Improved bio-energy yields via sequential ethanol fermentation and biogas digestion of steam exploded oat straw

Using standard laboratory equipment, thermochemically pretreated oat straw was enzymatically saccharified and fermented to ethanol, and after removal of ethanol the remaining material was subjected to biogas digestion. A detailed mass balance calculation shows that, for steam explosion pretreatment, this combined ethanol fermentation and biogas digestion converts 85-87% of the higher heating value (HHV) of holocellulose (cellulose and hemicellulose) in the oat straw into biofuel energy. The energy (HHV) yield of the produced ethanol and methane was 9.5-9.8 MJ/(kg dry oat straw), which is 28-34% higher than direct biogas digestion that yielded 7.3-7.4 MJ/(kg dry oat straw). The rate of biogas formation from the fermentation residues was also higher than from the corresponding pretreated but unfermented oat straw, indicating that the biogas digestion could be terminated after only 24 days. This suggests that the ethanol process acts as an additional pretreatment for the biogas process.     

Effect of hemicellulose and lignin removal on enzymatic hydrolysis of steam pretreated corn stover

Ethanol can be produced from lignocellulosic biomass using steam pretreatment followed by enzymatic hydrolysis and fermentation. The sugar yields, from both hemicellulose and cellulose are critical parameters for an economically-feasible ethanol production process. This study shows that a near-theoretical glucose yield (96-104%) from acid-catalysed steam pretreated corn stover can be obtained if xylanases are used to supplement cellulases during hydrolysis. Xylanases hydrolyse residual hemicellulose, thereby improving the access of enzymes to cellulose. Under these conditions, xylose yields reached 70-74%. When pre-treatment severity was reduced by using autocatalysis instead of acid-catalysed steam pretreatment, xylose yields were increased to 80-86%. Partial delignification of pretreated material was also evaluated as a way to increase the overall sugar yield. The overall glucose yield increased slightly due to delignification but the overall xylose yield decreased due to hemicellulose loss in the delignification step. The data also demonstrate that steam pretreatment is a robust process: corn stover from Europe and North America showed only minor differences in behaviour.     

Effects of temperatures and organic loading rates on biomethanation of acidic petrochemical wastewater using an anaerobic upflow fixed-film reactor

The effect of temperature and organic loading rate on the rate of methane production from acidic petrochemical wastewater without neutralization was investigated by continuously feeding an anaerobic upflow fixed-film reactor. The temperatures selected for the studies were 25, 37, 45 and 55 degrees C. Organic loading rate (OLR) for each temperature was varied from 3.6 to 21.7 kg COD m(-3) d(-1). Best performance with respect to COD and BOD reduction, total gas production and methane yield was obtained with the reactor operating at 37 degrees C. OLR could be increased to a maximum of 21.7 kg COD m(-3) d(-1) with 90-95% COD and BOD reduction and methane yield of 0.450 m3 kg(-1) COD d(-1) added. The reactor operating at 55 degrees C gave the highest methane yield of 0.666 m3 kg(-1) COD d(-1) at an OLR of 6 kg COD m(-3) d(-1). This decreased to 0.110 m3 kg(-1) COD d(-1) when the OLR was increased to 18.1 kg COD m(-3) d(-1). The reactor operating at 45 degrees C gave a maximum methane yield of 0.416 m3 kg(-1) COD d(-1) added at an OLR of 6 kg COD m(-3) d(-1). On further increasing the OLR to 9 kg COD m(-3) d(-1), COD reduction was 89%, however, methane yield decreased to 0.333 m3 kg(-1) COD d(-1) added. The highest methane yield of 0.333 m3 kg(-1) COD d(-1) added at an OLR of 6 kg COD m(-3) d(-1) was obtained with reactors operating at 25 degrees C. These studies indicate potential rates of methane production from acidic petrochemical wastewater under different temperatures. This provides a guideline for various kinetic analyses and economic evaluation of the potential feasibility of fermenting acidic wastewater to methane.     

Effect of various factors on ethanol yields from lignocellulosic biomass by Thermoanaerobacterium AK₁₇

The ethanol production capacity from sugars and lignocellulosic biomass hydrolysates (HL) by Thermoanaerobacterium strain AK(17) was studied in batch cultures. The strain converts various carbohydrates to, acetate, ethanol, hydrogen, and carbon dioxide. Ethanol yields on glucose and xylose were 1.5 and 1.1 mol/mol sugars, respectively. Increased initial glucose concentration inhibited glucose degradation and end product formation leveled off at 30 mM concentrations. Ethanol production from 5 g L(-1) of complex biomass HL (grass, hemp, wheat straw, newspaper, and cellulose) (Whatman paper) pretreated with acid (0.50% H(2) SO(4)), base (0.50% NaOH), and without acid/base (control) and the enzymes Celluclast and Novozyme 188 (0.1 mL g(-1) dw; 70 and 25 U g(-1) of Celluclast and Novozyme 188, respectively) was investigated. Highest ethanol yields (43.0 mM) were obtained on cellulose but lowest on hemp leafs (3.6 mM). Chemical pretreatment increased ethanol yields substantially from lignocellulosic biomass but not from cellulose. The influence of various factors (HL, enzyme, and acid/alkaline concentrations) on end-product formation from 5 g L(-1) of grass and cellulose was further studied to optimize ethanol production. Highest ethanol yields (5.5 and 8.6 mM ethanol g(-1) grass and cellulose, respectively) were obtained at very low HL concentrations (2.5 g L(-1)); with 0.25% acid/alkali (v/v) and 0.1 mL g(-1) enzyme concentrations. Inhibitory effects of furfural and hydroxymethylfurfural during glucose fermentation, revealed a total inhibition in end product formation from glucose at 4 and 6 g L(-1), respectively.     

Liquefaction of lignocellulose at high-solids concentrations

To improve process economics of the lignocellulose to ethanol process a reactor system for enzymatic liquefaction and saccharification at high-solids concentrations was developed. The technology is based on free fall mixing employing a horizontally placed drum with a horizontal rotating shaft mounted with paddlers for mixing. Enzymatic liquefaction and saccharification of pretreated wheat straw was tested with up to 40% (w/w) initial DM. In less than 10 h, the structure of the material was changed from intact straw particles (length 1-5 cm) into a paste/liquid that could be pumped. Tests revealed no significant effect of mixing speed in the range 3.3-11.5 rpm on the glucose conversion after 24 h and ethanol yield after subsequent fermentation for 48 h. Low-power inputs for mixing are therefore possible. Liquefaction and saccharification for 96 h using an enzyme loading of 7 FPU/g.DM and 40% DM resulted in a glucose concentration of 86 g/kg. Experiments conducted at 2%-40% (w/w) initial DM revealed that cellulose and hemicellulose conversion decreased almost linearly with increasing DM. Performing the experiments as simultaneous saccharification and fermentation also revealed a decrease in ethanol yield at increasing initial DM. Saccharomyces cerevisiae was capable of fermenting hydrolysates up to 40% DM. The highest ethanol concentration, 48 g/kg, was obtained using 35% (w/w) DM. Liquefaction of biomass with this reactor system unlocks the possibility of 10% (w/w) ethanol in the fermentation broth in future lignocellulose to ethanol plants.     

Production of bioethanol, methane and heat from sugarcane bagasse in a biorefinery concept

The potential of biogas production from the residues of second generation bioethanol production was investigated taking into consideration two types of pretreatment: lime or alkaline hydrogen peroxide. Bagasse was pretreated, enzymatically hydrolyzed and the wastes from pretreatment and hydrolysis were used to produce biogas. Results have shown that if pretreatment is carried out at a bagasse concentration of 4% DM, the highest global methane production is obtained with the peroxide pretreatment: 72.1 L methane/kg bagasse. The recovery of lignin from the peroxide pretreatment liquor was also the highest, 112.7 ± 0.01 g/kg of bagasse. Evaluation of four different biofuel production scenarios has shown that 63-65% of the energy that would be produced by bagasse incineration can be recovered by combining ethanol production with the combustion of lignin and hydrolysis residues, along with the anaerobic digestion of pretreatment liquors, while only 32-33% of the energy is recovered by bioethanol production alone.     

High solid simultaneous saccharification and fermentation of wet oxidized corn stover to ethanol

In this study ethanol was produced from corn stover pretreated by alkaline and acidic wet oxidation (WO) (195 degrees C, 15 min, 12 bar oxygen) followed by nonisothermal simultaneous saccharification and fermentation (SSF). In the first step of the SSF, small amounts of cellulases were added at 50 degrees C, the optimal temperature of enzymes, in order to obtain better mixing condition due to some liquefaction. In the second step more cellulases were added in combination with dried baker's yeast (Saccharomyces cerevisiae) at 30 degrees C. The phenols (0.4-0.5 g/L) and carboxylic acids (4.6-5.9 g/L) were present in the hemicellulose rich hydrolyzate at subinhibitory levels, thus no detoxification was needed prior to SSF of the whole slurry. Based on the cellulose available in the WO corn stover 83% of the theoretical ethanol yield was obtained under optimized SSF conditions. This was achieved with a substrate concentration of 12% dry matter (DM) acidic WO corn stover at 30 FPU/g DM (43.5 FPU/g cellulose) enzyme loading. Even with 20 and 15 FPU/g DM (corresponding to 29 and 22 FPU/g cellulose) enzyme loading, ethanol yields of 76 and 73%, respectively, were obtained. After 120 h of SSF the highest ethanol concentration of 52 g/L (6 vol.%) was achieved, which exceeds the technical and economical limit of the industrial-scale alcohol distillation. The SSF results showed that the cellulose in pretreated corn stover can be efficiently fermented to ethanol with up to 15% DM concentration. A further increase of substrate concentration reduced the ethanol yield significant as a result of insufficient mass transfer. It was also shown that the fermentation could be followed with an easy monitoring system based on the weight loss of the produced CO2.     

Biogas Production from Steam-Exploded Miscanthus and Utilization of Biogas Energy and CO2 in Greenhouses

The costs of producing protected vegetables comprise up to 78 % of the total operating costs in greenhouses. These expenses mainly result from energy consumption. Increasing energy efficiency and expanding the use of renewable energy sources are essential for global competitiveness. The aim of this study is to optimize methane production from miscanthus and to evaluate the potential use of miscanthus as a source of electrical energy, heat, and CO₂ in vegetable greenhouses. To optimize methane yield, miscanthus was pretreated by steam explosion using different time/temperature combinations. Pretreatment resulted in a more than threefold increase of methane yield from anaerobic digestion (374 l_N?kgVS^?1) compared with untreated miscanthus. Based on technical parameters from two greenhouses (in Northern and Southern Europe), four different energy balances were established. The balances showed that using methane produced by pretreated miscanthus in vegetable greenhouses can enhance the entire process and therefore make it more sustainable.     

Variation due to Growth Environment in Alfalfa Yield, Cellulosic Ethanol Traits, and Paper Pulp Characteristics

Alfalfa (Medicago sativa L.) is a promising bioenergy and bioproduct feedstock because of its high yield, N-fixation capacity, potential for planting in rotation with corn (Zea mays L.), and valuable protein co-product (leaf meal). Our objective was to examine the effect of growth environment on biomass yield, cellulosic ethanol traits, and paper pulp fiber characteristics of alfalfa stems. Landscape position (summit and mild slope), season of harvest (four harvests per season), and multiple years (2005 and 2006) provided environmental variation. Alfalfa stem samples were analyzed for cell wall carbohydrate and lignin concentration. Stems were subjected to dilute acid pre-treatment, enzymatic saccharification, and pulping processes to measure relevant cellulosic ethanol and paper production traits. Landscape position was not a significant source of variation for yield or any biomass quality trait. Yields varied among harvests in 2005 (1,410–3,265 kg ha^?1) and 2006 (1,610–3,795 kg ha^?1). All cell wall, conversion test, and paper production traits exhibited year by harvest interactions with no clear pattern. Total carbohydrates and lignin ranged from 440 to 531 g?kg^?1 DM and from 113 to 161 g?kg^-1 DM, respectively. Release of cell wall sugars by the conversion test ranged widely (419 to 962 g?kg^?1 DM). Fiber traits were similarly variable with length and fine content ranging from 1.24 to 1.59 mm and from 15.2% to 21.9%, respectively. Utilizing alfalfa biomass for cellulosic ethanol and paper pulp production will involve dealing with significant feedstock quality variation due to growth environment.     

The effect of temperature variation on biomethanation at high altitude

The aim of the current study was to examine effects of daily temperature variations on the performance of anaerobic digestion. Forced square-wave temperature variations (between 11 and 25, 15 and 28, and 19 and 32 degrees C) were imposed on a bench-scale digester using a mixture of llama-cow-sheep manure in a semi-continuous process. The volumetric biogas production rate, methane yield, and the volatile solid reductions were compared with the results obtained from anaerobic digestion (AD) at constant temperatures. The forced cyclic variations of temperature caused large cyclic variations in the rate of gas production and the methane content. As much as 94-97% of the daily biogas was obtained in the 12h half-cycle at high temperature. The values for volumetric biogas production rate and methane yield increased at higher temperatures. The average volumetric biogas production rate for cyclic operation between 11 and 25 degrees C was 0.22Ld(-1)L(-1) with a yield of 0.07m3CH4kg(-1) VS added (VSadd), whereas for operation between 15 and 29 degrees C the volumetric biogas production rate increased by 25% (to 0.27Ld(-1)L(-1) with a yield of 0.08m3CH4kg(-1) VSadd). In the highest temperature region a further increase of 7% in biogas production was found and the methane yield was 0.089m(3)CH(4)kg(-1) VSadd. The employed digester showed an immediate response when the temperature was elevated, which indicates a well-maintained metabolic capacity of the methanogenic bacteria during the period of low temperature. Overall, periodic temperature variations appear to give less decrease in process performance than a priori anticipated.     

Process considerations and economic evaluation of two-step steam pretreatment for production of fuel ethanol from softwood

To increase the overall ethanol yield from softwood, the steam pretreatment stage can be carried out in two steps. The two-step pretreatment process was evaluated from a techno-economic standpoint and compared with the one-step pretreatment process. The production plants considered were designed to utilize spruce as raw material and have a capacity of 200,000 tons/year. The two-step process resulted in a higher ethanol yield and a lower requirement for enzymes. However, the two-step process is more capital-intensive and has a higher energy requirement. The estimated ethanol production cost was the same, 4.13 SEK/L (55.1 cent /L) for both alternatives. For the two-step process different energy-saving options were considered, such as a higher concentration of water-insoluble solids in the filter cake before the second step, and the possibility of excluding the pressure reduction between the steps. The most optimistic configuration, with 50% water-insoluble solids in the filter cake in the feed to the second pretreatment step, no pressure reduction between the pretreatment steps, and 77% overall ethanol yield (0.25 kg EtOH/kg dry wood), resulted in a production cost of 3.90 SEK/L (52.0 cent /L). This shows the potential for the two-step pretreatment process, which, however, remains to be verified in pilot trials.     

Willow growth in response to nutrients and moisture on a clay landfill cap soil. I. Growth and biomass production

The growth and biomass production by willow (Salix viminalis L.) was studied in lysimeters containing Oxford clay landfill cap soil with different amendments, bulk densities and watering regimes. Three years from planting, stem biomass in well-watered plants was least (0.28 kg plant(-1)) with high bulk density soil (1480 kg m(-3)) and no nutritional amendment but was increased 10-fold (2.53 kg plant(-1)) by reducing soil bulk density (1200 kg m3) and adding amendments. In comparison, on a sandy loam soil it was 6.23 kg plant(-1). There were similar differences in number of stems plant(-1), stem basal area plant(-1) and plant leaf area which can be attributed to low nitrogen and phosphorus levels in Oxford clay. Water stress reduced stem biomass production by 26-37% and caused higher root:stem ratios. These were also higher on Oxford clay than on the sandy loam. Successful biomass production from willow on Oxford clay landfill caps will therefore require nutritional amendment.     

The enzymatic hydrolysis and fermentation of pretreated wood substrates

Aspenwood chips were pretreated by steam explosion. The various wood fractions obtained were assayed for their ability to act as substrates for growth and cellulase production of different Trichoderma and Clostridium thermocellum species. Steam exploded aspenwood was as efficiently utilized as solka floc and correspondingly high cellulase activities were detected in the various culture filtrates. When T. harzianum E58 was grown on increasing concentrations of solka floc, highest cellulase and xylanase activities were detected at 1% substrate concentrations while high substrate concentrations (10-20%) inhibited growth and enzyme production. When the cellulosic substrates were supplemented with increasing amounts of glucose, cellulase and xylanase production were inhibited when the glucose concentration exceeded 0.1%. Highest xylanase activities were detected after growth of T. reesei C30 and T. harianum E58 on xylan and solka floc respectively. All of the steam exploded fractions were at least partially hydrolyzed by the T. harzianum E58 cellulase system. The extent of the pretreatment also influenced the ability of Zymomonas mobilis and Saccharomyces cerevisiae to ferment the liberated sugars to ethanol. About 85% of the theoretical yield of ethanol from cellulose could be obtained from the combined hydrolysis and fermentation of pretreated aspenwood.     

The techno-economic potential of renewable energy through the anaerobic digestion of microalgae

The potential of microalgae as feedstock for methane production is evaluated from a process technical and economic point of view. Production of mixed culture algae in raceway ponds on non-agricultural sites, such as landfills, was identified as a preferred approach. The potential of straightforward bio-methanation, which includes pre-concentration of microalgae and utilization of a high rate anaerobic reactor was examined based on the premises of achievable up-concentration from 0.2-0.6 kg m(-3) to 20-60 kg dry matter (DM) m(-3) and an effective bio-methanation of the concentrate at a loading rate of 20 kg DM m(-3) d(-1). The costs of biomass available for bio-methanation under such conditions were calculated to be in the range of €86-€124 ton(-1) DM. The levelized cost of energy by means of the process line "algae biomass--biogas--total energy module" would be in the order of €0.170-0.087 kWh(-1), taking into account a carbon credit of about €30 ton(-1) CO2(eq).     

Enhancement of the saccharification yields of Ulva pertusa kjellmann and rape stems by the high-pressure steam pretreatment process

The high-pressure steam process was used to hydrolyze rape stems and Ulva pertusa kjellmann using only water. The biomass was hydrolyzed in a compressed cell at a high temperature and high pressure. The optimal pretreatment conditions were determined to be 180 and 10 bar for 8 min, with 8.5 and 7.4% (w/w) glucose conversion yields, respectively. After the pretreatments, the residues were easily hydrolyzed by treating the enzymes with 1 FPU/mL cellulase, and the 56.8 and 77% (w/w) total cellulose in the results were converted into glucose in 24 h. These results imply that using only water and not any other chemical can efficiently hydrolyze rape stems and Ulva pertusa kjellmann because the high-pressure steam pretreatment process can easily decompose the cellulose structure via XRD analysis, which will result in a high conversion yield with low doses of cellulase. This process was proven to generate a low amount (16.9 ppm) of HMF (hydroxymethylfurfural), which resulted in ethanol production with a 48.7% theoretical maximum conversion yield of glucose. It is believed that this process can be widely used to hydrolyze other agricultural and marine resources for bioethanol production.     

Enzyme characterization for hydrolysis of AFEX and liquid hot-water pretreated distillers' grains and their conversion to ethanol

Dried distillers' grains with solubles (DDGS), a co-product of corn ethanol production, was investigated as a feedstock for additional ethanol production. DDGS was pretreated with liquid hot-water (LHW) and ammonia fiber explosion (AFEX) processes. Cellulose was readily converted to glucose from both LHW and AFEX treated DDGS using a mixture of commercial cellulase and beta-glucosidase; however, these enzymes were ineffective at saccharifying the xylan present in the pretreated DDGS. Several commercial enzyme preparations were evaluated in combination with cellulase to saccharify pretreated DDGS xylan and it was found that adding commercial grade (e.g. impure) pectinase and feruloyl esterase (FAE) preparations were effective at releasing arabinose and xylose. The response of sugar yields for pretreated AFEX and LHW DDGS (6wt%/solids) were determined for different enzyme loadings of FAE and pectinase and modeled as a response surfaces. Arabinose and xylose yields rose with increasing FAE and pectinase enzyme dosages for both pretreated materials. When hydrolyzed at 20wt%/solids with the same blend of commercial enzymes, the yields were 278 and 261g sugars (i.e. total of arabinose, xylose, and glucose) per kg of DDGS (dry basis, db) for AFEX and LHW pretreated DDGS, respectively. The pretreated DDGS's were also evaluated for fermentation using Saccharomyces cerevisiae at 15wt%/solids. Pretreated DDGS were readily fermented and were converted to ethanol at 89-90% efficiency based upon total glucans; S. cerevisiae does not ferment arabinose or xylose.     

Differential effects of oilseed supplements on methane production and milk fatty acid concentrations in dairy cows

It is known that supplementing dairy cow diets with full-fat oilseeds can be used as a strategy to mitigate methane emissions, through their action on rumen fermentation. However, direct comparisons of the effect of different oil sources are very few, as are studies implementing supplementation levels that reflect what is commonly fed on commercial farms. The objective was to investigate the effect of feeding different forms of supplemental plant oils on both methane emissions and milk fatty acid (FA) profile. Four multiparous, Holstein-Friesian cows in mid-lactation were randomly allocated to one of four treatment diets in a 4×4 Latin square design with 28-day periods. Diets were fed as a total mixed ration with a 50 : 50 forage : concentrate ratio (dry matter (DM) basis) with the forage consisting of 75 : 25 maize silage : grass silage (DM). Dietary treatments were a control diet containing no supplemental fat, and three treatment diets containing extruded linseed (EL), calcium salts of palm and linseed oil (CPLO) or milled rapeseed (MR) formulated to provide each cow with an estimated 500 g additional oil/day (22 g oil/kg diet DM). Dry matter intake (DMI), milk yield, milk composition and methane production were measured at the end of each experimental period when cows were housed in respiration chambers for 4 days. There was no effect of treatment diet on DMI or milk protein or lactose concentration, but oilseed-based supplements increased milk yield compared with the control diet and milk fat concentration relative to control was reduced by 4 g/kg by supplemental EL. Feeding CPLO reduced methane production, and both linseed-based supplements decreased methane yield (by 1.8 l/kg DMI) and intensity (by 2.7 l/kg milk yield) compared with the control diet, but feeding MR had no effect on methane emission. All the fat supplements decreased milk total saturated fatty acid (SFA) concentration compared with the control, and SFA were replaced with mainly cis-9 18:1 but also trans FA (and in the case of EL and CPLO there were increases in polyunsaturated FA concentration). Supplementing dairy cow diets with these oilseed-based preparations affected milk FA profile and increased milk yield. However, only the linseed-based supplements reduced methane production, yield or intensity, whereas feeding MR had no effect.     

Prediction of the metabolisable energy content of forages and mixed diets for horses: validation and comparison of two evaluation systems

The metabolisable energy (ME) content of feeds is a better estimate of their ‘true’ energy value than their digestible energy (DE) content, because ME takes account of the gross energy of methane (GEgas) and the gross energy of urine (GEurine) losses. The accuracy and precision of the Gesellschaft für Ernährungsphysiologie (GfE) and Institut National de la Recherche Agronomique (INRA) systems for predicting the DE and ME contents of diets for horses were compared using the results of a study comprising 15 mixed diets. The INRA system was more accurate than the GfE system for predicting DE, GEurine and ME: the biases between the predicted and the measured values were − 0.26 vs –0.46 MJ/kg DM for DE (P < 0.05), − 0.03 vs 0.13 MJ/kg DM for GEurine (P < 0.05) and − 0.09 vs –0.62 MJ/kg DM for ME (P < 0.05). The biases for GEgas were not significantly different (P > 0.05) between systems. In addition, a study was carried out with 24 forages to compare the ME value of permanent meadow and lucerne hays predicted with the GfE and the INRA systems. The INRA system gave higher prediction values of DE than the GfE system (P < 0.001) and lower estimates of GEgas (0.34 vs 0.63 MJ/kg DM for permanent meadow hays and 0.38 vs 0.63 MJ/kg DM for lucerne hays) (P < 0.001) and GEurine (0.85 vs 0.93 MJ/kg DM for grassland hays and 1.08 vs 1.37 MJ/kg DM for lucerne hays) (P < 0.001). The INRA system thus gave higher estimates of ME (7.57 vs 6.77 MJ/kg DM for permanent meadow hays and 8.80 vs 6.46 MJ/kg DM for lucerne hays, P < 0.001) in agreement with the results obtained with mixed diets. The ME values of permanent meadow hays and legume hays should therefore be predicted separately using specific equations as previously established for the DE value.     

Enhancing alfalfa conversion efficiencies for sugar recovery and ethanol production by altering lignin composition

Alfalfa (Medicago sativa L.) biomass was evaluated for biochemical conversion into ethanol using dilute-acid and ammonia pretreatments. The two alfalfa lines compared were a reduced S-lignin transgenic cultivar generated through down regulation of the caffeic acid O-methyltransferase gene and a wild-type control. Both were harvested at two maturities. All the samples had similar carbohydrate contents including a mean composition of 316 g glucan and 497 g total neutral carbohydrates per kg dry biomass, which corresponds to a theoretic ethanol yield of 382 l/ton. Ethanol yields for alfalfa stems pretreated with dilute-acid were significantly impacted by harvest maturity and lignin composition, whereas when pretreated with dilute-ammonia, yield was solely affected by lignin composition. Use of a recombinant xylose-fermenting Saccharomyces strain, for converting the ammonia pretreated alfalfa samples, further increased ethanol yields. Ethanol yields for the xylose-fermenting yeast were 232-278 l/ton and were significantly enhanced for the reduced S lignin cultivars.     

广西中粮20万吨/年木薯燃料乙醇净能量分析

广西中粮20万吨/年木薯燃料乙醇装置建成后经历多次工艺改造,为了评估广西装置的能量投入/产出,利用国内已有的全生命周期模型进行了净能量分析。计算结果表明,广西装置的净能量为9.56 MJ/L乙醇。其中乙醇转化环节的能量投入占总能量投入的51.3%,而其中精馏工序仅蒸汽消耗即占乙醇转化总能耗的61.5%。副产品提供的能量可补偿5.03 MJ/L乙醇。因此,原料的综合利用是广西装置提高能源利用效率的重要措施,精馏工序的节能改造对净能量具有重要影响。最后展望了木薯燃料乙醇的发展前景。