Semi-simultaneous Saccharification And Fermentation Research Articles

Semi-Simultaneous Saccharification and Fermentation Improved by Lignin and Extractives Removal from Sugarcane Bagasse

Lignocellulosic biomass and agro-industrial residues are a source of fermentable sugars; however, pretreatments are needed to overcome biomass recalcitrance. This study evaluated the effect of sugarcane bagasse hydrolysis and fermentation in response to dilute acid pretreatment. In natura bagasse, extractive-free bagasse, partially delignified bagasse, and bagasse with added butylated hydroxytoluene antioxidant were pretreated with diluted acid and investigated in semi-simultaneous saccharification and fermentation (S-SSF). The effect of butylated hydroxytoluene (BHT) resulted in lower yields of inhibitors in the liquid fraction of the acid pretreatment (0.01 g L−1 of furfural, 0.01 g L−1 of 5-hydroxymethylfurfural, and 0.68 g L−1 of acetic acid). Partially delignified material and material with BHT resulted in biomass with low hemicellulose and lignin contents, indicating that BHT influenced lignin removal. Extractives removal showed benefits for the acid pretreatment, decreasing the dioxane-soluble material, and a higher yield of glucose and ethanol via S-SSF for the partially delignified material. Enzymatic saccharification of partially delignified material showed 87% of cellulose conversion (24 h with 15 FPU/g), and after 48 h of S-SSF (25 FPU/g), residual 7.06 g L−1 of glucose and production of 15.17 g L−1 of ethanol were observed. The low content of extractives, lignin, and dioxane soluble material resulted in better cellulose accessibility and ethanol yield. Chemical compounds can help remove lignin from biomass favoring ethanol production by S-SSF.

Ethanol production from Agave salmiana leaves by semi and simultaneous saccharification and fermentation at high temperature using Kluyveromycesmarxianus

Second-generation ethanol production by separate hydrolysis and fermentation (SHF) currently remains economically unviable, and thus more profitable alternatives are being sought. In the present study, the lignocellulosic biomass (LB) of Agave salmiana leaves was evaluated in the production of bioethanol through the processes of SHF, semi-simultaneous saccharification and fermentation (SSSF), and simultaneous saccharification and fermentation (SSF). The leaves of A. salmiana were subjected to acid pretreatment (1% H2SO4) and then to saccharification at temperatures of 40 and 50 °C. The processes of SHF, SSSF, and SSF were evaluated at 40 °C using the yeast Kluyveromyces marxianus OFF1. The results show that saccharification at 50 °C released up to 103.12 ± 1.07 g/L of reducing sugars, while at a temperature of 40 °C, the value was 78.41 ± 0.80 g/L, and thus the enzyme retained 76% of its activity at the latter temperature. In the fermentation processes, sugar consumption was up to 89% and ethanol yield up to 94%. The maximum ethanol production was recorded with the process of SSF, with concentrations of 51.5 g/L, which were significant and at least 13% higher compared to the other processes. The results show that the thermotolerance of K. marxianus OFF1 allows fermentation at 40 °C and a more efficient SSF process for transforming the sugars from this agro-industrial waste into ethanol.

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.

Reusing the acetone-butanol-ethanol separated broth as the lignocellulose pretreatment liquor for fresh corn stalk biorefinery

In this study, fresh corn stalk was used as the feedstock for the production of bio-butanol via acetone-butanol-ethanol (ABE) fermentation, in which process the wastewater from the first stage sugar containing juice fermentation was recycled by ex situ pervaporation and reused as the pulping liquor of the residual corn stalk bagasse (CSB), affording to effective ABE production in the subsequential second stage fermentation process. Results indicated that the juice fermentation wastewater could effectively depolymerize the CSB. Under optimized conditions of the pulping process (180 °C and 10% (w/v) of biomass loading), 32.45 ± 0.85 g/L of total monomer sugars was obtained in CSB enzymatic hydrolysate, which can be directly used as the substrate for the second-stage cellulosic ABE production. Semi-simultaneous saccharification and fermentation (S-SSF) was carried out using the CSB pulps, so that improving the cellulosic ABE production. 10.94 ± 0.65 g/L of ABE concentration with 0.18 ± 0.01 g/L h of productivity were realized. After hybrid the first-stage juice fermentation and the second-stage CSB biotransformation, total 54.07 ± 1.25 g (ABE) can be produced from 1 kg of fresh corn stalk. The alternative process showed great significance in reduction of the wastewater discharge and ensuring high pulping performances.

Semi-simultaneous Saccharification and Fermentation of Ethanol Production from Sargassum horneri and Biosorbent Production from Fermentation Residues

One of the fundamental goals of bio-ethanol production is to find the alternative of traditional land-relied feedstock. A kind of macroalgae, Sargassum horneri (S. horneri) was chosen as the bio-source for ethanol production in the present investigation. The bioethanol was achieved by acid-pretreated, hydrolysis, and semi-simultaneous saccharification and fermentation (S-SSF) at small pilot scale. Immobilization of Pichia stipites in calcium alginate was adapted in the S-SSF process. Furthermore, effects of pre-hydrolysis time, cellulase loading, fermentation temperature and fermentation time on the concentration, and yield of bio-ethanol were evaluated by using response surface methodology (RSM). A maximum bioethanol concentration (2.89 g/L), and maximum bioethanol yield (0.11 g/g raw material) at cellulase loading (10 IU/g raw material), pre-hydrolysis time (53 min), SSF temperature (32 °C) and SSF time (14 h) were observed. The optimized bioethanol production data series fit the Gompertz model and modified Logistic model with an R2 value of 0.997. The obtained Gompertz and modified Logistic coefficients indicated that S. horneri can serve as an efficient substrate for bioethanol production. The fermentation residues were used for typical dyeing contamination adsorption, the existence of the residual lignin and exposure functional groups made it an effective adsorbent, which followed the pseudo-second-order kinetics. These results are helpful for the scale-up development of lignocellulosic macroalgae based bioethanol production and fermentation residue use.

Different schemas of saccharification and fermentation for bioethanol production from Opuntia ficus-indica cladode flour with wild strains

In the present work, two wild microorganisms were studied for saccharification and fermentation. A wild Acinetobacter pittii isolated from decaying cladodes (Opuntia ficus-indica) was capable of producing extracellular cellulases and a wild yeast Kluyveromyces marxianus isolated from termite was capable of producing alcohol. In Mexico, there are surpluses of cladode production and where it is essential to take advantage and use this carbon source for alcohol production due to currently fossil fuels depletion. Separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF) and semi-simultaneous saccharification and fermentation (SSSF) for cellulase and alcohol production using Opuntia ficus-indica cladode as a unique carbon source was evaluated. In SHF process the best conditions for FPase activity (Filter paper activity for total cellulases) were 37 °C and pH 6.5 obtaining 0.67±0.02 U/ml and 0.61±0.03 U/ml for Acinetobacter pittii and Kluyveromyces marxianus, respectively. For alcohol production, the best conditions were 40 °C and pH 5.5 obtaining 12.95±0.3 g/L with K. marxianus while A. pittii did not produce significant alcohol concentration. Both processes were made with agitation (200 rpm). The SSF process was made with both microorganisms inoculated at the same time at 37 °C and without agitation. The maximum FPase activity of 0.28±0.004 U/ml and the maximum alcohol concentration was 7.5±0.27 g/L. Finally, an SSSF was performed, initially with A. pittii at 37 °C and after 8 h K. marxianus was then inoculated with temperature switched to 40 °C, the all process was performed without agitation. The maximum FPase activity was 0.45±0.001 U/ml, and the maximum alcohol concentration was 11.7±0.02 g/L. There was a significant difference (ANOVA) between SHF and SSSF in alcohol production. The best process for FPase activity and alcohol production is separate hydrolysis and fermentation using only yeast Kluyveromyces marxianus.

Co-production of bio-ethanol, xylonic acid and slow-release nitrogen fertilizer from low-cost straw pulping solid residue

A novel bio-refinery sequence yielding varieties of co-products was developed using straw pulping solid residue. This process utilizes neutral sulfite pretreatment which under optimal conditions (160 °C and 3% (w/v) sulfite charge) provides 64.3% delignification while retaining 90% of cellulose and 67.3% of xylan. The pretreated solids exhibited excellent enzymatic digestibility, with saccharification yields of 86.9% and 81.1% for cellulose and xylan, respectively. After pretreatment, the process of semi-simultaneous saccharification and fermentation (S-SSF) and bio-catalysis was investigated. The results revealed that decreased ethanol yields were achieved when solid loading increased from 5% to 30%. An acceptable ethanol yield of 76.8% was obtained at 20% solid loading. After fermentation, bio-catalysis of xylose remaining in fermentation broth resulted in near 100% xylonic acid (XA) yield at varied solid loadings. To complete the co-product portfolio, oxidation ammoniation of the dissolved lignin successfully transformed it into biodegradable slow-release nitrogen fertilizer with excellent agricultural properties.

Efficient production of succinic acid from duckweed (Landoltia punctata) hydrolysate by Actinobacillus succinogenes GXAS137

A novel process of enzyme pretreatment and semi-simultaneous saccharification and fermentation (SSSF) was developed in this work to improve succinic acid (SA) productivity from duckweed (Landoltia punctata) and achieve low viscosity. Viscosity (83.86%) was reduced by the pretreatment with combined enzymes at 50 °C for 2 h to a greater extent than that by single enzyme (26.19–71.75%). SSSF was an optimal combination with 65.31 g/L of SA content, which was remarkably higher than those obtained through conventional separate hydrolysis and fermentation (62.12 g/L) and simultaneous saccharification and fermentation (52.41 g/L). The combined approach was effective for SA production. Approximately 75.46 g/L of SA content with a yield of 82.87% and a productivity of 1.35 g/L/h was obtained after 56 h in a 2 L bioreactor. Further studies will focus on increasing the working scale of the proposed method.

Hydrolysate-Recycled Liquid Hot Water Pretreatment of Reed Straw and Corn Stover for Bioethanol Production with Fed-Batch, Semi-Simultaneous Saccharification and Fermentation

Prehydrolysates and water-insoluble solids (WISs) were produced from reed straw and corn stover pretreated with hydrolysate-recycled liquid hot water (LHW) at different cycle times. The chemical components of the prehydrolysates and WISs were then investigated to assess the possible effects of hydrolysate recycling on bioethanol production. The WISs were subjected to fed-batch, semi-simultaneous saccharification and fermentation (S-SSF) to investigate the changes in bioethanol concentration and evaluate the efficiency of the pretreatment. The pretreatment conditions consisted of a temperature of 195 °C, time of 20 min, and liquid ratio of 1:20. The prehydrolysates were recycled using a circulation volume of 50% and were applied to 10 cycles. The results showed that recycling did not significantly decrease the pH of the hydrolysates. The content of glucose and xylan in the hydrolysates decreased and then increased with increasing cycle times. In the WISs, the contents of benzene alcohol extractives and ash increased remarkably. The content of acid-insoluble lignin and glucan increased slightly. The amounts of xylan and acid-soluble lignin in the WISs were low, and the changes in these contents were not significant. Thus, hydrolysate-recycled LHW pretreatment was beneficial for bioethanol production from reed straw, but not from corn stover.

Hydrothermal and Acid Pretreatments Improve Ethanol Production from Lignocellulosic Biomasses

Hydrothermal and acid pretreatments using different acid charges (1.5%, 3.0%, and 4.5% H2SO4) were proposed for eucalyptus, sugarcane bagasse, and sugarcane straw prior to their bioconversion into ethanol using the semi-simultaneous saccharification and fermentation (SSSF) process. The hydrothermal and acid pretreatments were efficient for hemicelluloses removal from eucalyptus (63 to 96%), bagasse (25 to 98%), and straw (23 to 95%) and to remove a substantial amount of lignin from eucalyptus (10 to 34%) and bagasse (10 to 27%). During pretreatments, pseudo-extractives and pseudo-lignin were generated from biomasses. The SSSF was performed in pretreated biomasses using 24 h presaccharification followed by an additional 10 h of simultaneous saccharification and fermentation (SSF). With hydrothermal pretreatment, the eucalyptus presented the highest ethanol production, but only low values for SSSF parameters were obtained, as follows: ethanol yield (0.017 gethanol/gbiomass), volumetric productivity of ethanol (0.16 g L-1 h-1), and ethanol concentration (1.6 g L-1). On the other hand, using acid pretreatment, the straw (pretreated using 4.5% H2SO4) presented the highest ethanol production among the biomasses, assessed based on ethanol yield (0.056 gethanol/gbiomass), volumetric productivity of ethanol (0.51 g L-1 h-1), and ethanol concentration (5.1 g L-1).

Comparison of several ethanol productions using xylanase, inorganic salts, surfactant

Liquid hot water (LHW) pretreatment is an effective and environmentally friendly method to produce bioethanol with lignocellulosic materials. Corn stover was pretreated with liquid hot water (LHW) and then subjected to semi-simultaneous saccharification and fermentation (S-SSF) to obtain high ethanol concentration and yield. The present study aimed to confirm the effect of several additives on the fermentation digestibility of unwashed WIS of corn stover pretreated with LHW. So we also investigated the process, such as enzyme addition, inorganic salts, surfactant and different loading Triton. Results show that high ethanol concentration is necessary to add xylanase in the stage of saccharification. The ethanol concentration increased mainly with magnesium ion on fermentation. Comparing with Tween 80, Span 80 and Polyethylene glycol, Triton is the best surfactant. In contrast to using xylanase and Triton respectively, optimization can make up the lack of stamina and improve effect of single inorganic salts.

Assessment of alkaline pretreatment for the production of bioethanol from eucalyptus, sugarcane bagasse and sugarcane straw

The impact of alkaline pretreatment at different alkaline charges (5%, 10% and 15% NaOH w/w, on dry basis) on the chemical composition of eucalyptus, sugarcane bagasse and straw were compared with the subsequent bioconversion into ethanol, using semi-simultaneous saccharification and fermentation (SSSF). By increasing alkaline charge in pretreatments, substantial amount of lignin, hemicelluloses and cellulose were fractionated. The chemical composition of biomasses was expressed based on the complete mass balance. The chemical transformation of biomasses during pretreatments was assessed by comparing the chemical composition of pretreated biomasses and their untreated counterparts. Pretreatments promoted delignification in the range of 11%–51% for eucalyptus, 22%–90% for bagasse, and 60%–99% for straw for the alkaline charges in the range of 5%–15% (NaOH w/w). The removal of lignin from bagasse and straw was higher than that from eucalyptus, which was due to the combined effect of higher frequency of both, the free phenolic groups and the ester bonds in grass lignin that made the lignin solubility escalate in alkaline conditions. It was also observed that bagasse had a removal by 37%–45% hemicelluloses and 0.8%–11% cellulose. For straw, higher amount of carbohydrates was removed, in the range of 55%–66% hemicelluloses and 19%–36% cellulose. Fragments of lignin and carbohydrates were converted into new structures called “pseudo-extractives” in eucalyptus during pretreatments. Pseudo-extractives and native extractives were quantified together, thus increasing the total extractives contents by 3.3 (5% NaOH), 3.5 (10% NaOH) and 2.9 (15% NaOH) times, in line with the original raw materials. Maximum ethanol yield and maximum volumetric productivity of ethanol were achieved for eucalyptus pretreated using 10% NaOH, bagasse pretreated using 15% NaOH and straw pretreated using 5% NaOH. At the optimal pretreatment condition, just about 51% glucose was released from pretreated bagasse. Sugarcane bagasse presented the highest values for the respective parameters, namely: 8.8gL−1 ethanol concentration, 0.101gethanol/gbiomass ethanol yield and 0.88gL−1h−1 volumetric productivity of ethanol. Alkaline charge proved to be an important control variable for alkaline pretreatments, with determinant effect on chemical transformations of biomasses and result on ethanol production.

Lignocellulosic Ethanol Production from the Recovery of Stranded Driftwood Residues

This paper builds upon a research project funded by the Italian Ministry of Environment, and aims to recover stranded driftwood residues (SDRs), in order to transform a potential pollution and safety issue into valuable bio-resources. In particular, one of the experiments consisted of bioethanol production from lignocellulosic residues. The SDRs were gathered from the Italian coast (Abruzzo Region, Italy) after an intense storm. The biomass recalcitrance, due to its lignocellulosic structure, was reduced by a steam explosion (SE) pretreatment process. Four different pretreatment severity factors (R0) were tested (LogR0 3.65, 4.05, 4.24 and 4.64) in order to evaluate the pretreated material’s accessibility to enzymatic attack and the holocellulose (cellulose plus hemicellulose) recovery. A first enzymatic hydrolysis was performed on the pretreated materials by employing a solid/liquid (S/L) ratio of 1% (w/w) and an enzyme dosage of 30% (w enzyme/w cellulose), in order to estimate the maximum enzymatically accessible cellulose content. Since the primary goal of pretreatment and hydrolysis is to convert as much cellulose as possible into monomeric glucose and recover all the holocellulose, the two pretreated materials showing these features were selected for bioethanol production process. The pretreated materials underwent a semi-simultaneous saccharification and fermentation (SSSF). The SSSF process was performed into two lab-scale bioreactors (5 L) with an S/L ratio of 15% and an enzyme dosage of 15% for five days. The efficiency of the whole bioethanol production process was assessed as ethanol overall yields (g ethanol/100 g raw material). The best overall yield was achieved by sample BS04 (8.98 g ethanol/100 g raw material).

Cold alkaline extraction as a pretreatment for bioethanol production from eucalyptus, sugarcane bagasse and sugarcane straw

Optimal conditions for the cold alkaline extraction (CAE) pretreatment of eucalyptus, sugarcane bagasse and sugarcane straw are proposed in view of their subsequent bioconversion into ethanol through the semi-simultaneous saccharification and fermentation (SSSF) process (with presaccharification followed by simultaneous saccharification and fermentation, or SSF). The optimum conditions, which are identified based on an experiment with a factorial central composite design, resulted in the removal of 46%, 52% and 61% of the xylan and 15%, 37% and 45% of the lignin for eucalyptus, bagasse and straw, respectively. The formation of pseudo-extractives was observed during the CAE of eucalyptus. Despite the similar glucose concentration and yield for all biomasses after 12h of presaccharification, the highest yield (0.065gethanol/gbiomass), concentrations (5.74gL−1) and volumetric productivity for ethanol (0.57gL−1h−1) were observed for the sugarcane straw. This finding was most likely related to the improved accessibility of cellulose that resulted from the removal of the largest amount of xylan and lignin.

Bioethanol production by Saccharomyces cerevisiae, Pichia stipitis and Zymomonas mobilis from delignified coconut fibre mature and lignin extraction according to biorefinery concept

In search to increase the offer of liquid, clean, renewable and sustainable energy in the world energy matrix, the use of lignocellulosic materials (LCMs) for bioethanol production arises as a valuable alternative. The objective of this work was to analyze and compare the performance of Saccharomyces cerevisiae, Pichia stipitis and Zymomonas mobilis in the production of bioethanol from coconut fibre mature (CFM) using different strategies: simultaneous saccharification and fermentation (SSF) and semi-simultaneous saccharification and fermentation (SSSF). The CFM was pretreated by hydrothermal pretreatment catalyzed with sodium hydroxide (HPCSH). The pretreated CFM was characterized by X-ray diffractometry and SEM, and the lignin recovered in the liquid phase by FTIR and TGA. After the HPCSH pretreatment (2.5% (v/v) sodium hydroxide at 180 °C for 30 min), the cellulose content was 56.44%, while the hemicellulose and lignin were reduced 69.04% and 89.13%, respectively. Following pretreatment, the obtained cellulosic fraction was submitted to SSF and SSSF. Pichia stipitis allowed for the highest ethanol yield – 90.18% – in SSSF, 91.17% and 91.03% were obtained with Saccharomyces cerevisiae and Zymomonas mobilis, respectively. It may be concluded that the selection of the most efficient microorganism for the obtention of high bioethanol production yields from cellulose pretreated by HPCSH depends on the operational strategy used and this pretreatment is an interesting alternative for add value of coconut fibre mature compounds (lignin, phenolics) being in accordance with the biorefinery concept.

Bioethanol production from coconuts and cactus pretreated by autohydrolysis

The use of coconut fiber mature, green coconut shell, mature coconut shell and cactus is an important alternative as substrates for bioethanol production, since these lignocellulosic materials (LCMs) are abundant in Brazil, mainly in the Northeast Region. The first objective of this work was to evaluate the autohydrolysis pretreatment (AP) on these LCMs and the susceptibility of the treated materials to enzymatic hydrolysis (EH). The second part of the work deals with the application of semi-simultaneous saccharification and fermentation (SSSF) and simultaneous saccharification and fermentation (SSF) using Zymomonas mobilis, Pichia stipitis, Saccharomyces cerevisiae and as substrate the green coconut shell (selected according to the results obtained in the first part of the work). The LCMs after AP using the highest severity factor (4.64) showed changes in the chemical composition in comparison to the untreated LCMs: between the LCMs the cellulose increase was 48.55%, the hemicellulose decrease was 76.77% and an increase of 62.26% was observed for lignin. The green coconut shell was characterized by SEM, X-ray and FTIR after AP and its EH conversion into glucose was 92.52%. The best results on ethanol yield (90.09%) and ethanol productivity (0.21g/(Lh)) from green coconut shell were obtained by S. cerevisiae using SSSF. Overall, an efficient process for the bioethanol production from green coconut shell was developed.

Optimizing Semisimultaneous Saccharification and Fermentation for Ethanol Production from Chinese Distiller's Spent Grains

Spent grains are a main byproduct for Chinese liquor production. In this study, the semisimultaneous saccharification and fermentation (S-SSF) for ethanol production based on multi-enzyme degradation of the spent grains was investigated. After optimization with orthogonal design experiments, an enzyme combination composed of cellulase NS22086 at 0.30 mL/g, β-glucosidase NS22118 at 0.20 mL/g, xylanase NS22083 at 0.08 mL/g, complex enzyme NS22119 at 0.08 mL/g, complex enzyme NS22002 at 0.02 mL/g, and glucoamylase NS22035 at 0.01 mL/g was obtained. With 14% of the substrate concentration and the optimal enzyme combination, reducing sugar, glucose, and xylose at 109.97, 60.02, and 16.05 g./L, respectively, were attained in the saccharified solution, which are approximately fourfold of those obtained before optimizing and are among the highest values reported for different lignocellulosic materials. Experiments of batch and fed-batch S-SSF for ethanol production from the spent grains were then performed, and higher efficiency of saccharification and ethanol formation was observed in the fed-batch S-SSF, where an ethanol concentration of over 30 g/L was attained. Kinetic models satisfactorily describing the processes of S-SSF were developed and analyzed. This study contributes to the utilization of Chinese distiller's spent grains and other similar materials.

A comparison between SHF and SSSF processes from cardoon for ethanol production

The purpose of the present work is the evaluation of Cynara cardunculus L. potential in terms of ethanol production from lignocellulosic feedstock for industrial purposes. After a steam explosion (SE) pretreatment at different severity conditions, to obtain the dissolution of hemicellulose and the separation between cellulose and lignin, two different processes were tested: separate hydrolysis and fermentation (SHF) and semi-simultaneous saccharification and fermentation (SSSF). The enzymatic hydrolysis was carried out with ™Ctec2 cellulase enzyme and fermentation with Saccharomyces cerevisiae yeast.The results showed slightly better performances by SSSF process compared to SHF, especially at low severity conditions, with a maximum overall ethanol yield of 13.64g of ethanol/100g of raw material. For the SHF process the best overall ethanol yield achieved was 13.17g of ethanol/100g of raw materials. In addition, the SSSF process required at least 24h less than the SHF to achieve the same final ethanol concentration for every severity condition tested.

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.

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.