Enhanced ethanol production from enzymatically treated steam‐exploded rice straw using extractive fermentation

Alcohol fermentation of an enzymatic hydrolyzate of exploded rice straw was studied experimentally. Rice straw was treated under variable conditions, such as steam pressure and steaming time. The exploded rice straw was separated into water‐soluble material, methanol‐soluble lignin, Klason lignin, and a mixture of cellulose and a low molecular weight substance. The effects of steam explosion on the characteristics of the exploded rice straw were clarified from the point of view of the amounts of extractive components. Steam explosion was found to be effective for the delignification of rice straw and for increasing its susceptibility to enzyme hydrolysis and alcohol fermentation. The polysaccharides (cellulose and hemicellulose) in the rice straw treated at a steam pressure of 3.5 MPa with a steaming time of 2 min were hydrolyzed almost completely into monosaccharides, (ie glucose and xylose) by a mixture of Trichoderma viride cellulase (Meicelase) and Aspergillus aculeatus cellulase (Acucelase). The enzymatic hydrolyzate of exploded rice straw was converted into ethanol efficiently by Pichia stipitis and the ethanol yield from sugar was about 86%(w/w) of the theoretical value. The ethanol concentration in a membrane bioreactor coupled with a pervaporation system reached 50 gdm^?3 and was about five times higher than that in the culture broth. The energy efficiency (ratio of combustion energy of ethanol produced to energy for steam explosion) reached a maximum value at a pressure of 3.5 MPa for 2 min. © 2001 Society of Chemical Industry     

蒸汽爆破麦草同步糖化发酵转化乙醇的研究

近年来对木质生物资源同步糖化发酵转化乙醇的研究较多,但是,麦草同步糖化发酵转化乙醇的最佳工艺条件还未确定。文中采用正交试验设计的方法,对在混合酶(纤维素酶Celluclast 1.5 1,β-葡萄糖苷酶Novozym 188)与酿酒酵母菌作用下,稀硫酸催化的蒸汽爆破麦草原料同步糖化发酵转化乙醇的工艺条件进行研究,详细讨论了反应温度、底物质量浓度、发酵液pH值、纤维素酶浓度对乙醇质量浓度和得率的影响。结果表明,工艺条件对乙醇质量浓度和得率的影响程度由高到低依次为:底物质量浓度、纤维素酶浓度、发酵液pH值、反应温度。最佳工艺条件为反应温度35℃,底物质量浓度100 g/L,发酵液pH值5.0,纤维素酶浓度30 FPU/g。在此条件下,随着反应时间的延长,乙醇质量浓度持续上升。反应72 h后,乙醇质量浓度和得率分别达到22.7 g/L和65.8%。     

Study of simultaneous saccharification and fermentation for steam exploded wheat straw to ethanol

Although simultaneous saccharification and fermentation (SSF) has been investigated extensively, the optimum condition for SSF of wheat straw has not yet been determined. Dilute sulfuric acid impregnated and steam explosion pretreated wheat straw was used as a substrate for the production of ethanol by SSF through orthogonal experiment design in this study. Cellulase mixture (Celluclast 1.5 l and ?-glucosidase Novozym 188) were adopted in combination with the yeast Saccharomyces cerevisiae AS2.1. The effects of reaction temperature, substrate concentration, initial fermentation liquid pH value and enzyme loading were evaluated and the SSF conditions were optimized. The ranking, from high to low, of influential extent of the SSF affecting factors to ethanol concentration and yield was substrate concentration, enzyme loading, initial fermentation liquid pH value and reaction temperature, respectively. The optimal SSF conditions were: reaction temperature, 35°C; substrate concentration, 100 g·L^-1; initial fermentation liquid pH, 5.0; enzyme loading, 30 FPU·g^-1. Under these conditions, the ethanol concentration increased with reaction time, and after 72 h, ethanol was obtained in 65.8% yield with a concentration of 22.7 g·L^-1.     

Study of simultaneous saccharification and fermentation for steam exploded wheat straw to ethanol

Although simultaneous saccharification and fermentation (SSF) has been investigated extensively, the optimum condition for SSF of wheat straw has not yet been determined. Dilute sulfuric acid impregnated and steam explosion pretreated wheat straw was used as a substrate for the production of ethanol by SSF through orthogonal experiment design in this study. Cellulase mixture (Celluclast 1.5 l and β-glucosidase Novozym 188) were adopted in combination with the yeast Saccharomyces cerevisiae AS2.1. The effects of reaction temperature, substrate concentration, initial fermentation liquid pH value and enzyme loading were evaluated and the SSF conditions were optimized. The ranking, from high to low, of influential extent of the SSF affecting factors to ethanol concentration and yield was substrate concentration, enzyme loading, initial fermentation liquid pH value and reaction temperature, respectively. The optimal SSF conditions were: reaction temperature, 35°C; substrate concentration, 100 g·L⁻¹; initial fermentation liquid pH, 5.0; enzyme loading, 30 FPU·g⁻¹. Under these conditions, the ethanol concentration increased with reaction time, and after 72 h, ethanol was obtained in 65.8% yield with a concentration of 22.7 g·L⁻¹. __________ Translated from Chemical Engineering (China), 2007, 35(12): 42–45 [译自: 化学工程]     

Increase in bioethanol production yield from triticale by simultaneous saccharification and fermentation with application of ultrasound

BACKGROUND: Bioethanol produced from renewable biomass, such as sugar, starch or lignocellulosic materials, is one of the alternative energy resources that is environmentally friendly. Triticale crops have a high yield as well as a high starch content and amylolytic enzyme activity and are therefore considered to be ideal for bioethanol production. RESULTS: This study examined the feasibility of ultrasound pretreatment to enhance the release of fermentable sugars from triticale meal during pretreatment and consequently increase bioethanol yield in the simultaneous saccharification and fermentation (SSF) process by Saccharomyces cerevisiae yeast. Ultrasonic pretreatment effectively increased the glucose and maltose content after liquefaction by 15.71% and 52.57%, respectively, compared with the untreated control sample under determined optimal conditions of sonication (5 min, 60 °C). The ultrasound pretreatment consequently improved bioethanol production during SSF processing since the bioethanol content was increased by 10.89%. CONCLUSION: Taking into consideration significant process parameters obtained in the SSF process of triticale meal with ultrasound pretreatment at 60 °C, the process time may be reduced from 72 to 48 h. At that point of the SSF, maximum bioethanol content of 9.55% (w/v), bioethanol yield of 0.43 g g^?1 of triticale starch, and percentage of the theoretical bioethanol yield of 84.56% were achieved. Copyright © 2011 Society of Chemical Industry     

Simultaneous saccharification and fermentation of sludge‐containing cassava mash for batch and repeated batch production of bioethanol by Saccharomyces cerevisiae CHFY0321

BACKGROUND: The aim of this study was to examine the repeated batch production of bioethanol from sludge‐containing cassava mash as starchy substrate by flocculating yeast to improve volumetric bioethanol productivity and to simplify the process of a pre‐culture system. RESULTS: For the repeated batch production of bioethanol using cassava mash, the optimal recycling volume ratio was found to be 5%. The repeated batch fermentation was completed within 36 h, while the batch fermentation was completed after 42 h. Volumetric productivity, final ethanol concentration, and ethanol yield were attained to 2.15 g L^?1 h^?1, 83.64 g L^?1, and 85.15%, respectively. Although cell accumulation in the repeated batch process is difficult due to the cassava mash, the repeated batch process using Saccharomyces cerevisiae CHFY0321 could exhibited 10‐fold higher initial viable cell number (1.7 × 10⁷ CFU mL^?1) than that of the batch process. CONCLUSION: The liquefied cassava powder was directly used for the repeated batch process without removal of sludge. Repeated batch bioethanol production by simultaneous saccharification and fermentation using self‐flocculating yeast could reduce process costs and accelerate commercial applications. This result was probably due in part to the effect of the initial viable cell density. Copyright © 2008 Society of Chemical Industry     

Optimization of the enzymatic hydrolysis conditions of steam‐exploded wheat straw for maximum glucose and xylose recovery

BACKGROUND: The enzymatic hydrolysis of steam‐exploded wheat straw using commercial enzyme complexes has been studied. A cellulase enzyme complex (Accellerase 1500), along with specific xylanase complements (Accellerase‐XC and Accellerase‐XY) provided by Genencor, have been used to enhance glucose and xylose recovery. A systematic study with response surface methodology (RSM) was used to check the effect of the operating conditions: pH (4–5), temperature (50–60 °C) and enzyme/substrate ratio (0.1–0.5 mL g_cellulose^?1) on the enzymatic hydrolysis with Acellerase 1500 to maximize the sugar yield. Xylanases were used as complements to increase the release of xylose. RESULT: Statistical results from ANOVA analysis demonstrated that the enzymatic hydrolysis was clearly improved by temperature and enzyme/substrate ratio. The optimum conditions for higher glucose and xylose releases were obtained with the higher enzyme dosage ratio (0.5 mL g^?1_cellulose), 50 °C and pH 4. CONCLUSION: Model validation at optimum operating conditions showed good agreement between the experimental results and the predicted responses for a confidence level of 95%. The use of the xylanase complements, Accellerase‐XY (accessory xylanase enzyme complex) and Accellerase‐XC (accessory xylanase/cellulase enzyme complex), increases the conversion of hemicellulose. Accellerase‐XC supplementation was more effective, obtaining an increase in yields of glucose and xylose of 11.8% and 23.6%, respectively, using a dosage of 0.125 mL g^?1_cellulose. © 2012 Society of Chemical Industry     

Comparison of bioethanol production of simultaneous saccharification & fermentation and separation hydrolysis & fermentation from cellulose-rich barley straw

Cellulose rich barley straw, which has a glucan content of 62.5%, followed by dilute acid pretreatment, was converted to bioethanol by simultaneous saccharification and fermentation (SSF). The optimum fractionation conditions for barley straw were an acid concentration of 1% (w/v), a reaction temperature of 158 °C and a reaction time of 15 min. The maximum saccharification of glucan in the fractionated barley straw was 70.8% in 72 h at 60 FPU/gglucan, while the maximum digestibility of the untreated straw was only 18.9%. With 6% content WIS (water insoluble solid) for the fractionated barley straw, 70.5 and 83.2% of the saccharification yield were in SHF and SSF (representing with glucose equivalent), respectively, and a final ethanol concentration of 18.46 g/L was obtained under the optimized SSF conditions: 34 °C with 15 FPU/g-glucan enzyme loading and 1 g dry yeast cells/L. The results demonstrate that the SSF process is more effective than SHF for bioethanol production by around 18%.     

Stabilized production of highly concentrated bioethanol from fermentation broths by Zymomonas mobilis by pervaporation using silicone rubber‐coated silicalite membranes

Since pervaporation performance of ethanol‐permselective silicalite membrane, which is an aluminum‐free hydrophobic zeolite, in the separation of fermentation broths by yeast are negatively affected by succinic acid, the potential of pervaporation using silicone rubber‐coated silicalite membranes of ethanol fermentation broths, not containing succinic acid, by Zymomonas mobilis was investigated for the reliable production of concentrated bioethanol. In the separation of fermentation broths, the pervaporation performance was influenced by nutrients used for the preparation of fermentation broths. In the separation of a broth prepared with yeast extract, pervaporation performance was greatly compromised by accumulation of a substance(s) having an ultraviolet absorption maximum at approximately 260 nm not only in total flux, but also in permeate ethanol concentration compared to the separation of binary ethanol/water mixtures. When supplying a prepared broth with corn steep liquor without the accumulation of a substance(s) having an ultraviolet absorption maximum at approximately 260 nm, the permeate ethanol concentration did not decrease. Treating the prepared broth with activated carbon was effective in restraining the decrease in total flux. Pervaporation performance is also deteriorated by the adsorption of lactic acid contained in corn steep liquor onto the silicalite crystals. In the separation of ternary mixtures of ethanol/water/lactic acid, accomplished by adjusting the ternary mixtures to pH > 5, more than 90% of the permeation flux in the separation of binary ethanol/water mixtures was obtained, and the permeate ethanol concentration was comparable to that obtained in the separation of binary mixtures. For stably performing pervaporation, it is important to prepare ethanol fermentation broths by Zymomonas mobilis in which lactic acid concentration is as low as possible. Copyright © 2007 Society of Chemical Industry     

Simultaneous saccharification and fermentation of sweet potato powder for the production of ethanol under conditions of very high gravity

Due to its merits of drought tolerance and high yield, sweet potatoes are widely considered as a potential alterative feedstock for bioethanol production. Very high gravity (VHG) technology is an effective strategy for improving the efficiency of ethanol fermentation from starch materials. However, this technology has rarely been applied to sweet potatoes because of the high viscosity of their liquid mash. To overcome this problem, cellulase was added to reduce the high viscosity, and the optimal dosage and treatment time were 8 U/g (sweet potato powder) and 1 h, respectively. After pretreatment by cellulase, the viscosity of the VHG sweet potato mash (containing 284.2 g/L of carbohydrates) was reduced by 81%. After liquefaction and simultaneous saccharification and fermentation (SSF), the final ethanol concentration reached 15.5% (v/v), and the total sugar conversion and ethanol yields were 96.5% and 87.8%, respectively.     

Processing of ethanol fermentation broths by Candida krusei to separate bioethanol by pervaporation using silicone rubber‐coated silicalite membranes

BACKGROUND: Pervaporation employing ethanol‐permselective silicalite membranes as an alternative to distillation is a promising approach for refining low‐concentration bioethanol solutions. However, to make the separation process practicable, it is extremely important to avoid the problems caused by the adsorption of succinate on the membrane during the separation process. In this work, the pervaporation of an ethanol fermentation broth without succinate was investigated, as well as the influence of several fermentation broth nutrient components. RESULTS: Candida krusei IA‐1 produces an extremely low level of succinate. The decrease in permeate ethanol concentration through a silicone rubber‐coated silicalite membrane during the separation of low‐succinate C. krusei IA‐1 fermentation broth was significantly improved when compared with that obtained using Saccharomyces cerevisiae broth. By treating the fermentation broth with activated carbon, bioethanol was concentrated as efficiently as with binary mixtures of ethanol/water. The total flux was improved upto 56% of that obtained from the separation of binary mixtures, compared with 43% before the addition of activated carbon. Nutrients such as peptone, yeast extract and corn steep liquor had a negative effect on pervaporation, but this response was distinct from that caused by succinate. CONCLUSION: For consistent separation of bioethanol from C. krusei IA‐1 fermentation broth by pervaporation, it is useful to treat the low nutrient broth with activated carbon. To further improve pervaporation performance, it will be necessary to suppress the accumulation of glycerol. Copyright © 2009 Society of Chemical Industry     

Optimal engineered algae composition for the integrated simultaneous production of bioethanol and biodiesel

The optimization of the composition of the algae for the simultaneous production of bioethanol and biodiesel is presented. We consider two alternative technologies for the biodiesel synthesis from algae oil, enzymatic or homogeneous alkali catalyzed that are coupled with bioethanol production from algae starch. In order to determine the optimal operating conditions, we not only couple the technologies, but simultaneously optimize the production of both biofuels and heat integrate them while optimizing the water consumption. Multi‐effect distillation is included to reduce the energy and cooling water consumption for ethanol dehydration. In both cases, the optimal algae composition results in 60% oil, 30% starch, and 10% protein. The best alternative for the production of biofuels corresponds to a production price of 0.35 $/gal, using enzymes, with energy and water consumption values (4.00 MJ/gal and 0.59 gal/gal). © 2013 American Institute of Chemical Engineers AIChE J, 59: 2872–2883, 2013     

Simultaneous saccharification and fermentation of wheat bran flour into ethanol using coculture of amylotic Aspergillus niger and thermotolerant Kluyveromyces marxianus

Studies on simultaneous saccharification and fermentation (SSF) of wheat bran flour, a grain milling residue as the substrate using coculture method were carried out with strains of starch digesting Aspergillus niger and nonstarch digesting and sugar fermenting Kluyveromyces marxianus in batch fermentation. Experiments based on central composite design (CCD) were conducted to maximize the glucose yield and to study the effects of substrate concentration, pH, temperature, and enzyme concentration on percentage conversion of wheat bran flour starch to glucose by treatment with fungal α-amylase and the above parameters were optimized using response surface methodology (RSM). The optimum values of substrate concentration, pH, temperature, and enzyme concentration were found to be 200 g/L, 5.5, 65°C and 7.5 IU, respectively, in the starch saccharification step. The effects of pH, temperature and substrate concentration on ethanol concentration, biomass and reducing sugar concentration were also investigated. The optimum temperature and pH were found to be 30°C and 5.5, respectively. The wheat bran flour solution equivalent to 6% (w/V) initial starch concentration gave the highest ethanol concentration of 23.1 g/L after 48 h of fermentation at optimum conditions of pH and temperature. The growth kinetics was modeled using Monod model and Logistic model and product formation kinetics using Leudeking-Piret model. Simultaneous saccharificiation and fermentation of liquefied wheat bran starch to bioethanol was studied using coculture of amylolytic fungus A. niger and nonamylolytic sugar fermenting K. marxianus.     

Minimization of the nonrenewable energy consumption in bioethanol production processes using a solar‐assisted steam generation system

The multiobjective optimization of a corn‐based bioethanol plant coupled with a solar‐assisted steam generation system with heat storage is described. Our approach relies on the combined use of process simulation, rigorous optimization tools, and economic and energetic plant analysis. The design task is posed as a bicriteria nonlinear programming problem that considers the simultaneous optimization of the plant profitability and the energy consumption. The capabilities of the proposed methodology are illustrated through a 120,000,000 kg/year corn‐based bioethanol plant considering weather data of Tarragona (Spain). © 2013 American Institute of Chemical Engineers AIChE J 60: 500–506, 2014     

Preparation of chitosan‐coated magnetite nanoparticles and application for immobilization of laccase

In this study, immobilization of laccase (L) enzyme on magnetite (Fe₃O₄) nanoparticles was achieved, so that the immobilized enzyme could be used repeatedly. For this purpose, Fe₃O₄ nanoparticles were coated and functionalized with chitosan (CS) and laccase from Trametes versicolor was immobilized onto chitosan‐coated magnetic nanoparticles (Fe₃O₄‐CS) by adsorption or covalent binding after activating the hydroxyl groups of chitosan with carbodiimide (EDAC) or cyanuric chloride (CC). For chitosan‐coated magnetic nanoparticles, the thickness of CS layer was estimated as 1.0–4.8 nm by TEM, isoelectric point was detected as 6.86 by zeta (ζ)‐potential measurements, and the saturation magnetization was determined as 25.2 emu g^?1 by VSM, indicating that these nanoparticles were almost superparamagnetic. For free laccase and immobilized laccase systems, the optimum pH, temperature, and kinetic parameters were investigated; and the change of the activity against repeated use of the immobilized systems were examined. The results indicated that all immobilized systems retained more than 71% of their initial activity at the end of 30 batch uses. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Applicability of sub- and supercritical water hydrolysis of woody biomass to produce monomeric sugars for cellulosic bioethanol fermentation

In this study two woody biomasses, poplar and pitch pine wood, were treated with sub- and supercritical water (SCW) at temperature of 325–425 °C, at pressure of 220 ± 10 atm and residence time of 60 s, respectively, to develop a time saving and efficient conversion process for the production of fermentable sugars from woody biomasses using supercritical water system. Cellulose/hemicellulose was easily hydrolyzed during SCW treatment into monomeric sugars with the total yield of 7.3% and 8.2% based on the oven dried weight of poplar and pitch pine, respectively. Total yield of the monomeric sugars was increased about threefolds to 23.0% and 25.1% in the presence of 0.05% of hydrochloric acid. Model experiment confirmed that glucose and xylose were readily converted into low molecular weight compounds during SCW hydrolysis. According to GC/MS analysis main compounds converted from glucose and xylose by SCW were identified to 5-hydroxymethyl furfural and 4-oxo-5-methoxy-2-penten-5-olide, respectively.