Dilute acid pretreatment, enzymatic saccharification and fermentation of wheat straw to ethanol

Wheat straw consists of 48.57 ± 0.30% cellulose and 27.70 ± 0.12% hemicellulose on dry solid (DS) basis and has the potential to serve as a low cost feedstock for production of ethanol. Dilute acid pretreatment at varied temperature and enzymatic saccharification were evaluated for conversion of wheat straw cellulose and hemicellulose to monomeric sugars. The maximum yield of monomeric sugars from wheat straw (7.83%, w/v, DS) by dilute H₂SO₄ (0.75%, v/v) pretreatment and enzymatic saccharification (45 °C, pH 5.0, 72 h) using cellulase, β-glucosidase, xylanase and esterase was 565 ± 10 mg/g. Under this condition, no measurable quantities of furfural and hydroxymethyl furfural were produced. The yield of ethanol (per litre) from acid pretreated enzyme saccharified wheat straw (78.3 g) hydrolyzate by recombinant Escherichia coli strain FBR5 was 19 ± 1 g with a yield of 0.24 g/g DS. Detoxification of the acid and enzyme treated wheat straw hydrolyzate by overliming reduced the fermentation time from 118 to 39 h in the case of separate hydrolysis and fermentation (35 °C, pH 6.5), and increased the ethanol yield from 13 ± 2 to 17 ± 0 g/l and decreased the fermentation time from 136 to 112 h in the case of simultaneous saccharification and fermentation (35 °C, pH 6.0).     

Dilute acid pretreatment, enzymatic saccharification, and fermentation of rice hulls to ethanol

Rice hulls, a complex lignocellulosic material with high lignin (15.38 +/- 0.2%) and ash (18.71 +/- 0.01%) content, contain 35.62 +/- 0.12% cellulose and 11.96 +/- 0.73% hemicellulose and has the potential to serve as a low-cost feedstock for production of ethanol. Dilute H2SO4 pretreatments at varied temperature (120-190 degrees C) and enzymatic saccharification (45 degrees C, pH 5.0) were evaluated for conversion of rice hull cellulose and hemicellulose to monomeric sugars. The maximum yield of monomeric sugars from rice hulls (15%, w/v) by dilute H2SO4 (1.0%, v/v) pretreatment and enzymatic saccharification (45 degrees C, pH 5.0, 72 h) using cellulase, beta-glucosidase, xylanase, esterase, and Tween 20 was 287 +/- 3 mg/g (60% yield based on total carbohydrate content). Under this condition, no furfural and hydroxymethyl furfural were produced. The yield of ethanol per L by the mixed sugar utilizing recombinant Escherichia colistrain FBR 5 from rice hull hydrolyzate containing 43.6 +/- 3.0 g fermentable sugars (glucose, 18.2 +/- 1.4 g; xylose, 21.4 +/- 1.1 g; arabinose, 2.4 +/- 0.3 g; galactose, 1.6 +/- 0.2 g) was 18.7 +/- 0.6 g (0.43 +/- 0.02 g/g sugars obtained; 0.13 +/- 0.01 g/g rice hulls) at pH 6.5 and 35 degrees C. Detoxification of the acid- and enzyme-treated rice hull hydrolyzate by overliming (pH 10.5, 90 degrees C, 30 min) reduced the time required for maximum ethanol production (17 +/- 0.2 g from 42.0 +/- 0.7 g sugars per L) by the E. coli strain from 64 to 39 h in the case of separate hydrolysis and fermentation and increased the maximum ethanol yield (per L) from 7.1 +/- 2.3 g in 140 h to 9.1 +/- 0.7 g in 112 h in the case of simultaneous saccharification and fermentation.     

Study of the enzymatic hydrolysis of cellulose for production of fuel ethanol by the simultaneous saccharification and fermentation process

The biochemical conversion of cellulosic biomass to ethanol, a promising alternative fuel, can be carried out efficiently and economically using the simultaneous saccharification and fermentation (SSF) process. The SSF integrates the enzymatic hydrolysis of cellulose to glucose, catalyzed by the synergistic action of cellulase and beta-glucosidase, with the fermentative synthesis of ethanol. Because the enzymatic step determines the ethanol. Because the enzymatic step determines the availability of glucose to the ethanologenic fermentation, the kinetic of cellulose hydrolysis by cellulase and beta-glucosidase and the susceptibility of the two enzymes to inhibition by hydrolysis and fermentation products are of significant importance to the SSF performance and were investigated under realistic SSF conditions. A previously developed SSF mathematical model was used to conceptualize the depolymerization of cellulose. The model was regressed to the collected data to determine the values of the enzyme parameters and was found to satisfactorily predict the kinetics of cellulose hydrolysis. Cellobiose and glucose were identified as the strongest inhibitors of cellulase and beta-glucosidase, respectively. Experimental and modeling results are presented in light of the impact of enzymatic hydrolysis on fuel ethanol production. (c) 1993 Wiley & Sons, Inc.     

Modelling ethanol production from cellulose: separate hydrolysis and fermentation versus simultaneous saccharification and fermentation

In ethanol production from cellulose, enzymatic hydrolysis, and fermentative conversion may be performed sequentially (separate hydrolysis and fermentation, SHF) or in a single reaction vessel (simultaneous saccharification and fermentation, SSF). Opting for either is essentially a trade-off between optimal temperatures and inhibitory glucose concentrations on the one hand (SHF) vs. sub-optimal temperatures and ethanol-inhibited cellulolysis on the other (SSF). Although the impact of ethanol on cellobiose hydrolysis was found to be negligible, formation of glucose and cellobiose from cellulose were found to be significantly inhibited by ethanol. A previous model for the kinetics of enzymatic cellulose hydrolysis was, therefore, extended with enzyme inhibition by ethanol, thus allowing a rational evaluation of SSF and SHF. The model predicted SSF processing to be superior. The superiority of SSF over SHF (separate hydrolysis and fermentation) was confirmed experimentally, both with respect to ethanol yield on glucose (0.41 g g^?1 for SSF vs. 0.35 g g^?1 for SHF) and ethanol production rate, being 30% higher for an SSF type process. High conversion rates were found to be difficult to achieve since at a conversion rate of 52% in a SSF process the reaction rate dropped to 5% of its initial value. The model, extended with the impact of ethanol on the cellulase complex proved to predict reaction progress accurately.     

Effect of surfactants on separate hydrolysis fermentation and simultaneous saccharification fermentation of pretreated lodgepole pine

The effects of surfactants addition on enzymatic hydrolysis and subsequent fermentation of steam exploded lodgepole pine (SELP) and ethanol pretreated lodgepole pine (EPLP) were investigated in this study. Supplementing Tween 80 during cellulase hydrolysis of SELP resulted in a 32% increase in the cellulose‐to‐glucose yield. However, little improvement was obtained from hydrolyzing EPLP in the presence of the same amount of surfactant. The positive effect of surfactants on SELP hydrolysis led to an increase in final ethanol yield after the fermentation. It was found that the addition of surfactant led to a substantial increase in the amount of free enzymes in the 48 h hydrolysates derived from both substrates. The effect of surfactant addition on final ethanol yield of simultaneous saccharification and fermentation (SSF) was also investigated by using SELP in the presence of additional furfural and hydroxymethylfurfural (HMF). The results showed that the surfactants slightly increased the conversion rates of furfural and HMF during SSF process by Saccharomyces cerevisiae. The presence of furfural and HMF at the experimental concentrations did not affect the final ethanol concentration either. The strategy of applying surfactants in cellulase recycling to reduce enzyme cost is presented. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Production of bio-ethanol from pretreated agricultural byproduct using enzymatic hydrolysis and simultaneous saccharification

Global warming alerts and threats are on the rise due to the utilization of fossil fuels. Alternative fuel sources like bio-ethanol and biodiesel are being produced to combat against these threats. Bio-ethanol can be produced from a range of substrate. The present study is aimed at the Production of bioethanol from pretreated agricultural substrate using enzymatic hydrolysis and simultaneous saccharification with the addition of purified fungal enzyme. Most cellulosic biomass is not fermentable without appropriate pretreatment methods and so dilute sulfuric acid pretreatment was applied to make the cellulose contained in the waste susceptible to endoglucanase enzyme. A range of acid pretreatment of wheat bran was made in which the sample that was pretreated with 1% dilute sulfuric acid gave maximum yield of ethanol in both methods such as 5.83 g L(-1) and 5.27 g L(-1), respectively. Ethanol produced from renewable and cheap agricultural products (wheat bran) provides reduction in green house gas emission, carbon monoxide, sulfur, and helps to eliminate smog from the environment.     

Production of bio-ethanol from pretreated agricultural byproduct using enzymatic hydrolysis and simultaneous saccharification

Global warming alerts and threats are on the rise due to the utilization of fossil fuels. Alternative fuel sources like bio-ethanol and biodiesel are being produced to combat against these threats. Bio-ethanol can be produced from a range of substrate. The present study is aimed at the Production of bioethanol from pretreated agricultural substrate using enzymatic hydrolysis and simultaneous saccharification with the addition of purified fungal enzyme. Most cellulosic biomass is not fermentable without appropriate pretreatment methods and so dilute sulfuric acid pretreatment was applied to make the cellulose contained in the waste susceptible to endoglucanase enzyme. A range of acid pretreatment of wheat bran was made in which the sample that was pretreated with 1% dilute sulfuric acid gave maximum yield of ethanol in both methods such as 5.83 g L⁻¹ and 5.27 g L⁻¹, respectively. Ethanol produced from renewable and cheap agricultural products (wheat bran) provides reduction in green house gas emission, carbon monoxide, sulfur, and helps to eliminate smog from the environment.     

A comparison between simultaneous saccharification and fermentation and separate hydrolysis and fermentation using steam-pretreated corn stover

Two different process configurations, simultaneous saccharification and fermentation (SSF) and separate hydrolysis and fermentation (SHF), were compared, at 8% water-insoluble solids (WIS), regarding ethanol production from steam-pretreated corn stover. The enzymatic loading in these experiments was 10 FPU/g WIS and the yeast concentration in SSF was 1 g/L (dry weight) of a Saccharomyces cerevisiae strain. When the whole slurry from the pretreatment stage was used as it was, diluted to 8% WIS with water and pH adjusted, SSF gave a 13% higher overall ethanol yield than SHF (72.4% versus 59.1% of the theoretical). The impact of the inhibitory compounds in the liquid fraction of the pretreated slurry was shown to affect SSF and SHF in different ways. The overall ethanol yield (based on the untreated raw material) decreased when SSF was run in absence on inhibitors compared to SSF with inhibitors present. On the contrary, the presence of inhibitors decreased the overall ethanol yield in the case of SHF. However, the SHF yield achieves in the absence of inhibitors was still lower than the SSF yield achieves with inhibitors present.     

Effects of growth stage on enzymatic saccharification and simultaneous saccharification and fermentation of bamboo shoots for bioethanol production

Bamboo is a fast-growing renewable biomass that is widely distributed in Asia. Although bamboo is recognised as a useful resource, its utilization is limited and further development is required. Immature bamboo shoots harvested before branch spread were found to be a good biomass resource to achieve a high saccharification yield. The saccharification yield of the shoots increased (up to 98% for immature Phyllostachys bambusoides) when xylanase was used in addition to cellulase. Simultaneous saccharification and fermentation (SSF) processing converted immature shoots of P. bambusoides and Phyllostachys pubescens to ethanol with an ethanol yield of 169 and 139 g kg⁻¹, respectively (98% and 81%, respectively, of the theoretical yields based on hexose conversion) when 12 FPU g⁻¹ enzyme and the yeast Saccharomyces cerevisiae were used.     

Scale-up and integration of alkaline hydrogen peroxide pretreatment, enzymatic hydrolysis, and ethanolic fermentation

Alkaline hydrogen peroxide (AHP) has several attractive features as a pretreatment in the lignocellulosic biomass‐to‐ethanol pipeline. Here, the feasibility of scaling‐up the AHP process and integrating it with enzymatic hydrolysis and fermentation was studied. Corn stover (1 kg) was subjected to AHP pretreatment, hydrolyzed enzymatically, and the resulting sugars fermented to ethanol. The AHP pretreatment was performed at 0.125 g H₂O₂/g biomass, 22°C, and atmospheric pressure for 48 h with periodic pH readjustment. The enzymatic hydrolysis was performed in the same reactor following pH neutralization of the biomass slurry and without washing. After 48 h, glucose and xylose yields were 75% and 71% of the theoretical maximum. Sterility was maintained during pretreatment and enzymatic hydrolysis without the use of antibiotics. During fermentation using a glucose‐ and xylose‐utilizing strain of Saccharomyces cerevisiae, all of the Glc and 67% of the Xyl were consumed in 120 h. The final ethanol titer was 13.7 g/L. Treatment of the enzymatic hydrolysate with activated carbon prior to fermentation had little effect on Glc fermentation but markedly improved utilization of Xyl, presumably due to the removal of soluble aromatic inhibitors. The results indicate that AHP is readily scalable and can be integrated with enzyme hydrolysis and fermentation. Compared to other leading pretreatments for lignocellulosic biomass, AHP has potential advantages with regard to capital costs, process simplicity, feedstock handling, and compatibility with enzymatic deconstruction and fermentation. Biotechnol. Bioeng. 2012; 109:922–931. © 2011 Wiley Periodicals, Inc.     

Wet disk milling pretreatment without sulfuric acid for enzymatic hydrolysis of rice straw

Rice straw has recently attracted interest in Japan as a potential source of raw material for ethanol production. Wet disk milling, a continuous pretreatment to enhance the enzymatic digestibility of rice straw, was compared with conventional ball milling and hot-compressed water treatment. Pretreated rice straw was evaluated by enzymatic hydrolysis using Acremonium cellulase and characterized by X-ray diffraction and scanning electron microscopy. Glucose and xylose yields by wet disk milling, ball milling, and hot-compressed water treatment were 78.5% and 41.5%, 89.4% and 54.3%, and 70.3% and 88.6%, respectively. Wet disk milling and hot-compressed water treatment increased sugar yields without decreasing their crystallinity. The feature size of the wet disk milled rice straw was similar to that of hot-compressed water-treated rice straw. The energy consumption of wet disk milling was lower than that of other pretreatments. Thus, wet disk milling is an economical, practical pretreatment for the enzymatic hydrolysis of lignocellulosic biomass, especially herbaceous biomass such as rice straw.     

Ethanol production from rice straw using optimized aqueous-ammonia soaking pretreatment and simultaneous saccharification and fermentation processes

Rice straw was pretreated using aqueous-ammonia solution at moderate temperatures to enable production of the maximum amount of fermentable sugars from enzymatic hydrolysis. The effects of various operating variables including pretreatment temperature, pretreatment time, the concentration of ammonia and the solid-to-liquid ratio on the degree of lignin removal and the enzymatic digestibility were optimized using response surface methodology. The optimal reaction conditions, which resulted in an enzymatic digestibility of 71.1%, were found to be 69 °C, 10 h and an ammonia concentration of 21% (w/w). The effects of different commercial cellulases and the additional effect of a non-cellulolytic enzyme, xylanase, were also evaluated. Additionally, simultaneous saccharification and fermentation was conducted with rice straw to assess the ethanol production yield and productivity.     

Acid-catalyzed steam pretreatment of lodgepole pine and subsequent enzymatic hydrolysis and fermentation to ethanol

Utilization of ethanol produced from biomass has the potential to offset the use of gasoline and reduce CO(2) emissions. This could reduce the effects of global warming, one of which is the current outbreak of epidemic proportions of the mountain pine beetle (MPB) in British Columbia (BC), Canada. The result of this is increasing volumes of dead lodgepole pine with increasingly limited commercial uses. Bioconversion of lodgepole pine to ethanol using SO(2)-catalyzed steam explosion was investigated. The optimum pretreatment condition for this feedstock was determined to be 200 degrees C, 5 min, and 4% SO(2) (w/w). Simultaneous saccharification and fermentation (SSF) of this material provided an overall ethanol yield of 77% of the theoretical yield from raw material based on starting glucan, mannan, and galactan, which corresponds to 244 g ethanol/kg raw material within 30 h. Three conditions representing low (L), medium (M), and high (H) severity were also applied to healthy lodgepole pine. Although the M severity conditions of 200 degrees C, 5 min, and 4% SO(2) were sufficiently robust to pretreat healthy wood, the substrate produced from beetle-killed (BK) wood provided consistently higher ethanol yields after SSF than the other substrates tested. BK lodgepole pine appears to be an excellent candidate for efficient and productive bioconversion to ethanol.     

Enhanced enzymatic saccharification of rice straw by microwave pretreatment

In this study, Box-Behnken design and response surface methodology were employed to plan experiments and optimize the microwave pretreatment of rice straw. Experimental results show that microwave intensity (MI), irradiation time (IT) and substrate concentration (SC) were main factors governing the enzymatic saccharification of rice straw. The maximal efficiencies of cellulose, hemicellulose and total saccharification were respectively increased by 30.6%, 43.3% and 30.3% under the optimal conditions of MI 680 W, IT 24 min and SC 75 g/L. The chemical composition analysis of straw further confirmed that microwave pretreatment could disrupt the silicified waxy surface, break down the lignin-hemicellulose complex and partially remove silicon and lignin.     

Biomass conversion to butanediol by simultaneous saccharification and fermentation

The efficient biological conversion of all the available sugars in biomass residues to fuels and chemicals is crucial to the efficiency of any process intended to compete economically with petrochemical products. Both hemicellulose- and cellulose-derived carbohydrates from wood and agricultural wastes can be converted to 2,3-butanediol by simultaneous saccharification and fermentation. This approach results in improved butanediol yields and process productivities, and also enables biomass substrates, after a simple pretreatment (steam-explosion), to be directly used for efficient butanediol production.     

Simultaneous saccharification and fermentation of broken rice: an enzymatic extrusion liquefaction pretreatment for Chinese rice wine production

Broken rice, pretreated by enzymatic extrusion liquefaction, was used to produce Chinese rice wine by simultaneous saccharification and fermentation (SSF) process in this study. The study compared the novel process and traditional process for Chinese rice wine fermentation utilizing broken rice and head rice, respectively. With the optimum extrusion parameters (barrel temperature, 98 °C; moisture content, 42 % and amylase concentration, 1 ‰), 18 % (v/v at 20 °C) alcoholic degree, 37.66 % fermentation recovery and 93.63 % fermentation efficiency were achieved, indicating enzymatic extrusion-processed rice wine from broken rice exhibited much higher fermentation rate and efficiency than traditional-processed rice wine from head rice during SSF. The starch molecule distribution data indicated that the alcoholic degree was related to the oligosaccharides’ formation during enzymatic extrusion. Sum of amino acid (AA) in the extrusion-processed wine was 53.7 % higher than that in the traditional one. These results suggest that the enzymatic extrusion pretreatment for broken rice is a feasible and alternative process in the fermentation of Chinese rice wine.     

Effects of fungal pretreatment and steam explosion pretreatment on enzymatic saccharification of plant biomass

The effects of consecutive treatments by a lignin-degrading fungus Phanerochaete chrysosporium and by steam explosion for the enzymatic saccharification of plant biomass were studied experimentally, and the optimal operational conditions for obtaining the maximum saccharification were evaluated. Beech wood-meal was treated by the fungus for 98 days and then by high steam temperatures of 170-230 degrees C with steaming times of 0-10 min. The treatment of the wood-meal by fungus prior to steam explosion enhanced the saccharification of wood-meal. The treated wood-meal was separated into holo-cellulose, water soluble material, methanol soluble lignin, and Klason lignin. The saccharification decreased linearly with the increase in the amount of Klason lignin. It was estimated by the equation for the saccharification of exploded wood-meal expressed as a function of steam temperature and steaming time that the maximum saccharification of wood-meal was obtained by consecutive treatments such as fungal treatment for 28 days and then steam explosion at a steam temperature of 215 degrees C and a steaming time of 6.5 min. (c) 1995 John Wiley & Sons, Inc.     

Lime pretreatment and enzymatic hydrolysis of corn stover

Corn stover was pretreated with an excess of calcium hydroxide (0.5 g Ca(OH)2/g raw biomass) in non-oxidative and oxidative conditions at 25, 35, 45, and 55 degrees C. The optimal condition is 55 degrees C for 4 weeks with aeration. Glucan (91.3%) and xylan (51.8%) were converted to glucose and xylose respectively, when the treated corn stover was enzymatically hydrolyzed with 15 FPU/g cellulose. Only 0.073 g Ca(OH)2 was consumed per g of raw corn stover. Of the initial lignin, 87.5% was maximally removed. Almost all acetyl groups were removed. After 4 weeks at 55 degrees C with aeration, some cellulose and hemicellulose were solubilized as monomers and oligomers in the pretreatment liquor. When considering the dissolved fragments of glucan and xylan in the pretreatment liquor, the overall yields of glucose and xylose were 93.2% and 79.5% at 15 FPU/g cellulose. The pretreatment liquor has no inhibitory effect on ethanol fermentation.