖和酶水解得率分别提高了65.04%、20.82%、65.06%。分步糖化发酵5天后,相比单一酶解发酵乙醇含量提高了72.5%。说明利用三种酶复合处理,能明显提高酶解产糖量。研究结果为玉米秸秆转化为可发酵糖技术的研究提供重要参考。     

Use of Spectroscopic and Imaging Techniques to Evaluate Pretreated Sugarcane Bagasse as a Substrate for Cellulase Production Under Solid-State Fermentation

The enzymatic cocktail of cellulases is one of the most costly inputs affecting the economic viability of the biochemical route for biomass conversion into biofuels and other chemicals. Here, the influence of liquid hot water, dilute acid, alkali, and combined acid/alkali pretreatments on sugarcane bagasse (SCB) used for cellulase production was investigated by means of spectroscopic and imaging techniques. Chemical composition and structural characteristics, such as crystallinity (determined by X-ray diffraction), functional groups (Fourier transform infrared spectroscopy), and microstructure (scanning electron microscopy), were used to correlate SCB pretreatments with enzymatic biosynthesis by a strain of the filamentous fungus Aspergillus niger under solid-state fermentation. The combined acid/alkali pretreatment resulted in a SCB with higher cellulose content (86.7 %). However, the high crystallinity (74 %) of the resulting biomass was detrimental to microbial uptake and enzyme production. SCB pretreated with liquid hot water yielded the highest filter paper cellulase (FPase), carboxymethyl cellulase (CMCase), and xylanase activities (0.4, 14.9, and 26.1 U g^?1, respectively). The results showed that a suitable pretreatment for SCB to be used as a substrate for cellulase production should avoid severe conditions in order to preserve amorphous cellulose and to enhance the physical properties that assist microbial access.     

Evaluation of Cashew Apple Juice for the Production of Fuel Ethanol

A commercial strain of Saccharomyces cerevisiae was used for the production of ethanol by fermentation of cashew apple juice. Growth kinetics and ethanol productivity were calculated for batch fermentation with different initial sugar (glucose + fructose) concentrations. Maximal ethanol, cell, and glycerol concentrations were obtained when 103.1 g L⁻¹ of initial sugar concentration was used. Cell yield (Y _X/S) was calculated as 0.24 (g microorganism)/(g glucose + fructose) using cashew apple juice medium with 41.3 g L⁻¹ of initial sugar concentration. Glucose was exhausted first, followed by fructose. Furthermore, the initial concentration of sugars did not influence ethanol selectivity. These results indicate that cashew apple juice is a suitable substrate for yeast growth and ethanol production.     

Optimization of Dilute Sulfuric Acid Pretreatment to Maximize Combined Sugar Yield from Sugarcane Bagasse for Ethanol Production

Increasing fermentable sugar yields per gram of biomass depends strongly on optimal selection of varieties and optimization of pretreatment conditions. In this study, dilute acid pretreatment of bagasse from six varieties of sugarcane was investigated in connection with enzymatic hydrolysis for maximum combined sugar yield (CSY). The CSY from the varieties were also compared with the results from industrial bagasse. The results revealed considerable differences in CSY between the varieties. Up to 22.7 % differences in CSY at the optimal conditions was observed. The combined sugar yield difference between the best performing variety and the industrial bagasse was 34.1 %. High ratio of carbohydrates to lignin and low ash content favored the release of sugar from the substrates. At mild pretreatment conditions, the differences in bioconversion efficiency between varieties were greater than at severe condition. This observation suggests that under less severe conditions the glucose recovery was largely determined by chemical composition of biomass. The results from this study support the possibility of increasing sugar yields or improving the conversion efficiency when pretreatment optimization is performed on varieties with improved properties.     

Cascade Enzymatic Hydrolysis Coupling with Ultra ne Grinding Pretreatment for Sugarcane Bagasse Sacchari cation

The biorefinery process for sugarcane bagasse saccharification generally requires significant accessibility of cellulose. We reported a novel method of cascade cellulase enzymatic hydrolysis coupling with ultrafine grinding pretreatment for sugarcane bagasse saccharification. Three enzymatic hydrolysis modes including single cellulase enzymatic hydrolysis, mixed cellulase enzymatic hydrolysis, and cascade cellulase enzymatic hydrolysis were compared. The changes on the functional group and surface morphology of bagasse during cascade cellulase enzymatic hydrolysis were also examined by FT-IR and SEM respectively. The results showed that cascade enzymatic hydrolysis was the most efficient way to enhance the sugarcane bagasse sacchari cation. More than 65% of reducing sugar yield with 90.1% of glucose selectivity was achieved at 50 oC, pH=4.8 for 72 h (1200 r/min) with cellulase I of 7.5 FPU/g substrate and cellulase II of 5 FPU/g substrate.     

High Solids Enzymatic Hydrolysis of Pretreated Lignocellulosic Materials with a Powerful Stirrer Concept

In this study, we present a powerful stirred tank reactor system that can efficiently hydrolyse lignocellulosic material at high solid content to produce hydrolysates with glucose concentration > 100 g/kg. As lignocellulosic substrates alkaline-pretreated wheat straw and organosolv-pretreated beech wood were used. The developed vertical reactor was equipped with a segmented helical stirrer, which was specially designed for high biomass hydrolysis. The stirrer was characterised according to mixing behaviour and power input. To minimise the cellulase dosage, a response surface plan was used. With the empirical relationship between glucose yield, cellulase loading and solid content, the minimal cellulase dosage was calculated to reach at least 70 % yield at high glucose and high substrate concentrations within 48 h. The optimisation resulted in a minimal enzyme dosage of 30 FPU/g dry matter (DM) for the hydrolysis of wheat straw and 20 FPU/g DM for the hydrolysis of beech wood. By transferring the hydrolysis reaction from shaking flasks to the stirred tank reactor, the glucose yields could be increased. Using the developed stirred tank reactor system, alkaline-pretreated wheat straw could be converted to 110 g/kg glucose (76 %) at a solid content of 20 % (w/w) after 48 h. Organosolv-pretreated beech wood could be efficiently hydrolysed even at 30 % (w/w) DM, giving 150 g/kg glucose (72 %).     

Surfactant-Assisted Acid Pretreatment of Sugarcane Tops for Bioethanol Production

Sugarcane tops is one of the largest biomass resources in India and in tropical countries such as Brazil in terms of surplus availability. Conversion of this feedstock to ethanol requires pretreatment to make it more accessible for the enzymes used in saccharification. Though several pretreatment regimens have been developed for addressing biomass recalcitrance, very few seem to be promising as an industrial process. A novel hybrid method involving use of mild acid and surfactant was developed which could effectively remove lignin and improve the sugar yield from sugar cane tops. Operational parameters that affect the pretreatment efficiency (measured as yield of sugars) were studied and optimized. Changes in structural properties of the biomass were studied in relation to the pretreatment process using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier Transform Infrared (FTIR) analysis, and the changes in chemical composition was also monitored. The biomass pretreated with the optimized novel method could yield 0.798?g of reducing sugars per gram of pretreated biomass upon enzymatic hydrolysis.     

Formic Acid as a Potential Pretreatment Agent for the Conversion of Sugarcane Bagasse to Bioethanol

In recent years, growing attention has been focused on the use of lignocellulosic biomass as a feedstock for the production of ethanol, a possible renewable alternative to fossil fuels. Several pretreatment processes have been developed for decreasing the biomass recalcitrance, but only a few of them seem to be promising. In this study, effect of various organic solvents and organic acids on the pretreatment of sugarcane bagasse was studied. Among the different organic acids and organic solvents tested, formic acid was found to be effective. Optimization of process parameters for formic acid pretreatment was carried out. The structural changes before and after pretreatment was investigated by scanning electron microscopy, X-ray diffraction (XRD), and Fourier transform infrared (FTIR) analysis. The X-ray diffraction profile showed that the degree of crystallinity was more for pretreated biomass than that of untreated. The FTIR spectra shown at the stretching of hydrogen bonds of pretreated sugarcane bagasse arose at higher number. It also revealed that the cellulose content in the solid residue increased because the hemicelluloses fraction in raw materials was released by acid hydrolytic reaction.     

Effects of Substrate Loading on Enzymatic Hydrolysis and Viscosity of Pretreated Barley Straw

In this study, the applicability of a “fed-batch” strategy, that is, sequential loading of substrate or substrate plus enzymes during enzymatic hydrolysis was evaluated for hydrolysis of steam-pretreated barley straw. The specific aims were to achieve hydrolysis of high substrate levels, low viscosity during hydrolysis, and high glucose concentrations. An enzyme system comprising Celluclast and Novozyme 188, a commercial cellulase product derived from Trichoderma reesei and a β-glucosidase derived from Aspergillus niger, respectively, was used for the enzymatic hydrolysis. The highest final glucose concentration, 78 g/l, after 72 h of reaction, was obtained with an initial, full substrate loading of 15% dry matter weight/weight (w/w DM). Conversely, the glucose yields, in grams per gram of DM, were highest at lower substrate concentrations, with the highest glucose yield being 0.53 g/g DM for the reaction with a substrate loading of 5% w/w DM after 72 h. The reactions subjected to gradual loading of substrate or substrate plus enzymes to increase the substrate levels from 5 to 15% w/w DM, consistently provided lower concentrations of glucose after 72 h of reaction; however, the initial rates of conversion varied in the different reactions. Rapid cellulose degradation was accompanied by rapid decreases in viscosity before addition of extra substrate, but when extra substrate or substrate plus enzymes were added, the viscosities of the slurries increased and the hydrolytic efficiencies decreased temporarily.     

Evaluation of Cashew Apple Juice for Surfactin Production by Bacillus subtilis LAMI008

Bacillus subtilis LAMI008 strain isolated from the tank of Chlorination at the Wastewater Treatment Plant on Campus do Pici in Federal University of Ceará, Brazil has been screened for surfactin production in mineral medium containing clarified cashew apple juice (MM-CAJC). Results were compared with the ones obtained using mineral medium with glucose PA as carbon source. The influence on growth and surfactin production of culture medium supplementation with yeast extract was also studied. The substrate concentration analysis indicated that B. subtilis LAMI008 was able to degrade all carbon sources studied and produce biosurfactant. The highest reduction in surface tension was achieved with the fermentation of MM-CAJC, supplemented with yeast extract, which decreased from 58.95?±?0.10 to 38.10?±?0.81 dyn cm^?1. The biosurfactant produced was capable of emulsifying kerosene, achieving an emulsification index of 65%. Surfactin concentration of 3.5 mg L^?1 was obtained when MM-CAJC, supplemented with yeast extract, was used, thus indicating that it is feasible to produce surfactin from clarified cashew apple juice, a renewable and low-cost carbon source.     

Vanadium Catalysts Promoted with Magnesium Compounds for Production of Sulfuric Acid

The feasibility and efficiency of promotion with magnesium compounds of supported and mixed catalysts for sulfuric acid production were studied.