Response surface optimization of corn stover pretreatment using dilute phosphoric acid for enzymatic hydrolysis and ethanol production

Enhanced fermentable sugar production in lignocellulosic biorefinery by exploring a novel corn stover and configuring high-solid pretreatment conditions

This study aimed to produce enhanced fermentable sugars from a novel stover system through the bioprocessing of its soluble sugars and insoluble carbohydrates. The pretreatment conditions were optimized for this high sugar-containing stover (HSS) to control inhibitor formation and obtain enhanced fermentable sugar concentrations. The optimum temperature, acid loading, and reaction time for the pretreatment were 155 °C, 0.5%, and 30 min, respectively, providing up to 97.15% sugar yield and 76.51 g/L total sugars at 10% solid-load. Sugar concentration further increased to 126.9 g/L at 20% solid-load, generating 3.89 g/L acetate, 0.92 g/L 5-hydroxymethyl furfural, 0.82 g/L furfural, and 3.75 g/L total phenolics as inhibitors. To determine the effects of soluble sugars in HSS on fermentable sugar yield and inhibitor formation, sugar-removed HSS was further studied under the optimum conditions. Although prior removal of sugars exhibited a reduction in inhibitor generation, it also decreased total fermentable sugar production to 115.45 g/L.

High-efficiency carbon-coated steel wool filter for controlling cooking-induced oil smoke

Cooking oil smoke (COS) contains many harmful substances, such as particulate matter, formaldehyde, and phenyl esters. Currently, commercial COS treatment equipment is expensive and requires a large space. Furthermore, a large amount of agricultural waste is generated and is mainly burned onsite, producing large amounts of greenhouse gases and air pollutants. This waste could be reused as a precursor for biochar and activated carbon. Therefore, this research used saccharification and catalytic hydrothermal carbonization to process rice straw and produce compact carbon-based filters (steel wool-C) for removing cooking-induced pollutants. Scanning electron microscopy indicated that carbon layers were coated on the steel wool. The Brunauer-Emmett-Teller surface area of the carbon filter was 71.595 m2/g, 43 times larger than that of steel wool. The steel wool filter removed 28.9%-45.4% of submicron aerosol particles. Adding a negative air ionizer (NAI) to the filter system enhanced the particle removal efficiency by 10%-25%. The removal efficiency of total volatile organic compounds was 27.3%-37.1% with the steel wool filter, but 57.2%-74.2% with the carbon-containing steel wool filter, and the NAI improved the removal efficiency by approximately 1%-5%. The aldehyde removal efficiency of the carbon filter with NAI was 59.0%-72.0%. Conclusively, the compact steel wool-C and NAI device could be promising COS treatment equipment for households and small eateries.

Pretreatment Strategies to Enhance Enzymatic Hydrolysis and Cellulosic Ethanol Production for Biorefinery of Corn Stover

There is a rising interest in bioethanol production from lignocellulose such as corn stover to decrease the need for fossil fuels, but most research mainly focuses on how to improve ethanol yield and pays less attention to the biorefinery of corn stover. To realize the utilization of different components of corn stover in this study, different pretreatment strategies were used to fractionate corn stover while enhancing enzymatic digestibility and cellulosic ethanol production. It was found that the pretreatment process combining dilute acid (DA) and alkaline sodium sulfite (ASS) could effectively fractionate the three main components of corn stover, i.e., cellulose, hemicellulose, and lignin, that xylose recovery reached 93.0%, and that removal rate of lignin was 85.0%. After the joint pretreatment of DA and ASS, the conversion of cellulose at 72 h of enzymatic hydrolysis reached 85.4%, and ethanol concentration reached 48.5 g/L through fed-batch semi-simultaneous saccharification and fermentation (S-SSF) process when the final concentration of substrate was 18% (w/v). Pretreatment with ammonium sulfite resulted in 83.8% of lignin removal, and the conversion of cellulose and ethanol concentration reached 86.6% and 50 g/L after enzymatic hydrolysis of 72 h and fed-batch S-SSF, respectively. The results provided a reference for effectively separating hemicellulose and lignin from corn stover and producing cellulosic ethanol for the biorefinery of corn stover.

Direct Furfural Production from Deciduous Wood Pentosans Using Different Phosphorus-Containing Catalysts in the Context of Biorefining

This study seeks to improve the effectiveness of the pretreatment stage when direct furfural production is integrated into the concept of a lignocellulosic biomass biorefinery. First of all, the catalytic effects of different phosphorus-containing salts (AlPO₄, Ca₃(PO₄)₂, FePO₄, H₃PO₄, NaH₂PO₄) were analysed in hydrolysis for their ability to convert birch wood C-5 carbohydrates into furfural. The hydrolysis process was performed with three different amounts of catalyst (2, 3 and 4 wt.%) at a constant temperature (175 °C) and treatment time (90 min). It was found that the highest amount of furfural (63–72%, calculated based on the theoretically possible yield (% t.p.y.)) was obtained when H₃PO₄ was used as a catalyst. The best furfural yield among the used phosphorus-containing salts was obtained with NaH₂PO₄: 40 ± 2%. The greatest impact on cellulose degradation during the hydrolysis process was observed using H₃PO₄ at 12–20% of the initial amount, while the lowest degradation was observed using NaH₂PO₄ as a catalyst. The yield of furfural was 60.5–62.7% t.p.y. when H₃PO₄ and NaH₂PO₄ were combined (1:2, 1:1, or 2:1 at a catalyst amount of 3 wt.%); however, the amount of cellulose that was degraded did not exceed 5.2–0.3% of the starting amount. Enzymatic hydrolysis showed that such pretreated biomass could be directly used as a substrate to produce glucose. The highest conversion ratio of cellulose into glucose (83.1%) was obtained at an enzyme load of 1000 and treatment time of 48 h.

Co-immobilization of Cellulase and β-Glucosidase into Mesoporous Silica Nanoparticles for the Hydrolysis of Cellulose Extracted from Eriobotrya japonica Leaves

Fungal cellulases generally contain a reduced amount of β-glucosidase (BG), which does not allow for efficient cellulose hydrolysis. To address this issue, we implemented an easy co-immobilization procedure of β-glucosidase and cellulase by adsorption on wrinkled mesoporous silica nanoparticles with radial and hierarchical open pore structures, exhibiting smaller (WSN) and larger (WSN-p) inter-wrinkle distances. The immobilization was carried out separately on different vectors (WSN for BG and WSN-p for cellulase), simultaneously on the same vector (WSN-p), and sequentially on the same vector (WSN-p) in order to optimize the synergy between cellulase and BG. The obtained results pointed out that the best biocatalyst is that prepared through simultaneous immobilization of BG and cellulase on the same vector (WSN-p). In this case, the adsorption resulted in 20% yield of immobilization, corresponding to an enzyme loading of 100 mg/g of support. 82% yield of reaction and 72 μmol/min·g activity were obtained, evaluated for the hydrolysis of cellulose extracted from Eriobotrya japonica leaves. All reactions were carried out at a standard temperature of 50 °C. The biocatalyst retained 83% of the initial yield of reaction after 9 cycles of reuse. Moreover, it had better stability than the free enzyme mixture in a wide range of temperatures, preserving 72% of the initial yield of reaction up to 90 °C.

A Detoxification-Free Process for Enhanced Ethanol Production From Corn Fiber Under Semi-Simultaneous Saccharification and Fermentation

Corn fiber, a by-product from the corn-processing industry, is an attractive feedstock for cellulosic ethanol because of its rich carbohydrate content (mainly residual starch, cellulose, and hemicellulose), abundant reserves, easy collection, and almost no transportation cost. However, the complex structure and components of corn fiber, especially hemicellulose, make it difficult to be effectively hydrolyzed into fermentable sugars through enzymatic hydrolysis. This study developed a simple and easy industrialized process without detoxification treatment for high-yield ethanol produced from corn fiber. Corn fiber was pretreated by dilute acid under the conditions optimized by Box-Behnken design (0.5% H₂SO₄ at 105°C for 43 min), and 81.8% of total sugars, including glucose, xylose, and arabinose, could be recovered, then the mixture (solid and hydrolysates) was directly used for semi-simultaneous saccharification and fermentation without detoxification, and ethanol yield reached about 81% of the theoretical yield.

Acid-based lignocellulosic biomass biorefinery for bioenergy production: Advantages, application constraints, and perspectives

The production of chemicals and fuels from renewable biomass with the primary aim of reducing carbon footprints has recently become one of the central points of interest. The use of lignocellulosic biomass for energy production is believed to meet the main criteria of maximizing the available global energy source and minimizing pollutant emissions. However, before usage in bioenergy production, lignocellulosic biomass needs to undergo several processes, among which biomass pretreatment plays an important role in the yield, productivity, and quality of the products. Acid-based pretreatment, one of the existing methods applied for lignocellulosic biomass pretreatment, has several advantages, such as short operating time and high efficiency. A thorough analysis of the characteristics of acid-based biomass pretreatment is presented in this review. The environmental concerns and future challenges involved in using acid pretreatment methods are discussed in detail to achieve clean and sustainable bioenergy production. The application of acid to biomass pretreatment is considered an effective process for biorefineries that aim to optimize the production of desired products while minimizing the by-products.

Isolation and identification of an osmotolerant Bacillus amyloliquefaciens strain T4 for 2, 3-butanediol production with tobacco waste

Microbial biomass and waste materials conversion for biochemicals production has been an alternative for energy conservation and emission reduction. While toxic substances in biomass materials and high osmotic pressure formed in fermentation-based systems block the bioconversion processes of microorganisms. In the present study, strain T4 that isolated from tobacco waste could resist toxic inhibitors such as nicotine and was suitable for generation of 2, 3-butanediol (2, 3-BD) with a high concentration of glucose (up to 20%). 30.06 and 1.54 g/L of 2, 3-BD was generated respectively from 50 g/L of tobacco waste with and without 200 g/L glucose after fermentation for 48 h. Besides, the results of biochemical tests showed that it was gram-positive and able to liquefy gelatin, hydrolyze starch and produce catalases. It could utilize glucose but not lactose as carbohydrates during fermentation. The 16S rRNA sequence and systematic analysis revealed that T4 was identified to be a Bacillus amyloliquefaciens (B. amyloliquefaciens). This work presents a promising model microorganism chassis to use the biomass waste for high value-added biochemicals production.

An integrated biorefinery process for co-production of xylose and glucose using maleic acid as efficient catalyst

This study aims to valorize wheat straw for xylose and glucose recovery using maleic acid in the pretreatment. The process conditions of maleic acid hydrolysis of wheat straw for xylose recovery were optimized by response surface methodology, through which the maximum xylose recovery of 77.12% versus minimum furfural yield of 1.61% were achieved using 70 g/L solid-to-liquid ratio and 0.1 mol/L maleic acid for 40 min at 150 °C. Moreover, 88.58% cellulose conversion was achieved by enzymatic hydrolysis of maleic acid-pretreated wheat straw. Results showed that maleic acid was an effective pretreatment solvent for sugars recovery: 19.88 g xylose and 30.89 g glucose were respectively obtained from 100 g wheat straw due to acidic and enzymatic hydrolysis, with only 0.37 g furfural produced. This study provides a strategy for hydrolyzing wheat straw to produce fermentable sugars with low amount of degradation product.

Bioethanol Production from Corn, Pumpkin and Carrot of Bangladesh as Renewable Source using Yeast Saccharomyces cerevisiae

Bangladesh produces a large amount of corn, pumpkin and carrots every year. To meet its huge energy demand and to lessen dependence on traditional fossil fuel these products are cost effective, renewable and abundant source for bioethanol production. The research was aimed to evaluate Bangladeshi corn, rotten carrot and pumpkin for bioethanol production. About 100 g of substrates was mixed with 300 ml distilled water and blended and sterilized. All the experiment was conducted with a temperature of 35oC, pH 6.0 and 20% sugar concentration. For fermentation, 200 ml yeast (Saccharomyces cerevisiae CCD) was added to make the total volume 500 ml. Addition of small amount of 1750 unit α-amylase enzyme to the substrate solution was found to enhance the fermentation process quicker. After 6- days of incubation, corn produced 63.00 ml of ethanol with 13.33 % (v/v) purity. Bioethanol production capacity of two different local varieties of pumpkin (red and black color) was assessed. Red pumpkin (Cucurbita maxima L.) produces 53 ml of ethanol with purity 6 %v/v and black color pumpkin produces 40 ml of yield with a low purity 4 %v/v. Carrot (Daucus carota L.) produces 73.67 ml of ethanol with 12.66 % (v/v) purity.

Artificial neural network and response surface methodology: a comparative analysis for optimizing rice straw pretreatment and saccharification

The present study demonstrates a comparative analysis between the artificial neural network (ANN) and response surface methodology (RSM) as optimization tools for pretreatment and enzymatic hydrolysis of lignocellulosic rice straw. The efficacy for both the processes, that is, pretreatment and enzymatic hydrolysis was evaluated using correlation coefficient (R²) & mean squared error (MSE). The values of R² obtained by ANN after training, validation, and testing were 1, 0.9005, and 0.997 for pretreatment and 0.962, 0.923, and 0.9941 for enzymatic saccharification, respectively. On the other hand, the R² values obtained with RSM were 0.9965 for cellulose recovery and 0.9994 for saccharification efficiency. Thus, ANN and RSM together successfully identify the substantial process conditions for rice straw pretreatment and enzymatic saccharification. The percentage of error for ANN and RSM were 0.009 and 0.01 for cellulose recovery and for 0.004 and 0.005 for saccharification efficiency, respectively, which showed the authority of ANN in exemplifying the non-linear behavior of the system.

Pretreatment and fermentation of lignocellulosic biomass: reaction mechanisms and process engineering

At a time of rapid depletion of oil resources, global food shortages and solid waste problems, it is imperative to encourage research into the use of appropriate pre-treatment techniques using regenerative raw materials such as lignocellulosic biomass.

Biochemical conversion of sweet sorghum bagasse to succinic acid

Succinic acid, an important intermediate in the manufacture of plastics and other commodity and specialty chemicals, is currently made primarily from petroleum. We attempted to biosynthesize succinic acid through microbial fermentation of cellulosic sugars derived from the bagasse of sweet sorghum, a renewable feedstock that can grow in a wide range of climates around the world. We investigated pretreating sweet sorghum bagasse (SSB) with concentrated phosphoric acid at mild conditions (40-85°C) at various residence times and biomass concentrations. We then subjected the pretreated SSB to enzymatic hydrolysis with a commercial cellulase to release glucose. The highest glucose yield was obtained when SSB was pretreated at 50°C for 43 min at 130 g/L biomass concentration on dry basis. Fermentation was carried out with Actinobacillus succinogenes 130Z, which readily converted 29.2 g/L of cellulosic glucose to 17.8 g/L of succinic acid in a 3.5-L bioreactor sparged with CO₂ at a rate of 0.5 vvm, thus reducing the carbon footprint of the process. Overall, we demonstrated, for the first time, the use of SSB for production of succinic acid using practices that lower energy use, future equipment cost, waste generation, and carbon footprint.

Simultaneous Bioconversion of Gelatinized Starchy Waste from the Rice Noodle Manufacturing Process to Lactic Acid and Maltose-Forming α-Amylase by Lactobacillus plantarum S21, Using a Low-Cost Medium

A direct bioconversion of gelatinized starchy waste (GSW) to lactic acid by amylolytic lactic acid bacterium Lactobacillus plantarum S21 was investigated. Corn steep liquor (CSL) was selected as the most suitable low-cost nitrogen source for replacing yeast extract, beef extract, and peptone in De Man, Rogosa and Sharpe (MRS) medium. Plackett–Burman design results indicated that GSW and CSL were the two most nutrients that significantly influence lactic acid production, among eight medium components, including GSW, CSL, K2HPO4, CH3COONa, (NH4)2HC6H5O7, MgSO4, MnSO4, and Tween 80. A new low-cost medium containing only GSW (134.4 g/L) and CSL (187.7 g/L) was achieved as omitting other six components from the optimized medium had no effect on lactic acid yield. Batch fermentation at 37 °C both in 1 L and 10 L jar fermenters showed non-significantly different productivity. A by-product, maltose-forming α-amylase, was successfully achieved up to 96% recovery yield using an ultrafiltration unit equipped with a 50 kDa cut-off membrane. Crude lactic acid exhibited the additional benefit of antimicrobial activity against food and feed pathogens Salmonella enterica serovar Typhimurium TISTR 292, Vibrio cholerae TH-001, and also E. coli ATCC 25922. This study presents a promising bioprocess for the simultaneous production of lactic acid, and a value-added food enzyme, using only two industrial wastes, GSW and CSL, as the medium components.

Evaluation of inhibitory effect and feasible utilization of dilute acid-pretreated rice straws on succinate production by metabolically engineered Escherichia coli AS1600a

This work demonstrated a pioneer work in the pre-treatment of rice straw by phosphoric acid (H₃PO₄) for succinate production. The optimized pre-treatment condition of rice straw was at 121 °C for 30 min with 2 N H₃PO₄. With this condition, total sugar concentration of 31.2 g/L with the highest hemicellulose saccharification yield of 94% was obtained. The physicochemical analysis of the pre-treated rice straw showed significant changes in its structure thus enhancing enzymatic saccharification. Succinate concentrations of 78.5 and 63.8 g/L were produced from hydrolysate liquor (L) and solid fraction (S) of the pre-treated rice straw respectively, with a comparable yield of 86% by E. coli AS1600a. Use of a combined L + S fraction in simultaneous saccharification and fermentation (LS + SSF) further improved succinate production at a concentration and yield of 85.6 g/L and 90% respectively. The results suggested that H₃PO₄ pre-treated rice straw may be utilized for economical succinate production by E. coli AS1600a.

Production, purification, characterization and application of a new halotolerant and thermostable endoglucanase of Botrytis ricini URM 5627

A halotolerant endoglucanase with a molecular mass of 39 kDa was obtained from the solid fermentation of sugarcane bagasse by the fungus Botrytis ricini URM 5627 and isolated using only two purification processes: fractionation with ammonium sulphate and size-exclusion chromatography resulting in an activity of 1289.83 U/mL. After the isolation, biochemical characterizations were performed, giving a temperature of 50 °C and optimum pH of 5. The enzyme was stable at 39-60 °C for 60 min and at a pH of 4-6. The enzymatic activity increased in the presence of Na⁺, Mn²⁺, Mg²⁺ and Zn²⁺ and decreased in the presence of Ca²⁺, Cu²⁺, and Fe²⁺. The endoglucanase revealed a halotolerant profile since its activity increased proportionally to an increase in NaCl concentration. The maximum activity was reached at 2 M NaCl with a 75% increase in activity. The enzyme had a K_m of 0.1299 ± 0.0096 mg/mL and a V_max of 0.097 ± 0.00121 mol/min/mL. During application in saccharification tests, the enzyme was able to hydrolyse sugarcane bagasse, rice husk, and wheat bran, with the highest production of reducers/fermentable sugars within 24 h of saccharification for wheat bran (137.21 mg/g). Therefore, these properties combined make this isolated enzyme a potential candidate for biotechnological and industrial applications.

Optimization of alkaline extraction of hemicellulose from sweet sorghum bagasse and its direct application for the production of acidic xylooligosaccharides by Bacillus subtilis strain MR44

As predominant components of hemicelluloses in grasses, methylglucuroarabinoxylans (MeGAX_n) are sources for the production of acidic xylooligosaccharides (U-XOS). Bacillus subtilis MR44, an engineered biocatalyst to secrete only the XynC xylanase and Axh43 arabinoxylan hydrolase is capable of processing MeGAX_n to exclusively U-XOS. The present studies are directed at the explosion on direct alkaline extraction serving for production of U-XOS. Response Surface Methodology was used to optimize xylan extraction conditions on the sweet sorghum bagasse to achieve maximum hemicelluloses yield. The optimized condition was as follows: extraction time of 3.91 h, extraction temperature of 86.1°C, and NaOH concentration (w/w) of 12.33%. Crude xylan extracted with NaOH revealed a compositional analysis of xylose (79.0%), arabinose (5.3%), glucose (1.7%), lignin and ash (5.6%). After neutralization this xylan preparation supported growth of MR44, processing MeGAX_n from sweet sorghum and accumulating U-XOS. The quality of U-XOS produced by MR44 using alkaline-treated sweet sorghum bagasse was comparable to that obtained from purified MeGAX_n. Overall, the present study demonstrates that direct alkaline treatment of sweet sorghum bagasse is useful to improve the bioavailability of MeGAX_n for MR44-mediated conversion to U-XOS with average degrees of polymerization of 11–12, providing alternative resources with applications in nutrition and human and veterinary medicine.

Phosphoric acid based pretreatment of switchgrass and fermentation of entire slurry to ethanol using a simplified process

Switchgrass (Alamo) was pretreated with phosphoric acid (0.75 and 1%, w/w) at three temperatures (160, 175 and 190 °C) and time (5, 7.5 and 10 min) using a steam gun. The slurry after pretreatment was liquefied by enzymes and the released sugars were fermented in a simultaneous saccharification and co-fermentation process to ethanol using ethanologenic Escherichia coli strain SL100. Among the three variables in pretreatment, temperature and time were critical in supporting ethanol titer and yield. Enzyme hydrolysis significantly increased the concentration of furans in slurries, apparently due to release of furans bound to the solids. The highest ethanol titer of 21.2 ± 0.3 g/L ethanol obtained at the pretreatment condition of 190-1-7.5 (temperature-acid concentration-time) and 10% solids loading accounted for 190 ± 2.9 g ethanol/kg of raw switch grass. This converts to 61.7 gallons of ethanol per ton of dry switchgrass, a value that is comparable to other published pretreatment conditions.

Efficient and repeated production of succinic acid by turning sugarcane bagasse into sugar and support

Here we reported an endeavor in making full use of sugarcane bagasse for biological production of succinic acid. Through NaOH pre-treatment and multi-enzyme hydrolysis, a reducing sugar solution mainly composed of glucose and xylose was obtained from the sugarcane bagasse. By optimizing portions of cellulase, xylanase, β-glucanase and pectinase in the multi-enzyme "cocktail", the hydrolysis percentage of the total cellulose in pre-treated sugarcane bagasse can be as high as 88.5%. A. succinogenes CCTCC M2012036 was used for converting reducing sugars into succinic acid in a 3-L bioreactor with a sugar-fed strategy to prevent cell growth limitation. Importantly, cells were found to be adaptive on the sugarcane bagasse residue, offering possibilities of repeated batch fermentation and replacement for MgCO3 with soluble NaHCO3 in pH modulation. Three cycles of fermentation without activity loss were realized with the average succinic acid yield and productivity to be 80.5% and 1.65g·L(-1)·h(-1).

Study of a High-Yield Cellulase System Created by Heavy-Ion Irradiation-Induced Mutagenesis of Aspergillus niger and Mixed Fermentation with Trichoderma reesei

The aim of this study was to evaluate and validate the efficiency of ¹²C⁶⁺ irradiation of Aspergillus niger (A. niger) or mutagenesis via mixed Trichoderma viride (T. viride) culturing as well as a liquid cultivation method for cellulase production via mixed Trichoderma reesei (T. reesei) and A. niger culture fermentation. The first mutagenesis approach was employed to optimize yield from a cellulase-producing strain via heavy-ion mutagenesis and high-throughput screening, and the second was to effectively achieve enzymatic hydrolysis of cellulase from a mixed culture of mutant T. viride and A. niger. We found that ¹²C⁶⁺-ion irradiation induced changes in cellulase biosynthesis in A. niger but had no effect on the time course of the synthesis. It is notable that the exoglucanases (CBH) activities of A. niger strains H11-1 and H differed (6.71 U/mL vs. 6.01 U/mL) and were significantly higher than that of A. niger mutant H3-1. Compared with strain H, the filter paper assay (FPA), endoglucanase (EG) and β-glucosidase (BGL) activities of mutant strain H11-1 were increased by 250.26%, 30.26% and 34.91%, respectively. A mixed culture system was successfully optimized, and the best ratio of T. reesei to A. niger was 5:1 for 96 h with simultaneous inoculation. The BGL activity of the mixed culture increased after 72 h. At 96 h, the FPA and BGL activities of the mixed culture were 689.00 and 797.15 U/mL, respectively, significantly higher than those of monocultures, which were 408.70 and 646.98 U/mL for T. reesei and 447.29 and 658.89 U/mL for A. niger, respectively. The EG activity of the mixed culture was 2342.81 U/mL, a value that was significantly higher than that of monocultures at 2206.57 U/mL for T. reesei and 1727.62 U/mL for A. niger. In summary, cellulose production and hydrolysis yields were significantly enhanced by the proposed combination scheme.

Non-severe thermochemical hydrolysis of stover from white corn and sequential enzymatic saccharification and fermentation to ethanol

A parametric study, with an initial load of 15%w/w of dry stover from white corn, was conducted to evaluate the sequential thermochemical hydrolysis (TH), enzymatic saccharification (ES) and fermentation of the whole slurry with ethanologenic Escherichia coli. The TH was designed to release the maximum amount of xylose with a concomitant formation of minimal amounts of furans. It was found that 29.0% or 93.2% of the xylan was recovered as free xylose at 130°C after 8 min in the presence of 1% or 2%w/w H2SO4 and produced only 0.06 or 0.44 g/L of total furans, respectively. After 24h of ES, 76.14-77.18 g/L of monosaccharides (pentoses and hexoses) were obtained. These slurries, which contained 0.03-0.26 g/L of total furans and 5.14-5.91 g/L of acetate, were fermented with 3.7 g/L of ethanologenic E. coli to produce 24.5-23.5 g/L of ethanol.

Optimising the (Microwave) Hydrothermal Pretreatment of Brewers Spent Grains for Bioethanol Production

For the production of bioethanol from lignocellulosic biomass, it is important to optimise the thermochemical pretreatment which is required to facilitate subsequent liberation of monomeric sugars. Here, we report optimisation of pretreatment conditions for brewers spent grains (BSG) with the main objectives of (1) working at commercially relevant high solids content, (2) minimising energy and chemical inputs, and (3) maximising downstream sugar yields. Studies indicated there to be a play-off between pretreatment solids content, the usage of an acid catalyst, and pretreatment temperature. For example, yields of 80–90% theoretical glucose could be obtained following pretreatment at 35% w/v solids and 200°C, or at 140–160°C with addition of 1% HCl. However, at very high solids loadings (40–50% w/v) temperatures of 180–200°C were necessary to attain comparable sugar yields, even with an acid catalyst. The feasibility of producing bioethanol from feedstocks generated using these protocols was demonstrated (but not optimised) at laboratory scale.

Optimization of Alkaline and Dilute Acid Pretreatment of Agave Bagasse by Response Surface Methodology

Utilization of lignocellulosic materials for the production of value-added chemicals or biofuels generally requires a pretreatment process to overcome the recalcitrance of the plant biomass for further enzymatic hydrolysis and fermentation stages. Two of the most employed pretreatment processes are the ones that used dilute acid (DA) and alkaline (AL) catalyst providing specific effects on the physicochemical structure of the biomass, such as high xylan and lignin removal for DA and AL, respectively. Another important effect that need to be studied is the use of a high solids pretreatment (≥15%) since offers many advantaged over lower solids loadings, including increased sugar and ethanol concentrations (in combination with a high solids saccharification), which will be reflected in lower capital costs; however, this data is currently limited. In this study, several variables, such as catalyst loading, retention time, and solids loading, were studied using response surface methodology (RSM) based on a factorial central composite design of DA and AL pretreatment on agave bagasse using a range of solids from 3 to 30% (w/w) to obtain optimal process conditions for each pretreatment. Subsequently enzymatic hydrolysis was performed using Novozymes Cellic CTec2 and HTec2 presented as total reducing sugar (TRS) yield. Pretreated biomass was characterized by wet-chemistry techniques and selected samples were analyzed by calorimetric techniques, and scanning electron/confocal fluorescent microscopy. RSM was also used to optimize the pretreatment conditions for maximum TRS yield. The optimum conditions were determined for AL pretreatment: 1.87% NaOH concentration, 50.3 min and 13.1% solids loading, whereas DA pretreatment: 2.1% acid concentration, 33.8 min and 8.5% solids loading.

Enhancement of xylose utilization from corn stover by a recombinant Escherichia coli strain for ethanol production

Effects of substrate-selective inoculum prepared by growing on glucose, xylose, arabinose, GXA (glucose, xylose, arabinose, 1:1:1) and corn stover hydrolyzate (dilute acid pretreated and enzymatically hydrolyzed, CSH) on ethanol production from CSH by a mixed sugar utilizing recombinant Escherichia coli (strain FBR5) were investigated. The initial ethanol productivity was faster for the seed grown on xylose followed by GXA, CSH, glucose and arabinose. Arabinose grown seed took the longest time to complete the fermentation. Delayed saccharifying enzyme addition in simultaneous saccharification and fermentation of dilute acid pretreated CS by the recombinant E. coli strain FBR5 allowed the fermentation to finish in a shorter time than adding the enzyme simultaneously with xylose grown inoculum. Use of substrate selective inoculum and fermenting pentose sugars first under glucose limited condition helped to alleviate the catabolite repression of the recombinant bacterium on ethanol production from lignocellulosic hydrolyzate.

Lignocellulosic agriculture wastes as biomass feedstocks for second-generation bioethanol production: concepts and recent developments

Production of liquid biofuels, such as bioethanol, has been advocated as a sustainable option to tackle the problems associated with rising crude oil prices, global warming and diminishing petroleum reserves. Second-generation bioethanol is produced from lignocellulosic feedstock by its saccharification, followed by microbial fermentation and product recovery. Agricultural residues generated as wastes during or after processing of agricultural crops are one of such renewable and lignocellulose-rich biomass resources available in huge amounts for bioethanol production. These agricultural residues are converted to bioethanol in several steps which are described here. This review enlightens various steps involved in production of the second-generation bioethanol. Mechanisms and recent advances in pretreatment, cellulases production and second-generation ethanol production processes are described here.

Significantly improving enzymatic saccharification of high crystallinity index's corn stover by combining ionic liquid [Bmim]Cl-HCl-water media with dilute NaOH pretreatment

In this study, a pretreatment by combining acidified aqueous ionic liquid 1-butyl-3-methylimidazolium chloride (IL [Bmim]Cl) solution with dilute NaOH extraction was employed to pretreat high crystallinity index (CrI) of corn stover before its enzymatic saccharification. After NaOH extraction, [Bmim]Cl-HCl-water (78.8:1.2:20, w/w/w) media was used for further pretreatment at 130 °C for 30 min. After being enzymatically hydrolyzed for 48 h, corn stover pretreated could be biotransformed into reducing sugars in the yield of 95.1%. Furthermore, SEM, XRD and FTIR analyses of untreated and pretreated corn stovers were examined. It was found that the intact structure was disrupted by combination pretreatment and resulted in a porous and amorphous regenerated cellulosic material that greatly improved enzymatic hydrolysis. Finally, the recovered hydrolyzates obtained from the enzymatic hydrolysis of pretreated corn stovers could be fermented into ethanol efficiently. In conclusion, the combination pretreatment shows high potential application in future.

A novel diffusion-biphasic hydrolysis coupled kinetic model for dilute sulfuric acid pretreatment of corn stover

Kinetic experiments on the dilute sulfuric acid pretreatment of corn stover were performed. A high xylan removal and a low inhibitor concentration were achieved by acid pretreatment. A novel diffusion-hydrolysis coupled kinetic model was proposed. The contribution to the xylose yield was analyzed by the kinetic model. Compared with the inhibitor furfural negatively affecting xylose yield, the fast and slow-hydrolyzing xylan significantly contributed to the xylose yield, however, their dominant roles were dependent on reaction temperature and time. The impact of particle size and acid concentration on the xylose yield were also investigated. The diffusion process may significantly influence the hydrolysis of large particles. Increasing the acid concentration from 0.15 M to 0.30 M significantly improved the xylose yield, whereas the extent of improvement decreased to near-quantitative when further increasing acid loading. These findings shed some light on the mechanism for dilute sulfuric acid hydrolysis of corn stover.

A two-step process for efficient enzymatic saccharification of rice straw

Response surface methodology was used to optimise a two-step process of cellulase mediated saccharification of rice straw by an isolated bacterium Lysinibacillus sphaericus. CMC concentration, yeast extract, pH and incubation temperature were optimised for cellulase production using a central composite design and their optimum values were determined to be 4.3% (w/v), 2.1% (w/v), 6.2 and 45.2 °C respectively. The CMCase activity at these values was 5.16±0.07 U/ml, which was 2.5 times that of the un-optimised system. Similarly, pretreated rice straw, enzyme load, incubation time and Tween-80 concentrations were optimised for enhanced saccharification of rice straw by optimised cellulase preparations, and their optimum values were calculated as 1.84% (w/v), 40 U, 57.4 h and 0.76 mM respectively. A percent saccharification of 69.5% was reported at optimal conditions. HPLC analysis revealed that hydrolysate produced at optimal conditions of saccharification constituted 70.8% of glucose.

Ethanol production from cotton gin trash using optimised dilute acid pretreatment and whole slurry fermentation processes

Cotton ginning trash (CGT) collected from Australian cotton gins was evaluated for bioethanol production. CGT composition varied between ginning operations and contained high levels of extractives (26-28%), acid-insoluble material (17-22%) and holocellulose (42-50%). Pretreatment conditions of time (4-20 min), temperature (160-220 °C) and sulfuric acid concentration (0-2%) were optimised using a central composite design. Response surface modelling revealed that CGT fibre pretreated at 180 °C in 0.8% H2SO4 for 12 min was optimal for maximising enzymatic glucose recoveries and achieved yields of 89% theoretical, whilst the total accumulated levels of furans and acetic acid remained relatively low at <1 and 2 g/L respectively. Response surface modelling also estimated maximum xylose recovery in pretreated liquors (87% theoretical) under the set conditions of 150 °C in 1.9% H2SO4 for 23.8 min. Yeast fermentations yielded high ethanol titres of 85%, 88% and 70% theoretical from glucose generated from: (a) enzymatic hydrolysis of washed pretreated fibres, (b) enzymatic hydrolysis of whole pretreated slurries and (c) simultaneous saccharification fermentations, respectively.

Perspective and prospective of pretreatment of corn straw for butanol production

Corn straw, lignocellulosic biomass, is a potential substrate for microbial production of bio-butanol. Bio-butanol is a superior second generation biofuel among its kinds. Present researches are focused on the selection of butanol tolerant clostridium strain(s) to optimize butanol yield in the fermentation broth because of toxicity of bio-butanol to the clostridium strain(s) itself. However, whatever the type of the strain(s) used, pretreatment process always affects not only the total sugar yield before fermentation but also the performance and growth of microbes during fermentation due to the formation of hydroxyl-methyl furfural, furfural and phenolic compounds. In addition, the lignocellulosic biomasses also resist physical and biological attacks. Thus, selection of best pretreatment process and its parameters is crucial. In this context, worldwide research efforts are increased in past 12 years and researchers are tried to identify the best pretreatment method, pretreatment conditions for the actual biomass. In this review, effect of particle size, status of most common pretreatment method and enzymatic hydrolysis particularly for corn straw as a substrate is presented. This paper also highlights crucial parameters necessary to consider during most common pretreatment processes such as hydrothermal, steam explosion, ammonia explosion, sulfuric acid, and sodium hydroxide pretreatment. Moreover, the prospective of pretreatment methods and challenges is discussed.

Efficient production of 2,3-butanediol from corn stover hydrolysate by using a thermophilic Bacillus licheniformis strain

In this study, a thermophilic Bacillus licheniformis strain X10 was newly isolated for 2,3-butanediol (2,3-BD) production from lignocellulosic hydrolysate. Strain X10 could utilize glucose and xylose simultaneously without carbon catabolite repression. In addition, strain X10 possesses high tolerance to fermentation inhibitors including furfural, vanillin, formic acid, and acetic acid. In a fed-batch fermentation, 74.0g/L of 2,3-BD was obtained from corn stover hydrolysate, with a productivity of 2.1g/Lh and a yield of 94.6%. Thus, this thermophilic B. licheniformis strain is a candidate for the development of efficient industrial production of 2,3-BD from corn stover hydrolysate.

Bioethanol production from wheat straw via enzymatic route employing Penicillium janthinellum cellulases

This study concerns in-house development of cellulases from a mutant Penicillium janthinellum EMS-UV-8 and its application in separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) processes for bioethanol production from pre-treated wheat straw. In a 5L fermentor, the above strain could produce cellulases having activity of 3.1 FPU/mL and a specific activity of 0.83 FPU/mg of protein. In-house developed cellulase worked more efficiently in case of SSF as ethanol concentration of 21.6g/L and yield of 54.4% were obtained which were higher in comparison to SHF (ethanol concentration 12 g/L and 30.2% yield). This enzyme preparation when compared with commercial cellulase for hydrolysis of pre-treated wheat straw was found competitive. This study demonstrates that P. janthinellum EMS-UV-8 is a potential fungus for future large-scale production of cellulases.

Characteristics of corn stover pretreated with liquid hot water and fed-batch semi-simultaneous saccharification and fermentation for bioethanol production

Corn stover is a promising feedstock for bioethanol production because of its abundant availability in China. To obtain higher ethanol concentration and higher ethanol yield, liquid hot water (LHW) pretreatment and fed-batch semi-simultaneous saccharification and fermentation (S-SSF) were used to enhance the enzymatic digestibility of corn stover and improve bioconversion of cellulose to ethanol. The results show that solid residues from LHW pretreatment of corn stover can be effectively converted into ethanol at severity factors ranging from 3.95 to 4.54, and the highest amount of xylan removed was approximately 89%. The ethanol concentrations of 38.4 g/L and 39.4 g/L as well as ethanol yields of 78.6% and 79.7% at severity factors of 3.95 and 4.54, respectively, were obtained by fed-batch S-SSF in an optimum conditions (initial substrate consistency of 10%, and 6.1% solid residues added into system at the prehydrolysis time of 6 h). The changes in surface morphological structure, specific surface area, pore volume and diameter of corn stover subjected to LHW process were also analyzed for interpreting the possible improvement mechanism.