Developments in oil extraction from microalgae

Microalgae are a diverse group of organisms with significant potential for industrial applications: as feedstock in aquaculture as well as in the production of valuable bioproducts such as lipids, carotenoids and enzymes. Lately, developments in molecular biology have improved production yields of algae bioproducts, thus increasing their industrial relevance. Additionally, variations in bioprocessing factors (i.e. temperature, pH, light, carbon source, salinity, nutrients, etc.) have been used to enhance both biomass and specific bioproducts' productivities. Particularly, microalgae have increasingly gained research interest as a source of specialty lipids such as arachidonic, eicosapentaenoic and docosahexaenoic acids, which are often reported in literature to provide several health benefits. Moreover, there has been a recent resurgence in interest in microalgae as an oil producer for biofuel applications. Significant advances have also been made in upstream processing to generate cellular biomass and oil. However, extracting and purifying oil from algae continues to prove a significant challenge in producing both microalgae bioproducts and biofuel, as microbial oil extraction is relatively energy‐intensive and costly. Thus, developing inexpensive and robust oil extraction and purification processes is a major challenge facing both the microalgae to bioproduct, and biofuel industries. This paper presents an overview, based on the last 10 years, of advances made in technologies for extracting and purifying microalgae oil. We compared solvent extraction technologies with extraction alternatives such as mechanical milling and pressing, enzymatic and supercritical fluid extraction. We also reviewed recent advances based on molecular engineering of microbes to aid oil extraction. Downstream processing for the potential commercial production of microalgae oil not only must consider economic costs, but should also consider minimizing environmental impacts in order to attain sustainable production processes.     

微藻培养光生物反应器内传递现象的研究进展

微藻规模化培养过程中光生物反应器内传递现象是影响微藻的生长及产量的重要因素。本文重点综述了光生物反应器内传递现象（光传递、传热、传质和传动量传递）及其数学模型研究进展,分析了光生物反应器结构和尺寸对光传递和传质的影响,总结影响各传递现象的重要参数,如光吸收系数、体积传质系数等,为高效光生物反应器的设计、优化及放大提供了参考依据。     

Ultrathin polymeric interpenetration network with separation performance approaching ceramic membranes for biofuel

Biofuel has emerged as one of the most strategically important sustainable fuel sources. The success of biofuel development is not only dependent on the advances in genetic transformation of biomass into biofuel, but also on the breakthroughs in separation of biofuel from biomass. The “separation” alone currently accounts for 60–80% of the biofuel production cost. Ceramic membranes made of sophisticated processes have shown separation performance far superior to polymeric membranes, but suffers fragility and high fabrication cost. We report the discovery of novel molecular engineering and membrane fabrication that can synergistically produce polymeric membranes exhibiting separation performance approaching ceramic membranes. The newly discovered Polysulfone/Matrimid composite membranes are fabricated by dual‐layer coextrusion technology in just one step through phase inversion. An ultrathin dense‐selective layer made of an interpenetration network of the two materials with a targeted and stable interstitial space is formed at the interface of two layers for biofuel separation. The combined molecular engineering and membrane fabrication approach may revolutionize future membrane research and development for purification and separation in energy, environment, and pharmaceuticals. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

Advances of macroalgae biomass for the third generation of bioethanol production

In recent years, utilization of renewable sources for biofuel production is gaining popularity due to growing greenhouse gas (GHG) emissions which causes global warming. There has been a great effort in exploring alternative feedstock for bioethanol production. In this context, the production of third-generation bioethanol from macroalgae has emerged as an alternative feedstock to food crop-based starch and lignocellulosic biomass. This is mainly due to the fast growth rate of macroalgae, no competition with agricultural land, high carbohydrate content and relatively simple processing steps compared to lignocellulosic biomass. This review paper provides an insight of recent innovative approaches for macroalgae bioethanol production, including conventional and advanced hydrolysis process to produce fermentable sugar, various fermentation technologies, economic analysis and life cycle assessment. With the current technology maturity, efficient utilization of macroalgae as sustainable source for bioethanol and other value-added chemicals production could be achieved in the near future.     

Integrated Biorefinery Design with Techno-Economic and Life Cycle Assessment Tools in Polyhydroxyalkanoates Processing

To support and move toward a sustainable bioeconomy, the production of polyhydroxyalkanoates (PHAs) using renewable biomass has acquired more attention. However, expensive biomass pretreatment and low yield of PHAs pose significant disadvantages in its large-scale production. To overcome such limitations, the most recent advances in metabolic engineering strategies used to develop high-performance strains that are leading to a new manufacturing concept converting biomass to PHAs with co-products such as amino acids, proteins, biohydrogen, biosurfactants, and various fine chemicals are critically summarized. This review article presents a comprehensive roadmap that highlights the integrated biorefinery strategies, lifecycle analysis, and techno-economic assessment for sustainable and economic PHAs production. Finally, current and future challenges that must be addressed to transfer this technology to real-world applications are reviewed.     

中国微藻生物柴油产业的发展机遇和挑战

介绍了国内外研发微藻生物柴油的动态,预见用工业装置生产微藻生物柴油的技术近几年内将取得重大突破,微藻生物柴油产业将成为一个新兴的替代能源产业.我国微藻生物柴油产业化研究和国际水平基本同步,是一个全新的自主创新领域,提出应抓住微藻生物柴油产业的发展机遇.对工业化生产微藻生物柴油的光生物反应器设计技术、微藻培养控制系统、配...     

微藻柱状式光生物反应器流动特性及结构的数值模拟优化

微藻作为最具潜力的可再生生物质能源,在生物固碳和生物燃料生产领域优势显著,有助于碳达峰、碳中和目标的实现。通过改善反应器曝气装置的性能可以大幅度提高微藻的培养效率,本工作采用数值模拟方法对柱式光生物反应器的球型曝气结构进行了优化。模拟采用欧拉模型,湍流模型选取k-ε模型,研究分析了不同曝气装置条件下气含率、平均液相速度、湍流动能几种参数的变化和光生物反应器内的流场情况。结果表明,曝气装置结构的变化对光生物反应器内的流动特性具有很大的影响,通过曝气装置向反应器内通气,气含率、平均液相速度、湍流动能随着曝气量的增大而增大,随着曝气装置孔径的增大而减小。综合各相关参数得到当总曝气量为1400 mL/min、曝气孔数为50、曝气孔径为30μm时,曝气装置性能最好,此时测得气含率为68.6%,平均液相速度为0.905 m/s,湍流动能为0.149 m²/s²。     

Design and synthesis of antifreeze glycoproteins and mimics

Antifreeze glycoproteins are an important class of biological antifreezes that have potential applications in many areas of medicine, agriculture and industry in which ice crystal growth is damaging. While the synthesis of antifreeze glycoproteins as pure glycoforms has recently been achieved by using ligation and polymerisation strategies, the routine production of large quantities of pure glycoforms remains challenging. A range of C-linked analogues that are readily produced by solid-phase synthesis have delivered novel compounds that are not biological antifreezes, but are potent, non-cytotoxic, ice-recrystallisation inhibitors. Structure-activity studies, the identification of cyclic antifreeze glycoproteins and conformational studies have provided further insight into the requirements for antifreeze activity. These results, coupled with significant advances in approaches to the routine synthesis of different glycoproteins and mimics, present opportunities for the design and synthesis of novel ice-growth-inhibiting and antifreeze compounds.     

Nanobiocatalysis for Enzymatic Biofuel Cells

Enzymatic biofuel cells promise a great potential as a small power source, but their practical applications are being hampered by two serious problems: low power density and short lifetime. This review will describe recent advances of nanobiocatalysis that can potentially solve these two problems, together with some of novel in vivo applications of biofuel cells for harvesting electrical energy from the body fluids of living insects and animals.     

Advances and Challenges on Algae Harvesting and Drying

Biodiesel production from algae offers a promising prospect for practical applications among the still developing biofuel technologies. The fact that algae are capable of producing much more yield provides an edge over other types of biofuel. Though algal biofuel research is still developing and its practical application is yet to be ascertained, promising work on laboratory- and pilot-scale algae harvesting systems has been extensively reported. Because algae harvesting and drying are vital elements in biofuel production, recent advances on various algae harvesting, dewatering, and drying technologies are reviewed and discussed. Challenges and prospects of algae harvesting and drying are also outlined.     

Evolution of polymeric hollow fibers as sustainable technologies: Past, present, and future

Energy, water, affordable healthcare and global warming are four major global concerns resulting from resource depletion, record high oil prices, clean water shortages, high costs of pharmaceuticals, and changing climate conditions. Among many potential solutions, advances in membrane technology afford direct, effective and feasible approaches to solve these sophisticated issues. Membrane technology encompasses numerous technology areas including materials science and engineering, chemistry and chemical engineering, separation and purification phenomena, molecular simulation, as well as process and product design. Currently, polymeric hollow fiber membranes made using a non-solvent-induced phase inversion process are the dominant products because polymers offer a broad spectrum of materials chemistry and result in membranes with desirable physicochemical properties for diverse applications. Their low cost and ease of fabrication make polymeric membranes superior to inorganic membranes. Therefore, this review focuses on state-of-the-art polymeric hollow fiber membranes made from non-solvent-induced phase inversion and the potential of membrane processes for sustainable water and energy production. The specific topics include: (i) basic principles of hollow fiber membrane formation and the phase inversion process; (ii) membranes for energy (natural gas, H₂, and biofuel) production; (iii) membranes for CO₂ capture; and (iv) emerging desalination technologies (forward osmosis and membrane distillation) for water production. Finally, future opportunities and challenges for the development of advanced membrane structures are discussed.     

微藻生物燃料的远景展望

藻类是生物燃料的理想原料,最近,由于对能源安全、温室气体排放和其它潜在的生物燃料原料竞争等的关注增加,藻类生物燃料引起人们的注意。然而开发藻类生物量的生产技术,仍处于萌芽阶段。微藻有生产生物燃料的潜力,但在商业化大规模生产前,需要对其技术进行讨论并克服经济障碍等问题。     

Modified Photobioreactor for Biofixation of Carbon Dioxide by Chlorella vulgaris at Different Light Intensities

The performance of a modified bioreactor inside a light enclosure for carbon dioxide biofixation by Chlorella vulgaris was investigated. The influence of different light intensities on the CO₂ biofixation and biomass production rates was evaluated. The results showed that the photon flux available to the microalgal cultures can be a key issue in optimizing the microalgae photobioreactor performance, particularly at high cell concentrations. Although the optimal pH values for C. vulgaris are in the range of 6–8, cell growth can take place even at pH 4 and 10. Batch microalgae cultivation in the photobioreactor was used to investigate the effect of different light intensities. The maximum biomass concentration of 1.83 g L^?1 was obtained at a light intensity of 100 μmol m^?2s^?1 and under aeration with 2 L min^?1 of 2 % CO₂‐enriched air.     

Flowsheet Modeling and Simulation of Biomass Steam Gasification for Hydrogen Production

Hydrogen production from biomass steam gasification is systematically reviewed. Equilibrium modeling and simulation studies using various techniques for effective hydrogen production are presented. Heat integration, economic analysis of the hydrogen production, and systematic design algorithms research publications are overviewed and discussed for energy-efficient and economic hydrogen production from various biomass feedstocks. Comparison and analysis of the results strongly suggest the viable potential of biomass steam gasification for hydrogen production from small to large scales with applications for thermal heat, power generation, and many other industrial fields.     

木质纤维素解聚平台分子催化合成航油技术的进展

航油作为一种重要的空中交通燃料,它的不可替代性和航空业碳减排的压力,迫使航空业对生物航油的需求不断加大。由于油脂原料的局限性,使得未来生物航油的原料将趋向多元化发展,逐渐延伸到糖、木质纤维素等原料。木质纤维素类生物质具有储量丰富、廉价易得的优势,以木质纤维素为原料制备航油的技术近年来得到了大力发展。然而木质纤维素组分中的碳链结构与航油分子的碳链结构不匹配,所以木质纤维素制备航油的技术关键在于如何以中间分子,如CO和H₂小分子的费托合成路线以及糠醛、乙酰丙酸等木质纤维素解聚平台分子的合成路线,通过合适的催化反应合成长链正/异构烷烃（C₈～C₁₆）。由于木质纤维素解聚平台分子保留了原料组分中的碳骨架以及多种功能官能团,比较容易通过合成方法来调控燃料的品质和特性,所以近年来有关木质纤维素解聚平台分子催化合成航油的技术途径及其催化工艺的报道不断涌现。为了充分认识此类航油技术的发展潜力,本文以糠醛、乙酰丙酸、多元醇等几种重要平台分子的碳链构建方式为线索总结了合成航油的各种技术途径和相应的催化工艺。并结合作者的研究工作,从技术应用性和化工过程实现的角度分析了各种技术途径的优缺点以及所面临的共性难题,同时对未来生物航油技术的发展进行了初步展望。     

Reaction network flux analysis: Optimization‐based evaluation of reaction pathways for biorenewables processing

Even though biomass is attracting increasing interest as a raw material in the chemical and the fuel industries, only few biobased production processes are yet established. At the same time a lot of new catalytic routes are proposed, but their potential in biorefinery applications is hard to predict. Reaction network flux analysis (RNFA) is introduced as a novel, rapid screening method which bridges the gap between chemo‐ or biocatalysis and process design by (1) systematically identifying and (2) subsequently analyzing and ranking the large number of alternative reaction pathways based on limited data. This optimization‐based method helps to detect promising production routes as well as bottlenecks in possible pathways. The potential and the application of the RNFA methodology will be demonstrated by means of a case study for the production of the potential biofuel 3‐methyl‐tetrahydrofuran (3‐MTHF) from the platform chemical itaconic acid (IA). © 2011 American Institute of Chemical Engineers AIChE J, 58: 1788–1801, 2012     

Strategies for directed and adapted evolution as part of microbial strain engineering

The industrial production of chemicals by microorganisms usually requires improvements to the enzymes, pathways, and strain that go beyond the capacity of innate enzymes. To achieve these phenotypes and overcome our limited capacity to de novo design these parts, directed and adaptive evolutionary approaches are used to explore new functions. This review highlights the recent advances in both sequence diversity generation and selection strategies from traditional in vitro mutagenesis to novel in vivo continuous evolution applications. The focus here is on comparison of the different gene diversity methods in an attempt to distinguish the best strategy for protein or strain engineering for a given goal. Furthermore, the important role that screening and selection can play in advancing directed and adapted evolution is discussed. © 2018 Society of Chemical Industry     

A tubular bioreactor for photosynthetic production of biomass from carbon dioxide: Design and performance

A theory of photobioreactor design is developed. A photobioreactor was constructed in the form of a loop made from 52 m of glass tubing of 1 cm bore; the loop covered about 0.5 m². The culture was illuminated with mercury halide lamps to reproduce sunlight. Computer control was used to maintain constant biomass concentration. The influence of radiation on the reactor temperature is quantitatively predicted. An air lift system was preferred to a liquid pump for culture recycle. The energy required for culture recycle in the loop with Reynolds number 2000 was 0.6 W m^?2. The CO₂ gas/liquid transfer rate achieved was sufficient to meet the maximum possible demand with solar irradiation. The O₂ gas/liquid transfer rate was sufficient to meet the maximum respiration demand at night. The maximum algal biomass concentration achieved exceeded 20 g dry weight litre^?1. A biomass concentration of 8 g dry weight litre^?1 was found to be convenient for normal operation. The maximum uptake of light in the available wavelength range (400–700 nm) was 38 W m^?2, this corresponds to utilisation of solar irradiation up to 89 W m^?2. Below the maximum light uptake rate the efficiency of storage of light energy in the biomass corresponded to 16.6% of solar energy.     

CO2 mass transfer and conversion to biomass in a horizontal gas–liquid photobioreactor

This study deals with CO₂ mass transfers and biomass conversion in an industrial horizontal tubular photobioreactor. An analytical approach is used to determine an expression modeling the influence of CO₂ mass transfers on the overall biomass conversion efficiency for a given culture broth, heat and light conditions. Fluid mechanics and mass transfer are predicted with a classical two-phase flow approach (Taitel and Dukler, 1976) combined with a dissolution correlation developed and tested in the laboratory (Valiorgue et al., 2011). The influence of the stripping gas, removing the excess of oxygen in the liquid, on the conversion to biomass efficiency is shown to be not negligible. The expression is used to evaluate how the photobioreactor's design and process parameters can be tuned in order to improve biomass conversion efficiency. The biomass conversion efficiency evolution with the photobioreactor's length was found to behave asymptotically and it was explained by the relative orders of magnitude of gas dissolution and gas stripping. It has been shown that the gas flow rate for stripping and therefore the oxygen removal will be limited when further increasing the industrial photobioreactor's length for a given objective of CO₂ conversion to biomass efficiency.     

High butanol production by regulating carbon,redox and energy in Clostridia? ?

Butanol is a promising biofuel with high energy intensity and can be used as gasoline substitute. It can be produced as a sustainable energy by microorganisms (such as Clostridia) from low-value biomass. However, the low productivity, yield and selectivity in butanol fermentation are still big challenges due to the lack of an efficient butanol-producing host strain. In this article, we systematically review the host cell engineering of Clostridia, focusing on (1) various strategies to rebalance metabolic flux to achieve a high butanol production by regulating the metabolism of carbon, redox or energy, (2) the challenges in pathway manipulation, and (3) the application of proteomics technology to understand the intracellular metabolism. In addition, the process engineering is also briefly described. The objective of this review is to summarize the previous research achievements in the metabolic engineering of Clostridium and provide guidance for future novel strain construction to effectively produce butanol.