Production of Ethanol and Feed by High Dry Matter Hydrolysis and Fermentation of Palm Kernel Press Cake

Palm kernel press cake (PKC) is a residue from palm oil extraction presently only used as a low protein feed supplement. PKC contains 50% fermentable hexose sugars present in the form of glucan and mainly galactomannan. This makes PKC an interesting feedstock for processing into bioethanol or in other biorefinery processes. Using a combination of mannanase, β-mannosidase, and cellulases, it was possible without any pretreatment to hydrolyze PKC at solid concentrations of 35% dry matter with mannose yields up to 88% of theoretical. Fermentation was tested using Saccharomyces cerevisiae in both a separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) setup. The hydrolysates could readily be fermented without addition of nutrients and with average fermentation yields of 0.43?±?0.02 g/g based on consumed mannose and glucose. Employing SSF, final ethanol concentrations of 70 g/kg was achieved in 216 h, corresponding to an ethanol yield of 70% of theoretical or 200 g ethanol/kg PKC. Testing various enzyme mixtures revealed that including cellulases in combination with mannanases significantly improved ethanol yields. Processing PKC to ethanol resulted in a solid residue enriched in protein from 17% to 28%, a 70% increase, thereby potentially making a high-protein containing feed supplement.     

Fumaric Acid Production from Alkali-Pretreated Corncob by Fed-Batch Simultaneous Saccharification and Fermentation Combined with Separated Hydrolysis and Fermentation at High Solids Loading

Production of fumaric acid from alkali-pretreated corncob (APC) at high solids loading was investigated using a combination of separated hydrolysis and fermentation (SHF) and fed-batch simultaneous saccharification and fermentation (SSF) by Rhizopus oryzae. Four different fermentation modes were tested to maximize fumaric acid concentration at high solids loading. The highest concentration of 41.32 g/L fumaric acid was obtained from 20 % (w/v) APC at 38 °C in the combined SHF and fed-batch SSF process, compared with 19.13 g/L fumaric acid in batch SSF alone. The results indicated that a combination of SHF and fed-batch SSF significantly improved production of fumaric acid from lignocellulose by R. oryzae than that achieved with batch SSF at high solids loading.     

Assessment of waxy and non-waxy corn and wheat cultivars as starch substrates for ethanol fermentation

The amylose/amylopectin ratio in cereal substrates is one of the parameters affecting starch hydrolysis and fermentation process. Waxy (less than 1 mass % of amylose) starch seems to be suitable for improving the fuel ethanol production. The main aim of this paper was to characterize the fermentation performance of corn and wheat waxy and non-waxy cultivars in terms of simultaneous saccharification and fermentation (SSF) as well as of the separated hydrolysis and fermentation (SHF) type. Two corn (waxy and non-waxy) and two wheat (waxy and non-waxy) cultivars were used for the comparison applying separate enzymatic hydrolysis and fermentation. In the SHF process, the glucose content was higher after saccharification in the waxy corn and wheat compared to that in non-waxy corn and wheat. In the SSF of waxy varieties, the glucose content after the pre-saccharification was also higher than in the non-waxy ones. Although the starch content did not vary significantly, differences in the glucose content after saccharification were observed. The ethanol yield obtained after the distillation of mash varied from 229.2–262.3 L per ton for the SHF fermentation, while it was in the range of 311.5–347.9 L per ton for the SSF process.     

Effect of Resistant Starch on Hydrolysis and Fermentation of Corn Starch for Ethanol

Starch samples with 0% or 30% amylose were subjected to four different liquefaction enzyme treatments (at various temperature and pH conditions) followed by simultaneous saccharification and fermentation (SSF). Resistant starch (RS) measurements were conducted for the initial starch sample, after liquefaction and after SSF. Initial RS was higher for 30% amylose starch samples (16.53 g/100 g sample) compared with 0% amylose (0.76 g/100 g sample). Higher initial RS resulted in lower conversion of starch into sugars and lower final ethanol yields. The four enzymes hydrolyzed RS, but in varying amounts. Higher temperature liquefaction hydrolyzed a larger portion of RS, resulting in higher ethanol concentrations and lower final residual solids (non-fermentables), whereas lower temperature liquefaction hydrolyzed a smaller portion of RS and resulted in lower ethanol concentrations and higher final residual solids. Decreases in resistant starch after high temperature liquefaction were 55% to 74%, whereas low temperature liquefaction decreases were 11% to 43%. For all enzyme treatments, RS content of starch samples decreased further after SSF.     

Ethanol Production from the Organic Fraction Obtained After Thermal Pretreatment of Municipal Solid Waste

In this work, the use of organic fraction from municipal solid waste (MSW) as substrate for ethanol production based on enzymatic hydrolysis was evaluated. MSW was subjected to a thermal pretreatment (active hygienization) at 160?°C from 5 to 50 min. The organic fiber obtained after 30 min was used as substrate in a simultaneous saccharification and fermentation (SSF) and fed-batch SSF process using cellulases and amylases. In a fed-batch mode with 25% (w/w) substrate loading, final ethanol concentration of 30 g/L was achieved (60% of theoretical). In these conditions, more than 160 L of ethanol per ton of dry matter could be produced from the organic fraction of MSW.     

Separate and simultaneous enzymatic hydrolysis and fermentation of wheat hemicellulose with recombinant xylose utilizing Saccharomyces cerevisiae

Fermentations with three different xylose-utilizing recombinant Saccharomyces cerevisiae strains (F12, CR4, and CB4) were performed using two different wheat hemicellulose substrates, unfermented starch free fibers, and an industrial ethanol fermentation residue, vinasse. With CR4 and F12, the maximum ethanol concentrations obtained were 4.3 and 4 g/L, respectively, but F12 converted xylose 15% faster than CR4 during the first 24 h. The comparison of separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) with F12 showed that the highest, maximum ethanol concentrations were obtained with SSF. In general, the volumetric ethanol productivity was initially, highest in the SHF, but the overall volumetric ethanol productivity ended up being maximal in the SSF, at 0.013 and 0.010 g/Lh, with starch free fibers and vinasse, respectively.     

Simultaneous saccharification and fermentation of lignocellulose

Simultaneous saccharification and fermentation (SSF) processes for producing ethanol from lignocellulose are capable of improved hydrolysis rates, yields, and product concentrations compared to separate hydrolysis and fermentation (SHF) systems, because the continuous removal of the sugars by the yeasts reduces the end-product inhibition of the enzyme complex. Recent experiments using Genencor 150L cellulase and mixed yeast cultures have produced yields and concentrations of ethanol from cellulose of 80% and 4.5%, respectively. The mixed culture was employed because B.clausenii has the ability to ferment cellobiose (further reducing end-product inhibition), while the brewing yeastS. cerevisiae provides a robust ability to ferment the monomeric sugars. These experimental results are combined with a process model to evaluate the economics of the process and to investigate the effect of alternative processes, conditions, and organisms.     

Ethanol production from corn starch in a fluidized-bed bioreactor

The production of ethanol from industrial dry-milled corn starch was studied in a laboratory-scale fluidized-bed bioreactor using immobilized biocatalysts. Saccharification and fermentation were carried out either simultaneously or separately. Simultaneous saccharification and fermentation (SSF) experiments were performed using small, uniform κ-carrageenan beads (1.5–2.5 mm in diameter) of co-immobilized glucoamylase and Zymomonas mobilis. Dextrin feeds obtained by the hydrolysis of 15% drymilled corn starch were pumped through the bioreactor at residence times of 1.5–4h. Single-pass conversion of dextrins ranged from 54–89%, and ethanol concentrations of 23–36 g/L were obtained at volumetric productivities of 9–15 g/L-h. Very low levels of glucose were observed in the reactor, indicating that saccharification was the rate-limiting step. In separate hydrolysis and fermentation (SHF) experiments, dextrin feed solutions of 150–160 g/L were first pumped through an immobilized-glucoamylase packed column. At 55°C and a residence time of 1 h, greater than 95% conversion was obtained, giving product streams of 162–172 g glucose/L. These streams were then pumped through the fluidized-bed bioreactor containing immobilized Z. mobilis. At a residence time of 2 h, 94% conversion and ethanol concentration of 70 g/L were achieved, resulting in an overall process productivity of 23 g/L-h. Atresidence times of 1.5 and 1 h, conversions of 75 and 76%, ethanol concentrations of 49 and 47 g/L, and overall process productivities of 19 and 25 g/L-h, respectively, were achieved.     

Optimization of Saccharification and Fermentation Process in Bioethanol Production from Oil Palm Fronds

Oil Palm Frond (OPF) is one of lignocellulosic biomass, which can be utilized as raw material for bioethanol production. Bioethanol is produced as alternative energy to substitute gasoline. There are four steps in bioethanol production from OPF, i.e pretreatement, saccharification, fermentation and purification process. In this study, optimization of saccharification and fermentation process for OPF was investigated. Two methods and the variations of enzyme concentration were carried out in the saccharification and fermentation process. Separate hydrolysis and fermentation process (SHF) and simultaneous saccharification and fermentation process (SSF) were conducted to produce ethanol optimally. Variations of enzyme concentration used in this process were 10, 20, 30 and 40 FPU/g substrate. The result shows that the highest ethanol concentration can be obtained in SSF process with 30 FPU/g substrate of enzyme concentration. The process produced 59.20 g/L ethanol (95.95% yield ethanol) at 96 h of SSF process.     

Soaking Pretreatment of Corn Stover for Bioethanol Production Followed by Anaerobic Digestion Process

The production of ethanol and methane from corn stover (CS) was investigated in a biorefinery process. Initially, a novel soaking pretreatment (NaOH and aqueous-ammonia) for CS was developed to remove lignin, swell the biomass, and improve enzymatic digestibility. Based on the sugar yield during enzymatic hydrolysis, the optimal pretreatment conditions were 1?% NaOH?+?8?% NH₄OH, 50°C, 48?h, with a solid-to-liquid ratio 1:10. The results demonstrated that soaking pretreatment removed 63.6?% lignin while reserving most of the carbohydrates. After enzymatic hydrolysis, the yields of glucose and xylose were 78.5?% and 69.3?%, respectively. The simultaneous saccharification and fermentation of pretreated CS using Pichia stipitis resulted in an ethanol concentration of 36.1?g/L, corresponding only to 63.3?% of the theoretical maximum. In order to simplify the process and reduce the capital cost, the liquid fraction of the pretreatment was used to re-soak new CS. For methane production, the re-soaked CS and the residues of SSF were anaerobically digested for 120?days. Fifteen grams CS were converted to 1.9?g of ethanol and 1337.3?mL of methane in the entire process.     

Bioethanol Production from Soybean Residue via Separate Hydrolysis and Fermentation

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

Hydrothermal pretreatment conditions to enhance ethanol production from poplar biomass

Pretreatment has been recognized as a key step in enzyme-based conversion processes of lignocellulose biomass to ethanol. The aim of this study is to evaluate two hydrothermal pretreatments (steam explosion and liquid hot water) to enhance ethanol production from poplar (Populus nigra) biomass by a simultaneous saccharification and fermentation (SSF) process. The composition of liquid and solid fractions obtained after pretreatment, enzymatic digestibility, and ethanol production of poplar biomass pretreated at different experimental conditions was analyzed. The best results were obtained in steam explosion pretreatment at 210°C and 4 min, taking into account cellulose recovery above 95%, enzymatic hydrolysis yield of about 60%, SSF yield of 60% of theoretical, and 41% xylose recovery in the liquid fraction. Large particles can be used for poplar biomass in both pretreatments, since no significant effect of particle size on enzymatic hydrolysis and SSF was obtained.     

Effect of surfactants and zeolites on simultaneous saccharification and fermentation of steam-exploded poplar biomass to ethanol

In this work, the effect of the addition of different concentrations of Tween-80 and three different zeolite-like products on enzymatic hydrolysis, ethanol fermentation, and simultaneous saccharification and fermentation (SSF) process has been investigated. The ability of these products to enhance the effectiveness of the SSF process to ethanol of steam-exploded poplar biomass using the thermotolerant strainKluyveromyces marxianus EMS-26 has been tested. Tween-80 (0.4 g/L) increased enzymatic hydrolysis yield by 20% when compared to results obtained in hydrolysis in absence of the additive. Zeolite-like products (ZESEP-56 and ZECER-56) (2.5 g/L) improved rates of conversion and ethanol yields in the fermentation of liquid fraction recovered from steam-exploded poplar. The periods required for the completion of fermentation were approx 10 h in the presence of zeolite-like products and 24 h in the absence of additives. The probable mode of action is through lowered levels of inhibitory substances because of adsorption by the additive.     

Simultaneous saccharification and fermentation of steam-pretreated spruce to ethanol

Ethanol production was studied in simultaneous saccharification and fermentation (SSF) of steam-pretreated spruce at 42°C, using a thermotolerant yeast. Three yeast strains of Kluyveromyces marxianus were compared in test fermentations. SSF experiments were performed with the best of these on 5% (w/w) of substrate at a cellulase loading of 37 filter paper units/g of cellulose, and a β-glucosidase loading of 38 IU/gof cellulose. The detoxification of the substrate and the lack of pH control in the experiments increased the final ethanol concentration. The final ethanol yield was 15% lower compared to SSF with Saccharomyces cerevisiae at 37°C, owing to the cessation of ethanol fermentation after the first 10 h.     

Design and Evaluation of an Optimal Controller for Simultaneous Saccharification and Fermentation Process

Ethanol from corn is produced using dry grind corn process in which simultaneous saccharification and fermentation (SSF) is one of the most critical unit operations. In this work an optimal controller based on a previously validated SSF model was developed by formulating the SSF process as a Bolza problem and using gradient descent methods. Validation experiments were performed to evaluate the performance of optimal controller under different process disturbances that are likely to occur in practice. Use of optimal control algorithm for the SSF process resulted in lower peak glucose concentration, similar ethanol yields (13.38±0.36% v/v and 13.50±0.15% v/v for optimally controlled and baseline experiments, respectively). Optimal controller improved final ethanol concentrations as compared to process without optimal controller under conditions of temperature (13.35±1.28 and 12.52±1.19% v/v for optimal and no optimal control, respectively) and pH disturbances (12.65±0.74 and 11.86±0.49% v/v for optimal and no optimal control, respectively). Cost savings due to lower enzyme usage and reduced cooling requirement were estimated to be up to $1 million for a 151 million L/yr (40 million gal/yr) dry grind plant.     

Effects of temperature and moisture on dilute-acid steam explosion pretreatment of corn stover and cellulase enzyme digestibility

Corn stover is emerging as a viable feedstock for producing bioethanol from renewable resources. Dilute-acid pretreatment of corn stover can solubilize a significant portion of the hemicellulosic component and enhance the enzymatic digestibility of the remaining cellulose for fermentation into ethanol. In this study, dilute H₂SO₄ pretreatment of corn stover was performed in a steam explosion reactor at 160°C, 180°C, and 190°C, approx 1 wt% H₂SO₄, and 70-s to 840-s residence times. The combined severity (Log₁₀ [R _o ] - pH), an expression relating pH, temperature, and residence time of pretreatment, ranged from 1.8 to 2.4. Soluble xylose yields varied from 63 to 77% of theoretical from pretreatments of corn stover at 160 and 180°C. However, yields >90% of theoretical were found with dilute-acid pretreatments at 190°C. A narrower range of higher combined severities was required for pretreatment to obtain high soluble xylose yields when the moisture content of the acid-impregnated feedstock was increased from 55 to 63 wt%. Simultaneous saccharification and fermentation (SSF) of washed solids from corn stover pretreated at 190°C, using an enzyme loading of 15 filter paper units (FPU)/g of cellulose, gave ethanol yields in excess of 85%. Similar SSF ethanol yields were found using washed solid residues from 160 and 180°C pretreatments at similar combined severities but required a higher enzyme loading of approx 25 FPU/g of cellulose.     

Detoxification of Organosolv-Pretreated Pine Prehydrolysates with Anion Resin and Cysteine for Butanol Fermentation

Bioconversion of lignocellulose to biofuels suffers from the degradation compounds formed during pretreatment and acid hydrolysis. In order to achieve an efficient biomass to biofuel conversion, detoxification is often required before enzymatic hydrolysis and microbial fermentation. Prehydrolysates from ethanol organosolv-pretreated pine wood were used as substrates in butanol fermentation in this study. Six detoxification approaches were studied and compared, including overliming, anion exchange resin, nonionic resin, laccase, activated carbon, and cysteine. It was observed that detoxification by anion exchange resin was the most effective method. The final butanol yield after anion exchange resin treatment was comparable to the control group, but the fermentation was delayed for 72 h. The addition of Ca(OH)₂ was found to alleviate this delay and improve the fermentation efficiency. The combination of Ca(OH)₂ and anion exchange resin resulted in completion of fermentation within 72 h and acetone–butanol–ethanol (ABE) production of 11.11 g/L, corresponding to a yield of 0.21 g/g sugar. The cysteine detoxification also resulted in good detoxification performance, but promoted fermentation towards acid production (8.90 g/L). The effect of salt on ABE fermentation was assessed and the possible role of Ca(OH)₂ was to remove the salts in the prehydrolysates by precipitation.     

Ethanol production from olive oil extraction residue pretreated with hot water

The olive pulp fraction contained in the residue generated in olive oil extraction by a two-step centrifugation process can be upgraded by using the cellulose fraction to produce ethanol and recovering high value phenols (tyrosol and hydroxytyrosol). Olive pulp was pretreated in a laboratory scale stirred autoclave at different temperatures (150–250°C). Pretreatment was evaluated regarding cellulose recovery, enzymatic hydrolysis effectiveness ethanol production by a simultaneous saccharification and fermentation process (SSF), and phenols recovery in the filtrate. The pretreatment of olive pulp using water at temperatures between 200°C and 250°C enhanced enzymatic hydrolysis. Maximum ethanol production (11.9 g/L) was obtained after pretreating pulp at 210°C in a SSF fed-batch procedure. Maximum hydroxytyrosol recovery was obtained in the liquid fraction when pretreated at 230°C.     

Understanding the Impacts of AFEX™ Pretreatment and Densification on the Fast Pyrolysis of Corn Stover,Prairie Cord Grass,and Switchgrass

Lignocellulosic feedstocks corn stover, prairie cord grass, and switchgrass were subjected to ammonia fiber expansion (AFEX?) pretreatment and densified using extrusion pelleting and ComPAKco densification technique. The effects of AFEX? pretreatment and densification were studied on the fast pyrolysis product yields. Feedstocks were milled in a hammer mill using three different screen sizes (2, 4, and 8 mm) and were subjected to AFEX? pretreatment. The untreated and AFEX?-pretreated feedstocks were moisture adjusted at three levels (5, 10, and 15 % wb) and were extruded using a lab-scale single screw extruder. The barrel temperature of the extruder was maintained at 75, 100, and 125 °C. Durability of the extruded pellets made from AFEX?-pretreated corn stover, prairie cord grass, and switchgrass varied from 94.5 to 99.2, 94.3 to 98.7, and 90.1 to 97.5 %, respectively. Results of the thermogravimetric analysis showed the decrease in the decomposition temperature of the all the feedstocks after AFEX? pretreatment indicating the increase in thermal stability. Loose and densified feedstocks were subjected to fast pyrolysis in a lab-scale reactor, and the yields (bio-oil and bio-char) were measured. Bio-char obtained from the AFEX?-pretreated feedstocks exhibited increased bulk and particle density compared to the untreated feedstocks. The properties of the bio-oil were statistically similar for the untreated, AFEX?-pretreated, and AFEX?-pretreated densified feedstocks. Based on the bio-char and bio-oil yields, the AFEX?-pretreated feedstocks and the densified AFEX?-pretreated feedstocks (pellets and PAKs) exhibited similar behavior. Hence, it can be concluded that densifying the AFEX?-pretreated feedstocks could be a viable option in the biomass-processing depots to reduce the transportation costs and the logistical impediments without affecting the product yields.     

Recirculation of process streams in fuel ethanol production from softwood based on simultaneous saccharification and fermentation

The effect of process stream recirculation on ethanol production from steam- pretreated softwood based on simultaneous saccharification and fermentation (SSF) was investigated for two process configurations. In the first configuration, a part of the stillage stream after distillation was recycled and, in the second configuration, the liquid after SSF was recycled. The aim was to minimize the energy consumption in the distillation of the fermentation broth and in the evaporation of the stillage, as well as the use of fresh water. However, recirculation leads to an increased concentration of nonvolatiles in the first configuration, and of both volatiles and nonvolatiles in the second configuration. These substances might be inhibitory to the enzymes and the yeast in SSF. When 60% of the fresh water was replaced by stillage, the ethanol yield and the productivity were the same as for the configuration without recirculation. The ethanol production cost was reduced by 17%. In the second configuration, up to 40% of the fresh water could be replaced without affecting the final ethanol yield, although the initial ethanol productivity decreased. The ethanol production cost was reduced by 12%. At higher degrees of recirculation, fermentation was clearly inhibited, resulting in a decrease in ethanol yield while hydrolysis seemed unaffected.