Already companies are breaking ground on commercial production facilities, and analysts predict 6 billion gallons by Is algal biomass a better feedstock for biofuels than corn, soy or other agricultural products?
We need a range of potential fuel feedstocks that can collectively add up to a significant volume in order to replace a dwindling and finite supply of petroleum fuels. Because algae are grown on marginal land that is unsuitable for traditional agriculture, the production of algae-based fuels does not compete with food.
In fact, when algae are grown for biofuels and the oil is extracted, the remaining carbohydrates and proteins in the residual biomass are a valuable source of animal and aquaculture feed, as well as fertilizer that can be used in traditional agriculture. Take our fun — and short — quiz to see how much you know about algae. Compare with your friends! There are many different methods. But algae do have some unique attributes: they grow efficiently; require less land mass to produce the same volume of fuel; digest carbon; and can be used for energy, fuel, feed and food.
Videos Watch quick videos to learn about algae from industry leaders. Test Your Knowledge! Learn more! We need your help! Join the growing number of people who are supporting the development of the algae industry. But multiple challenges stand between today and a time when algae-derived fuels are routinely pumped into fuel tanks.
We are confident that lipids derived from algae hold great promise as a supplemental biofuel feedstock. Algae have many inherent advantages in this context, with the high-lipid content found in some species being a fundamental edge. Also, since microalgae are not a common food source, algal cultivation for fuel is unlikely to interfere with food production at the levels that cultivation of other feedstocks, such as corn, might.
Because algae grow in many different environments, it could be produced on acreage that is not agriculturally productive. Algae farming could also make use of multiple types of water: fresh, brackish, saline and wastewater. It is widely believed—though research is needed to confirm this—that the use of algal-based fuel would result in a tiny fraction of the net greenhouse gases that can be traced to fossil-fuel use today.
And scaling up algae farming could lead to yields of other commercially viable products besides fuel. All this promise is conditional, of course. Highly productivity algal strains must be identified. New and reliable algae-farming methods must be developed. Hyper-efficient systems for extracting lipids and any other commercial products grown in algae must be invented too. If all that can be accomplished, there is still one potential deal breaker. All of this must be done at a cost that makes algae-derived biofuel competitive with petroleum-based fuels.
Research at NREL is attempting to address some of these challenges. Macroalgae, the seaweeds, grow in open waters, both fresh and marine. These aquatic plants are made up mainly of carbohydrates and have been harvested for centuries as food, including the nori used to wrap sushi, and thickening agents such as agar. The Aquatic Species Program explored the potential of macroalgae as fuel but dropped that project due to the significant challenges related to harvesting costs and fuel conversion.
Microalgae, on the other hand, are unicellular photosynthetic microorganisms. They are ubiquitous in nature, found in freshwater, seawater, hypersaline lakes and even in deserts and arctic ecosystems. They can be further subdivided into two main categories: eukaryotic algae, possessing defined organelles such as nuclei, chloroplasts, mitochondria and so on, and prokaryotic algae cyanobacteria or blue-green algae , possessing the simpler cellular structure of bacteria.
Although the relatedness of cyanobacteria to nonphotosynthetic bacteria allows for exploitation of genetic-engineering technologies and makes them an attractive starting point for biofuels research, they lack one very important thing that eukaryotic microalgae can possess in abundance—neutral lipids, which are rich in triacylglycerols TAGs.
Figure 2. Above are photomicrographs of algal cells that Lee Elliott, a doctoral candidate at the Colorado School of Mines and a National Renewable Energy Laboratory researcher, isolated from water samples collected in the southwestern United States.
BODIPY fluoresces green when dissolved in lipid droplets, and thus can be used to indicate high lipid content in algal cells. Here, chlorophyll fluoresces red. Photomicrographs courtesy of Lee Elliott. Of the eukaryotic microalgae, green algae are the taxonomic group most often referred to as oleaginous, or oil-rich, microalgae. They are ubiquitous in a variety of habitats and grow faster than species from other taxa, and as much as 60 percent of their cell dry weight can be oils.
However, the composition of the oils is highly dependent on the species and the conditions in which the algae grow. Oils that are rich in neutral lipids are desirable in a biofuel context because of their potential high fuel yield. Because TAGs are made up of three molecules of fatty acids that are esterified—or altered—to one molecule of glycerol, close to percent of their weight can be converted into fuels.
With polar lipids, on the other hand, only one or two fatty-acid molecules are esterified to glycerol and the remaining components e. As a result, these types of lipids generate lower fuel yields.
Figure 3. Only a small portion of algae species have been screened for their lipid content and only a share of those screened are considered oleaginous, meaning that lipids comprise 20 percent or more of their dry weight. Among those screened so far, green algae species produce the most lipids, mostly in the form of triacyglycerol TAG , which functions as carbon and energy storage in algae cells.
Studies have shown that some algal lipid production increases in stressed environments. Above are the percentages of cellular lipid contents found in different types of microalage and cynobacteria under normal green and stressed red growing conditions, including nitrogen depletion or other deficits. Illustration by Barbara Aulicino. The Plant Journal. Fatty acids, the building blocks for lipids, are synthesized by enzymes in the chloroplast, of which acetyl-CoA carboxylase ACCase is key in regulating the synthesis rates.
When cells are actively growing, their metabolic focus is on photosynthesis and the production of biomass. The fatty acids produced are mostly found in polar-membrane lipids, such as phospho- and glycolipids, which are invaluable to photosynthesis. Unfortunately only about 30 to 50 percent of polar lipids can be converted into fuel molecules. But when the cells experience metabolic stress, such as a lack of essential nutrients, including nitrogen, cell metabolism is redirected to reduce the growth rate and favor the production of carbon-storage compounds, mainly carbohydrates and TAGs.
Little is known about the regulation of TAG formation at the molecular and cellular level, but greater understanding could lead to the engineering of algae with higher ratios of neutral lipids.
Organic solvents can extract oils from actively growing cells. But oils extracted from stressed cells yield more fuel. In Chlorella vulgaris , a strain that our laboratory has studied extensively, the extracted oil content amounts to about 30 to 50 percent of the biomass under both active-growth and nutrient-limited conditions. However, the fatty-acid content, reflecting the potential fuel yield, can vary from 10 to 50 percent of the biomass over the growth cycle. This illustrates the big discrepancies often seen between the extracted algal oils and the actual fuel-yield potential.
Unlike typical terrestrial oil-producing plants, in which specialized cells yield oils, every algal cell can produce oils. Algal oils, just like oils produced by soy, canola, palm and the less-known jatropha plants, can be made good biodiesel feedstocks through transesterification.
In that process, a catalyst creates a biodiesel fuel consisting of fatty acid methyl esters by hydrolyzing and methylating fatty acids in the oils. Refining the mixture is typically the next step and involves removing the non—fatty-acid components—such as glycerol, polar lipids and residual pigments—from the fuel. Typical refinery processes such as hydrotreating, cracking and isomerization of the algal oils can also be used to produce renewable gasoline, diesel or jet fuels. These so-called drop-in fuels are much more like traditional petroleum-based fuels and can be blended, like for like, in existing fueling infrastructure.
Once algal oils have been extracted with organic solvents or removed in some other way, the remaining biomass will be made up of approximately equal amounts of carbohydrates and proteins. We expect that this residual material can be used as a feedstock for so-called coproducts to help the overall economics of algae farming.
Carbohydrates can be used to produce methane by anaerobic digestion or ethanol by fermentation. Proteins can be used for animal feed or even human food. Other higher-value algal products such as omega-3 fatty acids and antioxidants are already available commercially, but the potential market for biofuels dwarfs market for these nutraceuticals. The search for high-value coproducts with large market size remains an elusive goal for an integrated biorefinery based on algal biomass.
Research published this year by Mark Wigmosta and coworkers at the U. This report used fairly conservative assumptions for algal growth rates and lipid content, based on current technologies, and arrived at a value of 57 billion gallons of lipid-based algal biofuels per year. Thus algae represent a feedstock source that could be comparable in size to all the terrestrial biomass that could be harvested for biofuel production combined.
In order to produce that much algal biomass, it will be necessary to develop a new type of agriculture, comparable in scale to the amount of U. That will require novel methods for cultivation, harvesting and processing. As anyone with a poorly maintained swimming pool can attest, algae can grow without much prompting. But this agriculture will require crops that grow at maximum rates and achieve the highest possible concentration of cells per liter of cultivation medium.
Successful algae crops must be able to thrive in the presence of pests, predators and pathogens. All this will require a carefully engineered cultivation process. Figure 4. The map above shows where Lee Elliott of the Colorado School of Mines took water samples during algae bioprospecting expeditions in and The samples ranged from fresh water less than 0.
Strains from a range of water chemistries are needed to ensure that culture collections contain broad biodiversity.
Elliott bottom takes a sample from a pond with visible algal growth in Golden, Colorado. Much of our research focuses on the growth rate and lipid content of algae. At this stage, that includes bioprospecting—the search for natural strains with high growth rate and high lipid content, as well as robustness. We look for species that are resistant to pests, predators and pathogens and have the ability to thrive under environmental conditions—sunlight, temperature and water chemistry—expected at a cultivation site.
In this search, we use technologies developed for the biotechnology and pharmaceutical industries, such as robotics, liquid handling devices and fluorescence-activated cell sorting, to speed up the isolation of single algal cells from environmental samples and to test them for growth rate and lipid content. Learning from colleagues affiliated with the Culture Collection of Algae at the University of Texas, we developed methods to preserve culture samples cryogenically and to revive them at will, eliminating the laborious and sometimes counterproductive practice of maintaining algal cultures on agar plates and slants, which requires regular transfers to fresh media.
Our work in bioprospecting and our involvement with the Sustainable Algal Biofuels Consortium, led by Arizona State University, have made it clear to us that there is a widespread need to accelerate the quantification of lipids and tailor the analysis to rapidly screen several hundreds or thousands of individual strains, which is not feasible with traditional gravimetric or chromatographic separation processes.
At NREL, we have developed rapid, infrared-spectroscopic, high-throughput methods for the estimation of algal lipid content based on multivariate calibration models.
Algae are already important in numerous commercial uses: to produce nutritional supplements, to treat sewage, and as coloring agents. One of the most promising uses of algae is as renewable raw material for biofuels. The vegetable oil from algae can be used directly straight vegetable oil that is esterized into biodiesel or refined into various biofuels, including renewable diesel and jet fuel, in addition to other chemical ingredients for products such as cosmetics.
The carbohydrates sugars from algae can be fermented to make additional biofuels, including ethanol and butanol, as well as other products such as plastics and biochemicals. Biomass from algae can be used for pyrolysis oil or combined heat and power generation. Algae-derived renewable diesels and jet fuels are drop-in fuels that directly replace petroleum fuels without modification of engines.
They meet all the specifications for the petroleum fuel they replace. A significant advantage of using algae for biofuels is that it need not displace farmland used for growing food sources. The Department of Energy reports that algae have the potential to yield at least 30 times more energy than land-based crops currently used to produce biofuels.
Algae also efficiently recycle atmospheric carbon.
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