Theoretical Ethanol Yield Research Articles

Effect of Steam Explosion Pretreatment on Bamboo for Enzymatic Hydrolysis and Ethanol Fermentation

Based on the steam explosion pretreatment that has been applied to other types of lignocellulosic biomass, the steam explosion pretreatment of bamboo, along with a study of the chemical compositions and enzymatic hydrolyzability of substrates, was conducted. The results show that steam explosion pretreatment can greatly enhance the cellulose-to-glucose conversion yield after enzymatic hydrolysis, which is sometimes affected by bamboo age and steam explosion conditions. When the steam explosion pretreatment conditions were 2.0 MPa (pressure) and 4 min (time), the cellulose-to-glucose conversion yield of 2-year-old bamboo substrate was 62.5%. However, the cellulose-to-glucose conversion yield of bamboo substrates after direct (without steam explosion pretreatment) sodium chlorite/acetic acid delignification was 93.1%. Fermentation of enzymatic hydrolyzates with Saccharomyces cerevisiae resulted in about 88.1% to 96.2% of the corresponding theoretical ethanol yield after 24 h.

Simultaneous saccharification and fermentation of delignified lignocellulosic biomass at high solid loadings by a newly isolated thermotolerant Kluyveromyces sp. for ethanol production

Simultaneous saccharification and fermentation studies were carried out using thermotolerant newly isolated Kluyveromyces sp. with three different delignified lignocellulosic biomass viz. rice straw, wheat straw and sugarcane bagasse at 5–15% solid loading and 6–12FPUg−1 substrate enzyme loading for different time intervals 0–72h at 42°C. Maximum ethanol achieved from rice straw, wheat straw and sugarcane bagasse with in-house crude cellulases from Aspergillus terreus was 23.23, 18.29 and 17.91mgmL−1 at 60h with 10% solid load and 9FPUg−1 substrate enzyme loading. Tween 80 1% (v/v) enhanced the ethanol yield by 8.39%, 9.26% and 8.14% in rice straw, wheat straw and sugarcane bagasse, respectively. External supplementation of β-glucosidase to the crude as well commercial cellulases produced maximum theoretical ethanol yield of 71.76%, 63.77%, 57.15% and 84.56%, 72.47%, 70.55% from rice straw, wheat straw and sugarcane bagasse, respectively.

Improvement of cassava stem hydrolysis by two-stage chemical pretreatment for high yield cellulosic ethanol production

We used sodium chlorite followed by sodium hydroxide as a two-stage pretreatment of cassava stem for removal of lignin and hemicellulose to obtain a substrate with high cellulose content prior to hydrolysis. Response surface methodology was applied to determine the optimum hydrolysis conditions of two-stage pretreated cassava stem. After pretreatment, the cellulose content of cassava stem increased from 42.10% to 86.45%, concomitant with decreases in lignin (87.59%) and hemicellulose (78.18%) content. Acid hydrolysis of two-stage pretreated cassava stem under optimum conditions allowed obtaining a hydrolyzate rich in reducing sugar, with a yields up to 67.37%. Conversely, inhibitors were detected at very low concentrations. The fermentation of the hydrolyzate resulted in an ethanol yield of 22.58 g/100 g substrate corresponding to a theoretical ethanol yield of 84.41%. The results demonstrate that two-stage pretreatment is effective for improving cellulose hydrolyzability, resulting in high fermentable sugar and low fermentation inhibitor concentrations.

Co-production of bioethanol and biodiesel from corn stover pretreated with nitric acid

This research explores the application of glucose and xylose from corn stover pretreated with nitric acid (HNO3) for the co-production of bioethanol and biodiesel. Response surface methodology was employed to optimize HNO3 pretreatment condition including HNO3 concentration (0.2–1.0%), temperature (140–160°C), and reaction time (1–10min). The optimal reaction condition was 151.9°C, 0.68% HNO3 and 2.5min, which resulted in the highest xylose yield of 77.8% and glucan content of 57.1%. Quasi-simultaneous saccharification and fermentation (Q-SSF) of pretreated corn stover with Saccharomyces cerevisiae gave an ethanol concentration of 22.4g/L, corresponding to 69.1% theoretical ethanol yield based on initial cellulose weight. In addition, Cryptococcus curvatus in hydrolysate medium showed the lipid yield (final cell weight×lipid content) of 1.04g/L, which was higher than those in defined medium using pure xylose. Our work demonstrates that the simultaneous production of ethanol and lipid can be one potentially promising option for lignocellulose-derived fuel production.

Conversion of steam-exploded cedar into ethanol using simultaneous saccharification, fermentation and detoxification process

In this study, we investigated the simultaneous saccharification, fermentation and detoxification SSDF process of steam-exploded cedar using a detoxification microorganism, Ureibacillus thermosphaericus A1, to facilitate efficient ethanol production. Steam explosion was applied as a pretreatment before enzymatic saccharification followed by alcohol fermentation. The highest glucose conversion rate was observed in the sample pretreated with a steam pressure of 45atm for 5min. Alcohol production by a heat-tolerant yeast, Saccharomyces cerevisiae BA11, was inhibited strongly by inhibitory materials present in the steam-exploded cedar, such as formic acid, furfural, and 5-hydroxymethylfurfural. The maximum amount of ethanol, i.e., 0.155g ethanol/g dry steam-exploded cedar, which corresponded to 74% of the theoretical ethanol yield, was obtained using the SSDF when U. thermosphaericus A1 degraded the inhibitory materials. A fed batch SSDF culture, in which U. thermosphaericus A1 was used to maintain low concentrations of inhibitory materials, was effective for increasing the ethanol concentration.

Producing Ethanol from Water Hyacinth through Simultaneous Saccharification and Fermentation with Acclimatized Yeasts

The production rate and yield of ethanol was markedly increased when water hyacinth, pretreated with microwave-assisted dilute acid, was fermented with acclimatized yeasts through simultaneous saccharification and fermentation. Water hyacinth hydrolyzate microwaved with 1% (v/v) dilute sulfuric acid was fermented with the acclimatized mixed yeasts Pichia stipitis and Pachysolen tannophilus at a volume ratio of 1:1. The highest ethanol yield was 0.22 g/g (raw biomass of water hyacinth), which was 76.3% of the theoretical ethanol yield. A maximum ethanol production rate of 0.19 g/(L•h) was obtained after 24 h.

Pilot scale conversion of wheat straw to ethanol via simultaneous saccharification and fermentation

The production of ethanol from wheat straw (WS) by dilute acid pretreatment, bioabatement of fermentation inhibitors by a fungal strain, and simultaneous saccharification and fermentation (SSF) of the bio-abated WS to ethanol using an ethanologenic recombinant bacterium was studied at a pilot scale without sterilization. WS (124.2g/L) was pretreated with dilute H2SO4 in two parallel tube reactors at 160°C. The inhibitors were bio-abated by growing the fungus aerobically. The maximum ethanol produced by SSF of the bio-abated WS by the recombinant Escherichia coli FBR5 at pH 6.0 and 35°C was 36.0g/L in 83h with a productivity of 0.43gL−1h−1. This value corresponds to an ethanol yield of 0.29g/g of WS which is 86% of the theoretical ethanol yield from WS. This is the first report on the production of ethanol by the recombinant bacterium from a lignocellulosic biomass at a pilot scale.

Ethanol production from kelp slag hydrolysates using genetically engineered Escherichia coli KO11

Kelp slag refers to industrial waste produced during sodium alginate extraction from kelp. The chemical components of kelp slag were analyzed in this study. The kelp slag contained large amounts of cellulose (25.88 %) and hemicellulose (12.52 %) with minimal acid-insoluble lignin content, making it an ideal raw material for ethanol fuel production. The saccharification and ethanol transformation of kelp slag by Escherichia coli KO11 were evaluated. When glucose or xylose was used as the fermentation substrate, theoretical ethanol yields of 82.35 % (glucose) and 84.78 % (xylose) were obtained. Xylose was not used until the glucose content was below 1 % when mixed sugars were fermented. Sulfuric acid pretreatment at 121 °C for 1 h was performed before enzymatic hydrolysis. The maximum rate of enzymatic hydrolysis was 93.32 % after dilute sulfuric acid (0.2 M) pretreatment and enzymatic hydrolysis by cellulase (50 °C, pH 4.8, 16 h). Separate hydrolysis and co-fermentation (SHCF), simultaneous saccharification and co-fermentation (SSCF), and non-isothermal simultaneous saccharification and co-fermentation (NSSCF) were also performed in this study. NSSCF (co-fermentation began after enzymatic hydrolysis for 6 h) was the most effective process for kelp slag fermentation where ethanol yield reached 0.45 g g−1.

Metabolic characterization and modeling of fermentation process of an engineered Geobacillus thermoglucosidasius strain for bioethanol production with gas stripping

The recently engineered Geobacillus thermoglucosidasius strain is an industrially potent thermophilic ethanologen. We employ a systematic approach to improve our understanding of the fermentation process using cellobiose as the substrate. Dynamic metabolic flux analysis clearly shows that the fluxes from pyruvate to lactate and formate are both strictly constrained throughout the process and that both the maximum ethanol yield (0.46C/C) and the maximum specific productivity (19.8mmolC (gDCW)−1h−1) occur at late-exponential growth phase. Accordingly, extreme pathway analysis reduces the metabolic network into a macro reaction scheme, on which a dynamic metabolic model is built. The model is validated with experimental data, parameters are identified with confidence intervals, and global sensitivity analysis (Sobol׳ method) is performed. Model-based optimization predicts that ethanol productivity could increase from 34.2 in a typical batch process to 55.3mmolL−1h−1 in an optimum fed-batch process with higher ethanol yield. Furthermore, the optimal operating regime was identified to be continuous fermentation process with gas stripping, in which a high ethanol productivity of 113mmolL−1h−1, i.e., 26.8mmolC (gDCW)−1h−1, corresponding to 90.2% of the maximum theoretical ethanol yield could be achieved.

Optimisation of alkaline reagent based chemical pre-treatment of Brewers spent grains for bioethanol production

The pre-treatment step of lignocellulosic ethanol production is recognised as the most energy intensive part of the overall process. Key objectives are thus that pre-treatments should operate effectively at low to moderate temperatures and at high percentage solids, in order to minimise energy inputs.Chemical pre-treatment of BSG using alkaline reagents, at moderate process temperatures, was optimised in terms of sugar release following enzymatic saccharification of the pre-treated residues. An excess of Celluclast® cellulase enzyme was used to compare various pre-treatments in terms of the % of theoretical sugars that could be liberated. Using alkaline peroxide (5% H2O2/NaOH at pH 11) up to 87% of the theoretical glucose yield (based on composition of the pre-treated residue) was attained following pre-treatment of BSG at 25% (w/v) solids loading for 5h at 100°C. Pre-treatment using 5% NaOH at 25% (w/v) solids loading for 12h at 50°C liberated 92% of theoretical glucose This pre-treatment remained effective with process times as short as 2h (ca. 70% of theoretical glucose). For NaOH pre-treatments the extent of lignin removal from pre-treated residues broadly correlated with the efficacy of the pre-treatment in terms of final saccharification yields. However, for alkaline peroxide pre-treatments no such correlation was observed.Saccharified BSG was prepared following treatment with the optimised NaOH or alkaline peroxide pre-treatments and the resultant hydrolysates fermented with Saccharomyces cerevisiae. Fermentation performance was superior for the NaOH pre-treated samples relative to alkaline peroxide generated feedstocks with shorter lag phases and faster attenuation rates. Mean ethanol concentrations of ca. 17.3g/L and 8.4g/L were achieved for the NaOH and alkaline peroxide fermentations respectively which corresponded to 81% and 43% of theoretical ethanol yields.

Comparison of SHF and SSF of wet exploded corn stover and loblolly pine using in-house enzymes produced from T. reesei RUT C30 and A. saccharolyticus.

The aim of the present study was to compare bioethanol production from wet exploded corn stover (WECS) and loblolly pine (WELP) hydrolyzed with in-house and commercial enzymes and fermented separately (SHF) and simultaneously (SSF). In-house enzymes produced from Trichoderma reesei, RUT-C30 and a novel fungal strain, Aspergillus saccharolyticus were loaded as 5 and 15 FPU/g glucan and supplemented with 10 and 30 CBU/g glucan, respectively. For hydrolysis and fermentation, slurries of WECS and WELP at 5 and 10% (w/w) solids loading (SL) were utilized. Saccharomyces cerevisae was used for ethanol fermentation at 33°C. Maximally, 15.6 g/L and 13.4 g/L (corresponding to theoretical ethanol yield of 76% and 67%, respectively) were achieved in SSF process from WECS and WELP, respectively at 5% SL and 15 FPU/g glucan loading of in-house enzymes. Ethanol concentrations in all cases were higher for SSF compared to SHF under same conditions. A cross comparison of SSF with commercial enzymes (Celluclast 1.5 L + Novozym 188) showed highest ethanol concentration of 17.3 g/L and 15.4 g/L (corresponding to theoretical ethanol yield of 84% and 77%, respectively) from WECS and WELP, respectively at 5% SL and 15 FPU/g glucan. These findings demonstrated that in-house enzymes were comparable to commercial enzymes as these fungi produced other lignocellulolytic enzymes beyond cellulase and hence enhanced the overall enzyme activity.

Evaluation of ethanol fermentation parameters for bioethanol production from sugar beet pulp and juice

The aim of this study was to investigate the efficient utilization of sugar beet pulp, as well as raw, concentrated raw and thick sugar beet juice, for bioethanol production. Different fermentation conditions were examined. The influence of raw material pre-treatment (pasteurization or sterilization), type of batch culture process (stationary or shaken) as well as the type of Saccharomyces cerevisiae yeast preparation on the yields of the process were studied. Moreover, the fermentation process effectiveness was examined in connection with the quality of the obtained distillates. Sterilization, stationary batch culture and Safdistil C-70 yeast preparation were identified as the most profitable factors for sugar beet pulp fermentation, providing a high fermentation efficiency and ethanol yield (87.7% of theoretical ethanol yield). Concentrated raw beet juice resulted in a value of 94.2% of theoretical yield, and thick juice a 92.6% yield. The results suggest that bioethanol production from sugar beet pulp and sugar beet juice has promise as an alternative fuel. The raw spirits obtained from the sugar beet juice were characterized as having the lowest quantity of volatile by-products. Copyright © 2014 The Institute of Brewing & Distilling

Biomass Production of Switchgrass in Saline-Alkali Land

A field experiment was carried out to study the growth characteristics of switchgrass cultivated in saline-alkali lands. The results show that: the survival rate, plant height, tiller numbers per plant and biomass yield of switchgrass significantly reduce with the increasing magnitude of salinity-alkalinity stresses. Switchgrass can grow in saline-alkali environments, the survival rate is more than 85%, and the overwintering rate is more than 95%. Switchgrass plants grow better in mild and moderate saline-alkali lands, and it achieve the highest biomass yield and theoretical ethanol yield of 14.3 t/ha and 5958.8 l/ha respectively, in the third year. With saline-alkali stress, ash and lignin content of switchgrass biomass increase, calorific value, cellulose and hemicelluloses content of switchgrass biomass decrease, and fuel quality of switchgrass biomass reduce to a certain extent.

Expression and evaluation of enzymes required for the hydrolysis of galactomannan.

The cost-effective production of bioethanol from lignocellulose requires the complete conversion of plant biomass, which contains up to 30 % mannan. To ensure utilisation of galactomannan during consolidated bioprocessing, heterologous production of mannan-degrading enzymes in fungal hosts was explored. The Aspergillus aculeatus endo-β-mannanase (Man1) and Talaromyces emersonii α-galactosidase (Agal) genes were expressed in Saccharomyces cerevisiae Y294, and the Aspergillus niger β-mannosidase (cMndA) and synthetic Cellvibrio mixtus β-mannosidase (Man5A) genes in A. niger. Maximum enzyme activity for Man1 (374 nkat ml(-1), pH 5.47), Agal (135 nkat ml(-1), pH 2.37), cMndA (12 nkat ml(-1), pH 3.40) and Man5A (8 nkat ml(-1), pH 3.40) was observed between 60 and 70 °C. Co-expression of the Man1 and Agal genes in S. cerevisiae Y294[Agal-Man1] reduced the extracellular activity relative to individual expression of the respective genes. However, the combined action of crude Man1, Agal and Man5A enzyme preparations significantly decreased the viscosity of galactomannan in locust bean gum, confirming hydrolysis thereof. Furthermore, when complemented with exogenous Man5A, S. cerevisiae Y294[Agal-Man1] produced 56 % of the theoretical ethanol yield, corresponding to a 66 % carbohydrate conversion, on 5 g l(-1) mannose and 10 g l(-1) locust bean gum.

Production of Bioethanol from Office Waste via Simultaneous Saccharification Fermentation

Bioethanol is an attractive and sustainable fuel that can be used in the transportation sector. It is recognized as being a good alternative to conventional fossil based fuel as it is biodegradable and emits zero net carbon output into the atmosphere. In this study, bioethanol was produced from office waste by usinga commercial cellulase preparation and Saccharomyces cerevisiae via Simultaneous Saccharification Fermentation (SSF). The office waste feedstocks were loaded at 5.0%, 7.5% and 10.0% (w/v) against two cellulase dosages at 25 and 50 FPU/g paper. The fermentation products and residual sugars were then analyzed via High Performance Liquid Chromatography (HPLC). From the results obtained, the combination of 5.0% feedstock loading with 50 FPU/g paper cellulase produced the highest concentration of ethanol at 96 hr, which was at 67.64% of theoretical ethanol yield (TEY). Whilethe combination of 10.0% feedstock loading with 50 FPU/g paper cellulase produced the lowest concentration of ethanol at 32.69% of TEY. This study has shown that office waste can be converted to bioethanol via SSF, and may assist in reutilization and the waste management of office waste.

Comparisons of five Saccharomyces cerevisiae strains for ethanol production from SPORL-pretreated lodgepole pine.

The performances of five yeast strains under three levels of toxicity were evaluated using hydrolysates from lodgepole pine pretreated by Sulfite Pretreatment to Overcome the Recalcitrance of Lignocelluloses (SPORL). The highest level of toxicity was represented by the whole pretreated biomass slurry, while intermediate toxicity was represented by the hydrolysate with partial loading of pretreatment spent liquor. The zero toxicity was represented using the enzymatic hydrolysate produced from thoroughly washed SPORL lodgepole pine solids. The results indicate that strains D5A and YRH400 can tolerate the whole pretreated biomass slurry to produce 90.1 and 73.5% theoretical ethanol yield. Strains Y1528, YRH403, and FPL450 did not grow in whole hydrolysate cultures and were observed to have lower ethanol productivities than D5A and YRH400 on the hydrolysate with intermediate toxicity. Both YRH400 and YRH403 were genetically engineered for xylose fermentation but were not able to consume xylose efficiently in hydrolysate.

Use of NIRS to predict composition and bioethanol yield from cell wall structural components of sweet sorghum biomass

Sweet sorghum biomass is gaining importance as feedstock for second generation bioethanol production. Consequently, breeding programs are seeking to improve the quality of this feedstock in order to increase the productivity, with the generation of a great number of samples to be analyzed. Thus, this paper developed rapid and low cost methods based on partial least squares (PLS) and near infrared reflectance spectroscopy for determining cellulose, hemicellulose, lignin and theoretical ethanol yield (TEY) in sorghum biomass. The models were built with 957 samples, obtained from more than 100 hybrids and inbred strains, in the ranges of 21.4–49.1% w/w, 18.4–34.8% w/w, 1.8–11.5% w/w and 221–412Lt−1 for cellulose, hemicellulose, lignin and TEY, respectively. These models presented root mean square errors of prediction of 1.5%, 1.7%, 0.8% and 12Lt−1 (and ranges of relative errors of prediction between −5.3 and 6.5%, −9.8 and 12.2%, −28.8 and 37.6%, and −5.6 and 6.1%), respectively. The methods were submitted to a complete multivariate analytical validation in accordance with the Brazilian and international guidelines, and considered accurate, linear, sensitive and unbiased. Finally the stability of these methods was monitored for approximately six months by developing appropriate control charts.

Evaluation of potential ethanol production and nutrients for four varieties of sweet sorghum during maturation

Sweet sorghum was investigated to an alternate feedstock for fuel ethanol production. juices from 4 sorghum varieties (BRS 506, BRS 508, BRS 509, BRS 511 and BRS); all developed by Embrapa (Brazilian Agricultural Research Corporation) Maize and Sorghum) were evaluated for sugar, starch and nutrient contents and theoretical ethanol yields. The levels of nitrogen, phosphorus, calcium, magnesium, starch and sugars (glucose, fructose and sucrose) were measured weekly over a period of 70 days. Fermentations were performed using yeast Saccharomyces cerevisiae. BRS 508, BRS 509 and BRS 511 showed potential to be useful for industrial applications for maturities exceeding 30 days. BRS 511 showed the highest sugar production, with levels higher than 140 g/L during the majority of the experiment and reaching a maximum of 191 g/L. All varieties showed similar behaviors with respect to nutrient content, which was characterized by a decrease in nutrient concentrations over the period analyzed. Juice from BRS 508 was successfully fermented within 8 h with a productivity (9.0 g/L h) and yield (90.5% of theoretical) similar to those observed for sugar cane juice.

Direct ethanol production from dextran industrial waste water by Zymomonas mobilis

The direct production of ethanol from dextran industrial waste water was investigated by using Zymomonas mobilis via batch and semi-continuous fermentation mode. In batch fermentation, pretreated waste water (unsterilized and sterilized), pH value (3.8 and 6.0), and Mg2+ (with and without) was compared with OD600, sugar and ethanol concentration. After 24 h fermentation, sugar in the dextran waste water was almost exhausted, and the amount of ethanol accumulated reached 24.33–29.92 g/l, which is nearly 99% of the theoretical yield of ethanol. Kinetic parameters of Z. mobilis in batch fermentation were also investigated. The raw dextran waste water was also used in semi-continuous fermentation. After 48 h fermentation, the production of ethanol was 28.65 g/l. These results indicated that dextran waste water may be used as a candidate substrate and Z. mobilis could convert the raw material into ethanol directly.

Perennial grasses as lignocellulosic feedstock for second-generation bioethanol production in Mediterranean environment

In this paper the suitability of three perennial, herbaceous, lignocellulosic grasses (Arundo donax, Saccharum spontaneous spp. aegyptiacum and Miscanthus x giganteus) for the production of second-generation bioethanol in semi-arid Mediterranean environment was studied. Crops were established in spring 2002, supplying irrigation and nitrogen fertilization up to 2004/2005 growing season. Subsequently, crops were grown without any agronomic input and harvested annually. Data reported in this paper refers to 2008/2009 and 2009/2010 growing seasons. Aboveground dry matter (DM) yield was higher in Arundo (35.4±2.1 Mg ha–1 in 2009 and 32.2±1.9 Mg ha–1 in 2010 harvest) than in Saccharum (27.3±2.0 and 23.9±1.9 Mg ha–1, respectively) and Miscanthus (19.6±2.8 and 17.2±1.6 Mg ha–1, respectively). Structural polysaccharides of the raw material were higher in Miscanthus (63.4% w/w) followed by Saccharum (61.5% w/w) and Arundo (57.6% w/w). The same trend was identified for the cellulose content (41.0%, 36.8% and 34.6%, respectively). The highest values in the total hemicellulose complex were observed in Saccharum (24.7%), followed by Arundo (23.1%) and Miscanthus (22.4%). The composition of structural polysaccharides leads to a higher theoretical ethanol yield (TEY) from one dry ton of Miscanthus feedstock (kg DM Mg–1), followed by Saccharum and Arundo. On the other hand, the TEY per unit surface (Mg ha–1) was greater in Arundo than in Saccharum and Miscanthus. When compared to other lignocellulosic sources used in the second-generation bioethanol technology, such as agricultural residues, woody species and other herbaceous perennial crops, Arundo, Saccharum and Miscanthus showed a great potential in terms of TEY ha–1. Given the high levels of biomass yield and composition of structural polysaccharides, the three species might be introduced into the Mediterranean cropping systems to supply lignocellulosic biomass for second-generation industrial plants or bio-refineries.