微藻培养方法研究进展

微藻是一种有前景的生物柴油原料。微藻培养是微藻生物柴油生产过程的重要环节。本文就微藻培养方法的研究进展进行了阐述。对自养、异养及兼养三种培养方法进行了比较,并对微藻培养提出了建议。     

基于开放池培养的微藻生物柴油经济成本分析

通过广泛的文献调研和专家咨询,构建微藻生物柴油经济成本估算模型,依据中国市场行情对基于开放池培养的微藻生物柴油经济成本进行估算分析。结果表明:目前中国基于开放池培养的微藻生物柴油理论成本可达4.2~5.9万$/t,其中土地、营养盐、碳源以及设备折旧占较高比例,分别为25.50%、19.29%~27.04%、14.01%~19.65%和9.96%~14.13%。从技术环节看,79.44%~85.16%的经济成本集中于养殖环节。提高微藻生长率、油脂含量和碳吸收率,增强其对环境的适应能力以及寻找低成本的碳源和营养盐源是降低微藻生物柴油经济成本的主要途径。     

微藻制取生物柴油研究现状与发展

微藻作为制取生物柴油的原料具有很多特殊优势,近年来成为研究热点,阐述了国内外微藻生物柴油的研究现状以及超临界CO2萃取制造生物柴油的优势,微藻生产生物柴油的产业化瓶颈。     

微藻生物柴油发展与产油微藻资源利用

生物柴油作为目前全世界正积极推进的可再生能源项目,与清洁核能、风能、光伏发电等将成为人类21世纪的主要能源构成.产油微藻作为生产生物柴油的原料与其他原料相比具有较大优势,在解决成本及生产环节的瓶颈问题后,必将成为生物柴油的主要原料来源.文章探讨了生物柴油的研究现状和微藻生物柴油的优势:微藻商业化生产的主要方式:开放式跑道池、管道式光生物反应器的特点;微藻生物柴油产业链的形成及对促进生物柴油产业商业化的影响.     

新一代生物柴油原料—微藻

随着能源需求的剧增,政府和企业积极开发可替代的能源资源。生物柴油现已成为国际上发展最快、应用最广的石油替代燃料。介绍了微藻作为一种新型的生物柴油原料具有来源广泛、成本低廉、清洁可再生等优点和影响微藻油脂积累的因素,展望了微藻生物柴油的发展前景,为我国生物柴油的发展提供参考。     

微藻培养模式研究进展

微藻培养模式的选择对于提高微藻生长速率具有重要作用,批次培养、流加培养、半连续培养和连续培养是4种不同的微藻培养模式。文章综述了4种不同培养模式在微藻培养过程中的应用与最新研究进展,概括了不同培养模式的具体应用范围和实施效果,对不同培养模式促进微藻生长的机理进行了分析,旨在为能源微藻大规模培养技术的发展以及能源微藻工业化培养模式的选择和改进提供参考。     

微波辅助组合离子液体直接制备微藻生物柴油

采用小球藻、甲醇为原料,离子液体组合物作为提取催化剂,微波辅助原位一步法催化制备微藻生物柴油。考察微波功率、离子液体类型、离子液体用量、反应温度、反应时间、醇油物质的量之比等因素对酯交换率的影响,并与传统水浴加热机械搅拌法比较。结果表明:微波和离子液体对生物柴油的制备有协同促进作用,离子液体具有催化、提取与增溶的作用,能较好地消除醇油界面接触,微波的引入可强化传质传热过程,与传统加热方式水浴加热机械搅拌法相比,可缩短酯交换反应的时间,降低反应温度,减少离子液体、甲醇用量。离子液体[BMIM][HCOO]为提取剂,微藻油脂提取率最高;酸性离子液体催化效果明显高于碱性离子液体,离子液体[SO₃H-BMIM][HSO₄]为催化剂,微藻油脂转化率最高。在甲醇用量和藻粉质量比为6∶1,离子液体组合物和藻粉质量比为5∶1,[BMIM][HCOO]与[SO₃H-BMIM][HSO₄]体积比12∶1,微波功率400 W,反应温度为60℃,反应时间40 min条件下,生物柴油转化率可达93.3%。该方法将离子液体溶解提取性能、催化性能及微波的热效应相结合,将油脂的提取与油脂的酯化合二为一,能够实现微藻生物柴油的一步转化制备。     

基于微藻资源化利用的碳减排技术

微藻具有光合效率高、零净碳值、生长周期短、易培养、油含量高等优点,是一种极具前景的生物柴油原料。将微藻资源化利用与碳减排耦合的微藻生物柴油技术研究已受到政府和企业的广泛关注。综述了微藻高效固定CO2技术中微藻种类的筛选、培育、生长反应器及其系统的开发,微藻资源化利用的技术种类,展望了基于微藻资源化利用的碳减排技术的发展前景。     

中国微藻生物质能源专利技术分析

大力发展微藻生物质能源是解决能源危机和环境问题的有效途径。文章从微藻资源、微藻培养系统、培养物采收技术、微藻生物柴油炼制、含油微藻综合利用等方面出发,综述了中国微藻生物质能源专利的发展现状,旨在使科研工作者更加全面地了解这一领域发展趋势,并且促进科研工作者对自主知识产权的保护意识。     

微藻生物能源研究现状及展望

能源是现代社会发展的命脉,目前仍以化石燃料为主,而对化石燃料过度依赖导致的能源危机和环境问题日益突出,人类需要寻找可再生的清洁能源作为替代能源。微藻作为可持续的生物能源原料,具有巨大的发展潜力。本文综述了微藻原料获取各环节的研究现状,包括微藻育种、规模培养和采收,并重点论述了微藻生物质转化为生物能源产品的研究进展,包括生物柴油、生物乙醇、生物燃气、生物油,同时指出了微藻生物能源未来的研究方向。     

Microalgae for biodiesel production and other applications: A review

Sustainable production of renewable energy is being hotly debated globally since it is increasingly understood that first generation biofuels, primarily produced from food crops and mostly oil seeds are limited in their ability to achieve targets for biofuel production, climate change mitigation and economic growth. These concerns have increased the interest in developing second generation biofuels produced from non-food feedstocks such as microalgae, which potentially offer greatest opportunities in the longer term. This paper reviews the current status of microalgae use for biodiesel production, including their cultivation, harvesting, and processing. The microalgae species most used for biodiesel production are presented and their main advantages described in comparison with other available biodiesel feedstocks. The various aspects associated with the design of microalgae production units are described, giving an overview of the current state of development of algae cultivation systems (photo-bioreactors and open ponds). Other potential applications and products from microalgae are also presented such as for biological sequestration of CO₂, wastewater treatment, in human health, as food additive, and for aquaculture.     

Energy recovery from microalgal biomass via enhanced thermo-chemical process

This work showed that microalgae having low lipid content has high potential for energy recovery via thermo-chemical processes. As an example, Microcystis aeruginosa (M. aeruginosa) was considered and tested. Specifically, this work verified that the growth rate of M. aeruginosa was extremely fast compared to other microalgae (as a factor of ∼10). Moreover, this work investigated the CO₂ co-feed impact on thermo-chemical processes (pyrolysis/gasification) using M. aeruginosa. Introducing CO₂ in the thermo-chemical process as reaction media or feedstock can enhance the efficiency of thermo-chemical processes by expediting the cracking capability of condensable hydrocarbons (tar). The generation of CO was enhanced as a factor of ∼2. Further generation of H₂ could be achieved in the presence of CO₂. Thus, utilizing CO₂ as reaction media or chemical feedstock can modify the end products into environmentally benign and desirable ones. The CO₂ co-feed impact on thermo-chemical processes with lingo-cellulosic biomass can be universally applied.     

Microalgal biodiesel in China: Opportunities and challenges

With rapid economic development, energy consumption in China has tripled in the past 20 years, exceeding 2.8 billion tons of standard coal in 2008. The search for new green energy as substitutes for nonrenewable energy resources has become an urgent task. Biodiesel is one of the most important bioenergy sources. According to the Mid- and Long-term Development Plan for Renewable Energy in China, the consumption of biodiesel in China will reach 0.2 million tons in 2010 and 2.0 million tons in 2020. However, large-scale production of biodiesel is restricted by the limited sources of raw materials. Microalgal oil is a prospective raw material for biodiesel production. Development of technology for the production and commercialization of biodiesel from microalgae has become a hot topic in the field of bioenergy and CO₂ emission mitigation. Biodiesel from microalgae can be produced at laboratory-scale, but the cost is too high. Few studies on the commercialization of the technology of producing biodiesel from microalgae have been reported. In this review, recent progress on the research and development of biodiesel from microalgae that have resulted in scientific breakthroughs and innovation in engineering in China are introduced. The existing challenges are also discussed. Based on a detailed analysis, several novel strategies on commercial biodiesel production from microalgae are proposed.     

Effects of flocculants on lipid extraction and fatty acid composition of the microalgae Nannochloropsis oculata and Thalassiosira weissflogii

The aim of this study was to investigate the possible interference of anionic and cationic flocculants in the lipid extraction and fatty acid profiles of two species of marine microalgae: Nannochloropsis oculata and Thalassiosira weissflogii. Cells were grown in batch cultures (f/2 medium, salinity of 28, temperature of 20 °C, light intensity of 40 ??mol photons  m^-2 s^-1 and 12/12 h L/D photoperiod) and concentrated using sodium hydroxide (control), sodium hydroxide and the anionic polyacrylamide flocculant Magnafloc^® LT-25 (APF treatment) and sodium hydroxide plus the cationic polyacrylamide flocculant Flopam^® (CPF treatment). There were no statistically significant differences among treatments with respect to lipid extraction for both species. However, N. oculata which presented higher percentages of C16:0, C16:1 and C20:5 fatty acids showed an increase of C14:0 and a decrease of C20:5 with the use of anionic flocculant. Additionally, T. weissflogii which had high percentages of C16:0, C16:1, C16:3 and C20:5, showed a decrease of C18:0 and C18:1n9c when both flocculants were used and a small decrease of C16:0 in the APF treatment. The results indicate that the choice of flocculant should be based on the level of saturation desirable, i.e., if the goal is to produce more stable biodiesel, with low percentage unsaturated fatty acids, then anionic flocculants should be used. On the other hand, if the aim is to produce unsaturated fatty acids for commercial uses in the pharmacy or food industries, then anionic polymers should be avoided.     

Isolation and identification by 18S rDNA sequence of high lipid potential microalgal species for fuel production in Hainan Dao

To exploit indigenous microalgal species with the potential for biodiesel production, 101 algal cultures were isolated from partial waters in Hainan province. Eight cultures were selected based on their high biomass, high lipid content and ease of cultivation, then identified based on morphology and 18S rDNA sequence analysis. These isolates were identified as Tetranephris brasiliensis DL12, Ankistrodesmus gracilis DL25, Ankistrodesmus sp. CJ02, Desmodesmus subspicatus WC01, A. gracilis CJ09, Chlorella vulgaris CJ15, Desmodesmus sp. WC08, Chlorella sorokiniana XS04, respectively. Desmodesmus sp. WC08 reached the highest biomass concentration (2.32 g L⁻¹) with the lipid content of 31.30%. Higher lipid content of 47.90% and 47.39% were gained by A. gracilis CJ09 and C. vulgaris CJ15, respectively. However, C. vulgaris CJ15 and Desmodesmus sp. WC08 had higher lipid productivity (117.37 mg L⁻¹ d⁻¹and 115.73 mg L⁻¹ d⁻¹, respectively) in terms of comprehensive consideration. The fatty acid compositions of these microalgal species were mainly palmitic, palmitoleic, stearic, oleic with GC–MS (gas chromatography–mass spectrometer) analysis. A. gracilis CJ09, T. brasiliensis DL12, A. gracilis DL25 and Desmodesmus sp. WC08 had the higher oleic acid content (over 50% of the total fatty acids) than the others. The results suggest that marine microalgae strain Desmodesmus sp. WC08 can be the most appropriate candidate for producing oil for biodiesel, based on its higher biomass productivity, lipid productivity and fatty acid profile.     

Ultrasound-enhanced conversion of biomass to biofuels

Two important challenges need to be addressed to realize a practical biorefinery for the conversion of biomass to fuels and chemicals: (i) effective methods for the degradation and fractionation of lignocelluloses and (ii) efficient and robust chemical methods for the conversion of bio-feeds to target products via highly selective catalytic reactions. Ultrasonic energy promotes the pretreatment and conversion process through its special cavitational effects. In this review, recent progress and methods for combining and integrating sonication into biomass pretreatment and conversion for fuels and chemicals are critically assessed. Ultrasonic energy combined with proper solvents allows destruction of the recalcitrant lignocellulosic structure, fractionation of biomass components, and then assists many thermochemical and biochemical reactions, with increased equilibrium yields of sugars, bio-ethanol and gas products by 10–300%. Sonication promotes hydrolysis, esterification and transesterification in biodiesel synthesis and leads to reduced reaction time by 50–80%, lower reaction temperature, less amounts of solvent and catalyst than comparable unsonicated reaction systems. For algal biomass, sonication benefits the disruption, lysis and content release of macro and microalgae cells, and reduces the time required for subsequent extraction and chemical/biochemical reactions, with efficiencies typically being improved by 120–200%. High-frequency ultrasound of 1–3 MHz allows harvesting of microalgae, liquid product separation and in-situ process monitoring of biomass reactions, while high-intensity ultrasound at 20–50 kHz activates heterogeneous and enzymatic catalysis of the biomass reactions. The use of ultrasound in conversion of biomass to biofuels provides a positive process benefit.     

From piggery wastewater nutrients to biogas: Microalgae biomass revalorization through anaerobic digestion

Microalgae grown in swine wastewater were used as a promising strategy to produce renewable energy by coupling wastewater bioremediation and biomass revalorization. The efficiency of a microalgae consortium treating swine slurry at different temperature (15 and 23 °C) and illumination periods (11 and 14 h) was assessed for biomass growth and nutrient removal at two NH₄⁺ initial concentrations (80 and 250 mg L⁻¹ NH₄⁺). Favourable culture conditions (23 °C and 14 h of illumination) and high ammonium loads resulted in higher biomass production and greater nutrients removal rates. The initial N–NH₄⁺ load determined the removal mechanism, thus ammonia stripping and nitrogen uptake accounted similarly in the case of high NH₄⁺ load, while nitrogen uptake prevailed at low NH₄⁺ load. Under favourable conditions, nitrogen availability in the media determined the composition of the biomass. In this context, carbohydrate-rich biomass was obtained in batch mode while semi-continuous operation resulted in protein-rich biomass. The revalorization of the resultant biomass was evaluated for biogas production. Methane yields in the range of 106–146 and 171 ml CH₄ g COD⁻¹ were obtained for the biomasses grown in batch and semi-continuous mode, respectively. Biomass grown under favourable conditions resulted in higher methane yields and closer to the theoretically achievable.     

Biodiesel from microalgae – Life cycle assessment and recommendations for potential improvements

Microalgae are considered as one of the potential major source of biofuel for the future. However, their environmental benefit is still unclear and many scientific publications provide contradictory results. Here we perform the Life Cycle Assessment of the production and combustion of 1 MJ of algal methylester. The system under consideration uses standard open raceways under greenhouses. Lipid extraction and transesterification are carried out on a humid paste produced by centrifugation. Our environmental and energetic analysis shows that improving the energy balance is clearly the key priority to make microalgal cultivation sustainable and to reduce its greenhouse gas (GHG) emissions. To achieve significant reduction of the GHG emissions, most of the studies of the literature focus on technological breakthroughs, especially at the production step. However, since a large fraction of environmental impacts and especially GHG emissions do not occur directly at the production facility but stem from the production of the electricity required for producing, harvesting and transforming algae, it seems relevant to question the source of electricity as well as algae production technology. We consider a scenario where up to 45% of electricity was produced by a local renewable source and then we compare it to the improvements resulting from technological breakthroughs resulting in higher microalgal productivity or biomass concentration. It turns out that increasing the yield only drastically reduces the climate change for low starting productivity. The climate change is always significantly reduced by the use of local renewable electricity. It is therefore wiser to increase biomass productivity to easily achievable values (10–15 gm⁻² d⁻¹), and then radically change improvements pathways by considering the composition of the electricity mix used for example. At least, it must be underlined that the introduction of renewable electricity also affect energetic efficiency, leading to a positive cumulative energy balance due to better energetic ratios.     

Microalgae Chlorella as a potential bio-energy feedstock

Microalgae are promising biomass species owing to their fast growth rate and high CO₂ fixation ability as compared to terrestrial plants. Microalgae have long been recognized as potentially good source for biofuel production because of their high oil content and rapid biomass production. In this study Chlorella sp. MP-1 biomass was examined for its physical and chemical characteristics using Bomb calorimeter, TGDTA, CHN and FTIR. The proximate composition was calculated using standard ASTM methodology. Chlorella sp. MP-1 biomass shows low ash (5.93%), whereas high energy (18.59 MJ/kg), carbohydrate (19.46%), and lipid (28.82%) content. The algal de-oiled cake was characterized by FTIR spectroscopy and thermogravimetric study at 10 °C/min and 30 °C/min to investigate its feasibility for thermo-chemical conversion. The present investigation suggests that within the realm of biomass energy technologies the algal biomass can be used as feedstock for bio and thermo-chemical whereas the de-oiled cake for thermo-chemical conversion thereby serving the demand of second generation biofuels.