Refining bioethanol from stalk juice of sweet sorghum by immobilized yeast fermentation

The relationship between total soluble sugar content and Brix in stalk juice of sweet sorghum was determined through one-dimensional linear regression. Meanwhile, bioethanol fermentation experiments were conducted in shaking flasks and 10 l fluidized bed bioreactor with stalk juice of Yuantian No. 1 sweet sorghum cultivar when immobilized yeast was applied. The experimental results in the shaking flasks showed that the order of influence on improving ethanol yield was (NH₄)₂SO₄>MgSO₄>K₂HPO₄, and the optimum inorganic salts supplement dose was determined as follows: K₂HPO₄ 0%, (NH₄)₂SO₄ 0.2%, MgSO₄ 0.05%. When the optimum inorganic salts supplement dose was used in fermentation in 10 l fluidized bed reactor, the fermentation time and ethanol content were 5 h and 6.2% (v/v), respectively, and ethanol yield was 91.61%, which was increased by 9.73% than blank. In addition, the results showed that the fermentation time was about 6–8 times shorter in fluidized bed bioreactor with immobilized yeast than that of conventional fermentation technology. As a result, it can be concluded that the determined optimum inorganic salts supplement dose could be used as a guide for commercial ethanol production. The fluidized bed bioreactor with immobilized yeast technology has a great potential for ethanol fermentation of stalk juice of sweet sorghum.     

Optimization of biohydrogen production from sweet sorghum syrup using statistical methods

This study employed statistically based experimental designs to optimize fermentation conditions for hydrogen production from sweet sorghum syrup by anaerobic mixed cultures. Initial screening of important factors influencing hydrogen production, i.e., total sugar, initial pH, nutrient solution, iron (II) sulphate (FeSO₄), peptone and sodium bicarbonate was conducted by the Plackett–Burman method. Results indicated that only FeSO₄ had statistically significant (P ≤ 0.005) influences on specific hydrogen production (P_s) while total sugar and initial pH had an interdependent effect on P_s. Optimal conditions for the maximal P_s were 25 g/L total sugar, 4.75 initial pH and 1.45 g/L FeSO₄ in which P_s of 6897 mL H₂/L was estimated. Estimated optimum conditions revealed only 0.04% difference from the actual P_s of 6864 mL H₂/L which suggested that the optimal conditions obtained can be practically applied to produce hydrogen from sweet sorghum syrup with the least error.     

Optimization of ethanol production from high dry matter liquefied dry sweet sorghum stalks

The ability of sweet sorghum to be utilized as feedstock for ethanol production at high initial dry material concentration was investigated. Sweet sorghum, after being dried, was liquefacted employing commercial cellulase solution Celluclast^® 1.5L, in order submerged fermentation to be permitted under high-solids concentrations. The presence of a separate enzymatic liquefaction step at 350 kg m⁻³ initial DM enhanced both ethanol production and productivity by 29.76% and 250%, respectively. Response surface methodology, based on the central composite design was applied to explore the combined effect of liquefaction duration and enzyme loading in order liquefaction conditions to be optimized. When the optimum conditions were tested using an enzyme load of 8.32 FPU g⁻¹ of dry material for 8.6 h at 50 °C, high productivity (3.0 kg m⁻³ h⁻¹) and final ethanol production (62.5 kg m⁻³) were achieved.     

Optimization of ethanol production from sweet sorghum (Sorghum bicolor) juice using response surface methodology

Sweet sorghum juice was fermented into ethanol using Saccharomyces cerevisiae (ATCC 24858). Factorial experimental design, regression analysis and response surface method were used to analyze the effects of the process parameters including juice solid concentration from 6.5 to 26% (by mass), yeast load from 0.5 g L⁻¹ to 2 g L⁻¹ and fermentation temperature from 30 °C to 40 °C on the ethanol yield, final ethanol concentration and fermentation kinetics. The fermentation temperature, which had no significant effect on the ethanol yield and final ethanol concentration, could be set at 35 °C to achieve the maximum fermentation rate. The yeast load, which had no significant effect on the final ethanol concentration and fermentation rate, could be set at 1 g L⁻¹ to achieve the maximum ethanol yield. The juice solid concentration had significant inverse effects on the ethanol yield and final ethanol concentration but a slight effect on the fermentation rate. The raw juice at a solid concentration of 13% (by mass) could be directly used during fermentation. At the fermentation temperature of 35 °C, yeast solid concentration of 1 g L⁻¹ and juice solid concentration of 13%, the predicted ethanol yield was 101.1% and the predicted final ethanol concentration was 49.48 g L⁻¹ after 72 h fermentation. Under this fermentation condition, the modified Gompertz's equation could be used to predict the fermentation kinetics. The predicted maximum ethanol generation rate was 2.37 g L⁻¹ h⁻¹.     

Lipid production from sweet sorghum bagasse through yeast fermentation

Cryptococcus curvatus has great potential in fermenting unconditioned hydrolysates of sweet sorghum bagasse. With hydrolysates obtained by enzymatic hydrolysis of the solid pretreated by microwave with lime, the maximal yeast cell dry weight and lipid content were 10.83 g/l and 73.26%, respectively. For hydrolysates obtained in the same way but without lime, these two parameters were 15.50 g/l and 63.98%, respectively. During yeast fermentation, glucose and xylose were consumed simultaneously while cellobiose was released from the residual bagasse. The presence of lime, on one hand, made cellulose more accessible to enzymes as evidenced by higher total reducing sugar release compared to that without during enzymatic hydrolysis step; on the other hand, it caused the degradation of sugars to non-sugar chemicals during pretreatment step. As a result, higher lipid yield of 0.11 g/g bagasse or 0.65 ton/hectare of land was achieved from the pathway of microwave pretreatment and enzymatic hydrolysis while 0.09 g/g bagasse or 0.51 ton/hectare of land was attained from the process of lime-assisted microwave pretreatment followed by the same enzymatic saccharification.     

Optimization of media conditions for the production of ethanol from sweet sorghum juice by immobilized Saccharomyces cerevisiae

In order to obtain high ethanol yield and fermentation rate, response surface methodology (RSM) was employed to study the effect of culture medium on the ethanol productivity from stalk juice of sweet sorghum by immobilized yeast. A 2³ central composite design (CCD) was chosen to explain the combined effects of the medium constituents, viz. nitrogen (adjusted by adding (NH₄)₂SO₄), phosphorus (adjusted by adding KH₂PO₄), and pH. A mathematical correlation about the influence of the nitrogen, phosphorus, and pH on the ethanol productivity was established. It predicted that the maximum ethanol production rate (119.12 g/l h) was observed for a medium consisting of 0.77 g/l phosphorus, 2.15 g/l nitrogen, and pH = 6.39. Under this condition, the ethanol fermentation rate was 122.85 g/l h.     

甜高粱茎秆汁液制取酒精的试验研究

生物酒精越来越受到世界各国的广泛重视,在众多的生物酒精原料中,甜高粱是很有发展前途的一种.本试验以甜高粱茎秆汁液为发酵原料,采用近年来正在研究和开发的固定化酵母技术,并结合国内外试验正采用的添加豆饼粉工艺,在流化床生物反应器上进行了试验研究.     

Influence of pH on fermentative hydrogen production from sweet sorghum extract

The present study focused on the influence of pH on the fermentative hydrogen production from the sugars of sweet sorghum extract, in a continuous stirred tank bioreactor. The reactor was operated at a Hydraulic Retention Time of 12 h and a pH range of 3.5–6.5. The maximum hydrogen production rate and yield were obtained at pH 5.3 and were 1752 ± 54 mL H₂/d or 3.50 ± 0.07 L H₂/L reactor/d and 0.93 ± 0.03 mol H₂/mol glucose consumed or 10.51 L H₂/kg sweet sorghum, respectively. The main metabolic product at this pH value was butyric acid. The hydrogen productivity and yield were still at high levels for the pH range of 5.3–4.7, suggesting a pH value of 4.7 as optimum for hydrogen production from an economical point of view, since the energy demand for chemicals is lower at this pH. At this pH range, the dominant fermentation product was butyric acid but when the pH culture sharply decreased to 3.5, hydrogen evolution ceased and the dominant metabolic products were lactic acid and ethanol.     

Fuel ethanol production from sweet sorghum bagasse using microwave irradiation

Sweet sorghum is a hardy crop that can be grown on marginal land and can provide both food and energy in an integrated food and energy system. Lignocellulose rich sweet sorghum bagasse (solid left over after starch and juice extraction) can be converted to bioethanol using a variety of technologies. The largest barrier to commercial production of fuel ethanol from lignocellulosic material remains the high processing costs associated with enzymatic hydrolysis and the use of acids and bases in the pretreatment step. In this paper, sweet sorghum bagasse was pretreated and hydrolysed in a single step using microwave irradiation. A total sugar yield of 820 g kg⁻¹ was obtained in a 50 g kg⁻¹ sulphuric acid solution in water, with a power input of 43.2 kJ g⁻¹ of dry biomass (i.e. 20 min at 180 W power setting). An ethanol yield based on total sugar of 480 g kg⁻¹ was obtained after 24 h of fermentation using a mixed culture of organisms. These results show the potential for producing as much as 0.252 m³ tonne⁻¹ or 33 m³ ha⁻¹ ethanol using only the lignocellulose part of the stalks, which is high enough to make the process economically attractive.     

Batch-based enzymatic saccharification of sweet sorghum bagasse

To improve enzymatic digestibility and sugar concentration, sweet sorghum bagasse was pretreated with alkali and liquid hot water, and then subjected to fed-batch enzymatic hydrolysis. Scanning electron microscopy assay suggested that different pretreatment methods resulted in different composition and structure of residues; these changes had a significant influence on cellulose hydrolysis. Fresh substrate was pretreated and then added at different amounts during the first 48 h to yield a final dry matter content of 30% (w/v). For liquid hot water pretreatment, a maximal glucose concentration of 95.71 g/L, corresponding to 52.85% xylan removal, was obtained with the sweet sorghum bagasse pretreated at 184°C for 18 min. NaOH soaking at ambient conditions removed lignin up to 60%, and the subsequent hydrolysis with cellulase loading of less than 10 FPU/g DM, and substrate supplementation every few hours yield the high glucose and xylose concentrations of 114.89L and 29.93 g/L, respectively after 144 h.     

Net energy analysis of bioethanol production system from high-yield rice plant in Japan

This study analyzes the energy balance of a bioethanol production system from high-yield rice plant in Japan. Two systems are considered in which rice is converted to ethanol: one in which cellulose feedstocks, straw and husk, are used for cogeneration (scenario 1), and the other in which they are converted to ethanol, and byproducts such as lignin and unreacted holocellulose are used for cogeneration (scenario 2). Energy input in the agricultural process including transportation is estimated to be 52.3 GJ/ha from an Input Output Table. The heating values of produced rice and cellulose feedstocks are 120.7 GJ/ha and 162.3 GJ/ha, respectively. The net energy balance (NEB) of scenario 1 is 129.2 GJ/ha, which produces 3.6 kL/ha of ethanol and 9420 kWh/ha of external electricity. On the other hand, NEB of scenario 1 is 11.7 GJ/ha, which produces 7.1 kL/ha of ethanol. Both NEBs are positive, but NEB of scenario 2 is much higher than that of scenario 1. An acid hydrolysis technology of cellulosic biomass applied to scenario 2 needs a large amount of heat energy for sulfuric acid recovery. If an enzyme hydrolysis of cellulosic biomass is developed, there is a possibility of improving NEB of scenario 2.     

能源作物甜高粱及其可供应性研究

甜高粱是一种具有优良特性的能源作物，在我国利用甜高粱生产燃料酒精有着广阔的发展前景。文章在详细介绍了甜高粱生物学特性的基础上，对我国甜高粱新品种的研究和开发现状进行了汇总分析，对今后我国发展能源作物甜高粱的土地可供应性和生产燃料酒精的潜力进行了深入研究。     

Material balance studies for the conversion of sorghum stover to bioethanol

The conversion of lignocellulosic biomass to ethanol involves three major unit operations such as pretreatment, hydrolysis and fermentation. Each unit operation involves processing of biomass with changes in its structure, and release of fermentable and other sugars and lignin degrading compounds. The evaluation of biomass conversion processes through material balance is fundamentally crucial in its commercialization. This gives an idea about the transfer of biomass from one phase to another and hence eventually of the efficiency of the total process. In the present study, material balance has been evaluated in each unit operations for sorghum biomass to ethanol conversion. An account of carbohydrates in the native as well as pretreated sorghum biomass, the release of fermentable sugars and the conversion of sugars to ethanol was maintained and analysed. Ethanol yield of 91.94 g per kg sorghum was achieved without any detoxification and washing of pretreated biomass after mild acid pretreatment followed by enzymatic hydrolysis and fermentation.     

Effect of substrate concentration on fermentative hydrogen production from sweet sorghum extract

The aim of the present study was to assess the influence of substrate concentration on the fermentative hydrogen production from sweet sorghum extract, in a continuous stirred tank bioreactor. The reactor was operated at a Hydraulic Retention Time (HRT) of 12 h and carbohydrate concentrations ranging from 9.89 to 20.99 g/L, in glucose equivalents. The maximum hydrogen production rate and yield were obtained at the concentration of 17.50 g carbohydrates/L and were 2.93 ± 0.09 L H₂/L reactor/d and 0.74 ± 0.02 mol H₂/mol glucose consumed, corresponding to 8.81 ± 0.02 L H₂/kg sweet sorghum, respectively. The main metabolic product at all steady states was butyric acid, while ethanol production was high at high substrate concentrations. The experiments showed that hydrogen productivity depends significantly on the initial carbohydrate concentration, which also influences the distribution of the metabolic products.     

Study on genotypic variation for ethanol production from sweet sorghum juice

Sugarcane molasses is the main source for ethanol production in India. Sweet sorghum with its juicy stem containing sugars equivalent to that of sugarcane is a very good alternative for bio-ethanol production to meet the energy needs of the country. Sweet sorghum is drought resistant, water logging resistant and saline–alkaline tolerant. Growing sweet sorghum for ethanol production is relatively easy and economical and ethanol produced from sweet sorghum is eco-friendly. In view of this, it is important to identify superior genotypes for ethanol production in terms of percent juice brix, juice extractability, total fermentable sugars, ethanol yield and fermentation efficiency. This paper presents the study on the variability observed for the production of ethanol by various sweet sorghum genotypes in a laboratory fermentor. Five Sweet Sorghum (Sorghum bicolor L. Moench) genotypes were evaluated for ethanol production from stalk juice (Keller, SSV 84, Wray, NSSH 104 and BJ 248). Sweet sorghum juice differs from cane juice mainly in its higher content of starch and aconitic acid. Data were collected for biomass yield; stalk sugar yield and ethanol production in five genotypes. Maximum ethanol production of 9.0%w/v ethanol was obtained with Keller variety (20% sugar concentration was used), and decreased for other genotypes. A distiller's strain of Saccharomyces cerevisiae (gifted by Seagram Distilleries Ltd.) was employed for fermentation. The fermentation efficiency (FE) was 94.7% for this strain. High biomass of yeast was obtained with BJ 248 variety. When the similar experiments were conducted with unsterile sweet sorghum juice (15% sugar concentration) 6.47%w/v ethanol was produced.     

Isoconversional kinetic analysis of sweet sorghum bagasse pyrolysis by modified logistic mixture model

In order to overcome the noise problem when analyzing the experimental thermogravimetric analysis data and obtain the temperature values at different heating rates for various conversions, a modified logistic mixture model, the combination of two modified logistic functions and a constant, has been presented for fitting all thermogravimetric analysis curves at different heating rates. The thermogravimetric analysis curves of sweet sorghum bagasse pyrolysis at three heating rates of 15, 25 and 35 K min^?1 were analyzed. The modified logistic mixture model and logistic mixture model were used for fitting the experimental thermogravimetric analysis curves at all heating rates. The results have shown that the modified logistic mixture model fitted the experimental data better than the logistic mixture model. Making use of the data calculated by the modified logistic mixture model, the effective activation energy values as a function of conversion were obtained by means of the Friedman isoconversional method. The effective activation energies varied from 150 to 320 kJ mol^?1 when the conversion ranged from 0.05 to 0.85, which indicated that the pyrolysis of sweet sorghum bagasse was a complex process.     

甜高粱秸秆燃料乙醇产业化问题与对策的探讨

甜高粱具有极高的光合速率,有"高能植物"之称,其单位种植面积的乙醇产量较高.甜高粱特别适合在我国栽培,甜高粱燃料乙醇极具开发价值,它对能源安全和环境保护具有举足轻重的作用.文章简单介绍了新疆甜高粱用于生产低成本燃料乙醇的优势、试验情况以及产业化过程中面临的问题,并提出了解决这些问题应采取的对策.     

Techno-economic analysis of integrating sweet sorghum into sugar mills: The Central American case

This paper aims to evaluate the potential for electricity and ethanol production in Central America using sweet sorghum, performing a techno-economic analysis. The study proposes the integration of sweet sorghum into Central American sugar mills, by using the existing machinery to process this crop during off-season. A process simulation and a cost model were developed to estimate the technical and economical feasibility of sweet sorghum integration. The data on various parameters used for techno-economic assessment were collected from an existing sugar mill and distillery in Central America. The results show that a sugar mill operating 2 months during off-season could obtain an average revenue of US$ 3 M for a crushing rate of 6500 t/d. Ethanol production costs are estimated to be 24.76 ¢US$/L. In case a new CHP plant is built, a sugar mill operating under the integrated scenario would have a payback period of 4.49 years, as compared to 7.47 years for a sugar mill using sugarcane bagasse as the only fuel. Although several studies highlight the potential of sweet sorghum for ethanol production, the results from this work prove that sweet sorghum must also be seen as a viable feedstock for electricity production. A sensitivity analysis was also performed to determine the variation of the average cost of electricity and ethanol with the variables used in the economic analysis. For all analysed scenarios the effects of installed capacity and crop yield prevailed over the increasing costs of land and transportation.     

Simultaneous saccharification and fermentation of sweet sorghum after acid pretreatment

The sweet sorghum bagasse pretreated with 5% (w/w) acetic acid at an accumulated solid concentration of 20% (w/v) during the 96-h fed-batch simultaneous saccharification and fermentation achieved a maximum ethanol concentration of 53.1 g/L and ethanol yield of 88.7%, compared to 25.7 g/L and 86.7% for the 96-h batch simultaneous saccharification and fermentation at a solid concentration of 10% (w/v), respectively. For comparison, the bagasse pretreated with 0.5% (w/w) sulfuric acid and water under the same fed-batch simultaneous saccharification and fermentation conditions produced maximum ethanol concentrations of 44.3 and 36.5 g/L, and ethanol yields of 77.6 and 69.7%, respectively.     

Optimization of bioethanol production from glycerol by Escherichia coli SS1

Bioethanol is a promising biofuel and has a lot of great prospective and could become an alternative to fossil fuels. Ethanol fermentation using glycerol as carbon source was carried out by local isolate, ethanologenic bacterium Escherichia coli SS1 in a close system. Factors affecting bioethanol production from pure glycerol were optimized via response surface methodology (RSM) with central composite design (CCD). Four significant variables were found to influence bioethanol yield; initial pH of fermentation medium, substrate concentration, salt content and organic nitrogen concentration with statistically significant effect (p ≤ 0.05) on bioethanol production. The significant factor was then analyzed using central composite design (CCD). The optimum conditions for bioethanol production were substrate concentration at 34.5 g/L, pH 7.61, and organic nitrogen concentration at 6.42 g/L in which giving ethanol yield approximately 1.00 mol/mol. In addition, batch ethanol fermentation in a 2 L bioreactor was performed at the glycerol concentration of 20 g/L, 35 g/L and 45 g/L, respectively. The ethanol yields obtained from all tested glycerol concentrations were approaching theoretical yield when the batch fermentation was performed at optimized conditions.