Chapter One - Microalgae for biofuel production
Introduction
One of the major themes of the 21st century to date is the need to replace fossil fuels with fuels based on renewable energy to mitigate the rise in atmospheric CO2, which is a major component in anthropogenic global warming. Renewable energy requires the use of biomass produced from recently fixed CO2. The term “fixed CO2” refers to CO2 absorbed by a photosynthetic organism (for oxygenic photosynthesis this is a plant, alga or cyanobacterium) and converted into sugar with oxygen as a by-product. The CO2 fixation reaction is shown below:
ATP and NADPH production is via electron transport driven by light energy absorbed by photosystems 1 and 2. The fixation of CO2 to sugars (C6H12O6) takes place in the Calvin cycle with the key CO2 fixation reaction catalyzed by ribulose bisphosphate carboxylase (Rubisco). Utilizing light energy to fix CO2 into biomass and then using the biomass (or components of the biomass) as a fuel can potentially lead to a carbon neutral fuel. The term “recently” indicates that the biomass has been grown in the recent past and this is to distinguish it from fossil fuel, in which the biomass was produced several 100 million years ago.
First-generation biofuels utilized crop plants as very well-established sources of recently produced biomass. The Brazilian model, set up originally in the 1970s, uses sugar cane waste as the source of its feedstock to produce bioethanol (Goldemberg, 2007). More recently, both the United States and Europe attempted to copy the Brazilian model, but using crops such as wheat as the biomass source. This led to a “food vs fuel” debate and claims that turning arable land to fuel production was increasing food prices (Rosillocalle & Hall, 1987). In response, second-generation biofuels utilize lignocellulose (inedible to humans) waste from agricultural crops or use non-crop plants grown specifically for lignocellulose such as switchgrass or Miscanthus. In either case, there is no direct competition with food crops, but to produce fuel from the chemically recalcitrant lignocellulose is an expensive process due to heating the biomass in the presence of acids—costly and environmentally unfriendly (Himmel et al., 2007). This brings us to third-generation biofuels based on microalgal biomass and the subject of this review. Microalgae do not compete for agricultural land and their simple morphology (single cells or filaments) makes extraction of fuel precursors easier and more environmentally friendly than lignocellulose. Microalgae in the oceans are responsible for over 45% of global CO2 fixation (Falkowski et al., 2004) and this makes them very good candidates to produce biofuels that are carbon neutral.
During the oil crisis of the 1970s, which kick started the Brazilian first-generation biofuel industry, attempts were made to utilize microalgae for biofuel production. However, the modern era of microalgal biofuels began with the review by Chisti published in 2007 in Biotechnology Advances. This highly cited review article (5081 citations on Web of Science at 3rd September 2019) stated the case for using microalgae as a source of biodiesel that could replace fossil fuel diesel (Chisti, 2007). As noted above, this was not a new idea, but the Chisti review was comprehensive and was published at a time when global environmental concerns about greenhouse gases were recognized by the intergovernmental panel on climate change (Metz, Davidson, Bosch, Dave, & Meyer, 2007). The organization of this review will be to treat the Chisti review as a “before and after” marker. The first section will examine the literature prior to 2007 and then the following section will look at the progress made since 2007. Section 4 will complete the review by examining the future prospects for microalgal biofuels.
Section snippets
History
Interest in microalgal biotechnology can be traced back to the 1940s and 1950s, when in the years after the second world war, algae were cultivated as a potential food source (Burlew, 1953). The green agriculture revolution based on the development of high yielding varieties of crop plants and the associated use of fertilizers dramatically increased crop yields from the 1950s onwards (Evenson & Gollin, 2003). Therefore, mass cultivation of microalgae became limited to parts of the Far East, in
Microalgal biofuels post 2007
As outlined in Chisti's, 2007 review and emphasized by his later review in 2013 there are a number of hurdles to overcome before biodiesel can be made commercially from microalgae (Chisti, 2007, Chisti, 2013). In his later review, Chisti suggested that the following were the major constraints on producing biodiesel from microalgae. First, the availability of industrial point sources of CO2, many pilot plant demonstration facilities do not use industrially sourced CO2, which is unrealistic in
Metabolomics and synthetic biology
Genetic and/or metabolic engineering may help to overcome many of the limitations of using microalgae to produce biofuels. The previous section demonstrated some of the methods already used and in this final section very recent work will be summarized to show what may be possible in the near future. The first limitation to metabolic engineering is that a single gene modification will not normally lead to the desired increase in product (Sun, Ren, Zhao, Ji, & Huang, 2019). There are exceptions
Acknowledgements
I would like to thank Tom Burns for his critical reading of the manuscript.
References (102)
- et al.
Flashing light in microalgae biotechnology
Bioresource Technology
(2016) - et al.
Continuous harvesting of microalgae biomass using foam flotation
Algal Research-Biomass Biofuels and Bioproducts
(2018) - et al.
Flocculation processes optimization for reuse of culture medium without pH neutralization
Algal Research-Biomass Biofuels and Bioproducts
(2019) - et al.
The biotechnology of cultivating the halotolerant alga Dunaliella
Trends in Biotechnology
(1990) - et al.
Microalgae biotechnology
Trends in Biotechnology
(1987) - et al.
Enhancing algal biomass and lipid production through bacterial co-culture
Biomass & Bioenergy
(2019) - et al.
Flocculation of microalgae with cationic polymers—Effects of medium salinity
Biomass
(1988) Commercial production of microalgae: Ponds, tanks, tubes and fermenters
Journal of Biotechnology
(1999)- et al.
Outdoor performance of Chlorococcum littorale at different locations
Algal Research-Biomass Biofuels and Bioproducts
(2017) - et al.
Enhancing production of lutein by a mixotrophic cultivation system using microalga Scenedesmus obliquus CWL-1
Bioresource Technology
(2019)
Biodiesel from microalgae
Biotechnology Advances
Constraints to commercialization of algal fuels
Journal of Biotechnology
Fluorometric-determination of the neutral lipid-content of microalgal cells using Nile Red
Journal of Microbiological Methods
Development of a foam flotation system for harvesting microalgae biomass
Algal Research-Biomass Biofuels and Bioproducts
A review on lipid production from microalgae: Association between cultivation using waste streams and fatty acid profiles
Renewable & Sustainable Energy Reviews
Increase in Chlorella strains calorific values when grown in low nitrogen medium
Enzyme and Microbial Technology
Enhanced production of astaxanthin by flashing light using Haematococcus pluvialis
Enzyme and Microbial Technology
Dependence of biodiesel fuel properties on the structure of fatty acid alkyl esters
Fuel Processing Technology
Growth and astaxanthin formation of Haematococcus-pluvialis in heterotrophic and mixotrophic conditions
Journal of Fermentation and Bioengineering
Liquid and gaseous fuels from biotechnology—Challenge and opportunities
FEMS Microbiology Reviews
Glucose supplementation-induced changes in the Auxenochlorella protothecoides fatty acid composition suitable for biodiesel production
Bioresource Technology
A type 2 diacylglycerol acyltransferase accelerates the triacylglycerol biosynthesis in heterokont oleaginous microalga Nannochloropsis oceanica
Journal of Biotechnology
Challenges and opportunity of recent genome editing and multi-omics in cyanobacteria and microalgae for biorefinery
Bioresource Technology
Solar energy conversion efficiencies in photosynthesis: Minimizing the chlorophyll antennae to maximize efficiency
Plant Science
TAG, You're it! Chlamydomonas as a reference organism for understanding algal triacylglycerol accumulation
Current Opinion in Biotechnology
Exploiting mixotrophy for improving productivities of biomass and co-products of microalgae
Renewable & Sustainable Energy Reviews
Resource demand implications for US algae biofuels production scale-up
Applied Energy
Effect of light conditions on mixotrophic cultivation of green microalgae
Bioresource Technology
Changes in the activities of various lipid and carbohydrate biosynthetic-enzymes in the diatom Cyclotella-cryptica in response to silicon deficiency
Archives of Biochemistry and Biophysics
Brazilian alcohol—Food versus fuel
Biomass
Flashing LEDs for microalgal production
Trends in Biotechnology
The use of a fuel containing Chlorella vulgaris in a diesel engine
Enzyme and Microbial Technology
Diesel fuel from vegetable-oils—Status and opportunities
Biomass & Bioenergy
Synergistic carbon metabolism in a fast growing mixotrophic freshwater microalgal species Micractinium inermum
Biomass & Bioenergy
The influence of exogenous organic carbon assimilation and photoperiod on the carbon and lipid metabolism of Chlamydomonas reinhardtii
Algal Research-Biomass Biofuels and Bioproducts
Macroalgae and microalgae as a potential source for commercial applications along with biofuels production: A biorefinery approach
Renewable & Sustainable Energy Reviews
Enhancement of lipid accumulation in microalgae by metabolic engineering
Biochimica et Biophysica Acta-Molecular and Cell Biology of Lipids
Lipids and membrane function in green algae
Biochimica Et Biophysica Acta-Lipids and Lipid Metabolism
Flocculation as a low-cost method for harvesting microalgae for bulk biomass production
Trends in Biotechnology
Potential of industrial biotechnology with cyanobacteria and eukaryotic microalgae
Current Opinion in Biotechnology
An integrated wavelength-shifting strategy for enhancement of microalgal growth rate in PMMA- and polycarbonate-based photobioreactors
European Journal of Phycology
Ultraviolet and 5'fluorodeoxyuridine induced random mutagenesis in Chlorella vulgaris and its impact on fatty acid profile: A new insight on lipid-metabolizing genes and structural characterization of related proteins
Marine Biotechnology
Direct photosynthetic recycling of carbon dioxide to isobutyraldehyde
Nature Biotechnology
Enhanced acetyl-CoA production is associated with increased triglyceride accumulation in the green alga Chlorella desiccata
Journal of Experimental Botany
Acetyl-CoA synthetase is activated as part of the PDH-bypass in the oleaginous green alga Chlorella desiccata
Journal of Experimental Botany
Role of glycerol in osmotic regulation of halophilic alga Dunaliella-parva
Plant Physiology
Biomass from microalgae: The potential of domestication towards sustainable biofactories
Microbial Cell Factories
Microalgae for biofuels and animal feeds
Energies
Uniformly C-13-labeled algal protein used to determine amino-acid essentiality in vivo
Proceedings of the National Academy of Sciences of the United States of America
Enhancement of Dunaliella salina growth by using wavelength shifting dyes
Journal of Applied Phycology
Cited by (31)
Changes in velocity distribution produced by paddlewheels in algae raceway ponds
2024, Algal ResearchMicroalgae as a source of bioavailable heme
2024, Algal ResearchBio-oil from microalgae: Materials, production, technique, and future
2023, Energy ReportsHormone released by the microalgae Neochloris aquatica and alkalinization influence growth of terrestrial and floating aquatic plants
2023, Plant Physiology and BiochemistryDiversity of algae and their biotechnological potential
2023, Advances in Microbial PhysiologyDrop-in biofuels production from microalgae to hydrocarbons: Microalgal cultivation and harvesting, conversion pathways, economics and prospects for aviation
2022, Biomass and BioenergyCitation Excerpt :However, due to the presence of oxygen in such compounds, there is a necessity to understand, control, and optimize deoxygenation strategies to effectively convert oxygen containing biomass into hydrocarbons (explained in Section 4) with a low O/C and high H/C ratio that are comparable to petroleum-based fuels. Microalgal biomass exhibits clear benefits over biomass from other plants [39,54–56]. Primarily, in contrast to crop plants used for second generation biofuels production, microalgae do not need arable land to grow, preserving agricultural areas and avoiding environmental problems related to deforestation.