A novel cost-effective technology to convert sucrose and homocelluloses in sweet sorghum stalks into ethanol
© Li et al.; licensee BioMed Central Ltd. 2013
Received: 21 June 2013
Accepted: 22 October 2013
Published: 29 November 2013
Sweet sorghum is regarded as a very promising energy crop for ethanol production because it not only supplies grain and sugar, but also offers lignocellulosic resource. Cost-competitive ethanol production requires bioconversion of all carbohydrates in stalks including of both sucrose and lignocellulose hydrolyzed into fermentable sugars. However, it is still a main challenge to reduce ethanol production cost and improve feasibility of industrial application. An integration of the different operations within the whole process is a potential solution.
An integrated process combined advanced solid-state fermentation technology (ASSF) and alkaline pretreatment was presented in this work. Soluble sugars in sweet sorghum stalks were firstly converted into ethanol by ASSF using crushed stalks directly. Then, the operation combining ethanol distillation and alkaline pretreatment was performed in one distillation-reactor simultaneously. The corresponding investigation indicated that the addition of alkali did not affect the ethanol recovery. The effect of three alkalis, NaOH, KOH and Ca(OH)2 on pretreatment were investigated. The results indicated the delignification of lignocellulose by NaOH and KOH was more significant than that by Ca(OH)2, and the highest removal of xylan was caused by NaOH. Moreover, an optimized alkali loading of 10% (w/w DM) NaOH was determined. Under this favorable pretreatment condition, enzymatic hydrolysis of sweet sorghum bagasse following pretreatment was investigated. 92.0% of glucan and 53.3% of xylan conversion were obtained at enzyme loading of 10 FPU/g glucan. The fermentation of hydrolyzed slurry was performed using an engineered stain, Zymomonas mobilis TSH-01. A mass balance of the overall process was calculated, and 91.9 kg was achieved from one tonne of fresh sweet sorghum stalk.
A low energy-consumption integrated technology for ethanol production from sweet sorghum stalks was presented in this work. Energy consumption for raw materials preparation and pretreatment were reduced or avoided in our process. Based on this technology, the recalcitrance of lignocellulose was destructed via a cost-efficient process and all sugars in sweet sorghum stalks lignocellulose were hydrolysed into fermentable sugars. Bioconversion of fermentable sugars released from sweet sorghum bagasse into different products except ethanol, such as butanol, biogas, and chemicals was feasible to operate under low energy-consumption conditions.
KeywordsSweet sorghum stalks Alkaline pretreatment Solid-state fermentation Bioethanol
Increased fossil fuel consumption has resulted in a series of social and environmental problems, such as the crisis of oil, global climate change and the emission of greenhouse gas. Sustainable and clean renewable energy as an alternative to fossil fuels has attracted extensive attention worldwide. Among various renewable energies, bioethanol is an important renewable liquid fuel due to its high octane number and heat of vaporization. Bioethanol is also less volatile than gasoline, has a lower photochemical reactivity in the atmosphere, and smog formation from emissions of pure ethanol can be less than from gasoline .
Sweet sorghum is a high photosynthetic-efficiency energy crop with high biomass (20 to 30 dry tonnes/ha) and sugar-yielding (16 to 18% fermentable sugar in juice) . It is also the only crop that provides grain and sugar, and a lignocellulosic biomass resource. Sweet sorghum has several primary advantages, such as (1) its adaptability to diverse climate zones and soil conditions (salinity, alkalinity and drought); (2) low requirement of fertilizers; (3) high water-usage efficiency compared with more conventional crops (1/3 of sugarcane and 1/2 of corn), and (4) short growth period (3 to 5 months) . Based on these advantages, sweet sorghum can be planted on marginal lands. It will avoid competing for land against other cultures that are used for food production . For these reasons, sweet sorghum has been regarded as an alcohol fuel crop with a promising future [5–7]. In fact, ethanol production from non-structural carbohydrates in sweet sorghum stalks is not difficult. There are two major kinds of technology to convert fermentable sugars to ethanol from sweet sorghum, one is liquid fermentation [4, 8, 9], the other is solid-state fermentation [10–12]. However, because there are approximately equal quantities of soluble and insoluble carbohydrates in sweet sorghum stalks , the major challenge for large-scale application of bioethanol production from sweet sorghum is how to deal with these lignocellulosic fractions (usually called bagasse). Cost-competitive ethanol production from sweet sorghum requires the bioconversion of all carbohydrates, including that of the sugar and lignocellulosic fraction, into ethanol.
Due to the recalcitrant nature of lignocellulosic materials, efficient bioconversion of sweet sorghum bagasse requires effective pretreatment to liberate cellulose from its physical seal and open up its crystalline structure before enzymatic hydrolysis can take place . Although a range of chemical, physical and biological processes have been configured to release structural sugars from lignocellulose, they have to face the challenges of cost, infrastructure needs and technological breakthroughs . An ideal pretreatment should have features as follows: (1) rendering high accessibility of biomass substrates to cellulases; (2) low capital and operational cost; (3) minimized size reduction of raw materials, and (4) producing low amounts of inhibitors to the enzymes and the fermentative microorganisms . Compared to other pretreatment technologies, alkaline pretreatment processes generally utilize lower temperatures, pressures and residence times, and produce lower concentration of inhibitors . Sodium hydroxide, potassium hydroxide and lime are usually used as an alkali reagent. The key role of alkaline is to partially remove lignin and hemicellulose in the biomass by disrupting the ester bonds cross-linking between lignin and xylan, thereby increasing the porosity of the biomass and resulting in cellulose and hemicellulose enriched fractions [18–20]. Enzymatic hydrolysis of sweet sorghum bagasse has been studied to some extent, and high enzymatic digestibility of sweet sorghum bagasse has also been reported [19–23]. However, the ethanol production cost is still high due to the complexity of the normal technology.
In the present study, a low energy-consumption and cost-efficient integrated process combining advanced solid-state fermentation technology (ASSF), alkaline pretreatment and C5-C6 co-fermentation in a whole process was configured. The effects of three alkalis, sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)2) on the ethanol recovery, pretreatment and enzymatic digestibility of sweet sorghum bagasse were investigated. In order to study the total ethanol yield of the overall process, C5-C6 co-fermentation of hydrolysed slurry was performed using an engineer strain Zymomonas mobilis (Z. mobilis) TSH-01.
Results and discussion
Novel process flow of ethanol production from sweet sorghum stalks
Sweet sorghum shows a potential for ethanol production because its stalk is rich in both non-structural carbohydrates (sucrose, glucose and fructose) and structural carbohydrates (cellulose and hemicellulose) . Cost-competitive ethanol production from sweet sorghum is challenged by the bioconversion of all carbohydrates from sugar and lignocellulose fractions into ethanol. The extraction of juice from the stalks is normally applied prior to pretreatment to prevent soluble sugar degradation. However, the squeezing operation needs high energy consumption. ASSF was studied in our previous work , and a demonstrated plant has been built up in Inner Mongolia province, China. The research on ASSF technology demonstrated that ASSF is a cost-efficient process, which can convert non-structural sugars to ethanol by anaerobic fermentation using the crushed sweet sorghum stalks directly in a rotatory drum fermenter [6, 11]. After fermentation, almost all the non-structural sugars were consumed. The ethanol produced in the solid state fermentation step remained in the fermented bagasse. The ethanol separation was achieved by heating this fermented bagasse with low-pressure steam in a distillation stripper. In our ASSF technology, ethanol distillation from fermented bagasse was carried out at approximately 100°C, which is the temperature required for alkaline pretreatment. Therefore, the implementation of alkaline pretreatment is feasible, provided that the alkali does not negatively influence the distillation process. After this special distillation operation with alkali, the recalcitrant structure of sweet sorghum bagasse was disrupted.
From Figure 1, it is obvious that the integrated process retains all the advantages of solid-state fermentation technology, such as lower energy consumption for biomass material preparation and less waste water. Moreover, the equipment and the extra energy and time consumption for pretreatment was avoided by combining distillation and alkaline pretreatment in one step. Compared with ethanol production technology using sweet sorghum bagasse (obtained after extraction of juice from sweet sorghum stalks), this integrated technology significantly reduced energy consumption and the investment of infrastructure needs of pretreatment. Moreover, alkaline-pretreated bagasse partially retained hemicellulose, increasing the potential fermentable sugars compared to acid-based pretreatments.
Influence of alkali in sugar-based ethanol distillation
Ethanol distillation of the fermented sweet sorghum bagasse
Distillation with 10% (w/w DM) NaOH
Sample mass for distillation (g)
Ethanol content in the sample (g/100 g WMa)
Ethanol in sample (g)
Recovered ethanolb (g)
Ethanol recovery (%)
Influence of alkali loading in the composition of sweet sorghum bagasse
NaOH, KOH, ammonia and lime are alkali reagents commonly investigated in alkaline pretreatment of lignocellulosic biomass. Due to the volatility of ammonia, it is released quickly at 100°C, so it cannot react completely with lignocellulosic substrates during the ethanol distillation. For this reason, ammonia was excluded from our work. The influence of other three alkali reagents in pretreatment was investigated by preliminary distillation experiments due to the limitation of the available amounts of fermented sweet sorghum bagasse. The pretreatment temperature was fixed at 100°C by ethanol distillation. In addition, to achieve high ethanol-recovery yield, distillation should be carried out for more than 24 minutes to achieve ethanol recovery yield of 99%. Efficient alkaline pretreatment time of sweet sorghum bagasse has been reported to be in the range of 30 minutes to 100 h [18, 19, 22]. To balance the requirement of distillation with pretreatment, the distillation duration was set at 30 minutes. The intensity of pretreatment increased with increasing alkali loading from 0.83 to 6.67 mmol/g of dry biomass. The alkali loading was commonly expressed in term of g/g biomass in the study in which only one alkali was investigated. However, the stoichiometric ratio was not shown directly using this unit when there were several different alkalis, so the alkali loading in this work was expressed in terms of mmol/g of dry biomass, which refers to the ratio of the amount of alkali to dry weight of sweet sorghum bagasse.
Sweet sorghum bagasse recovered after distillation combined with alkaline pretreatment and main composition
Alkali loading (mmol/g dry biomass)
Solid recovery (%)
30.33 ± 0.34
20.93 ± 0.23
20.46 ± 0.64
72.8 ± 1.3
41.22 ± 0.12
28.94 ± 0.78
15.93 ± 0.27
61.8 ± 2.4
48.62 ± 0.21
39.07 ± 0.56
13.62 ± 0.43
57.9 ± 1.7
51.31 ± 0.75
32.26 ± 0.37
11.21 ± 0.29
51.8 ± 3.9
57.25 ± 0.35
32.38 ± 0.74
8.21 ± 0.25
51.3 ± 3.3
57.69 ± 0.55
30.81 ± 0.63
7.34 ± 0.36
49.3 ± 2.2
60.04 ± 0.81
29.34 ± 0.39
7.27 ± 0.20
47.7 ± 0.9
61.63 ± 0.22
27.55 ± 0.49
7.86 ± 0.83
71.5 ± 1.8
42.01 ± 0.33
26.34 ± 0.52
16.94 ± 0.31
62.8 ± 3.1
47.84 ± 0.51
29.10 ± 0.16
13.23 ± 0.58
60.7 ± 1.6
49.28 ± 0.73
29.28 ± 0.63
9.92 ± 0.56
58.2 ± 1.2
51.07 ± 0.23
28.62 ± 0.04
8.01 ± 0.72
51.9 ± 2.4
57.10 ± 0.95
30.02 ± 0.77
6.50 ± 0.25
51.5 ± 0.7
57.55 ± 0.64
29.43 ± 0.19
7.02 ± 0.28
50.5 ± 2.1
57.97 ± 0.63
26.97 ± 0.83
7.26 ± 0.46
78.3 ± 1.2
38.33 ± 0.76
23.89 ± 0.36
16.72 ± 0.39
81.7 ± 0.8
36.73 ± 0.42
23.18 ± 0.73
15.98 ± 0.32
68.7 ± 1.3
43.59 ± 0.33
26.55 ± 0.53
13.64 ± 0.17
69.2 ± 0.5
42.98 ± 0.08
26.85 ± 0.71
15.05 ± 0.31
70.7 ± 2.1
41.95 ± 0.55
26.20 ± 0.81
14.52 ± 0.48
71.3 ± 1.7
41.57 ± 0.18
25.82 ± 0.31
13.18 ± 0.17
69.5 ± 1.4
42.14 ± 0.38
26.13 ± 0.75
13.51 ± 0.42
Cellulose was difficult to degrade under the alkaline condition , so the recovery yield of cellulose was more than 95% for all the samples following pretreatment. By increasing the intensity of the pretreatment, the cellulose content of bagasse increased gradually due to the removal of hemicellulose and lignin until the loading of 3.33 mmol/g of dry biomass. In accordance with the tendency of delignification, the cellulose content did not further increase significantly after the alkali loading used in the pretreatment exceeded 3.33 mmol/g of dry biomass. Ca(OH)2 pretreatment appeared to have weak ability to increase the cellulose content because the pretreatment time was too short. The cellulose content of bagasse treated with Ca(OH)2 varied from 38.33 to 42.98%, whereas that of bagasse treated with strong alkalis varied from 41.22 to 61.63% for NaOH, and from 42.01 to 57.97% for KOH.
The results of xylan removal are shown in Figure 4. With increasing concentration of strong alkalis, the removal of xylan increased linearly. Moreover, compared with KOH the hemicellulose had higher solubility in NaOH solution. The greatest xylan removal of 37.16% was caused by treatment with NaOH of 6.67 mmol/g of dry biomass, whereas it was 34.94% under KOH pretreatment. Compared with cellulose, the xylan content of bagasse following strong alkali pretreatment increased first to reach a peak, and then decreased gradually. The peak value occurred at alkali loading of 1.67 and 4.16 mmol/g of dry biomass for NaOH and KOH, respectively. This result was attributed to more hemicellulose dissolving in the alkaline solution at high alkali concentration. In contrast, lime has poor ability to dissolve the hemicellulose, and only less than 14% of xylan was removed from the bagasse under our process condition. Similar to lignin removal, the results demonstrated that to achieve the desirable pretreatment efficiency, lime needed more pretreatment time due to its low reactivity.
Pretreatment efficiency by enzymatic digestibility
Alkalis help to reduce recalcitrance of biomass through saponification of hemicellulose acetyl and lignin-carbohydrate complex linkages [26, 27]. As reported by Chang and Holtzapple, an effective lignocellulose treatment process should remove all the acetyl groups and reduce the lignin content to about 10% in the treated biomass. Further lignin reduction incurs an extra cost; therefore, it is not justified by increments in glucan conversion . Although the removal of hemicellulose could increase with increasing alkali loading, the glucan conversion did not increase linearly. Moreover, the high removal of xylan was negative to the efficient utility of sweet sorghum stalks. Taking into account solid recoveries and glucan conversion, the optimized alkali loading was determined to be 2.5 mmol of NaOH per gram of dry biomass. Using this alkali loading, 61.66% of lignin was removed from the sweet sorghum bagasse, and a relatively high carbohydrate recovery of 91.56% was achieved. Moreover, NaOH was a better choice and was used in the following experiments due to having a lower price than KOH.
Distillation combined with NaOH pretreatment operated in a distillation stripper
Composition of 10% (w/w dry mass) sodium hydroxide-treated sweet sorghum bagasse with ethanol distillation
57.28 ± 0.42
32.86 ± 0.64
Acid soluble lignin (ASL)
1.13 ± 0.12
Acid insoluble lignin (AIL)
5.54 ± 0.22
0.66 ± 0.06
Optimization of enzyme loading
C5-C6 anaerobic co-fermentation of hydrolysed slurry
Although partial hemicellulose was removed in the distillation with alkali, there was still a considerable amount of hemicellulose left in the residual bagasse. The results show that there was 8.69% of glucose and 2.99% of xylose in the hydrolysed slurry obtained from enzymatic hydrolysis of bagasse. Cost-competitive ethanol yield from lignocellulose requires fermentation of both hexose and pentose constituents , so C5-C6 anaerobic co-fermentation was performed with an engineered strain of Z. mobilis TSH-01 under the condition optimized by our research team. For 36-h fermentation, a fermentation broth containing 4.3% of ethanol was obtained. The glucose conversion was 95.1% and the xylose conversion was 65.2%. The lower conversion of xylose was attributed to the short fermentation time.
Energy input and output for novel cost-efficient integrated processes for ethanol production from sweet sorghum stalks
Enzymatic saccharification and fermentation
Distillation and separation
Analysis based on 1 tonne 99.5% ethanol. aIncluded process water, effluent restoration, capital equipment. Based on average of Energy and Resources Group (ERG) Biofuel Analysis Meta-Model (EBAMM) spreadsheet of Farrell .
In the present study, a novel low-energy consumption process for ethanol production involving first and second ethanol production from sweet sorghum was designed based on distillation combined with an alkali pretreatment process. NaOH loading of 10% (w/w DM) was determined as optimum in the pretreatment combined with the distillation step. Enzyme loading of 10 FPU/g of glucan during 72 h was selected for the enzymatic hydrolysis step. Enzyme loading of 10 FPU/g of glucan, and hydrolysis time of 72 h was confirmed in the enzymatic hydrolysis step: 91.9 kg of ethanol/tonne of fresh sweet sorghum stalk was obtained in the present work. Extraction of sweet sorghum juice, which has high energy-consumption, was avoided in our novel process. Energy and time consumption for pretreatment of sweet sorghum bagasse was also avoided by combining the pretreatment step and the first-generation ethanol distillation step in one step in one reactor, so the capital cost for the pretreatment reactor was also saved. This novel process is efficient to reduce the ethanol production cost and implement bioconversion of all carbohydrates in sweet sorghum stalks. Based on this technology, the recalcitrance of lignocellulose was destructed and the biodegradation of lignocellulose into fermentable sugar is feasible. Bioconversion of sweet sorghum bagasse into different product such as biogas, butanol, and chemicals from fermentation of sugar was feasibly performed under low-energy consumption conditions, so it is considered a promising process for a sugar-based lignocellulosic resource, such as sweet sorghum and sugarcane.
Composition analysis of the sweet sorghum stalk
Wet biomass %
Dry biomass %
14.03 ± 0.22
50.10 ± 0.78
4.94 ± 0.05
17.64 ± 0.18
3.38 ± 0.04
12.07 ± 0.14
Acid soluble lignin
0.91 ± 0.01
3.26 ± 0.05
1.84 ± 0.01
6.56 ± 0.04
0.09 ± 0.00
0.33 ± 0.02
S. cerevisiae TSH1 was used as the fermentation strain in the solid fermentation step. The microorganism was conserved in yeast extract peptone dextrose (YPD) medium at 4°C (1% yeast extract, 2% peptone, 2% glucose). In order to maintain the viability of the strain, the microorganism was sub-cultured before each experiment. An engineered Z. Mobilis TSH-01 recombined by Tsinghua University was used as the fermentation strain in the C5-C6 co-fermentation step. The microorganism was conserved in RM culture medium at 4°C (1% yeast extract, 0.2% monosodium phosphate (NaH2PO4), 2% glucose). In order to maintain the viability of the strain, the microorganism was sub-cultured before each experiment.
Enzymatic hydrolysis was carried out using the commercial enzyme Cellic CTec2 or Cellic CTec3, both kindly provided by Novozymes investment Co. Ltd (Beijing, China). The enzymatic activity was measured with Whatman No.1 filter paper according to the NREL method . The filter paper enzymatic activity was 113 FPU/mL and 213 FPU/mL for Cellic CTec2 or Cellic CTec3, respectively.
Advanced solid-state fermentation
Around 10 kg of crushed sweet sorghum was fully blended with 15% (v/w) of TSH1 seed (about 25 g /L, dry weight) and loaded onto 50 L fermenter, 0.7 m in length and 0.3 m in diameter, designed by our laboratory. The fermentation was carried out at 30°C for 24 h with a rotary speed at 0.5 rpm. Samples were collected at the start and end points of fermentation. Ethanol concentration was determined by gas chromatography (GC). Sugar concentration was determined by high-performance liquid chromatography (HPLC).
Distillation combined with alkaline pretreatment
Preliminary experiments of distillation combined with alkaline pretreatment
The loading dose of different alkalines used in the distillation
Loading dose (mmol/g dry biomass )
Distillation combined with NaOH pretreatment performed in a distillation stripper
Around 4 kg of fermented bagasse were mixed completely with 250 mL of NaOH (8 mol/L) concentrated solution, which provided the final alkali loading of 10% (w/w DM). The final moisture content was 76.3%. This mixture was loaded into a 50-L distillation stripper, 0.45 m in height, and 0.4 m in diameter, designed by our laboratory. Then, 0.15 MPa of steam was injected into the distillation stripper. The monitored operating temperature was kept at 100°C during the distillation stage. The operation time was 30 minutes, which started at the moment when the first drop of the distillate was observed. Another 4 kg of fermented bagasse without alkali was distilled as a control. The distillate was collected and ethanol concentration was analyzed by GC.
Following treatment the solid residues were centrifuged to remove the black liquor fraction and were washed by tap water (until the pH was 7.0) as required. The wet solid sample was stored in sealed plastic bags at -20°C. Some of it was dried in an oven at 50°C to determine the moisture and composition.
Enzymatic hydrolysis of sweet sorghum bagasse followed the preliminary experiment of distillation combined with alkali pretreatment. Enzymatic hydrolysis of sweet sorghum bagasse following pretreatment was carried out in a 100-mL shake flask, using 50 mM sodium citrate buffer (pH = 5.0) at 50°C and 120 rpm for 72 h. Sodium azide (3 g L-1) was added to inhibit microbial growth: 1 g of dry biomass was added in each flask, and then the buffer solution was added to the final solid concentration of 5% (w/w). Cellulase used in enzymatic hydrolysis was a commercial cellulase mixture, Cellic CTec2 (113 FPU/mL). The cellulase loading was 20 FPU g-1 of glucan. After enzymatic hydrolysis, 1 mL of the sample was taken from reaction mixture and centrifuged at 10,000 rpm for 10 minutes. The supernatant was stored at -20°C prior to HPLC analysis of reducing sugar concentration. All the experiments were performed in triplicate. One control experiment without cellulase was carried out to avoid the effect of residual sugars in sweet sorghum bagasse.
Enzymatic hydrolysis of sweet sorghum bagasse following distillation combined with alkaline pretreatment operated in a distillation stripper
Enzymatic hydrolysis of sweet sorghum bagasse following pretreatment was carried out in a 500-mL shake flask with 20 glass balls (4 mm in diameter), at 50°C and 150 rpm for 120 h. Then, 1 M of sodium citrate buffer solution was added to the flask containing the washed bagasse, and distilled water was added until the final buffer concentration of 50 mM and pH of 5.0 was obtained. The mixture was sterilized in an autoclave at 121°C for 30 minutes. Sterile water was added until the final solid loading was 15% (w/w). The cellulase used in enzymatic hydrolysis was a commercial cellulase mixture, Cellic CTec3 (214 FPU/mL). Aliquots of the enzyme hydrolysates were taken at different time intervals (Figure 5) and the concentration of the reducing sugar in the hydrolysate was measured by HPLC. All the experiments were performed in triplicate. One control experiment without cellulase was carried out to determine the soluble sugars in the pretreated materials. This value as a blank was subtracted from the final sugar concentration after enzymatic hydrolysis, to calculate the glucan conversion yield.
The enzymatic hydrolysis of the washed bagasse, following distillation combined with 10% (w/w DM) NaOH treated in a distillation stripper for C5-C6 co-fermentation, was performed for 72 h. Other conditions were the same as previously mentioned in this section. At end of hydrolysis, 0.5 mL of enzyme hydrolysate was taken out with a sterilized pipette and heated at 95°C for 5 minutes. The concentration of the reducing sugar in the hydrolysate was measured by HPLC. Ten parallel experiments were performed.
Volume is the volume of C5-C6 hydrolysed slurry.
C5-C6 anaerobic co-fermentation of hydrolysed slurry
As nutrient, 10% (v/v) of concentrated YP (1% yeast extract, 10% peptone) was added to the shake flask containing the hydrolysed slurry, and then the hydrolysed slurry was inoculated with 10% (v/w) of Z. Mobilis TSH-01 seed (2.5 g/L dry weight). All the fermentations were performed at 37°C, pH 6.0, and 100 rpm for 48 h. Samples were taken at 0 h and 24 h, centrifuged at 15,000 rpm, and 4°C for 10 minutes. The supernatant was stored at -20°C for the sugar and ethanol measurement. Ten parallel experiments were performed.
Percent solids (% TS) measurements were made using a 105°C-oven method according to standard procedures developed at NREL .
Sugar concentrations were measured using HPLC (Shimadzu LC-20 AD, Tokyo, Japan) equipped with a column (Bio-Rad HPX-87H, 250 mm × 4.6 mm, Beijing, China) operating at 60°C with a mobile phase of 5 mM sulfuric acid (H2SO4) aqueous solution with a flow rate of 0.5 mL/minute using a refractive index (RI) detector. Prior to analysis, the samples were diluted with ultrapure water, and then filtered through 0.45 mm filter (Millipore, Beijing, China).
Ethanol concentrations were determined by a gas chromatography (Shimadzu GC-14C, Japan) equipped with a flame ionization detector. A 0.125-cm I.D., 2 m, SS column was used using nitrogen gas (N2) as a carrier gas and hydrogen gas (H2) as a flaming gas. The injector temperature was 80°C, and the detector temperature was 220°C. The running time was 18 minutes.
Acid insoluble lignin
Acid insoluble lignin
Advanced solid-state fermentation technology
Energy and Resources Group (ERG) Biofuel Analysis Meta-Model
Filter paper cellulase unit
High performance liquid chromatography
Laboratory Analytical Procedures
National Renewable Energy Laboratory
- S. cerevisiae:
Yeast extract peptone dextrose
- Z. mobilis:
The study was supported by Ministry of Science and Technology of China (International scientific and technological cooperation projects, Grant No. 2013DFA60470 and 2012DFG61720), National Key Technologies R&D Program of China (Grant No. 2011BAD22B03), and Low Carbon Energy University Alliance. We also thank Novozymes China Research Center for generously providing the cellulase.
- Bailey BK: Performance of ethanol as a transportation fuel. In handbook on bioethanol: production and utilization. Edited by: Wyman CE. Washington DC: Taylor and Francis; 1996:37-60.Google Scholar
- Sipos B, Reczey J, Somorai Z, Kada Z, Dienes D, Reczey K: Sweet sorghumas feedstock for ethanol production: enzymatic hydrolysis of steam-pretreatedbagasse. Appl Biochem Biotechnol 2009, 153: 151-162. 10.1007/s12010-008-8423-9View ArticleGoogle Scholar
- Ratnavathi C, Chakravarthy S, Komala V, Chavan U, Patil J: Sweet sorghum as feedstock for biofuel production: a review. Sugar Tech 2011, 13: 399-407. 10.1007/s12355-011-0112-2View ArticleGoogle Scholar
- Matsakas L, Christakopoulos P: Optimization of ethanol production from high drymatter liquefied dry sweet sorghum stalks. Biomass Bioenerg 2013, 51: 91-98.View ArticleGoogle Scholar
- FAO: Sweet sorghum in China. Rome, Italy: Food and Agriculture Organization of the United Nations (FAO); 2002.Google Scholar
- Li SZ, Chan-Halbrendt C: Ethanol production in (the) People’s Republic of China: potential and technologies. Appl Energy 2009, 86: S162-S169.View ArticleGoogle Scholar
- Gnansounou E, Dauriat A, Wyman CE: Refining sweet sorghum to ethanol and sugar: economic trade-offs in the context of North China. Bioresour Technol 2005, 96: 985-1002. 10.1016/j.biortech.2004.09.015View ArticleGoogle Scholar
- Chohnan S, Nakane M, Rahman MH, Nitta Y, Yoshiura T, Ohta H, Kurusu Y: Fuel ethanol production from sweet sorghumusing repeated batch fermentation. J Biosci Bioeng 2011, 111: 433-436. 10.1016/j.jbiosc.2010.12.014View ArticleGoogle Scholar
- Ratnavathi CV, Suresh K, Kumar BSV, Pallavi M, Komala VV, Seetharama N: Study on genotypic variation for ethanolproduction from sweet sorghum juice. Biomass Bioenerg 2010, 34: 947-952. 10.1016/j.biombioe.2010.02.002View ArticleGoogle Scholar
- Wang EQ, Li SZ, Tao L, Geng X, Li TC: Modeling of rotating drum bioreactor for anaerobic solid-state fermentation. Appl Energy 2010, 87: 2839-2845. 10.1016/j.apenergy.2009.05.032View ArticleGoogle Scholar
- Yu ZL, Zhang X, Tan TW: Ethanol production by solid state fermentation of sweet sorghum using thermotolerant yeast strain. Fuel Process Technol 2008, 89: 1056-1059. 10.1016/j.fuproc.2008.04.008View ArticleGoogle Scholar
- Bryan WL: Solid-state fermentation of sugars in sweet sorghum. Enzyme and microb technol 1990, 12: 437-442. 10.1016/0141-0229(90)90054-TView ArticleGoogle Scholar
- Yu J, Zhong J, Zhang X, Tan T: Ethanol production from H 2 SO 3 -steampretreatedfresh sweet sorghum stem by simultaneous saccharification andfermentation. Appl Biochem Biotechnol 2010, 160: 401-409. 10.1007/s12010-008-8333-xView ArticleGoogle Scholar
- Sun Y, Cheng J: Hydrolysis of lignocellulosic materials forethanol production: a review. Bioresour Technol 2002, 83: 1-11. 10.1016/S0960-8524(01)00212-7View ArticleGoogle Scholar
- Antizar-Ladislao B, Turrion-Gomez J: Second-generation biofuels and local bioenergy systems. Biofuels Bioprod Bior 2008, 2: 455-469. 10.1002/bbb.97View ArticleGoogle Scholar
- Agbor VB, Cicek N, Sparling R, Berlin A, Levin DB: Biomass pretreatment: fundamentals toward application. Biotechnology Adv 2011, 29: 675-685. 10.1016/j.biotechadv.2011.05.005View ArticleGoogle Scholar
- Taherzadeh MJ, Karimi K: Pretreatment of lignocellulosic wastes to improve ethanol and biogas production: a review. Int J Mol Sci 2008, 9: 1621-1651. 10.3390/ijms9091621View ArticleGoogle Scholar
- Xu J, Cheng JJ, Sharma-Shivappa RR, Burns JC: Sodium hydroxide pretreatment of switchgrass for ethanol production. Energy Fuels 2010, 24: 2113-2119. 10.1021/ef9014718View ArticleGoogle Scholar
- Zhang J, Ma X, Yu J, Zhang X, Tan T: The effects of four different pretreatments on enzymatic hydrolysis of sweet sorghum bagasse. Bioresour Technol 2011, 102: 4585-4589. 10.1016/j.biortech.2010.12.093View ArticleGoogle Scholar
- Cao WX, Sun C, Liu RH, Yin RZ, Wu XW: Comparison of the effects of five pretreatment methods on enhancing the enzymatic digestibility and ethanol production from sweet sorghum bagasse. Bioresour Technol 2012, 111: 215-221.View ArticleGoogle Scholar
- Billa E, Koullas DP, Monties B, Koukios EG: Structure and composition of sweet sorghum stalk components. Ind Crop Prod 1997, 6: 297-302. 10.1016/S0926-6690(97)00031-9View ArticleGoogle Scholar
- Li SZ, Li GM, Zhang L, Zhou Z, Han B, Hou W, Wang J, Li T: A demonstration study of ethanol production from sweet sorghum stems with advanced solid state fermentation technology. Appl Energy 2013, 102: 260-265.View ArticleGoogle Scholar
- Mclntosh S, Vancov T: Ethanol enzyme saccharification of Sorghum bicolor straw using dilute alkali pretreatment. Bioresour Technol 2010, 101: 6718-6727. 10.1016/j.biortech.2010.03.116View ArticleGoogle Scholar
- Gupta R, Lee YY: Investigation of biomass degradation mechanism inpretreatment of switchgrass by aqueous ammonia and sodiumhydroxide. Bioresour Technol 2010, 101: 8185-8191. 10.1016/j.biortech.2010.05.039View ArticleGoogle Scholar
- Rabelo SC, Filho RM, Costa AC: Lime pretreatment and fermentation of enzymatically hydrolyzed sugarcane bagasse. Appl Biochem Biotechnol 2013, 169: 1696-1712. 10.1007/s12010-013-0097-2View ArticleGoogle Scholar
- Chen Y, Stevens MA, Zhu Y, Holmes J, Xu H: Understanding of alkaline pretreatment parameters for corn stover enzymaticsaccharification. Biotech for Biofuels 2013, 6: 1-10. 10.1186/1754-6834-6-1View ArticleGoogle Scholar
- Chang VS, Holtzapple MT: Fundamental factors affecting biomass enzymatic reactivity. Appl Biochem Biotechnol 2000, 84–86: 5-37.View ArticleGoogle Scholar
- Laureno-Perez L, Teymouri F, Alizadeh H, Dale B: Understanding factors that limit enzymatic hydrolysis of biomass characterization of pretreated corn stover. Appl Biochem Biotechnol 2005, 124: 1081-1099. 10.1385/ABAB:124:1-3:1081View ArticleGoogle Scholar
- Gable M, Sassner P, Wingren A, Zacchi G: Process engineering economics of bioethanol production. Adv Biochem Eng/Biotechnol 2007, 108: 303-327. 10.1007/10_2007_063View ArticleGoogle Scholar
- Lai YZ: Wood and Cellulose Chemistry. In Chemical Degradation. 2nd edition. Edited by: Hon DNS, Shiraishi N. New York: Marcel Dekker Inc; 1991:455-473.Google Scholar
- Zhu JY, Zhuang XS: Conceptual net energy output for biofuel production from lignocellulosic biomass through biorefining. Prog Energ Combust 2012, 38: 583-598. 10.1016/j.pecs.2012.03.007View ArticleGoogle Scholar
- Farrell AE, Plevin RJ, Turner BT, Jones AD, O’Hare M, Kammen DM: Ethanol can contribute to energy and environmental goals. Science 2006, 311: 506-508. 10.1126/science.1121416View ArticleGoogle Scholar
- Sluiter A, Hames B, Ruiz R, Scarlata C, Sluiter J, Templeton D, Crocker D: Determination of structural carbohydrates and lignin in biomass: Laboratory Analytical Procedure. 2008. NREL/TP-510-42618. Updated 2010Google Scholar
- Sluiter A, Hyman D, Payne C, Wolfe J: Determination of total solids in biomass and total dissolved solids in liquid process samples. http://www.nrel.gov/biomass/pdfs/42621.pdf
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