微藻固定CO2研究进展

空气中CO₂ 浓度升高所导致的温室效应已成为重大的环境问题 ,受到人们普遍关注。概述了高效固定CO₂ 微藻藻种的筛选和培养方法 ,分析了微藻固定CO₂ 的无机碳利用形式和浓缩机制 ,讨论了高效光生物反应器设计和运行目标 ,简要介绍了微藻 (酶 ) 膜生物反应器集成新技术。并认为今后的研究方向主要是在进一步探索微藻固定CO₂ 有关机理的基础上 ,构建高效固定CO₂ 的转基因微藻 ,开发高效膜生物反应集成系统。     

光生物反应器脱除空气中CO2的模型研究

微藻光生物反应器具有脱除空气中CO₂能力。从光生物反应器构型、进气流速、混合传质,及微藻光合/呼吸速率等方面,探讨气升式光生物反应器脱除空气中CO₂效果,提出了时间离散化和集中参数法两种分析方法。运用集中参数法建立了气升式柱型光生物反应器脱除CO₂的数学模型,模拟了藻液中溶氧浓度（DO）、pH随时间的变化情况,及进气CO₂浓度影响,预测并验证了光照条件下出气CO₂、O2浓度的变化趋势。模拟结果和实验数据基本吻合,所提出的模型对光生物反应器的优化设计、微藻的高密度培养,及CO2去除能力预测具有参考意义。     

地质封存二氧化碳与深地微生物相互作用研究进展

地质封存将工业和能源相关领域生产活动产生的二氧化碳（CO₂）进行捕集并注入到深部地下岩石构造中,以实现长期储存的目标,是降低温室气体排放、实现CO₂长期封存的重要可行性手段之一。向深部地下地质构造中注入大量CO₂会导致深地环境发生显著变化,进而引起原生微生物活性及群落结构发生明显改变。因此,地质封存CO₂能够直接或间接影响深地微生物驱动的生物地球化学过程。同时,微生物在短期和长期的超临界CO₂（scCO₂）胁迫作用下,也会通过不同的适应性进化方式影响CO₂在地下环境中的迁移、转化和赋存形态。本文介绍了国内外二氧化碳捕获与封存发展现状以及地质封存CO₂影响条件下的scCO₂-水-微生物-矿物的相互作用领域的最新科研进展,并展望了利用深地微生物强化CO₂固定以及将其转化为高附加值产物的潜力。     

氧化铝气体分布器应用小球藻培养的研究

光生物反应器设计中,气体分布器对微藻生长有较大的影响,尤其是在鼓泡式光生物反应器中更为显著。实验考察了采用氧化铝烧制的多孔气体分布器的5L鼓泡式光生物反应器中通气速率、CO₂ 浓度对小球藻LICME002生物量、叶绿素含量、油脂积累的影响。对该气体分布器下的CO₂浓度和通气速率对小球藻的作用机理进行了初步的探讨。结果表明,CO₂浓度为3%时,该株微藻生物量、叶绿素、油脂积累的最佳;CO₂浓度超过6%时各项指标显著下降。通过对0.1vvm,0.4vvm,0.7vvm、1.0vvm的通气速条件下的各项指标的分析,确定最佳通气条件为0.4vvm。结论显示,在最佳通气速率和CO₂浓度下,微藻生物量能达到1.52g/L,油脂含量达到31.5%。     

全球CO2 水平升高对浮游植物生理和生态影响的研究进展

工业革命以来由于化石燃料的大量燃烧,大气CO₂水平不断增加,预计在21世纪末将增至现有水平的两倍,达到750 μL/L。作为全球初级生产力的重要贡献者,浮游植物应对CO₂水平升高的生理生态响应必然会对水生生态系统和碳、氮等元素的生物地球化学循环产生重要影响。全球CO₂水平的升高将显著改变水体的碳化学环境,淡水生态系统(湖泊和河流)由于容量小变化比海洋更为显著。水体碳化学环境的改变首先会影响浮游植物个体,在高CO₂水平下,浮游植物的细胞会有变小的趋势,并且细胞的光合作用强度也会有不同程度的增加,其中细胞较小或者不具有碳浓缩机制(CCM)的浮游植物增加较多,此外浮游植物细胞的化学元素计量值也将显著改变。随后浮游植物个体水平上的变化会进一步影响水生生态系统,例如水体初级生产力水平的提高,浮游植物、浮游动物群落结构组成以及水体微食物网结构的变化等。此外浮游植物对CO₂水平升高的生理生态响应程度还与水体的营养水平有关。总结了大气CO₂水平升高对浮游植物生理生态影响的研究方法,展望了未来可能的研究方向。     

温度与CO2浓度升高对集胞藻PCC 6803修复UV损伤的关键基因转录量的影响

通过Taqman探针绝对定量法研究了集胞藻PCC 6803在5种不同的环境条件下:(1)25℃+400μmol/mol CO₂,(2)29℃+400μmol/mol CO₂,(3)25℃+800μmol/mol CO₂,(4)29℃+800μmol/mol CO₂,(5)25℃+1200μmol/mol CO₂,其phrA/psbA1/psbA2/psbA3等UV修复基因和16S rRNA基因的转录本拷贝数的变化情况。结果表明:温度与CO₂浓度的升高可以导致集胞藻PCC 6803的psbA2/psbA3基因和16S rRNA转录本拷贝数的大幅减少,说明温室效应将有可能导致蓝藻的UV损伤修复能力与核糖体合成能力的下降;温度升高和CO₂浓度升高对psbA2/psbA3基因和16S rRNA转录本拷贝数的联合作用表现为互相抵消,说明温度升高与CO₂浓度升高的联合作用的机制较复杂,值得深入研究。     

地质封存CO2泄漏对玉米根系形态的影响

碳捕集与封存（Carbon Capture and Storage,CCS）是应对全球气候变化、实现煤炭清洁利用的有效手段之一,但是地质封存的CO₂存在泄漏的风险,可能对农田生态系统产生重大威胁,影响我国粮食安全。根系生长是地上部和地下部相互作用、相互促进的统一过程,其形态特征对作物生产力有显著影响,但CCS泄漏对植物根系的影响评估尚不多见。本文以玉米为研究对象,采用盆栽底部通入CO₂的方法模拟不同CO₂泄漏情景,研究CK（0 g m^-2 d^-1）和G1000（1000 g m^-2 d^-1）和G2000（2000 g m^-2 d^-1）三种泄漏情景下CO₂对玉米根系形态的影响。结果表明：CO₂泄漏对玉米根系形态有明显的影响,随着泄漏量的增大总根长从40290.81 cm减少至21448.18 cm,减少46.77%,其中细根大幅减少;CO₂泄漏造成玉米明显减产,最大减产率达26.64%;玉米的地上部生物量较地下部生物量对CO₂泄漏更加敏感。综合来看,随着CO₂泄漏量增大,对玉米根的生长、地上部生物量、地下部生物量以及产量有显著的抑制作用。作物根系形态对封存CO₂泄漏的响应可为CCS泄漏监测和生态修复提供系统科学依据。     

CO2对牟氏角毛藻高密度培养的影响

以牟氏角毛藻为材料,通过对比实验研究了CO₂和CO₂通入方式对光合生物反应器中高密度培养的牟氏角毛藻的生长速度和细胞密度的影响;并以水体pH值为指标,控制CO₂的通入数量,进而研究了牟氏角毛藻在我们自行研制的卧式光合生物反应器中的生长情况。结果表明细胞悬浮培养达到一定密度之后,CO₂的供应,可以有效地提高生长速度和细胞密度。对CO₂通入方式的实验结果表明,不同的CO₂通入方式,产生的效果不同,其中以空气和纯CO₂混合后通入,效果最好。     

光驱动二氧化碳转化系统的构建、优化与应用

利用光能驱动二氧化碳(carbon dioxide, CO₂)还原生产化学品对于缓解环境压力、解决能源危机具有重要意义。光捕获、光电转化和CO₂固定等作为影响光合作用效率的关键因素,同时也制约着CO₂的资源化利用效率。为了解决上述问题,本文从生物化学与代谢工程相结合的角度,系统总结了光驱动杂合系统的构建、优化与应用,并从酶杂合系统、生物杂合系统以及杂合系统应用3个方面分析了光驱动CO₂还原合成化学品的最新研究进展。在酶杂合系统方面,采用的策略主要有提升酶催化活性、增强酶稳定性等;在生物杂合系统方面,采用的方法主要包括增强生物捕光能力、优化还原力供应以及改善能量再生等;在杂合系统应用方面,主要阐述了光驱动CO₂还原生产一碳含能化合物、生物燃料以及生物食品等。最后,从纳米材料(包括有机材料和无机材料)和生物催化剂(包括酶和微生物)两个方面,展望了人工光合系统的进一步发展方向。     

空间互动视角下CO2排放驱动因素及溢出效应——基于全球98个国家的数据分析

全球气候变暖已成为21世纪威胁人类可持续发展的严峻挑战,减少CO₂排放是抑制气候变暖的重要路径。从全球碳减排的宏观视角出发,以98个国家为研究对象,基于总商品贸易和化石能源贸易的引力模型构建两种空间互动关系,利用扩展后的S-STIRPAT模型对2000、2005、2010年和2014年人均CO₂排放的驱动机制和空间溢出效应展开实证分析,并基于发展差异视角进一步探究发达和欠发达国家CO₂排放驱动机制异同。研究结果表明：（1）2000、2005、2010年和2014年人均CO₂排放溢出效应呈增强态势。（2）城市化水平、人均GDP、能源强度对人均CO₂排放产生显著正向影响,可再生能源使用率对人均CO₂排放产生显著负向影响。（3）发展差异视角下,城市化水平、人均GDP和能源强度对欠发达国家影响更大,可再生能源使用率对发达国家影响更为显著。根据研究结果建议加强发达国家和欠发达国家低碳技术交流与合作,同时积极调整能源结构以减少CO₂排放。     

Review of advances in biological CO<Subscript>2</Subscript> mitigation technology

CO₂ fixation by microalgae has emerged as a promising option for CO₂ mitigation. Intensive research work has been carried out to develop a feasible system for removing CO₂ from industrial exhaust gases. However, there are still several challenging points to overcome in order to make the process more practical. In this paper, recent research activities on three key technologies of biological CO₂ fixation, an identification of a suitable algal strain, development of high efficient photobioreactor and utilization of algal cells produced, are described. Finally the barriers, progress, and prospects of commercially developing a biological CO₂ fixation process are summarized.     

Anaerobic digestion of microalgae as a necessary step to make microalgal biodiesel sustainable

The potential of microalgae as a source of biofuels and as a technological solution for CO₂ fixation is subject to intense academic and industrial research. In the perspective of setting up massive cultures, the management of large quantities of residual biomass and the high amounts of fertilizers must be considered. Anaerobic digestion is a key process that can solve this waste issue as well as the economical and energetic balance of such a promising technology. Indeed, the conversion of algal biomass after lipid extraction into methane is a process that can recover more energy than the energy from the cell lipids. Three main bottlenecks are identified to digest microalgae. First, the biodegradability of microalgae can be low depending on both the biochemical composition and the nature of the cell wall. Then, the high cellular protein content results in ammonia release which can lead to potential toxicity. Finally, the presence of sodium for marine species can also affect the digester performance. Physico-chemical pretreatment, co-digestion, or control of gross composition are strategies that can significantly and efficiently increase the conversion yield of the algal organic matter into methane. When the cell lipid content does not exceed 40%, anaerobic digestion of the whole biomass appears to be the optimal strategy on an energy balance basis, for the energetic recovery of cell biomass. Lastly, the ability of these CO₂ consuming microalgae to purify biogas and concentrate methane is discussed.     

Converting carbon dioxide to high value-added products: Microalgae-based green biomanufacturing

Today's world faces the dual pressure of carbon dioxide (CO₂) emission reduction and an energy crisis. Microalgae, which can use solar energy to convert CO₂ to organic matter, have emerged as a promising and renewable cell factory for producing nutrients, biofuels, and various high value-added compounds (HVACs). They possess numerous advantages, such as high photosynthetic efficiency, fast growth rate, and use of agro-industrial waste and nonagricultural land for cultivation. Microalgae can also effectively remove eutrophic elements (e.g., nitrogen and phosphorus) from wastewater and atmospheric pollutants (e.g., SO_x and NO_x) from flue gas, thus providing great environmental benefits. However, microalgae-based production often faces low productivity, limiting applicability in industrial settings. Genetic and metabolic modifications of certain microalgal strains have proven effective in improving productivity. Here, we review the latest developments regarding the microalgae-based production of platform compounds, biofuels, and other HVACs. Although still in the early exploration stage, the rapid development of gene editing tools, a deeper understanding of the metabolic pathways of microalgae and their regulatory mechanisms, and further optimization of cultivation procedures and photosynthetic efficiency can eventually enable the launch of microalgae-based biomanufacturing for green industrial production. Therefore, this technology is strategically important for solving the current energy crisis problems of excessive CO₂ emissions and environmental pollution. This review provides information about the advancement and development of microalgae-based production over the past two decades and discusses possible future directions in the field.     

Perspectives on microalgal CO2-emission mitigation systems — A review

The problem of climate change arising mainly from CO₂ emission is currently a critical environmental issue. Biofixation using microalgae has recently become an attractive approach to CO₂ 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 CO₂ emissions, photobioreactor systems used to cultivate microalgae for CO₂ 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 CO₂-emission mitigation process. The desired microalgae species should have a high growth rate, high CO₂ fixation ability, low contamination risk, low operation cost, be easy to harvest and rich in valuable components in their biomass.     

Effects of salinity on the CO<Subscript>2</Subscript> permeation across lipid bilayer for microalgae biofixation: a molecular dynamics study

The continuous threat of increasing CO₂ concentration in the atmosphere has altered the carbon balance of our planet causing global climate change. Biological fixation of atmospheric CO₂ by unicellular microorganisms such as microalgae is a promising technology pursued extensively by researchers as a means for carbon capture. The study aimed to provide an atomic level of study that will demonstrate the effect of the salinity on the mechanism of CO₂ absorption across microalgae lipid bilayer. Molecular dynamics simulations were utilized to calculate the free energies of CO₂ molecule as it permeates inside the microalgae cell. In thermodynamics, the transport process of a molecule can be demonstrated through its free energy gradient. Thus, calculating the free energies of CO₂ molecule across microalgae lipid bilayer can elucidate the mechanisms of permeation processes. Four microalgae lipid bilayer structures were constructed that contains 128-DPPC (dipalmitoylphosphatidylcholine) lipid bilayer with 3640 water molecules with different NaCl concentrations: 0, 3, 13, and 19 NaCl molecules which correspond to a salinity level of 0, 50, 200, and 300 mM, respectively. The cavity insertion Widom method was used to calculate the free energy of CO₂ molecule along the lipid bilayer. The results demonstrated that the salinity does not affect the free energies significantly, thus, it does not hamper CO₂ transport across microalgae lipid membrane.     

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.     

Challenges and opportunities for hydrogen production from microalgae

The global population is predicted to increase from ~7.3 billion to over 9 billion people by 2050. Together with rising economic growth, this is forecast to result in a 50% increase in fuel demand, which will have to be met while reducing carbon dioxide (CO₂) emissions by 50–80% to maintain social, political, energy and climate security. This tension between rising fuel demand and the requirement for rapid global decarbonization highlights the need to fast‐track the coordinated development and deployment of efficient cost‐effective renewable technologies for the production of CO₂ neutral energy. Currently, only 20% of global energy is provided as electricity, while 80% is provided as fuel. Hydrogen (H₂) is the most advanced CO₂‐free fuel and provides a ‘common’ energy currency as it can be produced via a range of renewable technologies, including photovoltaic (PV), wind, wave and biological systems such as microalgae, to power the next generation of H₂ fuel cells. Microalgae production systems for carbon‐based fuel (oil and ethanol) are now at the demonstration scale. This review focuses on evaluating the potential of microalgal technologies for the commercial production of solar‐driven H₂ from water. It summarizes key global technology drivers, the potential and theoretical limits of microalgal H₂ production systems, emerging strategies to engineer next‐generation systems and how these fit into an evolving H₂ economy.     

Efficacy of microalgae for industrial wastewater treatment: a review on operating conditions,treatment efficiency and biomass productivity

Sustainable, clean, renewable energy without negotiating contiguous environment is a challenging task mainly comprises of natural resource management which involves operational efficiency, waste minimisation and energy recovery. Disposal of untreated industrial wastewater with chemical nutrients especially compounds containing nitrogen and phosphorous lead to eutrophication and related environmental issues that affect the recycling processes of bio system. Biotransformation of pollutants using microalgae has proven to be proficient and economic method of wastewater treatment due to their adaptability of growing in various wastewater streams and also useful in the process of CO₂ fixation. Moreover this technology has the competence of producing bio fuels as an alternative energy resource in the form of bio diesel, bio ethanol and biogas. In this review paper, the applicability of microalgae cultivation in industrial wastewater treatment has been discussed extensively including the processes involved, influencing operational parameters such as study mode, cultivation mode and time, method of aeration, pH and intensity of light. Further, the cultivation methods, harvesting techniques involved in the treatment process have been presented. In addition, the analysis on removal efficiency of algal treatment, biomass productivity and lipid content of the cultivated biomass has been discussed widely which possibly will be helpful in adopting the process integration in industrial wastewater treatment with bio energy production.     

A simple and rapid harvesting method for microalgae by in situ magnetic separation

A simple and rapid harvesting method by in situ magnetic separation with naked Fe₃O₄ nanoparticles has been developed for the microalgal recovery of Botryococcus braunii and Chlorella ellipsoidea. After adding the magnetic particles to the microalgal culture broth, the microalgal cells were adsorbed and then separated by an external magnetic field. The maximal recovery efficiency reached more than 98% for both microalgae at a stirring speed of 120 r/min within 1 min, and the maximal adsorption capacity of these Fe₃O₄ nanoparticles reached 55.9 mg-dry biomass/mg-particles for B. braunii and 5.83 mg-dry biomass/mg-particles for C. ellipsoidea. Appropriate pH value and high nanoparticle dose were favorable to the microalgae recovery, and the adsorption mechanism between the naked Fe₃O₄ nanoparticles and the microalgal cells was mainly due to the electrostatic attraction. The developed in situ magnetic separation technology provides a great potential for saving time and energy associated with improving microalgal harvesting.