Abstract:More and more attentions have been being paid to seeking alternatives for fossil fuels. Bioenergy, as a renewable energy, is one of the best solutions. Bioenergy has been developed rapidly in China, which became the third largest producer and consumer of fuel ethanol. In order to promote the research of bioenergy technology in China, this special issue includes latest reports and articles on the fields of bioethanol, biodiesel, microbial lipid and biofuel system analysis.

Abstract:During the bioconversion of lignocellulose to ethanol, the biomass always undergoes pretreatment in order to increase the enzymatic digestibility of cellulose. In present work, we conducted the pretreatment of sugarcane bagasse with aqueous acetic acid for delignification and alkali for deacetylation respectively (Acetoline process) to increase cellulose accessibility for enzymatic hydrolysis. The effects of several factors on the pretreatment effectiveness were investigated. The enzymatic digestibility of pretreated bagasse was further studied. The enzymatic glycan conversion of pretreated solid reached about 80% when it was digested under 7.5% solid consistency with cellulase of 15 FPU/g solid and β-glucosidase of 10 CBU/g solid for 48 h. Compared with dilute acid pretreatment, Acetoline pretreatment could obtain higher enzymatic glycan conversion. The experimental results indicate that Acetoline is an effective pretreatment method to increase the enzymatic digestibility of sugarcane bagasse.

Abstract:High-concentration sugars production from stover is an important perspective technology for the cellulosic ethanol industrialization. Fed-batch process is an effective way to achieve this goal in the fermentation industry. In this study, based on fed-batch process, high-concentration sugars were produced from pretreated corn stover by enzymatic hydrolysis. After being pretreated by the dilute sulphuric acid, the impacts of the ratio of solid raw material to liquid culture, the content of supplementary materials and the refilling time on the saccharification rate were investigated. Results showed that the initial ratio of solid raw material to liquid culture was 20% (W/V) and the initial concentrations of enzymes for xylanase, cellulose and pectinase were 220 U, 6 FPU, and 50 U per gram of substrates, respectively. After 24 hours and 48 hours, 8% pretreated corn stovers were added respectively together with the additions of xylanase (20 U) and cellulose (2 FPU) per gram of substrates. After 72 hours, the final concentration of reducing sugar was increased to 138.5 g/L from 48.5 g/L of the non fed-batch process. The rate of enzyme hydrolysis of the raw material was 62.5% of the thoretical value in the fed-batch process. This study demonstrated that the fed-batch process could significantly improve the concentration of reducing sugar.

Abstract:Pyrolysis of cellulose with different catalysts has been conducted in a fixed-bed reactor. Micro-mesoporous composite molecular sieves of ZSM-5(38)/Al-MCM-41 with different Si/Al ratios were prepared under hydrothermal conditions. With powder X-ray diffraction (XRD), the catalyst samples were characterized. GC-MS was used to analyze the bio-oil composition. The effects of catalysts on the pyrolysis product yields were investigated and the results were compared with the results of experiments performed without catalyst under the same pyrolitic conditions. The presence of the catalysts decreased the liquid yield, while increased the moisture content. The major improvement in the quality of bio-oil with the use of catalysts was the increase of DL-2,3-Butanediol. ZSM-5(38)/Al-MCM-41(20) favored the formation of phenol and 2-methoxy-phenol. In addition, these catalysts were all benefit for the generation of small molecular compounds. Also, it was found that ZSM-5(38) was better for the production of C4?C5 compounds. And micro-mesoporous composite molecular sieves mainly promoted the production of C6?C8 compounds.

Abstract:Plackett-Burman (PB) design and central composite design (CCD) were applied to optimize of xylose fermentation for ethanol production by Candida shehatae HDYXHT-01. The PB results showed that (NH4)2SO4, KH2PO4, yeast extract and inoculum volume were the main affecting factors. With ethanol productivity as the target response, the optimal fermentation was determined by CCD and response surface analysis (RSM). The optimal fermentation conditions were (NH4)2SO4 1.73 g/L, KH2PO4 3.56 g/L, yeast extract 2.62 g/L and inoculum volume 5.66%. Other fermentation conditions were xylose 80 g/L, MgSO4·7H2O 0.1g/L, pH 5.0 and 250 mL flask containing 100 mL medium and cultivated at 30 °C for 48 h and the agitation speed was 140 r/min. Under this fermentation conditions, ethanol productivity was 26.18 g/L, which was 1.15 times of the initial.

Abstract:The effects of reaction temperature, ethanol concentration and weight hourly space velocity (WHSV) on the ethylene production from ethanol dehydration using zinc, manganese and cobalt modified HZSM-5 catalyst were investigated by response surface methodology (RSM). The results showed that the most significant effect among factors was reaction temperature and the factors had interaction. The optimum conditions were found as 34.4% ethanol concentration, 261.3 °C of reaction temperature and 1.18 h?1 of WHSV, under these conditions the yield of ethylene achieved 98.69%.

Abstract:In order to obtain high β-glucosidase productivity, we optimized the fermentation parameters for β-glucosidase production by Aspergillus niger HDF05. First, we screened the important parameters by Plackeet-burman design. Second, we used the path of steepest ascent to approach to the biggest response region of parameters affecting β-glucosidase production. Then, we obtained the optimal parameters by central composite design and response surface analysis. We developed a quadratic polynomial equation for predicting β-glucosidase production level. The results showed that the important parameters were temperature, packing volume, concentrations of wheat bran and (NH4)2SO4. The optimal fermentation parameters were as follows: temperature 28 °C, packing volume 71.4 mL/250 mL, wheat bran 36 g/L and (NH4)2SO4 5.5 g/L. Under the optimal conditions, we obtained the maximum enzyme activity of 60.06 U/mL, with an increase of 23.9% compared to the original fermentation parameters. During enzymatic hydrolysis of acid-pretreated corncob, addition of β-glucosidase from Aspergillus niger HDF05 greatly reduced the inhibition caused by cellobiose, and the hydrolysis yield was improved from 66.7% to 80.4%.

Abstract:Microbial lipid is a potential raw material for biofuel industry. In this review, we summarized recent progress in microbial lipid production by oleaginous fungi in terms of identifying cheap feedstock, developing robust lipid producer, establishing novel strategies and better culture modes for cellular lipid accumulation, as well as revealing the molecular mechanism of oleaginity. We discussed issues, solutions and directions for further development of microbial lipid technology.

Abstract:We studied the effects of three inorganic carbon sources, Na2CO3, NaHCO3 and CO2, and their initial concentrations on lipid production of Chlorella vulgaris. Chlorella vulgaris could utilize Na2CO3, NaHCO3 and CO2 to produce lipids. After 10-day cultivation with each of the three inorganic carbon sources, lipid yield of Chlorella vulgaris reached its peak with the concentration increase of the inorganic carbon source, but dropped again by further increase of the concentration. The pH value of the culture medium for Chlorella vulgaris increased after the cultivation on inorganic carbon source. The optimal concentration of both Na2CO3 and NaHCO3 was 40 mmol/L, and their corresponding biomass dry weight was 0.52 g/L and 0.67 g/L with their corresponding lipid yield 0.19 g/L and 0.22 g/L. When the concentration of CO2 was 6%, Chlorella vulgaris grew the fastest and its biomass dry weight was 2.42 g/L with the highest lipid yield of 0.72 g/L. When the concentration of CO2 was too low, the supply of inorganic carbon was insufficient and lipid yield was low. A too high concentration of CO2 caused a low pH and lipid accumulation was inhibited. Na2CO3 and NaHCO3 were more favorable for Chlorella vulgaris to accumulate unsaturated fatty acids than that of CO2.

Abstract:Municipal wastewater is usually problematic for the environment. The process of oleaginous microalgal culture requires large amounts of nutrients and water. Therefore, we studied the feasibility of oleaginous microalgal culture of Scenedesmus dimorphus in bubbled column photobioreactor with municipal wastewater added with different nutrients. S. dimorphus could adapt municipal nutrient-rich wastewater by adding some nutrients as nitrogen, phosphorus, ferric ammonium citrate and trace elements, and the amounts of such nutrients have significant effects on cell growth, biomass yield and lipid accumulation. At optimum compositions of wastewater medium, the algal cell concentration could reach 8.0 g/L, higher than that of 5.0 g/L in standard BG11. Furthermore, S. dimorphus had strong capacity to absorb inorganic nitrogen and phosphorus from its culture water. There was almost no total nitrogen and phosphorus residues in culture medium after three or four days culturing when the adding mounts of nitrate and phosphate in wastewater medium were no more than 185.2 mg/L and 16.1 mg/L respectively under the experimental conditions. As a conclusion, it was feasible to cultivate oleaginous microalgae with municipal nutrient-rich wastewater, not only producing feedstock for algal biodiesel, but also removing inorganic nitrogen and phosphorus from wastewater.

Abstract:Microbial oil, as raw material for biodiesel, can be produced by Trichosporon cutaneum B3 using cassava starch hydrolysate. Batch cultures demonstrated that there was little inhibitory effect with the concentration of cassava starch hydrolysate up to 90 g/L. The favorable initial pH, C/N molar ratio, nitrogen source and its concentration were 6.0, 116, yeast extract and 3.0 g/L, respectively. Under the optimized conditions, dry biomass reached 15.2 g/L and lipid content reached 40.9% after culture for 144 h in flask. Batch cultures in a 2 L stirred-tank fermenter were run for 44 h and resulted in dry biomass, lipid content and lipid yield of 28.7 g/L, 42.8% and 12.27 g/L, respectively. The chemical compositions of biodiesel prepared from lipids of T. cutaneum B3 mainly included palmitic acid methyl ester, stearic acid methyl ester, oleic acid methyl ester and linoleic acid methyl ester etc., and its main physicochemical properties were in compliance with relevant national diesel standards. Therefore, the biodiesel prepared from lipids of T. cutaneum B3 can serve as a potential fossil fuel alternatives.

Abstract:To obtain oleaginous yeast mutants with improved lipid production and growth rates, an atmospheric and room temperature plasma (ARTP) jet was used with a 96-well plate for high throughput screening. Mutants with changes in growth rates and lipid contents were obtained. At a lethality rate of 99%, the positive mutation rate of the yeast cells was 27.2% evaluated by the growth rates of the mutants and the comparison with the wild strain. The fermentation in a medium composed of yeast extract (10 g/L), peptone (10 g/L) and D-glucose (20 g/L) resulted in the lipid yield of the mutant (C4) with 4.07% (W/W) compared with that of the wild strain (1.87%).

Abstract:To improve microbial lipid production, we inserted mTn-lacZ/leu2 into Trichosporon fermentans 2.1368-Leu? to obtain high lipid production mutants. By observing the LacZ chromogenic change, the positive reaction between Cerulenin (inhibitor of fatty acid synthase) and phosphate vanillin, a higher lipid-producing mutant 2.1368-Leu?-7 grown on corn-stalk hydrolysate was obtained. The lipid content of this mutant reached 38.30% (8.97% higher than that of the control) and the lipid production rate was 8.35% (20.63% higher than that of the control). The rate of sugar utilization was 77%, meaning that 100 g corn-stalk could be converted to 8.32 g lipid. The study provided an effective method for microbial lipid production by using cheap raw materials for biodiesel.

Abstract:In order to investigate the effects of pyrolysis conditions on bio-oil production from biomass in molten salt, experiments of biomass pyrolysis were carried out in a self-designed reactor in which the molten salt ZnCl2-KCl (with mole ratio 7/6) was selected as heat carrier, catalyst and dispersion agent. The effects of metal salt added into ZnCl2-KCl and biomass material on biomass pyrolysis were discussed, and the main compositions of bio-oil were determined by GC-MS. Metal salt added into molten salt could affect pyrolysis production yields remarkably. Lanthanon salt could enhance bio-oil yield and decrease water content in bio-oil, when mole fraction of 5.0% LaCl3 was added, bio-oil yield could reach up to 32.0%, and water content of bio-oil could reduce to 61.5%. The bio-oil and char yields were higher when rice straw was pyrolysed, while gas yield was higher when rice husk was used. Metal salts showed great selectivity on compositions of bio-oil. LiCl and FeCl2 promoted biomass to pyrolyse into smaller molecular weight compounds. CrCl3, CaCl2 and LaCl3 could restrain second pyrolysis of bio-oil. The research provided a scientific reference for production of bio-oil from biomass pyrolysis in molten salt.

Abstract:To recover and use protein resources in excess sludge and decrease the cost of microbial lipid production, heat-alkaline was used to treat the sludge, and the hydrolysate was preliminarily used as nitrogen source to cultivate Rhodosporidium toruloides AS 2.1389 for lipid accumulation. Firstly, we treated the excess sludge under different alkaline conditions (pH 10, pH 12, pH 13) within the reaction time of 5–10 h to investigate the effect of nitrogen source release. Secondly, we used the sludge hydolysate to culture R. toruloides AS, and test the effect on cell growth. Results showed that treatment of excess sludge at pH 13 for 5 h was the most effective for nitrogen release. However, the hydrolysate obtained at pH 10 (5 h) was the most suitable for culturing R. toruloides AS, and under this condition, the inner-cellular lipid content could reach 35% of the total biomass weight.

Abstract:Five Klebsiella pneumonia strains (including two strains whose genes for lactic acid were knocked out) were used to produce 2,3-butanediol, in which K. pneumonia HR521 LDH (gene for lactic acid was knocked out) was the best for the production, and then the fermentation medium was optimized by orthogonal design. The optimum compositions were as follows: glucose 90 g/L, (NH4)2HPO4 3 g/L, CLSP 6 g/L, sodium acetate 5 g/L, KCl 0.4 g/L, MgSO4 0.1 g/L, FeSO4·7H2O 0.02 g/L, MnSO4 0.01 g/L. Under the above conditions, final concentration of acetone and 2,3-butanediol could reach 37.46 g/L, 10 g/L higher than that under the initial conditions, the yield was 90.53% of the theory, and the productivity was 1.5 g/(L·h), and no lactic acid was detected, which could be benefit for the downstream processing and industrial application.

Abstract:1,3-propanediol is an important raw material in chemical industry. Microbial conversion of glycerol or glucose into 1,3-propanediol has been given much attention due to its renewable resource, mild reaction conditions, and other advantages. It is a challenge to efficiently separate 1,3-propanediol from a mixture of multiple components, such as 1,3-propanediol, 2,3-butanediol, water, residual glycerol, ethanol, macromolecules and salts, for the reason that 1,3-propanediol, glycerol and 2,3-butanediol are all very hydrophilic and have intense polarity. The conventional evaporation and distillation techniques used in the purification of 1,3-propanediol suffer from the problem of high energy consumption and low recovery. It makes the recovery of 1,3-propanediol from a fermentation broth become a bottleneck in industrial production. The down-stream processing of biologically produced 1,3-propanediol mainly includes the removal of protein, salts, water and other impurities. This paper analyze the research progress of these separation technologies and point out the developing direction worth further investigation.

Abstract:Model-based system analysis is an important tool for evaluating the potential and impacts of biofuels, and for drafting biofuels technology roadmaps and targets. The broad reach of the biofuels supply chain requires that biofuels system analyses span a range of disciplines, including agriculture/forestry, energy, economics, and the environment. Here we reviewed various models developed for or applied to modeling biofuels, and presented a critical analysis of Agriculture/Forestry System Models, Energy System Models, Integrated Assessment Models, Micro-level Cost, Energy and Emission Calculation Models, and Specific Macro-level Biofuel Models. We focused on the models’ strengths, weaknesses, and applicability, facilitating the selection of a suitable type of model for specific issues. Such an analysis was a prerequisite for future biofuels system modeling, and represented a valuable resource for researchers and policy makers.

Abstract:The national standards of biofuels specify the technique specification and analytical methods. A water content certified reference material based on the water saturated octanol was developed in order to satisfy the needs of the instrument calibration and the methods validation, assure the accuracy and consistency of results in water content measurements of biofuels. Three analytical methods based on different theories were employed to certify the water content of the reference material, including Karl Fischer coulometric titration, Karl Fischer volumetric titration and quantitative nuclear magnetic resonance. The consistency of coulometric and volumetric titration was achieved through the improvement of methods. The accuracy of the certified result was improved by the introduction of the new method of quantitative nuclear magnetic resonance. Finally, the certified value of reference material is 4.76% with an expanded uncertainty of 0.09%.

Abstract:Life Cycle Assessment (LCA) is the only standardized tool currently used to assess environmental loads of products and processes. The life cycle analysis, as a part of LCA, is a useful and powerful methodology for studying life cycle energy efficiency and life cycle GHG emission. To quantitatively explain the potential of energy saving and greenhouse gas (GHG) emissions reduction of corn stover-based ethanol, we analyzed life cycle energy consumption and GHG emissions of corn stover-based ethanol by the method of life cycle analysis. The processes are dilute acid prehydrolysis and enzymatic hydrolysis. The functional unit was defined as 1 km distance driven by the vehicle. Results indicated: compared with gasoline, the corn stover-based E100 (100% ethanol) and E10 (a blend of 10% ethanol and 90% gasoline by volume) could reduce life cycle fossil energy consumption by 79.63% and 6.25% respectively, as well as GHG emissions by 53.98% and 6.69%; the fossil energy consumed by biomass stage was 68.3% of total fossil energy input, N-fertilizer and diesel were the main factors which contributed 45.78% and 33.26% to biomass stage; electricity production process contributed 42.06% to the net GHG emissions, the improvement of technology might reduce emissions markedly.