Simultaneous effect of irradiance and temperature on biochemical composition of the microalga Pavlova lutheri

The biochemical composition of microalgae can be modulated through the environmental conditions prevailing during growth. The simultaneous effects of irradiance and temperature on the biochemical composition of Pavlova lutheri were evaluated using an experimental star factorial design. Five levels were tested for each parameter (temperature, 10, 14, 18, 22 and 26°C; irradiance, 60, 105, 150, 195 and 240 μmol photons m⁻² s⁻¹), whereas the carbohydrate, protein, lipid, pigments and elementary compound contents were measured as response variables. Additionally, in order to rapidly measure parameters to define the status of the culture, the validation of the relationships between biochemical parameters and physiological status were estimated through regression analysis. It was observed that irradiance and temperature play a major role in the determination of the biochemical composition of microalgae. Their effects are synergistic, and it can be observed that a trend in behaviour at a certain temperature can be reversed at a different temperature; therefore, when selecting the environmental conditions to a culture they must be studied in a combined fashion. Although there are consistent relationships between pigment contents and elementary compounds in cells, its linearity is influenced by the irradiance of the culture and its age; therefore, they can only be applied in specific circumstances. On the other side, population biomass was well estimated in terms of carotenoid content, irrespective of the environmental conditions provided and the growth phase.     

Microalgae biofuels: A critical review of issues, problems and the way forward

Culturing of microalgae as an alternative feedstock for biofuel production has received a lot of attention in recent years due to their fast growth rate and ability to accumulate high quantity of lipid and carbohydrate inside their cells for biodiesel and bioethanol production, respectively. In addition, this superior feedstock offers several environmental benefits, such as effective land utilization, CO(2) sequestration, self-purification if coupled with wastewater treatment and does not trigger food versus fuel feud. Despite having all these 'theoretical' advantages, review on problems and issues related to energy balance in microalgae biofuel are not clearly addressed until now. Base on the maturity of current technology, the true potential of microalgae biofuel towards energy security and its feasibility for commercialization are still questionable. Thus, this review is aimed to depict the practical problems that are facing the microalgae biofuel industry, covering upstream to downstream activities by accessing the latest research reports and critical data analysis. Apart from that, several interlink solutions to the problems will be suggested with the purpose to bring current microalgae biofuel research into a new dimension and consequently, to revolutionize the entire microalgae biofuel industry towards long-term sustainability.     

二氧化碳减排产柴油微藻培养体系研究进展

污水资源化、二氧化碳减排及微藻生物柴油是当前能源与环境领域的前沿课题。以下围绕污水及烟道气资源化培养产油微藻的培养体系,就藻种、营养条件、培养方式、培养环境及微藻生物反应器等影响产油微藻培养的因素研究进展进行了综述。在综述的基础上提出：由于微藻具有特殊营养方式,通过藻种筛选、微藻营养条件和培养环境的优化以及高效光生物反应器和生产工艺等的创新,可利用污水进行产油微藻生产,以获得生物柴油等高附加值产品,实现微藻生物能源、污水资源化处理和CO2减排三者高度耦合的产油微藻生产体系,从而减少微藻培养费用及污水处理费用,因此,该体系具有重要的环境、社会、经济价值和商业化应用前景。     

Perspectives on microalgal CO₂-emission mitigation systems--a review

The problem of climate change arising mainly from CO? emission is currently a critical environmental issue. Biofixation using microalgae has recently become an attractive approach to CO? capture and recycling with additional benefits of downstream utilization and applications of the resulting microalgal biomass. This review summarizes the history and strategies of microalgal mitigation of CO? emissions, photobioreactor systems used to cultivate microalgae for CO? fixation, current microalgae harvesting methods, as well as applications of valuable by-products. It is of importance to select appropriate microalgal species to achieve an efficient and economically feasible CO?-emission mitigation process. The desired microalgae species should have a high growth rate, high CO? fixation ability, low contamination risk, low operation cost, be easy to harvest and rich in valuable components in their biomass.     

Linking microalgae and cyanobacteria culture conditions and key-enzymes for carbohydrate accumulation

Microalgae are regarded as a potential biomass source for biofuel purposes. With regard to bioethanol production, microalgae seem to overcome traditional substrate drawbacks. Enzymatic activities are responsible for carbon allocation and hence for carbohydrate profiles. Enzyme activities may be manipulated by metabolic engineering; however, this goal may also be achieved by controlling environmental conditions of the culture system. We outline the key-enzymes as well as the main operational conditions applied to microalgae growth (inorganic nutrient supplementation, irradiance and temperature) that affect carbohydrate synthesis on microalgae and cyanobacteria. Normally, harsh conditions are needed for such a goal and thus, arrested microalgae growth may occur. Potential strategies to avoid arrested growth, while enhancing carbohydrate accumulation, were also pointed out in this review.     

Progress in physicochemical parameters of microalgae cultivation for biofuel production

Microalgae have been exploited for biofuel generation in the current era due to its enormous energy content, fast cellular growth rate, inexpensive culture approaches, accumulation of inorganic compounds, and CO₂ sequestration. Currently, research is ongoing towards the advancement of the microalgae cultivation parameters to enhance the biomass yield. The main objective of this study was to delineate the progress of physicochemical parameters for microalgae cultivation such as gaseous transfer, mixing, light demand, temperature, pH, nutrients and the culture period. This review demonstrates the latest research trends on mass transfer coefficient of different microalgae culturing reactors, gas velocity optimization, light intensity, retention time, and radiance effects on microalgae cellular growth, temperature impact on chlorophyll production, and nutrient dosage ratios for cellulosic metabolism to avoid nutrient deprivation. Besides that, cultivation approaches for microalgae associated with mathematical modeling for different parameters, mechanisms of microalgal growth rate and doubling time have been elaborately described. Along with that, this review also documents potential lipid-carbohydrate-protein enriched microalgae candidates for biofuel, biomass productivity, and different cultivation conditions including open-pond cultivation, closed-loop cultivation, and photobioreactors. Various photobioreactor types, the microalgae strain, productivity, advantages, and limitations were tabulated. In line with microalgae cultivation, this study also outlines in detail numerous biofuels from microalgae.     

Microalgae–bacteria symbiosis in microalgal growth and biofuel production: a review

Photosynthetic microalgae can capture solar energy and convert it to bioenergy and biochemical products. In nature or industrial processes, microalgae live together with bacterial communities and may maintain symbiotic relationships. In general interactions, microalgae exude dissolved organic carbon that becomes available to bacteria. In return, the bacteria remineralize sulphur, nitrogen and phosphorous to support the further growth of microalgae. In specific interactions, heterotrophic bacteria supply B vitamins as organic cofactors or produce siderophores to bind iron, which could be utilized by microalgae, while the algae supply fixed carbon to the bacteria in return. In this review, we focus on mutualistic relationship between microalgae and bacteria, summarizing recent studies on the mechanisms involved in microalgae–bacteria symbiosis. Symbiotic bacteria on promoting microalgal growth are described and the relevance of microalgae–bacteria interactions for biofuel production processes is discussed. Symbiotic microalgae–bacteria consortia could be utilized to improve microalgal biomass production and to enrich the biomass with valuable chemical and energy compounds. The suitable control of such biological interactions between microalgae and bacteria will help to improve the microalgae-based biomass and biofuel production in the future.     

Outdoor cultivation of microalgae for carotenoid production: current state and perspectives

Microalgae are a major natural source for a vast array of valuable compounds, including a diversity of pigments, for which these photosynthetic microorganisms represent an almost exclusive biological resource. Yellow, orange, and red carotenoids have an industrial use in food products and cosmetics as vitamin supplements and health food products and as feed additives for poultry, livestock, fish, and crustaceans. The growing worldwide market value of carotenoids is projected to reach over US$1,000 million by the end of the decade. The nutraceutical boom has also integrated carotenoids mainly on the claim of their proven antioxidant properties. Recently established benefits in human health open new uses for some carotenoids, especially lutein, an effective agent for the prevention and treatment of a variety of degenerative diseases. Consumers’ demand for natural products favors development of pigments from biological sources, thus increasing opportunities for microalgae. The biotechnology of microalgae has gained considerable progress and relevance in recent decades, with carotenoid production representing one of its most successful domains. In this paper, we review the most relevant features of microalgal biotechnology related to the production of different carotenoids outdoors, with a main focus on β-carotene from Dunaliella, astaxanthin from Haematococcus, and lutein from chlorophycean strains. We compare the current state of the corresponding production technologies, based on either open-pond systems or closed photobioreactors. The potential of scientific and technological advances for improvements in yield and reduction in production costs for carotenoids from microalgae is also discussed.     

Bicarbonate produced from carbon capture for algae culture

Using captured CO(2) to grow microalgae is limited by the high cost of CO(2) capture and transportation, as well as significant CO(2) loss during algae culture. Moreover, algae grow poorly at night, but CO(2) cannot be temporarily stored until sunrise. To address these challenges, we discuss a process where CO(2) is captured as bicarbonate and used as feedstock for algae culture, and the carbonate regenerated by the culture process is used as an absorbent to capture more CO(2). This process would significantly reduce carbon capture costs because it does not require additional energy for carbonate regeneration. Furthermore, not only would transport of the aqueous bicarbonate solution cost less than for that of compressed CO(2), but using bicarbonate would also provide a superior alternative for CO(2) delivery to an algae culture system.     

橡胶林固定CO2和释放O2的服务功能及其价值估计

橡胶树除生产橡胶和提供优质木材外,还有长期不为人们注意的生态服务功能。以中国的橡胶林为研究对象,采用标准标木生物量法,对橡胶林固定CO2和释放O2的生态服务功能及其价值估计进行了研究。结果表明中国橡胶林目前每年从大气中固定的CO2总量为411万t,所释放的O2为299万t。经分别采用C税法和工业制氧成本法估计了CO2和O2的价值达到1238亿元和12亿元。二者价值之和相当于中国橡胶林每年生产橡胶和提供木材等直接产品价值的28.7倍。橡胶林CO2的固定能力是热带山地雨林的4.7倍。50a来中国橡胶林已累计固定CO2达到11292万t,释放O2达8212万t,对短期内缓解大气的温室效应发挥了巨大的作用。     

Mathematical model of Chlorella minutissima UTEX2341 growth and lipid production under photoheterotrophic fermentation conditions

To reduce the cost of algal biomass production, mathematical model was developed for the first time to describe microalgae growth, lipid production and glycerin consumption under photoheterotrophic conditions based on logistic, Luedeking-Piret and Luedeking-Piret-like equations. All experiments were conducted in a 2 L batch reactor without considering CO(2) effect on algae's growth and lipid production. Biomass and lipid production increased with glycerin as carbon source and were well described by the logistic and Luedeking-Piret equations respectively. Model predictions were in satisfactory agreement with measured data and the mode of lipid production was growth-associated. Sensitivity analysis was applied to examine the effects of certain important parameters on model performance. Results showed that S(0), the initial concentration of glycerin, was the most significant factor for algae growth and lipid production. This model is applicable for prediction of other single cell algal species but model testing is recommended before scaling up the fermentation of process.     

UV-B Radiation Suppresses the Growth and Antioxidant Systems of Two Marine Microalgae, Platymonas subcordiformis (Wille) Hazen and Nitzschia closterium (Ehrenb.) W. Sm

This study investigated whether increased solar UV-B radiation (280-315 nm) could suppress the growth of marine microalgae through effects on their antioxidant systems. Two marine microalgae species, Platymonas subcordiformis (Wille) Hazen and Nitzschia closterium (Ehrenb.) W. Sm, were exposed to a range of UV-B radiation and both showed reductions in their growth rates, and the chlorophyll a (Chl a) and carotenoid (Car) contents when UV-B radiation dose increased. Superoxide anion radical (O2)production and the concentration of hydrogen peroxide (H2O2) and malodiadehyde (MDA) also increased with the increasing of UV-B radiation. Antioxidant systems, non-enzymic components (Car and glutathione content) and enzymic components (superoxide dismutase (SOD) and catalase (CAT) activity), decreased as a result of enhanced UV-B radiation. When the exogenous glutathione (GSH) was added, the effects of UVB radiation on the growth of the two species were alleviated. These results suggest that enhanced UV-B radiation suppressed the antioxidant systems and caused some active oxygen species to accumulate, which in turns retarded the development of the marine microalgae.     

微藻固定燃烧烟气中CO2 的研究进展

空气中CO2浓度升高导致的气候变暖问题已经成为全球性的环境、科学、政治、经济问题。近年来,对可用于直接固定工业废气尤其是燃烧烟气中CO2的捕捉和封存 (CCS) 技术进行了广泛的研究。在这些技术中,微藻生物固定CO2是一种具有大规模应用前景和经济上可行的CCS技术。以下从藻种的筛选、烟气条件对微藻固定CO2的影响、高效光生物反应器的开发和微藻产物的利用等方面对微藻生物固定烟气中CO2的现状和发展以及作者所在实验室在这一领域的研究情况进行了分析和总结,最后对其技术前景进行了展望,以期对微藻固定燃烧烟气中CO     

Cyanobacteria and microalgae: a positive prospect for biofuels

Biofuel-bioenergy production has generated intensive interest due to increased concern regarding limited petroleum-based fuel supplies and their contribution to atmospheric CO2 levels. Biofuel research is not just a matter of finding the right type of biomass and converting it to fuel, but it must also be economically sustainable on large-scale. Several aspects of cyanobacteria and microalgae such as oxygenic photosynthesis, high per-acre productivity, non-food based feedstock, growth on non-productive and non-arable land, utilization of wide variety of water sources (fresh, brackish, seawater and wastewater) and production of valuable co-products along with biofuels have combined to capture the interest of researchers and entrepreneurs. Currently, worldwide biofuels mainly in focus include biohydrogen, bioethanol, biodiesel and biogas. This review focuses on cultivation and harvesting of cyanobacteria and microalgae, possible biofuels and co-products, challenges for cyanobacterial and microalgal biofuels and the approaches of genetic engineering and modifications to increase biofuel production.     

光生物反应器培养微藻研究进展

微藻具有固定CO2和净化有机废水的能力,在环保、食品饲（饵）料、医药和生物能源开发等领域备受关注,但规模化培养及其产业化仍是研究的难点,亟待解决。就常用于大规模培养微藻的光生物反应器的特点和结构进行了综述。其中,封闭式微藻光生物反应器能够较好地调控藻种的培养条件、不易遭受污染,藻种的纯度容易控制,但培养规模小,生产成本较高;而开放式微藻光生物反应器无法精确控制藻种生长环境,但生产规模大、产量高、生产成本低,因此应用广泛。最佳的方法是综合两者优点,即首先利用封闭式微藻光生物反应器进行中试放大,大量繁殖藻种,然后投入开放式微藻光生物反应器内进行大规模商业生产,此方法有望成为微藻光生物反应器的发展方向,以期为微藻大规模培养提供参考借鉴。     

Algal biofuels

The world is facing energy crisis and environmental issues due to the depletion of fossil fuels and increasing CO₂ concentration in the atmosphere. Growing microalgae can contribute to practical solutions for these global problems because they can harvest solar energy and capture CO₂ by converting it into biofuel using photosynthesis. Microalgae are robust organisms capable of rapid growth under a variety of conditions including in open ponds or closed photobioreactors. Their reduced biomass compounds can be used as the feedstock for mass production of a variety of biofuels. As another advantage, their ability to accumulate or secrete biofuels can be controlled by changing their growth conditions or metabolic engineering. This review is aimed to highlight different forms of biofuels produced by microalgae and the approaches taken to improve their biofuel productivity. The costs for industrial-scale production of algal biofuels in open ponds or closed photobioreactors are analyzed. Different strategies for photoproduction of hydrogen by the hydrogenase enzyme of green algae are discussed. Algae are also good sources of biodiesel since some species can make large quantities of lipids as their biomass. The lipid contents for some of the best oil-producing strains of algae in optimized growth conditions are reviewed. The potential of microalgae for producing petroleum related chemicals or ready-make fuels such as bioethanol, triterpenic hydrocarbons, isobutyraldehyde, isobutanol, and isoprene from their biomass are also presented.     

Environmental and cultural stimulants in the production of carotenoids from microorganisms

Commercial production of carotenoids from microorganisms competes mainly with synthetic manufacture by chemical procedures. Efficient stimulation of carotenoid biosynthesis is expected to promote accumulation of carotenoid by microbes. This review describes the variety of environmental and cultural stimulants studied during the last few decades which enhance volumetric production and cellular accumulation of commercially important carotenoids from microalgae, fungi and bacteria. Stimulation of carotenoid production by white-light illumination and temperature fluctuation is discussed along with supplementation of metal ions, salts, organic solvents, preformed precursors and several other chemicals in the culture broth. Reports on the improvements in yield are reviewed and assessed from a biotechnology point of view.     

Carotenoid production and change of photosynthetic functions in Scenedesmus sp. exposed to nitrogen limitation and acetate treatment

Under stress conditions, some microalgae up-regulate certain biosynthetic pathways, leading to the accumulation of specific compounds. For example, changing nutrient composition can induce stress in algae’s physiological activities, which may trigger an intense increase in carotenoid production. In this study, the change of photosynthetic functions and carotenoid production in the green microalga Scenedesmus sp. was investigated when algal cultures were exposed to conditions including limited nitrogen content with the addition of sodium acetate. Microalgal cultures were treated for 18 days under higher irradiance conditions. We observed a decrease of chlorophyll content induced concomitantly with a decline of photosystem II and I photochemistry. At the same time, an important increase in carotenoid content was detected. By using high-performance liquid chromatographic analysis, we found that the secondary carotenoids astaxanthin and canthaxanthin were accumulated compared to controls. During the process of carotenoid accumulation, chlorophyll degradation was found in addition to a strong decrease in photosynthetic electron transport. Such changes may be associated with the structural reorganization of the photosynthetic apparatus and can be a useful indicator of secondary carotenoid accumulation in algal cultures.     

Effects of light intensity and quality on the growth rate and photosynthetic pigment content of Spirulina platensis

The quantitative and qualitative effects of light on carotenoid production by Spirulina were studied. Maximum total carotenoid production was measured in cells grown under white light at an irradiance of 432 μmol photon m^?2 s^?1, the onset of light saturation for this organism as determined by growth rates. A true maximum may exist at irradiances above 1500 μmol photon m^?2 s^?1 under white light. Individual carotenoids responded differently to light conditions. Under white light, β-carotene and echinenone were most abundant at the lowest and highest irradiance levels tested. Myxoxanthophyll and lutein/zeaxanthin did not change over the same irradiance range. Under red and blue light, we found decreased values of myxoxanthophyll, while β-carotene increased and lutein/zeaxanthin and echinenone showed little change. In general, maximum carotenoid production requires optimization of the culture conditions that favor growth.     

Accurate method for rapid biomass quantification based on specific absorbance of microalgae species with biofuel importance

The development of microalgae culture technology has been an integral part to produce biomass feedstock to biofuel production. Due to this, numerous attempts have been made to improve some operational parameters of microalgae production. Despite this, specialized research in cell growth monitoring, considered as a fundamental parameter to achieve profitable applications of microalgae for biofuels production, presents some opportunity areas mainly related to the development of specific and accurate methodologies for growth monitoring. In this work, predictive models were developed through statistical tools that correlate a specific micro-algal absorbance with cell density measured by cell count (cells∙per ml), for three species of interest for biofuels production. The results allow the precise prediction of cell density through a logistic model based on spectrophotometry, valid for all the kinetics analysed. The adjusted determination coefficients () for the developed models were 0·993, 0·995 and 0·994 for Dunaliella tertiolecta, Nannochloropsis oculata and Chaetoceros muelleri respectively. The results showed that the equations obtained here can be used with an extremely low error (≤2%) for all the cell growth ranges analysed, with low operational cost and high potential of automation. Finally, a user-friendly software was designed to give practical use to the developed predictive models.