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2015 | Buch

Solar-to-fuel conversion in algae and cyanobacteria

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Über dieses Buch

​This volume is focused on solar-to-fuel conversion using algae and cyanobacteria for advanced generation biofuels. Production of biofuels needs to rely on cheap and renewable resources, in order to be economically viable and environmentally sustainable in the long term. Solar energy is an abundant and renewable resource, and strategies for solar-to-fuel conversion have the potential to sustain our energy demands in the long term and to be carbon-dioxide neutral. First generation biofuels are those already on the market, such as bio-ethanol from sugarcane and corn starch, biodiesel from oil seed crops. However, development of a single biofuel, as efficient as it may be, would be insufficient and could not sustain the global demand for energy.

The next generation of advanced biofuels explores alternative feedstocks and technologies, finding novel solar-to-fuel solutions. Algae and cyanobacteria can convert sunlight into chemical energy through the process of photosynthesis. They represent an alternative with respect to crops for solar-to-fuel conversion that does not compete with food for arable land. This SpringerBrief focuses only on solar-to-fuel conversion for production of advanced biofuels, pointing to the importance of relying on the sun for our sustainability in the long term. It is the only current publication to discuss the problem of light-utilization inefficiency during mass cultivation of micro-algae. This review also addresses the potential of cyanobacteria for the generation of direct photosynthesis-to-fuel platforms and discusses both possibilities and constraints for future developments.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Introduction
Abstract
Production of biofuels needs to rely on cheap and renewable resources, in order to be economically viable and environmentally sustainable in the long term. An energy carrier could not be more environmentally friendly than the process to generate it. Solar energy represents the most abundant and renewable resource, and strategies for solar-to-fuel conversion have the potentiality to sustain our energy demands in the long term and to be carbon-dioxide neutral. On the other hand, development of a single biofuel, as efficient as it may be, would be insufficient in sustaining alone the global energy demands. Generation of advanced biofuels explores alternative technologies and feedstocks. Algae and cyanobacteria offer novel solar-to-fuel solutions that would not compete with food for arable land. The economic viability is discussed, with respect to potential future developments. Sustainability of the system also depends on domestication and genetic improvement of algal strains, as domestication of currently cultivated crops has been necessary for agriculture development, turning wild ancestors into a resource for humans. Emphasis is given to photosynthesis and light-utilization efficiency, that in turn determine solar-to-biomass yield, and to metabolic pathways converting primary products of photosynthesis into fuels. General concepts are explained for the benefit of both expert and non-expert readers.
Cinzia Formighieri
Chapter 2. Biofuels: An Emerging Industry
Abstract
Dealing with the nonrenewable nature of fossil fuels, and with the effect of carbon dioxide emissions on global warming, requires transformation of the energy sector toward renewable, carbon neutral resources. This chapter introduces the biofuel industry, which relies on the energy derived from living organisms or from their metabolic products, in the contest of global energy supply.
Cinzia Formighieri
Chapter 3. Exploring Novel Feedstocks and Technologies for Advanced Biofuels: The Promises of Algae
Abstract
Biofuels are classified into first, second, and advanced generation, based on their current commercial development. Conversion of algal biomass into advanced biofuels is part of the effort to find alternative feedstocks and solar-to-fuel technologies that do not compete with food for arable land, opposed to energy crops currently dominating the biofuel industry.
Cinzia Formighieri
Chapter 4. Bioethanol from Algae Polysaccharides
Abstract
Bioethanol currently dominates the biofuel industry; however, the main bioethanol feeedstocks, sugarcane and maize, are all land-based crops. Algae polysaccharides represent an alternative substrate for bioconversion into ethanol, upon hydrolysis into fermentable sugars.
Cinzia Formighieri
Chapter 5. Biodiesel from Microalgae
Abstract
Microalgae have the almost unique ability among microorganisms to naturally store significant amounts of carbon as neutral lipids that can be converted to biodiesel. Accumulation of neutral lipids has mainly evolved as a response strategy to stress conditions, which on the other hand are detrimental for growth and biomass production. Genetic improvement would be required as part of the effort for algae domestication in order to meet industrial lipid production requirements.
Cinzia Formighieri
Chapter 6. Processing of Algal Biomass for the Production of Biogas and Bio-oil
Abstract
Microbial anaerobic digestion, or second-generation technologies of gasification and pyrolysis, can be performed on algal biomass for the conversion to biogas and bio-oil. These approaches can be adopted as the main strategy for biofuel production, or they can be integrated into a biorefinery concept and performed on the spent remaining biomass.
Cinzia Formighieri
Chapter 7. Cyanobacteria as a Platform for Direct Photosynthesis-to-Fuel Conversion
Abstract
Expression of heterologous genes allows to introduce novel biosynthetic pathways in cyanobacteria, more prone to genetic transformation than eukaryotic microalgae. Cyanobacteria are consequently endowed with the biosynthesis of fuel molecules, such as alcohols, free fatty acids, and terpene hydrocarbons, from photosynthesis-associated metabolism.
Cinzia Formighieri
Chapter 8. Economic Viability of Algal Biodiesel
Abstract
Production of biodiesel from oleaginous microalgae has been evaluated in terms of economic profitability, as an example that can be extended to other algal biofuels. Biodiesel has to reach cost parity with fossil fuels in order to be economically sustainable in the long term. Major costs for generation of algal biodiesel are not related to the feedstock, but they depend on construction and maintenance of the cultivation system, biomass harvesting and processing. The cost balance of the system can be improved by co-production of high value-added commodities and/or by substantial increase in biomass productivity and oil yield.
Cinzia Formighieri
Chapter 9. Photosynthesis: A Dynamic Process
Abstract
Algae are endowed with oxygenic photosynthesis, enabling conversion of solar energy into chemical energy. Production of biofuels from algae also depends on photosynthetic efficiency, and comprehension of the photosynthetic process is therefore essential, especially if production of cheap energy carriers is considered, and requires to maximize productivity for a sustainable system.
Cinzia Formighieri
Chapter 10. Solar-to-Biomass Conversion Efficiency
Abstract
A maximum theoretical yield in solar-to-biomass conversion can be estimated from the efficiency of the photosynthetic process, considering utilization of all available light. The solar-to-biomass conversion yield is expected to be higher in algae than in terrestrial plants, because algae do not need to consume energy for the development of supporting structures, but all algal biomass is photosynthetically active. However, photosynthetic productivities obtained during mass cultivation of wild type algal strains are far below theoretical calculations, mainly because of light utilization inefficiency.
Cinzia Formighieri
Chapter 11. Light Saturation of Photosynthesis
Abstract
Light-driven reactions of photosynthesis have to fit downstream biochemical reactions that become limiting at increasing light intensities. As a consequence, photosynthesis displays a light saturation curve. Dissipation of excess absorbed energy by non-photochemical energy quenching, although it is responsible for diminishing light utilization efficiency, is essential for protecting the photosynthetic apparatus from photo-oxidative stress.
Cinzia Formighieri
Chapter 12. Downstream Biochemical Reactions: Carbon Assimilation
Abstract
One way to increase light utilization by the single cell would be to reduce excess absorption of light by identifying bottlenecks in downstream electron transfer and biochemical reactions. The main rate-limiting step at increasing light intensity is carbon dioxide assimilation through the Calvin–Benson cycle. Proper supply of carbon dioxide during growth of algae in photobioreactor, coupled to genetic improvement of carbon dioxide fixation, could improve biomass productivity.
Cinzia Formighieri
Chapter 13. Light-Utilization Inefficiency of Wild-Type Algal Mass Cultures
Abstract
Photosynthetic productivity of microalgae depends on photosynthate production and utilization by the single cell. At the same time, large light-harvesting antenna systems found in wild-type strains are responsible for inefficient light-utilization by the culture as a whole. Growth conditions in the natural habitat are opposite compared to mass cultivation, and configurations positively selected in the wild may become detrimental in photobioreactors.
Cinzia Formighieri
Chapter 14. Genetic Modification of the Pigment Optical Density
Abstract
Large photosynthetic antenna systems are dispensable under conditions of mass cultivation and, in contrast to the detrimental effects on solar-to-biomass conversion efficiency of high pigment optical densities per cell, truncated antenna strains, with a reduced absorption cross section, could improve light utilization efficiency of the culture as a whole.
Cinzia Formighieri
Chapter 15. Development of Microalgae Cultivation and Biomass Harvesting Systems for Biofuel Production
Abstract
Algae-based technologies for mass production of cheap biofuels, that need to reach cost parity with fossil fuels, require to redesign the cultivation system, as to increase light distribution and photosynthetic productivity, and to cut down production costs. Open ponds and photobioreactor configurations are compared, as well as biomass harvesting technologies, that weighs on the economic sustainability of the system. In addition to dedicated industrial cultivation, the concept of an algae-powered building integrates algae cultivation into bioenergy-dependent urban planning.
Cinzia Formighieri
Chapter 16. Environmental Sustainability of Biofuel Production from Algae
Abstract
Beside evaluating the economic viability of algal biofuels, the impact that the system has on the environment and on the management of resources needs to be addressed as well, that in turn will determine the sustainability in the long term. Algal biofuels are compared to other solar technologies in terms of storage and transport of the generated energy, interaction with the environment, competition with other resources, and reduction in greenhouse gases emission.
Cinzia Formighieri
Chapter 17. Concluding Remarks
Abstract
Aquatic photosynthesis provides for a largely unexplored organic carbon feedstock and, although in infancy, its exploitation could represent a substantial contribution to renewable energy.
Cinzia Formighieri
Backmatter
Metadaten
Titel
Solar-to-fuel conversion in algae and cyanobacteria
verfasst von
Cinzia Formighieri
Copyright-Jahr
2015
Electronic ISBN
978-3-319-16730-5
Print ISBN
978-3-319-16729-9
DOI
https://doi.org/10.1007/978-3-319-16730-5