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	Réponses : 1124 Pages : ... 37 38 39 40 41 [42] 43 44 45 46 47 ... / 57

12/08/2010	Microalgal biomass as a cellulosic fermentation feedstock for, bioethanol production Razif Harun, W.S.Y. Jason, Tamara Cherrington and Michael K. Danquah
	The current problem of pollution caused by the burning of fossil fuels as well as their declining reserves is driving research into and development of biofuels. Bioethanol is one such fuel that might fulfil these prerequisites. Bioethanol can be developed from different feedstocks such as sucrose, starch and lignocellulosic based materials. Current global bioethanol production hinges on plantation feedstocks, and this creates a major competition for agricultural logistics between the food and fuel markets. To be a viable alternative, bioethanol must be produced in a cheap, environmentally friendly and sustainable manner. Microalgal biomass has the potential to meet the above criteria as it cannot be used directly in the human food chain, and can be sustainably processed at costs similar to or less than, for example, lignocellulosic biomass. Whilst the overall process can vary, the conversion of biomass to bioethanol usually contains the following steps: pre-treatment of feedstock, hydrolysis, fermentation and distillation of bioethanol. This paper reviews the different technologies under each of these process steps and critically assesses their applicability to bioethanol production from microalgal biomass. It suggests important strategies to improve the economics and sustainability of the entire bioprocess engineering of microalgae to produce bioethanol.
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12/08/2010	Evaluation of Methods to Extract and Quantify Lipids from Synechocystis PCC 6803 Jie Sheng, Raveender Vannela and Bruce E. Rittmann
	In order to use the photosynthetic cyanobacterium Synechocystis as asource of feedstock for carbon-neutral,non petroleum-based diesel fuel, we evaluated several solvents and solvent systems for their ability to extract lipid from wild-type Synechocystis PCC6803. Chloroform+methanol-basedFolch and Bligh & Dyer methods had the highest lipid recoveries. Less toxic solvents, such as methanol and MTBE, or direct transesterification of biomass(without pre-extraction step)gave only slightly lower lipid-extraction yields. Ethanol, isopropanol, butanol, hexane, acetic ester, and their combinations were not effective for lipid extraction from Synechocystis (>20% loss), even though they are widely used for non-polar lipid extraction from other feedstock, includingalgae. We confirmed the success of chloroform+methanol-based extraction by their penetration of the cell membrane system, higher polarity, and stronger interaction with hydrogen bonds. The less-polar solvents not only had lower lipid yield, but also extracted more non-lipid compounds that require extra purification to remove. We also characterized the fatty-acid profile of Synechocystis PCC 6803: C16:0 (60%), C16:1 (9.5%), C18:0 (1.2%), C18:1 (2%), C18:2 (9.8%), and C18:3 (16.5%).
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03/08/2010	Variations in lipid yields and compositions of marine microalgae during cell gro Xinxin Lv, Li Zou, Baowei Sun, Jiangtao Wang and Ming-Yi Sun
	To determine variability of marine microalgal lipids during cell growth and respiration, and within intracellular structures, we conducted two series of experiments: (1) batch culturing Isochrysis sp., Gymnodinium sp., Platymonas subcordiforus, Heterosigma akashiwo Hada, and Skeletonema costatum with lipid analysis for cell samples collected in exponential growth and stationary phase respectively; and (2) batch culturing Isochrysis sp. and Gymnodinium sp. from exponential growth to stationary phase and followed by dark incubation with progressive lipid analysis. Moreover, membrane and intracellular storage fatty acids were separated using Si-gel chromatography from representative samples of each species in the second experiment (respectively in exponential growth, stationary phase, and dark respiration). Results from the first experiment showed that no matter how differently microalgae grew, their lipid yields were 438× higher in stationary phase than in exponential growth phase. Progressive lipid analysis in the second experiment indicated that total fatty acid (FA) yields in two microalgal cultures continuously increased throughout exponential and stationary phases but total neutral lipid (NL) yields slowed or stopped to increases in stationary phase. During dark incubations, total FA yields decreased steadily in both Isochrysis (with constant cell density) and Gymnodinium (with declining cell density) cultures but total NL yields decreased only in Gymnodinium culture. Lipid compositions and proportions of membrane vs. intracellular fatty acids varied differently with growth phases and respiration in two cultures. This study suggests that the effect of cell growth phase on cellular lipid yield and composition is species-dependent and is likely related to the capacity of cells to synthesize membrane vs. intracellular storage lipids.
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02/08/2010	Oil extraction from microalgae for biodiesel production Halim R, Gladman B, Danquah MK, Webley PA.
	This study examines the performance of supercritical carbon dioxide (SCCO(2)) extraction and hexane extraction of lipids from marine Chlorococcum sp. for lab-scale biodiesel production. Even though the strain of Chlorococcum sp. used in this study had a low maximum lipid yield (7.1 wt% to dry biomass), the extracted lipid displayed a suitable fatty acid profile for biodiesel [C18:1 ( approximately 63 wt%), C16:0 ( approximately 19 wt%), C18:2 ( approximately 4 wt%), C16:1 ( approximately 4 wt%), and C18:0 ( approximately 3 wt%)]. For SCCO(2) extraction, decreasing temperature and increasing pressure resulted in increased lipid yields. The mass transfer coefficient (k) for lipid extraction under supercritical conditions was found to increase with fluid dielectric constant as well as fluid density. For hexane extraction, continuous operation with a Soxhlet apparatus and inclusion of isopropanol as a co-solvent enhanced lipid yields. Hexane extraction from either dried microalgal powder or wet microalgal paste obtained comparable lipid yields.
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02/08/2010	Future prospects of microalgal biofuel production systems Stephens E, Ross IL, Mussgnug JH, Wagner LD, Borowitzka MA, Posten C, Kruse O, Hankamer B.
	Climate change mitigation, economic growth and stability, and the ongoing depletion of oil reserves are all major drivers for the development of economically rational, renewable energy technology platforms. Microalgae have re-emerged as a popular feedstock for the production of biofuels and other more valuable products. Even though integrated microalgal production systems have some clear advantages and present a promising alternative to highly controversial first generation biofuel systems, the associated hype has often exceeded the boundaries of reality. With a growing number of recent analyses demonstrating that despite the hype, these systems are conceptually sound and potentially sustainable given the available inputs, we review the research areas that are key to attaining economic reality and the future development of the industry.
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02/08/2010	The tide turns towards microalgae. Philip Hunter
	doi:10.1038
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02/08/2010	In-field experimental verification of cultivation of microalgae Chlorella sp. using the flue gas from a cogeneration unit as a source of carbon dioxide Kastanek F, Sabata S, Solcova O, Maléterová Y, Kastanek P, Brányiková I, Kuthan K, Zachleder V.
	A complex treatment of agricultural waste including the following major steps: anaerobic fermentation of suitable waste, cogeneration of the obtained biogas and growth of microalgae consuming the CO2 from biogas and flue gas was verified under field conditions in a pilot-scale photobioreactor. The growth kinetics of microalgae Chlorella sp. consuming mixture of air and carbon dioxide (2% (v/v) of CO2), or flue gas (8-10% (v/v) of CO2) was investigated. The results obtained in the pilot photobioreactor were compared with results previously measured in laboratory photobioreactors. The field tests were performed in a pilot-scale outdoor solar-bubbled photobioreactor located at a biogas station. The pilot-scale photobioreactor was in the shape of a flat and narrow vertical prism with a volume of 300 L. The microalgae growth rates were correlated with empirical formulas. Laboratory analyses of the produced microalgae confirmed that it meets the strict EU criteria for relevant contaminants level in foodstuffs. Utilization of flue gases from cogeneration therefore was not found to be detrimental to the quality of microalgal biomass, and may be used in these types of bioreactors.
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02/08/2010	The economics of producing biodiesel from algae Brian J. Gallagher
	Biodiesel is an alternative fuel for conventional diesel that is made from natural plant oils, animal fats, and waste cooking oils. This paper discusses the economics of producing biodiesel fuel from algae grown in open ponds. There is potential for large-scale production of biodiesel from algal farms on non-arable land; however, previous studies have failed to demonstrate an economically viable process that could be scalable to a commercialized industry. The problems include inconsistent and insufficient algal productivities, uncertain capital and operating costs, volatile market prices and unknown levels of government support. Although intensive work is being done on many technological issues, the economic studies and data are incomplete and out of date. This paper presents an updated financial analysis of the production and economic conditions that could have a profound effect on the success of this important alternative fuel production process.
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02/08/2010	Enhancement Effect of Ethyl-2-methyl acetoacetate on Triacylglycerols Production by a Freshwater Microalga, Scenedesmus sp. LX1 Li Xin, Hu Hong-ying, Yang Jia and Wu Yin-hu
	Microalgae are very promising in biodiesel production. To reduce the production cost, approaches to enhance lipid and triacylglycerols (TAGs) production by microalgae have gained much attention. Effect of ethyl-2-methyl acetoacetate (EMA) on the lipid and TAGs production by a freshwater microalga, Scenedesmus sp. LX1, was studied in this paper. EMA below a concentration of 2 mg·L-1 had no significant effect on microalgal biomass or lipid production. The biomass and lipid productivity were about 0.47 g·L-1 and 139 mg·L-1, respectively, and the lipid content per biomass was about 30% (w/w). Promisingly, comparing with the one without EMA treatment, under EMA concentrations of 1.0 mg·L-1 not, vert, similar 2.0 mg·L-1 the TAGs content per lipid (about 20% (w/w)) and TAGs productivity (about 23 mg·L-1) were increased by 79% and 40%, respectively. Therefore, exposing algal cells with trace amount of EMA offers a viable method to enhance the TAGs production in Scenedesmus sp. LX1.
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02/08/2010	Evaluation of the composition of continuously-cultivated Arthrospira (Spirulina) platensis using ammonium chloride as nitrogen source C.E.N. Sassano, L.A. Gioielli, L.S. Ferreira, M.S. Rodrigues, S. Sato, A. Converti and J.C.M. Carvalho
	This work is focused on the influence of dilution rate (0.08 ≤ D ≤ 0.32 d−1) on the continuous cultivation and biomass composition of Arthrospira (Spirulina) platensis using three different concentrations of ammonium chloride (cNo = 1.0, 5.0 and 10 mol m−3) as nitrogen source. At cNo = 1.0 and 5.0 mol m−3 the biomass protein content was an increasing function of D, whereas, when using cNo = 10 mol m−3, the highest protein content (72.5%) was obtained at D = 0.12 d−1. An overall evaluation of the process showed that biomass protein content increased with the rate of nitrogen supply (D cNo) up to 72.5% at D cNo = 1.20 mol m−3 d−1. Biomass lipid content was an increasing function of D only when the nitrogen source was the limiting factor for the growth (D cNo ≤ 0.32 mol m−3 d−1), which occurred solely with cNo = 1.0 mol m−3. Under such conditions, A. platensis reduced its nitrogen reserve in the form of proteins, while maintaining almost unvaried its lipid content. The latter was affected only when the concentration of nitrogen was extremely low (cNo = 1.0 mol m−3). The most abundant fatty acids were the palmitic (45.8 ± 5.20%) and the γ-linolenic (20.1 ± 2.00%) ones. No significant alteration in the profiles either of saturated or unsaturated fatty acids was observed with cNo ≤ 5.0 mol m−3, prevailing those with 16 and 18 carbons.
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27/07/2010	Future prospects of microalgal biofuel production systems Evan Stephens, Ian L. Ross, Jan H. Mussgnug, Liam D. Wagner, Michael A. Borowitzka, Clemens Posten, Olaf Kruse and Ben Hankamer
	Climate change mitigation, economic growth and stability, and the ongoing depletion of oil reserves are all major drivers for the development of economically rational, renewable energy technology platforms. Microalgae have re-emerged as a popular feedstock for the production of biofuels and other more valuable products. Even though integrated microalgal production systems have some clear advantages and present a promising alternative to highly controversial first generation biofuel systems, the associated hype has often exceeded the boundaries of reality. With a growing number of recent analyses demonstrating that despite the hype, these systems are conceptually sound and potentially sustainable given the available inputs, we review the research areas that are key to attaining economic reality and the future development of the industry.
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27/07/2010	Study on the microalgal pigments extraction process: Performance of microwave assisted extraction Virginie Pasquet, Jean-René Chérouvrier, Firas Farhat, Valérie Thiéry, Jean-Marie Piot, Jean-Baptiste Bérard, Raymond Kaas, Benoît Serive, Thierry Patrice, Jean-Paul Cadoret and Laurent Picot
	The performance of microwaves irradiation (MAE and VMAE) to extract pigments from two marine microalgae was compared to conventional processes (cold and hot soaking and ultrasound-assisted extraction). Pigments were quantified by RP-HPLC and extraction performance was assessed regarding rapidity, reproducibility and extraction yields. Scanning electron microscopy was used at all extraction steps to assess the impact of the process on microalgal cell integrity. Freeze-drying and pigments extraction preserved microalgae cell integrity (except sonication) and evoked agglutination in superposed cells layers. All processes performed on Dunaliella tertiolecta (chlorophyte) lead to rapid pigments extraction, and equivalent pigments extraction yields, the absence of frustule allowing immediate solvent penetration in microalgae cells. In contrast, presence of the frustule in the diatom Cylindrotheca closterium (bacillariophyte) constituted a mechanical barrier to pigment extraction. MAE was identified as the best extraction process for CC pigments as it combined rapidity, reproducibility, homogeneous heating and high extraction yields.
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20/07/2010	Growth and neutral lipid synthesis in green microalgae: A mathematical model Packer A, Li Y, Andersen T, Hu Q, Kuang Y, Sommerfeld M
	Many green microalgae significantly increased their cellular neutral lipid content when cultured in nitrogen limited or high light conditions. Due to their lipid production potential, these algae have been suggested as promising feedstocks for biofuel production. However, no models for algal lipid synthesis with respect to nutrient and light have been developed to predict lipid production and to help improve the production process. A mathematical model is derived describing the growth dynamics and neutral lipid production of green microalgae grown in batch cultures. The model assumed that as the nitrogen was depleted, photosynthesis became uncoupled from growth, resulting in the synthesis and accumulation of neutral lipids. Simulation results were compared with experimental data for the green microalgae Pseudochlorococcum sp. For growth media with low nitrogen concentration, the model agreed closely with the data; however, with high nitrogen concentration the model overestimated the biomass. It is likely that additional limiting factors besides nitrogen could be responsible for this discrepancy. Copyright © 2010 Elsevier Ltd. All rights reserved.
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20/07/2010	A new tool to detect high viscous exopolymers from microalgae Badel S, Callet F, Laroche C, Gardarin C, Petit E, El Alaoui H, Bernardi T, Michaud P.
	Microalgae are microorganisms often surrounded by a slime layer made of secreted polymeric substances sometimes including polysaccharides. These polysaccharides, weakly described in the literature, can constitute value-added molecules in several industrial areas. The aim of this article is to show that a new tool, the BioFilm Ring Test ((R)), can be used to detect viscous microalgal exopolymers. Two red microalgal strains (Rhodella violacea and Porphyridium purpureum), one cyanobacterium (Arthrospira platensis) and their excreted polymeric fractions were studied. R. violacea and P. purpureum induced a positive response with the BioFilm Ring Test ((R)) contrary to A. platensis. Finally, the understanding of the fractions viscosity involvement in the BRT response was performed by a rheological study.
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20/07/2010	Hyphenated technique for the extraction and determination of isoflavones in algae: ultrasound-assisted supercritical fluid extraction followed by fast chromatography with tandem mass spectrometry B. Klejdus, L. Lojková, M. Plaza, M. nóblová and D. těrbová
	New hyphenated technique for the extraction and determination of isoflavones in sea and freshwater algae and cyanobacteria was developed. The method consists of sonication sample pretreatment, extraction by supercritical CO2 modified by 3% v/v of MeOH/H2O mixture (9:1 v/v) at 35 MPa and 40 °C for 60 min, fast chromatography analysis by the means of Agilent 1200 Series Rapid Resolution and MS/MS determination. Agilent 1200 Series RRLC was used with Zorbax SB-CN chromatographic column, (100 × 2.1 mm, particle size 3.5 μm), 3 μl injection volume, mobile phase consisting of 0.2% (v/v) acetic acid in water (solvent A) and acetonitrile (solvent B) and used with linear gradient (30% B at 0 min, from 0 min to 3 min up to 50%B, from 3 min to 6 min up to 80%B and from 6 min to 10 min down to 30% B). The flow rate was 0.4 mL/min, column oven temperature 35 °C. MS detector Agilent Technologies 6460 Triple quadrupole LC/MS with Agilent Jet Stream was used in a negative ESI mode under following conditions: gas temperature 350 °C, gas flow 13 L/min, nebulizer gas pressure 50 psi, sheath gas temperature 400 °C, sheath gas flow 12 L/min, capillary voltage was 4 kV. Samples were analysed in the Multiple Reaction Monitoring (MRM) mode. 8 isoflavone compounds were found for the first time in 7 real samples of sea algae and in 3 control samples of freshwater algae and cyanobacteria. Usual optimisation study of extraction parameters was performed. Pressure and temperature optima for algae matrix are different from those obtained sooner for other matrices for most of the analytes, but the results of modifier optimisation study are in good accordance with those obtained sooner for spiked samples and red clover matrix. It seems that matrix has very small or no effect on the modifier selection. Two different approaches of sonication pretreatment were tested: sonication bath and the thorn instrument. In longer extraction time experiments, thorn sonication was more efficient and recovery of following supercritical fluid extraction was higher.
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20/07/2010	Importance of algae oil as a source of biodiesel Ayhan Demirbas, and M. Fatih Demirbas
	Algae are the fastest-growing plants in the world. Industrial reactors for algal culture are open ponds, photobioreactors and closed systems. Algae are very important as a biomass source. Algae will some day be competitive as a source for biofuel. Different species of algae may be better suited for different types of fuel. Algae can be grown almost anywhere, even on sewage or salt water, and does not require fertile land or food crops, and processing requires less energy than the algae provides. Algae can be a replacement for oil based fuels, one that is more effective and has no disadvantages. Algae are among the fastest-growing plants in the world, and about 50% of their weight is oil. This lipid oil can be used to make biodiesel for cars, trucks, and airplanes. Microalgae have much faster growth-rates than terrestrial crops. the per unit area yield of oil from algae is estimated to be from 20,000 to 80,000 l per acre, per year; this is 731 times greater than the next best crop, palm oil. The lipid and fatty acid contents of microalgae vary in accordance with culture conditions. Most current research on oil extraction is focused on microalgae to produce biodiesel from algal oil. Algal-oil processes into biodiesel as easily as oil derived from land-based crops.
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15/07/2010	Life Cycle Analysis on Biodiesel Production from Microalgae: Water Footprint and Nutrients Balance Jia Yang, Ming Xu, Xuezhi Zhang, Qiang Hu, Milton Sommerfeld and Yongsheng Chen
	This research examines the life-cycle water and nutrients usage of microalgae-based biodiesel production. The influence of water types, operation with and without recycling, algal species, geographic distributions are analyzed. The results confirm the competitiveness of microalgae-based biofuels and highlight the necessity of recycling harvested water and using sea/wastewater as water source. To generate 1 kg biodiesel, 3,726 kg water, 0.33kg nitrogen, and 0.71 kg phosphate are required if freshwater used without recycling. Recycling harvest water reduces the water and nutrients usage by 84% and 55%. Using sea/wastewater decreases 90% water requirement and eliminates the need of all the nutrients except phosphate. The variation in microalgae species and geographic distribution are analyzed to reflect microalgae biofuel development in the U.S. The impacts of current federal and state renewable energy programs are also discussed to suggest suitable microalgae biofuel implementation pathways and identify potential bottlenecks.
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15/07/2010	Algal biodiesel economy and competition among bio-fuels D.H. Lee
	This investigation examines the possible results of policy support in developed and developing economies for developing algal biodiesel through to 2040. This investigation adopts the Taiwan General Equilibrium Model-Energy for Bio-fuels (TAIGEM-EB) to predict competition among the development of algal biodiesel, bioethanol and conventional crop-based biodiesel. Analytical results show that algal biodiesel will not be the major energy source in 2040 without strong support in developed economies. In contrast, bioethanol enjoys a development advantage relative to both forms of biodiesel. Finally, algal biodiesel will almost completely replace conventional biodiesel. CO2 reduction benefits the development of the bio-fuels industry.
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15/07/2010	Dispersed Ozone Flotation of Chlorella vulgaris Ya-Ling Cheng, Yu-Chuan Juang, Guan-Yu Liao, Shih-Hsin Ho, Kuei-Ling Yeh, Chun-Yen Chen, Jo-Shu Chang, Jhy-Chern Liu and Duu-Jong Lee
	Flotation separation of Chlorella vulgaris, a species with excellent potential for CO2 capture and lipid production, was studied using dispersed ozone gas. Pure oxygen aeration did not yield flotation. Conversely, applying ozone effectively separation algae from broth through flotation. The ozone dose applied for sufficient algal flotation is <0.05 mg/g biomass, much lower than those used in practical drinking waterworks (0.10.3 mg/g suspended solids). Main products, lipid C16:0, was effectively collected in the flotage phase. The algae removal rate, surface charge, and hydrophobicity of algal cells, and proteins and polysaccharides contents of algogenic organic matter (AOM) were determined. Certain quantities of proteins were present in the cultivated algal suspension, hence, minimal quantity of ozone was required to release intracellular proteins as surfactants to lead to effective flotation.
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15/07/2010	Cultivation, photobioreactor design and harvesting of microalgae for biodiesel production: A critical review Chun-Yen Chen, Kuei-Ling Yeh, Rifka Aisyah, Duu-Jong Lee and Jo-Shu Chang
	Microalgae have the ability to mitigate CO2 emission and produce oil with a high productivity, thereby having the potential for applications in producing the third generation of biofuels. The key technologies for producing microalgal biofuels include identification of preferable culture conditions for high oil productivity, development of effective and economical microalgae cultivation systems, as well as separation and harvesting of microalgal biomass and oil. This review presents recent advances in microalgal cultivation, photobioreactor design, and harvesting technologies with a focus on microalgal oil (mainly triglycerides) production. The effects of different microalgal metabolisms (i.e., phototrophic, heterotrophic, mixotrophic, and photoheterotrophic growth), cultivation systems (emphasizing the effect of light sources), and biomass harvesting methods (chemical/physical methods) on microalgal biomass and oil production are compared and critically discussed. This review aims to provide useful information to help future development of efficient and commercially viable technology for microalgae-based biodiesel production.
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