Application of simultaneous saccharification and fermentation (SSF) from viscosity reducing of raw sweet potato for bioethanol production at laboratory, pilot and industrial scales

The aim of this work was to research a bioprocess for bioethanol production from raw sweet potato by Saccharomyces cerevisiae at laboratory, pilot and industrial scales. The fermentation mode, inoculum size and pressure from different gases were determined in laboratory. The maximum ethanol concentration, average ethanol productivity rate and yield of ethanol after fermentation in laboratory scale (128.51 g/L, 4.76 g/L/h and 91.4%) were satisfactory with small decrease at pilot scale (109.06 g/L, 4.89 g/L/h and 91.24%) and industrial scale (97.94 g/L, 4.19 g/L/h and 91.27%). When scaled up, the viscosity caused resistance to fermentation parameters, 1.56 AUG/g (sweet potato mash) of xylanase decreased the viscosity from approximately 30000 to 500 cp. Overall, sweet potato is a attractive feedstock for be bioethanol production from both the economic standpoints and environmentally friendly.     

Co-fermentation of cassava waste pulp hydrolysate with molasses to ethanol for economic optimization

Cassava waste pulp (CWP)–enzymatic hydrolysate was co-fermented with molasses (CWP-EH/molasses mixture) with the aim to optimize ethanol production by Saccharomyces cerevisiae TISTR 5606 (SC 90). The optimal fermentation conditions for ethanol production using this mixture were 245 g/L initial total sugar supplemented with KH₂PO₄ (8 g/L), at 30 °C for 48 h of fermentation under an oxygen-limited condition with agitation at 100 rpm, producing an ethanol concentration of 70.60 g/L (0.31 g ethanol/g total sugar). The addition of cassava tuber fiber (solid residue of CWP after enzymatic hydrolysis) at 30 g/L dry weight to the CWP-EH/molasses mixture increased ethanol production to 74.36 g/L (0.32 g ethanol/g total sugar). Co-fermentation of CWP-EH with molasses had the advantage of not requiring any supplementation of the fermentation mixture with reduced nitrogen.     

Production of bio-ethanol from soybean molasses by Saccharomyces cerevisiae at laboratory, pilot and industrial scales

The aim of this work was to develop an economical bioprocess to produce the bio-ethanol from soybean molasses at laboratory, pilot and industrial scales. A strain of Saccharomyces cerevisiae (LPB-SC) was selected and fermentation conditions were defined at the laboratory scale, which included the medium with soluble solids concentration of 30% (w/v), without pH adjustment or supplementation with the mineral sources. The kinetic parameters - ethanol productivity of 8.08g/Lh, Y(P/S) 45.4%, Y(X/S) 0.815%, m 0.27h(-1) and mu(X) 0.0189h(-1) - were determined in a bench scale bioreactor. Ethanol production yields after the scale-up were satisfactory, with small decreases from 169.8L at the laboratory scale to 163.6 and 162.7L of absolute ethanol per ton of dry molasses, obtained at pilot and industrial scales, respectively.     

Acetone–Butanol–Ethanol Production by Clostridium acetobutylicum ATCC 824 Using Sago Pith Residues Hydrolysate

Sago pith residues (58 % starch, 23 % cellulose, 9.2 % hemicellulose, and 4 % lignin) are one of the abundant lignocellulosic residues generated after starch extraction process in sago mill. In this study, fermentable sugars from enzymatic hydrolysis of sago pith residues were converted to acetone–butanol–ethanol (ABE) by Clostridium acetobutylicum ATCC 824. With an initial concentration of 30 g/L of concentrated sago pith residues hydrolysate containing 23 g/L of glucose and 4.58 g/L of cellobiose, 4.22?±?0.17 g/L of ABE were produced after 72 h of fermentation with yield and productivity of 0.20 g/g glucose and 0.06 g/L/h, respectively. Results are in agreement when synthetic glucose was used as a carbon source. Increasing sago pith residue hydrolysate to 50 g/L (containing 40 g/L glucose) and supplementing with 0.5 g/L yeast extract, approximately 8.84?±?0.20 g/L of ABE (5.41?±?0.10 g/L of butanol) were produced with productivity and yield of 0.12 g/L/h and 0.30 g/g glucose respectively, providing a 52 % improvement.     

Fermentation of Detoxified Acid-Hydrolyzed Pyrolytic Anhydrosugars into Bioethanol with <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> 2.399

Pyrolysate obtained from the pyrolysis of waste cotton is a source of fermentable sugars that could be fermented into bioethanol fuel and other chemicals via microbial fermentation. However, pyrolysate is a complex mixture of fermentable and non-fermentable substrates causing inhibition of the microbial growth. The aim of this study was to detoxify the hydrolysate and then ferment it into bio-ethanol fuel in shake flasks and fermenter applying yeast strain Saccharomyces cerevisiae 2.399. Pyrolysate was hydrolyzed to glucose with 0.2 M sulfuric acid, neutralized with Ba(OH)₂ followed by treatment with ethyl acetate and activated carbon to remove fermentation inhibitors. The effect of various fermentation parameters such as inoculum concentration, pH and hydrolysate glucose was evaluated in shake flasks for optimum ethanol fermentation. With respect to inoculum concentration, 20% v/v inoculum i.e. 8.0 × 10⁸–1.2 × 10⁹ cells/mL was the optimum level for producing 8.62 ± 0.33 g/L ethanol at 9 h of fermentation with a maximum yield of 0.46 g ethanol/g glucose. The optimum pH for hydrolysate glucose fermentation was found to be 6.0 that produced 8.57 ± 0.66 g/L ethanol. Maximum ethanol concentration, 14.78 g/L was obtained for 4% hydrolysate glucose concentration after 16 h of fermentation. Scale-up studies in stirred fermenter produced much higher productivity (1.32 g/L/h^–1) compared to shake flask fermentation (0.92 g/L/h^–1). The yield of ethanol reached a maximum of 91% and 89% of the theoretical yield of ethanol in shake flasks and fermenter, respectively. The complex of integrated models of development was applied, that has been successfully tested previously for the mathematical analysis of the fermentation processes.     

Ethanol production from galactose by a newly isolated Saccharomyces cerevisiae KL17

A wild-type yeast strain with a good galactose-utilization efficiency was newly isolated from the soil, and identified and named Saccharomyces cerevisiae KL17 by 18s RNA sequencing. Its performance of producing ethanol from galactose was investigated in flask cultures with media containing various combination and concentrations of galactose and glucose. When the initial galactose concentration was 20 g/L, it showed 2.2 g/L/h of substrate consumption rate and 0.63 g/L/h of ethanol productivity. Although they were about 70 % of those with glucose, such performance of S. cerevisiae KL17 with galactose was considered to be quite high compared with other strains reported to date. Its additional merit was that its galactose metabolism was not repressed by the existence of glucose. Its capability of ethanol production under a high ethanol concentration was demonstrated by fed-batch fermentation in a bioreactor. A high ethanol productivity of 3.03 g/L/h was obtained with an ethanol concentration and yield of 95 and 0.39 g/L, respectively, when the cells were pre-cultured on glucose. When the cells were pre-cultured on galactose instead of glucose, fermentation time could be reduced significantly, resulting in an improved ethanol productivity of 3.46 g/L/h. The inhibitory effects of two major impurities in a crude galactose solution obtained from acid hydrolysis of galactan were assessed. Only 5-Hydroxymethylfurfural (5-HMF) significantly inhibited ethanol fermentation, while levulinic acid (LA) was benign in the range up to 10 g/L.     

Integrating sugarcane molasses into sequential cellulosic biofuel production based on SSF process of high solid loading

Background

Sugarcane bagasse (SCB) is one of the most promising lignocellulosic biomasses for use in the production of biofuels. However, bioethanol production from pure SCB fermentation is still limited by its high process cost and low fermentation efficiency. Sugarcane molasses, as a carbohydrate-rich biomass, can provide fermentable sugars for ethanol production. Herein, to reduce high processing costs, molasses was integrated into lignocellulosic ethanol production in batch modes to improve the fermentation system and to boost the final ethanol concentration and yield.

Results

The co-fermentation of pretreated SCB and molasses at ratios of 3:1 (mixture A) and 1:1 (mixture B) were conducted at solid loadings of 12% to 32%, and the fermentation of pretreated SCB alone at the same solid loading was also compared. At a solid loading of 32%, the ethanol concentrations of 64.10 g/L, 74.69 g/L, and 75.64 g/L were obtained from pure SCB, mixture A, and mixture B, respectively. To further boost the ethanol concentration, the fermentation of mixture B (1:1), with higher solid loading from 36 to 48%, was also implemented. The highest ethanol concentration of 94.20 g/L was generated at a high solid loading of 44%, with an ethanol yield of 72.37%. In addition, after evaporation, the wastewater could be converted to biogas by anaerobic digestion. The final methane production of 312.14 mL/g volatile solids (VS) was obtained, and the final chemical oxygen demand removal and VS degradation efficiency was 85.9% and 95.9%, respectively.

Conclusions

Molasses could provide a good environment for the growth of yeast and inoculum. Integrating sugarcane molasses into sequential cellulosic biofuel production could improve the utilization of biomass resources.

     

Acetic acid-catalyzed hydrothermal pretreatment of corn stover for the production of bioethanol at high-solids content

Corn stover (CS) was hydrothermally pretreated using CH₃COOH (0.3 %, v/v), and subsequently its ability to be utilized for conversion to ethanol at high-solids content was investigated. Pretreatment conditions were optimized employing a response surface methodology (RSM) with temperature and duration as independent variables. Pretreated CS underwent a liquefaction/saccharification step at a custom designed free-fall mixer at 50 °C for either 12 or 24 h using an enzyme loading of 9 mg/g dry matter (DM) at 24 % (w/w) DM. Simultaneous enzymatic saccharification and fermentation (SSF) of liquefacted corn stover resulted in high ethanol concentration (up to 36.8 g/L), with liquefaction duration having a negligible effect. The threshold of ethanol concentration of 4 % (w/w), which is required to reduce the cost of ethanol distillation, was surpassed by the addition of extra enzymes at the start up of SSF achieving this way ethanol titer of 41.5 g/L.     

Bench-scale bioethanol production from eucalyptus by high solid saccharification and glucose/xylose fermentation method

In the bioethanol production process, high solid saccharification and glucose/xylose co-fermentation are important technologies for obtaining increased ethanol concentrations; however, bench-scale studies using combinations of these methods are limited. In this study, we hydrolyzed high solid concentration of milled eucalyptus using commercial enzymes and obtained 138.4 g/L total monomeric sugar concentration. These sugars were fermented to 53.5 g/L of ethanol by a xylose-utilizing recombinant Saccharomyces cerevisiae strain, MA-R4. These experiments were performed in bench scale (using 50 L scale solid mixer and 70 L scale fermenter). The results obtained in this study were comparable to our previous results in laboratory scale, indicating that we successfully achieved an efficient high solid saccharification and glucose/xylose co-fermentation system in bench scale.     

Characterization of ethanol fermentation waste and its application to lactic acid production by Lactobacillus paracasei

In this study, an ethanol fermentation waste (EFW) was characterized for use as an alternative to yeast extract for bulk fermentation processes. EFW generated from a commercial plant in which ethanol is produced from cassava/rice/wheat/barley starch mixtures using Saccharomyces cerevisiae was used for lactic acid production by Lactobacillus paracasei. The effects of temperature, pH, and duration on the autolysis of an ethanol fermentation broth (EFB) were also investigated. The distilled EFW (DEFW) contained significant amounts of soluble proteins (2.91 g/l), nitrogen (0.47 g/l), and amino acids (24.1 mg/l). The autolysis of the EFB under optimum conditions released twice as much amino acids than in the DEFW. Batch fermentation in the DEFW increased the final lactic acid concentration, overall lactic acid productivity, and lactic acid yield on glucose by 17, 41, and 14 %, respectively, in comparison with those from comparable fermentation in a lactobacillus growth medium (LGM) that contained 2 g/l yeast extract. Furthermore, the overall lactic acid productivity in the autolyzed then distilled EFW (ADEFW) was 80 and 27 % higher than in the LGM and DEFW, respectively.     

Production of bioethanol from sugarcane bagasse using NH<Subscript>4</Subscript>OH-H<Subscript>2</Subscript>O<Subscript>2</Subscript> pretreatment and simultaneous saccharification and co-fermentation

In this study, we investigated the production of bioethanol from sugarcane bagasse (SCB) using an NH₄OH-H₂O₂ pretreatment and simultaneous saccharification and co-fermentation (SScF). Response surface methodology and a 2³ Box-Behnken design were used to evaluate the effect of different liquid mixture concentrations, liquid-to-solid ratios (LSRs) and pretreatment temperatures on the production of ethanol. The liquid mixture concentration and LSR significantly influenced the fermentation efficiency. Based on ridge max analysis, the following pretreatment conditions resulted in a fermentation efficiency of 95.79 ± 0.01%: liquid mixture concentration 53%, LSR 28, and a temperature of 63°C. A morphological analysis performed using scanning electron microscopy (SEM) and chemical characterization revealed that these pretreatment conditions were effective in disrupting the sugarcane fibers and removing lignin. Ethanol fermentation with the pretreated SCB using SScF in yeast SHY 07-1 resulted in an ethanol concentration of 14.65 ± 0.17 g/L, an ethanol yield of 0.48 ± 0.01 g/g, and an ethanol productivity of 0.12 ± 0.01 g/(L/h), which represents increases of 106.02, 89.98, and 107.02%, respectively, over the values obtained from SScF with untreated SCB.     

Consolidated ethanol production from Jerusalem artichoke tubers at elevated temperature by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> engineered with inulinase expression through cell surface display

Ethanol fermentation from Jerusalem artichoke tubers was performed at elevated temperatures by the consolidated bioprocessing strategy using Saccharomyces cerevisiae MK01 expressing inulinase through cell surface display. No significant difference was observed in yeast growth when temperature was controlled at 38 and 40 °C, respectively, but inulinase activity with yeast cells was substantially enhanced at 40 °C. As a result, enzymatic hydrolysis of inulin was facilitated and ethanol production was improved with 89.3 g/L ethanol produced within 72 h from 198.2 g/L total inulin sugars consumed. Similar results were also observed in ethanol production from Jerusalem artichoke tubers with 85.2 g/L ethanol produced within 72 h from 185.7 g/L total sugars consumed. On the other hand, capital investment on cooling facilities and energy consumption for running the facilities would be saved, since regular cooling water instead of chill water could be used to cool down the fermentation system.     

Valorization of Hemicelluloses: Production of Bioxylitol from Poplar Wood Prehydrolyzates by <Emphasis Type="Italic">Candida guilliermondii</Emphasis> FTI 20037

In this study on the valorization of hemicelluloses (a co-product generated during cellulosic bioethanol production), prehydrolyzates obtained from poplar woodchips pretreated in an industrial experimental steam-explosion pilot-plant facility were evaluated for the production of bioxylitol using the yeast, Candida guilliermondii FTI 20037, employing both batch and fed-batch fermentation modes in shake flasks on defined nutrient medium. The prehydrolyzates consisted of monosaccharides (pentose and hexose sugars) as well as xylo-oligosaccharides and undegraded hemicellulose. Xylose (31.6?±?0.57 g/L) was the major sugar in the prehydrolyzates that also contained acetic acid and degradation products of lignin and sugars (phenolic and furanic compounds). Xylose in the prehydrolyzates could be further increased (106.4?±?0.02 g/L) through an acid hydrolysis step (0.6 % (w/v) H₂SO₄). Compounds of a toxic nature in both the acid hydrolyzates and prehydrolyzates were removed by treatment with Amberlite IRA-400 resin (chloride form). Batch fermentation of pure xylose and poplar prehydrolyzate resulted in bioxylitol production of 9.9?±?0.01 and 4.9?±?0.17 g/L, respectively, indicating that the poplar prehydrolyzates exhibited an inhibitory effect on fermentation. After detoxification of the poplar prehydrolyzates, bioxylitol production increased to 8.9?±?0.01 g/L. Fed-batch fermentation of the prehydrolyzate increased the bioxylitol production to 12.39?±?0.33 g/L, while acid hydrolysis followed by detoxification resulted in a maximum bioxylitol production of 22.0?±?0.01 g/L, a 348 % increase. The results demonstrated that acid hydrolysis and detoxification followed by fed-batch fermentation was an efficient way to produce bioxylitol from poplar prehydrolyzates.     

Evaluation of ethanol production and bioadsorption of heavy metals by various red seaweeds

The objective of this study was to evaluate ethanol production and bioadsorption with four red seaweeds, Gelidium amansii, Gracilaria verrucosa, Kappaphycus alvarezii and Eucheuma denticulatum. To produce ethanol, thermal acid hydrolysis, enzymatic saccharification and fermentation was carried out. After pretreatment, 38.5, 39.9, 31.0 and 27.5 g/L of monosaccharides were obtained from G. amansii, G. verrucosa, K. alvarezii and E. denticulatum, respectively. Ethanol fermentation was performed with Saccharomyces cerevisiae KCCM 1129 adapted to 80 g/L galactose. The ethanol productions by G. amansii, G. verrucosa, K. alvarezii and E. denticulatum were 18.8 g/L with Y _EtOH = 0.49, 19.1 g/L with Y _EtOH = 0.48, 14.5 g/L with Y _EtOH = 0.47 and 13.0 g/L with Y _EtOH = 0.47, respectively. The waste seaweed slurries after the ethanol fermentation were reused to adsorb Cd(II), Pb(II) and Cu(II). Using langmuir isotherm model, Cu(II) had the highest affinity for waste seaweeds with the highest q _max and electronegativity values among three heavy metals.     

A novel structured bioreactor for solid-state fermentation

A novel patented solid-state bioreactor (251 L) with honeycomb loading device was designed and its performance was tested. First, this apparatus gave a 66.87 % of calculated loading coefficient (volume ratio), which was almost twofold compared with conventional fermenters. Next, considering the crucial effect of heat transfer on bed loading and microbial growth, the performance was validated by temperature variance during fermentation and spore viability of Bacillus cereus DM423. Air pressure pulsation or external water jacket was used to control temperature; the maximal temperature variation was 7.7 versus 19.8 °C, respectively during fermentation. The difference was mainly due to the continuous gas phase characterized by solid-state fermentation (SSF). The average living spores of (1.50 ± 0.07) × 10¹¹ cfu/g at 40 h obtained from the device was higher than (0.70 ± 0.03) × 10¹¹ cfu/g from flask at 48 h. The results indicated that this new loading bioreactor with air pressure pulsation could be a good prospect for industrialization of SSF employing bacterial cultures.     

Ethanol and sugar tolerance of Candida shehatae

Summary Candida shehatae ATCC 22984 fermented solutions of up to 260 g/L sugars derived by hydrolysis of whole barley. These solutions contained hexose: pentose 7030, the hexose being mainly glucose from the barley starch and the pentose being mainly xylose. At sugar concentrations of 180 g/L, fermentation was complete in 72 h, yielding 84 g/L ethanol, 0.47 g ethanol/g sugar. At 260 g/L, fermentation ceased when ethanol concentration reached 100 g/L, but resumed when the ethanol was removed by vacuum distillation, to yield finally 0.50 g ethanol/g sugar.     

Ethanol production from sunflower meal biomass by simultaneous saccharification and fermentation (SSF) with Kluyveromyces marxianus ATCC 36907

The lignocellulosic materials are considered promising renewable resources for ethanol production, but improvements in the processes should be studied to reduce operating costs. Thus, the appropriate enzyme loading for cellulose saccharification is critical for process economics. This study aimed at evaluating the concentration of cellulase and β-glucosidase in the production of bioethanol by simultaneous saccharification and fermentation (SSF) of sunflower meal biomass. The sunflower biomass was pretreated with 6 % H₂SO₄ (w/v), at 121 °C, for 20 min, for hemicellulose removal and delignificated with 1 % NaOH. SSF was performed with Kluyveromyces marxianus ATCC 36907, at 38 °C, 150 rpm, for 72 h, with different enzyme concentrations (Cellulase Complex NS22086-10, 15 and 20 FPU/g_substrate and β-Glucosidase NS22118, with a cellulase to β-glucosidase ratio of 1.5:1; 2:1 and 3:1). The best condition for ethanol production was cellulase 20 FPU/g_substrate and β-glucosidase 13.3 CBU/g_substrate, resulting in 27.88 g/L ethanol, yield of 0.47 g/g and productivity of 0.38 g/L h. Under this condition the highest enzymatic conversion of cellulose to glucose was attained (87.06 %).     

Production of biobutanol from acid-pretreated corncob using Clostridium beijerinckii TISTR 1461: Process optimization studies

Corncob is a potential feedstock in Thailand that can be used for fermentable sugar production through dilute sulfuric acid pretreatment and enzymatic hydrolysis. To recover high amounts of monomeric sugars from corncob, the sulfuric pretreatment conditions were optimized by using response surface methodology with three independent variables: sulfuric acid concentration, temperature, and time. The highest response of total sugars, 48.84 g/L, was found at 122.78°C, 4.65 min, and 2.82% (v/v) H₂SO₄. With these conditions, total sugars from the confirmation experiment were 46.29 g/L, with 5.51% error from the predicted value. The hydrolysate was used as a substrate for acetone–butanol–ethanol fermentation to evaluate its potential for microbial growth. The simultaneous saccharification and fermentation (SSF) showed that C. beijerinckii TISTR 1461 can generate acetone–butanol–ethanol products at 11.64 g/L (5.29 g/L acetone, 6.26 g/L butanol, and 0.09 g/L ethanol) instantly using sugars from the hydrolysed corncob with Novozymes 50013 cellulase enzyme without an overliming process.     

Ethanol Production from High-Solid SSCF of Alkaline-Pretreated Corncob Using Recombinant Zymomonas mobilis CP4

In this work, Zymomonas mobilis was genetically improved for pentose utilization to increase the final ethanol concentration. It showed good fermentation ability on both soluble sugar mixture and lignocellulose. Nearly all the glucose and xylose in sugar mixture can be consumed, corresponding to 86 % of theoretic ethanol yield. Simultaneous saccharification and co-fermentation (SSCF) of NaOH-pretreated corncob was then carried out in a high dry matter (DM) loading of 15–25?w/v%. At the DM loading of 15 %, the suitable operating conditions were determined, i.e., Z. mobilis loading of 0.30 g dry weight/L at 30 °C (pH?5.5), under which the ethanol concentration reached 49.2 g/L. Higher final ethanol concentrations were obtained when SSCF was operated at the fed-batch mode. Several amounts of substrate (1 % to 10 %) were added, and the highest final ethanol concentration (60.5 g/L) was obtained at 10 % DM addition.     

Effect of caffeine concentration on biomass production, caffeine degradation, and morphology of Aspergillus tamarii

The aim of the present study was to evaluate the effect of the initial caffeine concentration (1–8 g/L) on growth and caffeine consumption by Aspergillus tamarii as well as pellet morphology, in submerged fermentation. Caffeine was used as sole nitrogen source. At 1 g/L of initial caffeine concentration, caffeine degradation was not affected, resulting in a production of 8.7 g/L of biomass. The highest biomass production (12.4–14.8 g/L) was observed within a range of 2 to 4 g/L of initial caffeine concentration. At these initial caffeine concentrations, after 96 h of fermentation, 41–51 % of the initial caffeine was degraded. Using an initial caffeine concentration of 2–3 g/L, the highest specific growth rate was observed (μ?=?0.069 1/h). Biomass production decreased at 8 g/L of initial caffeine concentration. A. tamarii formed mainly pellets at all concentrations tested. The size of the pellet decreased at a caffeine concentration of 8 g/L.