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。     

Mixotrophic cultivation of Chlorella vulgaris and its potential application for the oil accumulation from non-sugar materials

Microbial lipid accumulation to provide alternative oil resources is an exciting research area, obtaining increasing attentions recently for the biodiesel production due to its high production efficiency and less demand of agricultural land. The aim of this study is to optimize the lipid accumulation of Chlorella vulgaris by using various carbon sources in heterotrophic and mixotrophic cultures. Different cultivation factors were studied on their influences to the cell growth and oil accumulation.Our results revealed that C. vulgaris could grow on autotrophic, mixotrophic and heterotrophic modes; and the mixotrophic cultivation especially could produce more cell biomass than the autotrophic or heterotrophic cultures individually or combined. The substrate concentration significantly influenced the final cell yield of the mixotrophic cultivations while the cell lipid content remained relatively constant. Glycerol was inhibitive to the cell growth while the microalgae strain could actively utilize acetate as the carbon source. This provides a promising niche in reducing the overall cost of biofuel production since this substrate can be obtained from some waste processes such as anaerobic digestion.     

Renewable biomass production by mixotrophic algae in the presence of various carbon sources and wastewaters

This study evaluated mixotrophic growth potential of native microalgae in media supplemented with different organic carbon substrates and wastewaters. Three robust mixotrophic microalgae viz. Chlamydomonas globosa, Chlorella minutissima and Scenedesmus bijuga were isolated after long-term enrichments from industrial wastewater. The mixotrophic growth of these microalgae resulted in 3–10 times more biomass production relative to phototrophy. Glucose, sucrose and acetate supported significant mixotrophic growth. Poultry litter extract (PLE) as growth medium recorded up to 180% more biomass growth compared to standard growth medium BG11, while treated and untreated carpet industry wastewaters also supported higher biomass, compared to BG11 growth with no significant effect of additional nitrogen supplementation. Supplementing treated wastewater and PLE with glucose and nitrogen resulted in 2–7 times increase in biomass relative to the unamended wastewaters or PLE. The consortia of Chlamydomonas–Chlorella and Scenedesmus–Chlorella were the best for PLE and untreated wastewater respectively, while a combination all three strains was suitable for both PLE and wastewater. These algae can be good candidates for biofuel feedstock generation as they would not require freshwater or fertilizers. Such mixotrophic algal consortia offer great promise for production of renewable biomass for bioenergy applications using wastewaters.     

Biodiesel production by microalgal biotechnology

Biodiesel has received much attention in recent years. Although numerous reports are available on the production of biodiesel from vegetable oils of terraneous oil-plants, such as soybean, sunflower and palm oils, the production of biodiesel from microalgae is a newly emerging field. Microalgal biotechnology appears to possess high potential for biodiesel production because a significant increase in lipid content of microalgae is now possible through heterotrophic cultivation and genetic engineering approaches. This paper provides an overview of the technologies in the production of biodiesel from microalgae, including the various modes of cultivation for the production of oil-rich microalgal biomass, as well as the subsequent downstream processing for biodiesel production. The advances and prospects of using microalgal biotechnology for biodiesel production are discussed.     

Synergistic carbon metabolism in a fast growing mixotrophic freshwater microalgal species Micractinium inermum

In recent years microalgae have attracted significant interest as a potential source of sustainable biofuel. Mixotrophic microalgae are able to simultaneously photosynthesise while assimilating and metabolising organic carbon. By combining autotrophic and heterotrophic metabolic pathways biomass productivity can be significantly increased. In this study, acetate-fed mixotrophic Micractinium inermum cultures were found to have a specific growth rate 1.74 times the sum of autotrophic and heterotrophic growth. It was hypothesised that gas exchange between the two metabolic pathways within mixotrophic cultures may have prevented growth limitation and enhanced growth. To determine the extent of synergistic gas exchange and its influence on metabolic activity, dissolved inorganic carbon (DIC), dissolved oxygen (DO) and photosynthesis and respiration rates were measured under different trophic conditions. A 32.7 fold and 2.4 fold increase in DIC and DO concentrations, relative to autotrophic and heterotrophic cultures respectively, were coupled with significant increases in rates of photosynthesis and respiration. These data strongly support the hypothesis of mixotrophic gas exchange within M. inermum cultures. In addition to enhanced growth, this phenomenon may provide reductions in aeration and oxygen stripping costs related to microalgae production.     

Co-culture for lipid production: Advances and challenges

The exploration of microbial communities to efficiently produce biofuels has become a critical approach among biochemical processes. Co-cultures have been intensively studied to address the limitations in substrate utilization by individual strains for the production of other bioproducts. Accordingly, many concerns have arisen about the effects of this strategy on lipid productivity. Despite the extensive research on lipid production by oleaginous microorganisms, co-culture strategy has been only well-reviewed in algal species and most of the original research has been concentrated on the different nutritional growth modes (e.g. heterotrophic and mixotrophic). Moreover, current literature indicates scarce information on strategies for the improvement of lipid production with other species rather than microalgae. From a systematic perspective, this review will highlight co-culture systems existing for the improved biomass and lipid productivity, among other species. The review first discloses the current state of microalgal assemblies and their strategies for lipid production. Subsequently, it summarizes other assemblies aimed at lipid production. Finally, it discusses the relative advantages and disadvantages and the possibilities to overcome inherent challenges.     

微藻生物膜去污技术应用研究进展

文章综述了微藻生物膜净化污水和生产生物燃料等方面的国内外最新成果,阐述了典型微藻去污生物膜系统的运行情况、综合效益、优缺点和推广价值,并对微藻生物膜去污技术存在的问题及关键技术进展及发展趋势进行了分析,就微藻生物膜去污技术的规模化及产业化应用提出了建议,以期为微藻生物膜去污技术的成熟和规模应用提供理论和实践支撑。     

Enhanced biohydrogen production from microalgae by diesel engine hazardous emissions fixation

Microalgae cultivation has gained increased attention from research and industry sectors in recent years, due to the wide variety of applications for the produced biomass, such as biofuels and substances of high economic value. Indirect biophotolysis biohydrogen production from microalgae has been shown recently to be limited by the amount of accumulated biomass during the growth phase. As a result, this study focused on developing a strategy to increase biohydrogen generation via biomass production increase through microalgae cultivation using exhaust gases from diesel engines. In order to achieve that objective, four simultaneous cultures were conducted to compare the growth of microalgae under pure air and emissions injection, in different flow regimes. An indigenous microalgae strain was selected to be robust under different weather conditions and was identified as Acutodesmus obliquus through rDNA sequence analysis. The results indicate an increase in biomass production of about 2.8 times for the best case of cultivation with emissions in comparison to a compressed air condition. Besides the growth analyses, the potential for treating the hazardous emissions injected into the system was investigated and the data demonstrated that the CO₂ and NO_x content was substantially reduced, showing that no damage to the microalgae is caused by the diesel engine emissions. Numerical simulation results for the H₂ production indirect biophotolysis demonstrate that there is an optimal rhythm for maximum time averaged H₂ production rate, and that the stoichiometrically limited total H₂ production is augmented by a similar factor to microalgae biomass production increase.     

Cultivation of filamentous cyanobacteria (blue-green algae) in agro-industrial wastes and wastewaters: A review

Recently research interest has focused on the production of biofuel from microalgae. Microalgae are photosynthetic microorganisms that grow utilizing solar energy, nevertheless, the quantities of fertilizers that should be used for their production are enormous. One alternative to the use of synthetic fertilizers is to employ wastes and wastewaters (W&WWs), especially from the agro-industrial sector which are rich in inorganic pollutants such as nitrogen and phosphorus, which can be recovered. Simultaneously with the cultivation of microalgae using wastes and wastewaters for biomass production, treatment of the wastes and wastewaters occur through removal of the pollutants. Filamentous cyanobacteria appear to be suitable candidates for cultivation in wastes and wastewaters because they produce biomass in satisfactory quantity and can be harvested relatively easily due to their size and structure. In addition their biomass composition can be manipulated by several environmental and operational factors in order to produce biomass with concrete characteristics. Herein we review the factors that affect the biomass composition of cyanobacteria and present several studies that discuss the culture of filamentous cyanobacteria in agro-industrial wastes and wastewaters, with special emphasis on Spirulina.     

Conversion of microalgae to biofuel

This paper primarily presents an overall review of the use of microalgae as a biofuel feedstock. Among the microalgae that have potential as biofuel feedstock, Chlorella, specifically, was thoroughly discussed because of its ability to adapt both to heterotrophic and phototrophic culture conditions. The lipid content and biomass productivity of microalgae can be up to 80% and 7.3 g/l/d based on the dried weight of biomass, respectively, making microalgae an ideal candidate as a biofuel feedstock. The set-up of the system and the biomass productivity of microalgae cultivated in an open pond and a photobioreactor were also compared in this work. The effect of the culture condition is discussed based on the two-stage culture period. The issues that were discussed include the light condition and the CO₂, DO and N supply. The microalgal productivities under heterotrophic and phototrophic culture conditions were also compared and highlighted in this work. The harvesting process and type of flocculants used to aid the harvesting were highlighted by considering the final yield of biomass. A new idea regarding how to harvest microalgae based on positive and negative charges was also proposed in this work. The extraction methods and solvents discussed were primarily for the conventional and newly invented techniques. Conversion processes such as transesterification and thermochemical processes were discussed, sketched in figures and summarized in tables. The cost–benefit analysis of heterotrophic culture and the cultivation system was highlighted at the end of this work. Other benefits of microalgae are also mentioned in this work to give further support for the use of microalgae as a feedstock for biofuel production.     

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。     

Mixotrophic cultivation of Botryococcus braunii

Cultivation of Botryococcus braunii has been mainly reported in photoautotrophic mode which has some disadvantages such as low cell growth rate and low cell density. For high density and high productivity, this study attempts to cultivate B. braunii in mixotrophic mode. Effects of different organic carbon sources (including maltose, glucose, saccharose, lactose, glycerol and starch), glucose and KNO₃ concentrations as well as inoculation amount on the growth of B. braunii were investigated in 250 mL shake flasks, and a fed-batch mixotrophic cultivation technique was developed in a 10 L enclosed automatic air-lift photobioreactor.B. braunii grew faster in mixotrophic cultivation with all the six organic carbon sources than that in photoautotrophic mode, and glucose was the optimum. The optimal concentrations of glucose and KNO₃ were 2.5 g L⁻¹ and 0.4 g L⁻¹ respectively. Within the inoculums of 46-200 g m⁻³, the lag phase of cell growth was very short, and cells grew fast into exponential phase after inoculation, the average cell growth rate of B. braunii increased with the increment of inoculation amount. With a 10 L air-lift photobioreactor, B. braunii was cultured by feeding glucose under mixotrophic condition for 19 days, and the cell density and hydrocarbon content in dry cell reached 4.55 g L⁻¹ and 29.7%, respectively.     

Water from the Vistula Lagoon as a medium in mixotrophic growth and hydrogen production by Platymonas subcordiformis

Platymonas subcordiformis is a marine microalgae that under favorable environmental conditions change metabolism pathways to hydrogen production in direct biophotolysis. Effective hydrogen production by Platymonas subcordiformis depends on application of efficient and economically viable biomass production technologies. In the study, the natural water from Vistula Lagoon was used for microalgae cultivation. No statistically significant differences were found regarding the biomass production in the natural water and synthetic medium. The influence of mixotrophic conditions on growth rate and biomass production of Platymonas subcordiformis was also examined. The highest biogas production of 138.45 ± 3.39 mL with the rate of 1.15 ± 0.03 mL/h was noted by the biomass cultivated on synthetic medium with glucose supplementation. Similarly high biogas production was observed by the biomass cultivated on natural water with glucose addition (1.11 ± 0.14 mL/h). The use of the waters from Vistula Lagoon resulted in high yields of hydrogen production, which might reduce costs of biofuel production.     

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。     

The effects of ultraviolet radiation on growth,biomass, lipid accumulation and biodiesel properties of microalgae

The effect of UV light on growth, biomass, lipid accumulation and biodiesel properties of microalgae was studied. A Microalgae strain Chlorella sorokiniana UUIND6 was cultivated for 14 days as under LED light (Control) and microalgae were exposed to UV light (280–320 nm) in the middle of the photoperiod for 3 days. The growth rate of microalgae was analyzed by spectrophotometer and cell counting, while oil accumulation was analyzed by improved Nile red method. Results showed that microalgae under UV light treated algal cells showed less growth. FAMEs profile of UV treated algal cells mainly contains hexadecanoic acid (C16), stearic acid (C18) fatty acids. PUFA found in very less amount in UV treated cells as compared to control.     

The cultivation of European kelp for bioenergy: Site and species selection

Seaweeds are receiving increasing attention as third generation biofuels, which do not compete for land or freshwater with agricultural crops and have a high polysaccharide content. Seaweed growth is dependent on the presence of suitable physical and chemical conditions. The selection of cultivation sites with suitable characteristics is therefore essential for the successful establishment of European seaweed mariculture. The growth conditions of the site directly impact the biomass yield and composition of the crop, which in turn control the conversion efficiency of biomass to bioenergy. This review focuses on three European brown phaeophyte kelp species which may be suitable for large-scale offshore cultivation: Laminaria digitata, Saccharina latissima and Sacchoriza polyschides. It describes the known responses of each to a number of important physical and chemical parameters: temperature, salinity, water motion, nutrient concentrations, carbon dioxide/pH, light and ultra-violet radiation. It also reports density effects on their growth rate and what is known concerning the impact of disease and grazing. Conclusions are made on the conditions necessary for the optimal growth of each species for biofuel production. Where conditions are sub-optimal, this review has made recommendations for the most suitable species for a particular set of environmental conditions.     

Biohydrogen production by a novel integration of dark fermentation and mixotrophic microalgae cultivation

Biohydrogen is usually produced via dark fermentation, which generates CO₂ emissions and produces soluble metabolites (e.g., volatile fatty acids) with high chemical oxygen demand (COD) as the by-products, which require further treatments. In this study, mixotrophic culture of an isolated microalga (Chlorella vulgaris ESP6) was utilized to simultaneously consume CO₂ and COD by-products from dark fermentation, converting them to valuable microalgae biomass. Light intensity and food to microorganism (F/M) ratio were adjusted to 150 μmol m⁻² s⁻¹ and F/M ratio, 4.5, respectively, to improve the efficiency of assimilating the soluble metabolites. The mixotrophic microalgae culture could reduce the CO₂ content of dark fermentation effluent from 34% to 5% with nearly 100% consumption of soluble metabolites (mainly butyrate and acetate) in 9 days. The obtained microalgal biomass was hydrolyzed with 1.5% HCl and subsequently used as the substrate for bioH₂ production with Clostridium butyricum CGS5, giving a cumulative H₂ production of 1276 ml/L, a H₂ production rate of 240 ml/L/h, and a H₂ yield of 0.94 mol/mol sugar.     

纤维藻培养及制备生物柴油的研究

探讨了纤维藻(Ankistudesmus sp)的低成本培养模式,考察了氮源和碳源以及反应器形式对纤维藻生物量、油脂积累以及油脂组成的影响。户外培养纤维藻在氮饥饿条件下油脂产率较高;通过槽式反应器和管式反应器的比较发现:槽式反应器更适合微藻的大规模培养;混养培养时能显著增加纤维藻的生物量和油脂含量,最佳添加条件下藻的生物量和油脂含量分别高达1.64 g/L和15.9%,1.41 g/L和11.9%。藻油经酸催化甲酯化制备生物柴油,经气相色谱分析,藻油主要成分为棕榈酸、油酸和亚油酸。氮缺陷、流加葡萄糖培养得到的纤维藻油含有25.32%的棕榈酸、44.74%的油酸,其制备得到的生物柴油具有更好的氧化稳定性和低温流动性。     

Commercialization potential of microalgae for biofuels production

Microalgae feedstocks are gaining interest in the present day energy scenario due to their fast growth potential coupled with relatively high lipid, carbohydrate and nutrients contents. All of these properties render them an excellent source for biofuels such as biodiesel, bioethanol and biomethane; as well as a number of other valuable pharmaceutical and nutraceutical products. The present review is a critical appraisal of the commercialization potential of microalgae biofuels. The available literature on various aspects of microalgae, e.g. its cultivation, life cycle assessment, and conceptualization of an algal biorefinery, has been scanned and a critical analysis has been presented. A critical evaluation of the available information suggests that the economic viability of the process in terms of minimizing the operational and maintenance cost along with maximization of oil-rich microalgae production is the key factor, for successful commercialization of microalgae-based fuels.     

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.