Fed-batch semi-simultaneous saccharification and fermentation of reed pretreated with liquid hot water for bio-ethanol production using Saccharomyces cerevisiae

Metabolomics Study Reveals Biomarker L-Proline as Potential Stress-Protectant Compound for High-Temperature Bioethanol Fermentation by Yeast Pichia kudriavzevii 1P4

High-temperature ethanol fermentation (> 40 °C) can be applied as effective bioprocess technology to increase ethanol production. Thermotolerant yeast Pichia kudriavzevii 1P4 showed the ability to produce ethanol at optimum 37 °C. Thus, this study evaluated the ethanol productivity of isolate 1P4 at high-temperature ethanol fermentation (42 and 45 °C) and the identification of metabolite biomarkers using untargeted metabolomics with liquid chromatography-tandem mass spectrometry (LC-MS/MS). 1P4 showed tolerance to temperature stress up to 45 °C and thus relevant for high-temperature fermentation. As measured by gas chromatography (GC), bioethanol production of 1P4 at 30, 37, 42, and 45 °C was 5.8 g/l, 7.1 g/l, 5.1 g/l, and 2.8 g/l, respectively. The classification of biomarker compounds was based on orthogonal projection analysis to latent structure discriminant analysis (OPLS-DA), resulting in L-proline being a suspected biomarker compound for isolate 1P4 tolerance against high-temperature stress. Indeed, supplementation of L-proline on fermentation medium supported the growth of 1P4 at high temperatures (> 40 °C) than without L-proline. The bioethanol production with the addition of the L-proline resulted in the highest ethanol concentration (7.15 g/l) at 42 °C. Supplementation of L-proline as a stress-protective compound increased ethanol productivity at high-temperature fermentation of 42 and 45 °C by 36.35% and 83.33%, respectively, compared without the addition of L-proline. Preliminary interpretation of these results indicates that bioprocess engineering through supplementation of stress-protective compounds L-proline increases the fermentation efficiency of isolate 1P4 at higher temperatures (42 °C and 45 °C).

Non-conventional yeast strains: Unexploited resources for effective commercialization of second generation bioethanol

The conventional yeast (Saccharomyces cerevisiae) is the most studied yeast and has been used in many important industrial productions, especially in bioethanol production from first generation feedstock (sugar and starchy biomass). However, for reduced cost and to avoid competition with food, second generation bioethanol, which is produced from lignocellulosic feedstock, is now being investigated. Production of second generation bioethanol involves pre-treatment and hydrolysis of lignocellulosic biomass to sugar monomers containing, amongst others, d-glucose and D-xylose. Intrinsically, S. cerevisiae strains lack the ability to ferment pentose sugars and genetic engineering of S. cerevisiae to inculcate the ability to ferment pentose sugars is ongoing to develop recombinant strains with the required stability and robustness for commercial second generation bioethanol production. Furthermore, pre-treatment of these lignocellulosic wastes leads to the release of inhibitory compounds which adversely affect the growth and fermentation by S. cerevisae. S. cerevisiae also lacks the ability to grow at high temperatures which favour Simultaneous Saccharification and Fermentation of substrates to bioethanol. There is, therefore, a need for robust yeast species which can co-ferment hexose and pentose sugars and can tolerate high temperatures and the inhibitory substances produced during pre-treatment and hydrolysis of lignocellulosic materials. Non-conventional yeast strains are potential solutions to these problems due to their abilities to ferment both hexose and pentose sugars, and tolerate high temperature and stress conditions encountered during ethanol production from lignocellulosic hydrolysate. This review highlights the limitations of the conventional yeast species and the potentials of non-conventional yeast strains in commercialization of second generation bioethanol.

A sustainable process for co-production of xylooligosaccharides and ethanol from alkali treated sugarcane bagasse: A strategy towards waste management

Present study aims at sustainable utilization of sugarcane bagasse (SCB) for production of valuable prebiotic xylooligosaccharides (XOS) along with second generation ethanol. Fractionation of SCB into hemicellulose rich liquid fraction and cellulose rich solid residue was achieved using alkaline treatment. Carbohydrate rich precipitate obtained from liquid fraction was utilized for XOS production using inhouse produced endoxylanase. XOS production from SCB xylan was optimized by employing response surface methodology. Under optimized conditions, maximum XOS yield was 227.72 mg/g of carbohydrate rich precipitates. The solid residue obtained after alkaline pretreatment was used for ethanol fermentation by prehydrolysis and simultaneous saccharification and fermentation (P-SSF) process using cellulolytic enzyme cocktail and Saccharomyces cerevisiae SM1. Maximum ethanol concentration, productivity and yield were 79.76 ± 0.16 g/L, 0.83 g/L/h and 69.38%, respectively by employing P-SSF process. Based on the experimental data it can be predicted that bioconversion of 100 g raw SCB can yield 6.26 g of XOS (DP 2-DP 5), 15.95 g ethanol and 1.44 g of xylitol. Present investigation reports an integrated process for effective bioconversion of SCB into value added products by maximum utilization of cellulosic and hemicellulosic fractions simultaneously using indigenously produced fungal enzymes.

Production of cellulosic ethanol and value-added products from corn fiber

Corn fiber, a by-product from the corn processing industry, mainly composed of residual starch, cellulose, and hemicelluloses, is a promising raw material for producing cellulosic ethanol and value-added products due to its abundant reserves and low costs of collection and transportation. Now, several technologies for the production of cellulosic ethanol from corn fiber have been reported, such as the D3MAX process, Cellerate™ process, etc., and part of the technologies have also been used in industrial production in the United States. The ethanol yields range from 64 to 91% of the theoretical maximum, depending on different production processes. Because of the multicomponent of corn fiber and the complex structures highly substituted by a variety of side chains in hemicelluloses of corn fiber, however, there are many challenges in cellulosic ethanol production from corn fiber, such as the low conversion of hemicelluloses to fermentable sugars in enzymatic hydrolysis, high production of inhibitors during pretreatment, etc. Some technologies, including an effective pretreatment process for minimizing inhibitors production and maximizing fermentable sugars recovery, production of enzyme preparations with suitable protein compositions, and the engineering of microorganisms capable of fermenting hexose and pentose in hydrolysates and inhibitors tolerance, etc., need to be further developed. The process integration of cellulosic ethanol and value-added products also needs to be developed to improve the economic benefits of the whole process. This review summarizes the status and progresses of cellulosic ethanol production and potential value-added products from corn fiber and presents some challenges in this field at present.

In Situ Corn Fiber Conversion for Ethanol Improvement by the Addition of a Novel Lignocellulolytic Enzyme Cocktail

Corn mashes have high-viscosity and high-sugar characteristics, which hinders yeast-fermentation efficiency and the ethanol yield increase. The excessive viscosity of corn mash is caused by the unutilized cellulose in corn kernel fiber. A novel lignocellulolytic enzymes cocktail with strong substrate specificity was prepared for high-viscosity, high-sugar corn mash. The in situ conversion of corn mashes with novel lignocellulolytic enzymes at the optimum cellulase dosage of 50 FPU/L resulted in about 12% increased ethanol concentration compared with the reference mash at different batch-fermentation scales. Adding the lignocellulolytic enzymes caused the greatest decrease in viscosity of corn mash and residual sugars by 40.9% and 56.3%, respectively. Simultaneously, the application of lignocellulolytic enzymes increased the value of the dried distiller’s grain with solubles (DDGS) by increasing the protein content by 5.51%. The in situ conversion of cellulose can decrease the fermentation broth viscosity and improve the rheological property, thereby improving the ethanol yield. With the same amount of material, the application of the novel enzymes cocktail can enhance the ethanol yield by more than 12%. A quarter of the ethanol yield increase was due to the further hydrolysis of starch, while three quarters to cellulose. Thus, this technology will increase the net revenue of bioethanol industrialization.

Lignocellulosic Biomass Valorization for Bioethanol Production: a Circular Bioeconomy Approach

Lignocellulosic biomass generated from different sectors (agriculture, forestry, industrial) act as biorefinery precursor for production of second-generation (2G) bioethanol and other biochemicals. The integration of various conversion techniques on a single platform under biorefinery approach for production of biofuel and industrially important chemicals from LCB is gaining interest worldwide. The waste generated on utilization of bio-resources is almost negligible or zero in a biorefinery along with reduced greenhouse gas emissions, which supports the circular bioeconomy concept. The economic viability of a lignocellulosic biorefinery depends upon the efficient utilization of three major components of LCB-cellulose, hemicellulose and lignin. The heterogeneous structure and recalcitrant nature of LCB is main obstacle in its valorization into bioethanol and other value-added products. The success of bioconversion process depends upon methods used during pre-treatment, hydrolysis and fermentation processes. The cost involved in each step of the bioconversion process affects the viability of cellulosic ethanol. The lignocellulose biorefinery has ample scope, but much-focused research is required to fully utilize major parts of lignocellulosic biomass with zero wastage. The present review entails lignocellulosic biomass valorization for ethanol production, along with different steps involved in its production. Various value-added products produced from LCB components were also discussed. Recent technological advances and significant challenges in bioethanol production are also highlighted in addition to future perspectives.

The hydrothermal-alkaline/oxygen two-step pretreatment combined with the addition of surfactants reduced the amount of cellulase for enzymatic hydrolysis of reed

This study aimed to provide a low cost feasible pretreatment and enzymatic hydrolysis (EH) method for the effective dissolution of xylan and the high glucan digestibility of reed with a low enzyme loading. The combination of polyethylene glycol (PEG) 3000-enhanced EH and hydrothermal-alkaline/oxygen pretreatment was studied. Process conditions were optimized through response surface methodology. Three models of glucan conversion rate, pretreated solids yield and lignin removal rate were established, and their determination coefficient (R²) values were 0.9218, 0.7939, and 0.8156, respectively. The models and experiments were reliable and significant. The optimal conditions favored 94.5% xylan dissolution rate and 95.6% glucan digestibility by using a cellulase loading of 3 filter paper units (FPU)/g-pretreated solids, which obviously enhanced 30.7% of the glucan conversion rate. This method was applicable due to effective xylan dissolution, lignin removal, and EH with PEG 3000 addition, which can help saved 85% cellulase loading.

An overview on bioethanol production from lignocellulosic feedstocks

Lignocellulosic ethanol has been proposed as a green alternative to fossil fuels for many decades. However, commercialization of lignocellulosic ethanol faces major hurdles including pretreatment, efficient sugar release and fermentation. Several processes were developed to overcome these challenges e.g. simultaneous saccharification and fermentation (SSF). This review highlights the various ethanol production processes with their advantages and shortcomings. Recent technologies such as singlepot biorefineries, combined bioprocessing, and bioenergy systems with carbon capture are promising. However, these technologies have a lower technology readiness level (TRL), implying that additional efforts are necessary before being evaluated for commercial availability. Solving energy needs is not only a technological solution and interlinkage of various factors needs to be assessed beyond technology development.

Combined liquid hot water with sodium carbonate-oxygen pretreatment to improve enzymatic saccharification of reed

In this work, two-stage combination of liquid hot water (LHW) and Na₂CO₃-O₂ pretreatment was performed efficiently on reed to obtain fermentable sugar. Reed was first treated with LHW at 170 °C for 60 min and then with Na₂CO₃-O₂. The optimal conditions for Na₂CO₃-O₂ pretreatment were as follow: reaction temperature of 150 °C, residence time of 40 min, Na₂CO₃ concentration of 33.3 g/L and oxygen pressure of 0.6 MPa. The total sugar yield of 79.1% was achieved with a cellulase of 20 FPU/g-pretreated solid for 48 h. The total sugar yield improved 36.0% compared with single Na₂CO₃-O₂ pretreatment. The combined pretreatment could avoid the loss of carbohydrate degradation. The total sugar yield was increased by 48.6% compared to only LHW pretreatment. Owing to advantages of the combined pretreatment breaking the restraint of lignin and cellulose, LHW combined with Na₂CO₃-O₂ pretreatment was a promising method for the production of fermentable sugar.

Effects of various inhibitory substances and immobilization on ethanol production efficiency of a thermotolerant Pichia kudriavzevii

BACKGROUND

Although bioethanol production has been gaining worldwide attention as an alternative to fossil fuel, ethanol productivities and yields are still limited due to the susceptibility of fermentation microorganisms to various stress and inhibitory substances. There is therefore an unmet need to search for multi-stress-tolerant organisms to improve ethanol productivity and reduce production cost, particularly when lignocellulosic hydrolysates are used as the feedstock.

RESULTS

Here, we have characterized a previously isolated Pichia kudriavzevii LC375240 strain which is thermotolerant to high temperatures of 37 °C and 42 °C. More excitingly, growth and ethanol productivity of this strain exhibit strong tolerance to multiple stresses such as acetic acid, furfural, formic acid, H₂O₂ and high concentration of ethanol at 42 °C. In addition, simple immobilization of LC375240 on corncobs resulted to a more stable and higher efficient ethanol production for successive four cycles of repeated batch fermentation at 42 °C.

CONCLUSION

The feature of being thermotolerant and multi-stress-tolerant is unique to P. kudriavzevii LC375240 and makes it a good candidate for second-generation bioethanol fermentation as well as for investigating the molecular basis underlying the robust stress tolerance. Immobilization of P. kudriavzevii LC375240 on corncobs is another option for cheap and high ethanol productivity.

Lignocellulosic biomass for bioethanol: an overview on pretreatment, hydrolysis and fermentation processes

Bioethanol is currently the only alternative to gasoline that can be used immediately without having to make any significant changes in the way fuel is distributed. In addition, the carbon dioxide (CO2) released during the combustion of bioethanol is the same as that used by the plant in the atmosphere for its growth, so it does not participate in the increase of the greenhouse effect. Bioethanol can be obtained by fermentation of plants containing sucrose (beet, sugar cane…) or starch (wheat, corn…). However, large-scale use of bioethanol implies the use of very large agricultural surfaces for maize or sugarcane production. Lignocellulosic biomass (LCB) such as agricultural residues for the production of bioethanol seems to be a solution to this problem due to its high availability and low cost even if its growth still faces technological difficulties. In this review, we present an overview of lignocellulosic biomass, the different methods of pre-treatment of LCB and the various fermentation processes that can be used to produce bioethanol from LCB.

Xylo-oligosaccharides enriched yeast protein feed production from reed sawdust

The aim of this study was to convert the cellulose and hemicellulose, in reed sawdust from the pulp mills, into yeast protein and xylo-oligosaccharide, then functionalize xylo-oligosaccharide as yeast feed. Both synchronous saccharification and fermentation and separate hydrolysis and fermentation of cellulase and Candida utilis were investigated to produce protein feed. By optimizing the fermentation conditions, 6.1 g/L of protein with 76.1% (7.1 g/L) xylo-oligosaccharide as the sugar was obtained. The final glucan and xylan utilization efficiencies in reed sawdust were 85.45% and 91.03%, respectively. Xylo-oligosaccharide enriched yeast protein feed from reed sawdust was thus realized by pretreatment, enzymatic hydrolysis and synchronous saccharification and fermentation.

Lignocellulosic bioethanol production: prospects of emerging membrane technologies to improve the process – a critical review

To meet the worldwide rapid growth of industrialization and population, the demand for the production of bioethanol as an alternative green biofuel is gaining significant prominence. The bioethanol production process is still considered one of the largest energy-consuming processes and is challenging due to the limited effectiveness of conventional pretreatment processes, saccharification processes, and extreme use of electricity in common fermentation and purification processes. Thus, it became necessary to improve the bioethanol production process through reduced energy requirements. Membrane-based separation technologies have already gained attention due to their reduced energy requirements, investment in lower labor costs, lower space requirements, and wide flexibility in operations. For the selective conversion of biomasses to bioethanol, membrane bioreactors are specifically well suited. Advanced membrane-integrated processes can effectively contribute to different stages of bioethanol production processes, including enzymatic saccharification, concentrating feed solutions for fermentation, improving pretreatment processes, and finally purification processes. Advanced membrane-integrated simultaneous saccharification, filtration, and fermentation strategies consisting of ultrafiltration-based enzyme recycle system with nanofiltration-based high-density cell recycle fermentation system or the combination of high-density cell recycle fermentation system with membrane pervaporation or distillation can definitely contribute to the development of the most efficient and economically sustainable second-generation bioethanol production process.

Yeasts in sustainable bioethanol production: A review

Bioethanol has been identified as the mostly used biofuel worldwide since it significantly contributes to the reduction of crude oil consumption and environmental pollution. It can be produced from various types of feedstocks such as sucrose, starch, lignocellulosic and algal biomass through fermentation process by microorganisms. Compared to other types of microoganisms, yeasts especially Saccharomyces cerevisiae is the common microbes employed in ethanol production due to its high ethanol productivity, high ethanol tolerance and ability of fermenting wide range of sugars. However, there are some challenges in yeast fermentation which inhibit ethanol production such as high temperature, high ethanol concentration and the ability to ferment pentose sugars. Various types of yeast strains have been used in fermentation for ethanol production including hybrid, recombinant and wild-type yeasts. Yeasts can directly ferment simple sugars into ethanol while other type of feedstocks must be converted to fermentable sugars before it can be fermented to ethanol. The common processes involves in ethanol production are pretreatment, hydrolysis and fermentation. Production of bioethanol during fermentation depends on several factors such as temperature, sugar concentration, pH, fermentation time, agitation rate, and inoculum size. The efficiency and productivity of ethanol can be enhanced by immobilizing the yeast cells. This review highlights the different types of yeast strains, fermentation process, factors affecting bioethanol production and immobilization of yeasts for better bioethanol production.

Co-generation of microbial lipid and bio-butanol from corn cob bagasse in an environmentally friendly biorefinery process

Biorefinery process of corn cob bagasse was investigated by integrating microbial lipid and ABE fermentation. The effects of NaOH concentration on the fermentations performance were evaluated. The black liquor after pretreatment was used as substrate for microbial lipid fermentation, while the enzymatic hydrolysates of the bagasse were used for ABE fermentation. The results demonstrated that under the optimized condition, the cellulose and hemicellulose in raw material could be effectively utilized. Approximate 87.7% of the polysaccharides were converted into valuable biobased products (∼175.7g/kg of ABE along with ∼36.6g/kg of lipid). At the same time, almost half of the initial COD (∼48.9%) in the black liquor could be degraded. The environmentally friendly biorefinery process showed promising in maximizing the utilization of biomass for future biofuels production.

Efficient l-lactic acid production from sweet sorghum bagasse by open simultaneous saccharification and fermentation

An open SSF process using B. coagulans LA1507 introduces an effective way to produce l-lactic acid from abundant SSB.

Improved growth and ethanol fermentation of Saccharomyces cerevisiae in the presence of acetic acid by overexpression of SET5 and PPR1

To better understand the contribution of zinc-finger proteins to environmental stress tolerance, particularly inhibition from acetic acid, which is a potent inhibitor for cellulosic ethanol production by microbial fermentations, SET5 and PPR1 were overexpressed in Saccharomyces cerevisiae BY4741. With 5 g/L acetic acid addition, engineered strains BY4741/SET5 and BY4741/PPR1 showed improved growth and enhanced ethanol fermentation performance compared to that with the control strain. Similar results were also observed in ethanol production using corn stover hydrolysate. Further studies indicated that SET5 and PPR1 overexpression in S. cerevisiae significantly improved activities of antioxidant enzymes and ATP generation in the presence of acetic acid, and consequently decreased intracellular accumulation of reactive oxygen species (50.9 and 45.7%, respectively). These results revealed the novel functions of SET5 and PPR1 for the improvement of yeast acetic acid tolerance, and also implicated the involvement of these proteins in oxidative stress defense and energy metabolism in S. cerevisiae. This work also demonstrated that overexpression of SET5 and PPR1 would be a feasible strategy to increase cellulosic ethanol production efficiency.

Amphipathic lignin derivatives to accelerate simultaneous saccharification and fermentation of unbleached softwood pulp for bioethanol production

Amphipathic lignin derivatives (A-LDs) were already demonstrated to improve enzymatic saccharification of lignocellulose. Based on this knowledge, two kinds of A-LDs prepared from black liquor of soda pulping of Japanese cedar were applied to a fed-batch simultaneous saccharification and fermentation (SSF) process for unbleached soda pulp of Japanese cedar to produce bioethanol. Both lignin derivatives slightly accelerated yeast fermentation of glucose but not inhibited it. In addition, ethanol yields based on the theoretical maximum ethanol production in the fed-batch SSF process was increased from 49% without A-LDs to 64% in the presence of A-LDs.

Improving ethanol production from alfalfa stems via ambient-temperature acid pretreatment and washing

The concept of co-production of liquid fuel (ethanol) along with animal feed on farm was proposed, and the strategy of using ambient-temperature acid pretreatment, ensiling and washing to improve ethanol production from alfalfa stems was investigated. Alfalfa stems were separated and pretreated with sulfuric acid at ambient-temperature after harvest, and following ensiling, after which the ensiled stems were subjected to simultaneous saccharification and fermentation (SSF) for ethanol production. Ethanol yield was improved by ambient-temperature sulfuric acid pretreatment before ensiling, and by washing before SSF. It was theorized that the acid pretreatment at ambient temperature partially degraded hemicellulose, and altered cell wall structure, resulted in improved cellulose accessibility, whereas washing removed soluble ash in substrates which could inhibit the SSF. The pH of stored alfalfa stems can be used to predict the ethanol yield, with a correlation coefficient of +0.83 for washed alfalfa stems.

Combined process for ethanol fermentation at high-solids loading and biogas digestion from unwashed steam-exploded corn stover

A combined process was designed for the co-production of ethanol and methane from unwashed steam-exploded corn stover. A terminal ethanol titer of 69.8 g/kg mass weight (72.5%) was achieved when the fed-batch mode was performed at a final solids loading of 35.5% (w/w) dry matter (DM) content. The whole stillage from high-solids ethanol fermentation was directly transferred in a 3-L anaerobic digester. During 52-day single-stage digester operation, the methane productivity was 320 mL CH₄/g volatile solids (VS) with a maximum VS reduction efficiency of 55.3%. The calculated overall product yield was 197 g ethanol + 96 g methane/kg corn stover. This indicated that the combined process was able to improve overall content utilization and extract a greater yield of lignocellulosic biomass compared to ethanol fermentation alone.

Ethanol production from xylan-removed sugarcane bagasse using low loading of commercial cellulase

Xylan was always extracted as the feedstock for xylooligosaccharides production. The xylan-removed residue may contain high content of cellulose and thus had a possibility to be converted into ethanol. After soaked in 12% of NaOH at room temperature overnight, solubilization of cellulose, xylan, and lignin was 4.64%, 72.06%, and 81.87% respectively. The xylan-removed sugarcane bagasse (XRSB) was enzymatically hydrolyzed by using decreased cellulase loadings. The results showed that 7.5 FPU/g cellulose could obtain a cellulose conversion yield of 82%. Increasing the cellulase loading did not result in higher yield. Based on this, bioethanol production was performed using 7.5 FPU/g cellulose by employing fed-batch fermentation mode. The final ethanol concentration reached 40.59 g/L corresponding to 74.2% of the theoretical maximum. The high titer ethanol and low cellulase loading may reduce the overall cost.

Enhanced fermentability of poplar by combination of alkaline peroxide pretreatment and semi-simultaneous saccharification and fermentation

To improve ethanol productivity with few inhibitors generated, a novel process of combined alkaline peroxide (AP) pretreatment and semi-simultaneous saccharification and fermentation (SSSF) was developed in this work. Pretreatment with 10% (g H2O2/g wood) H2O2 at 160°C for 2h followed by SSSF was found to be the optimal combination with remarkably increased ethanol yield. The proposed process resulted in 63.1% of ethanol yield, which was about five times more than that of the untreated sample that was processed using conventional simultaneous saccharification and fermentation (SSF). The efficient conversion was ascribed to the high delignification efficiency (64.9%) of AP pretreatment, which led to incompact structure and generation of fewer inhibitors during SSSF (c. 6g/L of lactic acid) than SSF (c. 10 g/L of lactic acid). This combined approach was proved to be an effective method for the promotion of the bioconversion of lignocellulosic materials.

Tween 40 pretreatment of unwashed water-insoluble solids of reed straw and corn stover pretreated with liquid hot water to obtain high concentrations of bioethanol

BACKGROUND

Liquid hot water (LHW) pretreatment is an effective and environmentally friendly method to produce bioethanol with lignocellulosic materials. In our previous study, high ethanol concentration and ethanol yield were obtained from water-insoluble solids (WIS) of reed straw and corn stover pretreated with LHW by using fed-batch semi-simultaneous saccharification and fermentation (S-SSF). However, high cellulase loading and the large amount of wash water possibly limit the practical application of LHW pretreatment. To decrease cellulase loading and the amount of wash water, we performed Tween 40 pretreatment before WIS was subjected to bioethanol fermentation.

RESULTS

Results showed that the optimum conditions of Tween 40 pretreatment were as follows: Tween 40 concentration of 1.5%, WIS-to-Tween 40 ratio of 1:10 (w/v), and pretreatment time of 1 hour at ambient temperature. After Tween 40 pretreatment, cellulase loading could be greatly reduced. After Tween 40 pretreatment, the residual liquid could be recycled for utilization but slightly affected ethanol concentration and yield. The unwashed WIS could obtain a high ethanol concentration of 56.28 g/L (reed straw) and 52.26 g/L (corn stover) by Tween 40 pretreatment using fed-batch S-SSF. Ethanol yield reached a maximum of 69.1% (reed straw) and 71.1% (corn stover).

CONCLUSIONS

Tween 40 pretreatment was a very effective and less costly method with unwashed WIS. This pretreatment could greatly reduce cellulase loading and save wash water. Higher ethanol concentration was obtained almost without reducing ethanol yield.