algae fuel

In 1942 Harder and Von Witsch were the first to propose that microalgae be grown as a source of lipids for food or fuel.{{cite journal | last1 = Harder | first1 = R. | last2 = von Witsch | first2 = H. | year = 1942 | title = Bericht über versuche zur fettsynthese mittels autotropher microorganismen | journal = Forschungsdienst Sonderheft | volume = 16 | pages = 270–275 }}{{cite journal | last1 = Harder | first1 = R. | last2 = von Witsch | first2 = H. | year = 1942 | title = Die massenkultur von diatomeen | journal = Berichte der Deutschen Botanischen Gesellschaft | volume = 60 | pages = 146–152 }} Following World War II, research began in the US,Cook P.M. 1950. Large-scale culture of Chlorella. In: Brunel J., G.W. Prescott (eds) The culture of algae. Charles F. Kettering Foundation, Dayton, p. 53–77.Burlew J.S. (ed). 1953. Algae culture: from laboratory to pilot plant. Carnegie Institution of Washington, Washington, DC, p. 1–357.Burlew J.S. 1953. Current status of large-scale culture of algae. In: Burlew J.S. (ed). Algal culture: from laboratory to pilot plant. Carnegie Institution, Washington, DC, p. 3–23. Germany,Gummert F., M.E. Meffert, and H. Stratmann. 1953. Nonsterile large-scale culture of Chlorella in greenhouse and open air. In: Burlew J.S. (ed). Algal culture: from laboratory to pilot plant. Carnegie Institution of Washington, Washington, DC, p. 166–176. Japan,Mituya A., T. Nyunoya, and H. Tamiya. 1953. Pre-pilot-plant experiments on algal mass culture. In: Burlew J.S. (ed). Algal culture: from labo- ratory to pilot plant. Carnegie Institution, Washington, DC, p. 273–281. England,Geoghegan M.J. 1953. Experiments with Chlorella at Jealott's Hill. In: Burlew J.S. (ed). Algal culture: from laboratory to pilot plant. Carnegie Institution, Washington, DC, p. 182–189. and IsraelEvenari M., A.M. Mayer, and E. Gottesman. 1953. Experiments of culture of algae in Israel. In: Burlew J.S. (ed). Algal culture. From laboratory to pilot plant. Carnegie Institution, Washington, DC, p. 197–203. on culturing techniques and engineering systems for growing microalgae on larger scales, particularly species in the genus Chlorella. Meanwhile, H. G. Aach showed that Chlorella pyrenoidosa could be induced via nitrogen starvation to accumulate as much as 70% of its dry weight as lipids.{{Cite journal | doi = 10.1007/BF00410827| title = Über Wachstum und Zusammensetzung von Chlorella pyrenoidosa bei unterschiedlichen Lichtstärken und Nitratmengen| journal = Archiv für Mikrobiologie| volume = 17| pages = 213–246| year = 1952| last1 = Aach | first1 = H. G.| issue = 1–4| bibcode = 1952ArMic..17..213A| s2cid = 7813967}} Since the need for alternative transportation fuel had subsided after World War II, research at this time focused on culturing algae as a food source or, in some cases, for wastewater treatment.{{Cite book | doi = 10.1007/978-94-007-5479-9_1| chapter = Energy from Microalgae: A Short History| title = Algae for Biofuels and Energy| pages = 1–15| year = 2013| last1 = Borowitzka | first1 = M. A. | isbn = 978-94-007-5478-2| url = https://books.google.com/books?id=ZJl0MAEACAAJ}}

Interest in the application of algae for biofuels was rekindled during the oil embargo and oil price surges of the 1970s, leading the US Department of Energy to initiate the Aquatic Species Program in 1978.{{cite web | url = http://www1.eere.energy.gov/bioenergy/pdfs/algal_biofuels_roadmap.pdf |title = National Algal Biofuels Technology Roadmap |publisher = US Department of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program | access-date=3 April 2014}} The Aquatic Species Program spent $25 million over 18 years to develop liquid transportation fuel from algae that would be price-competitive with petroleum-derived fuels.Sheehan J., T. Dunahay, J. Benemann, P. Roessler. 1998. A look back at the U.S. Department of Energy's Aquatic Species Program – biodiesel from algae. National Renewable Energy Laboratory: Golden, Colorado. NREL/TP-580-24190, p. 1–328. The research program focused on microalgae cultivation in open outdoor ponds, systems that are low in cost but vulnerable to environmental disturbances like temperature swings and biological invasions. 3,000 algal strains were collected from around the country and screened for desirable properties such as high productivity, lipid content, and thermal tolerance, and the most promising strains were included in the SERI microalgae collection at the Solar Energy Research Institute (SERI) in Golden, Colorado and used for further research. Among the program's most significant findings were that rapid growth and high lipid production were "mutually exclusive" since the former required high nutrients and the latter required low nutrients. The final report suggested that genetic engineering may be necessary to be able to overcome this and other natural limitations of algal strains and that the ideal species might vary with place and season. Although it was successfully demonstrated that large-scale production of algae for fuel in outdoor ponds was feasible, the program failed to do so at a cost that would be competitive with petroleum, especially as oil prices sank in the 1990s. Even in the best-case scenario, it was estimated that unextracted algal oil would cost $59–186 per barrel, while petroleum cost less than $20 per barrel in 1995. Therefore, under budget pressure in 1996, the Aquatic Species Program was abandoned.

Other contributions to algal biofuels research have come indirectly from projects focusing on different applications of algal cultures. For example, in the 1990s Japan's Research Institute of Innovative Technology for the Earth (RITE) implemented a research program with the goal of developing systems to fix {{chem|CO|2}} using microalgae.{{Cite journal | doi = 10.1016/0196-8904(95)00102-J| title = Biological CO2 fixation and utilization project| journal = Energy Conversion and Management| volume = 36| issue = 6–9| pages = 701–705| year = 1995| last1 = Michiki | first1 = H. }} Although the goal was not energy production, several studies produced by RITE demonstrated that algae could be grown using flue gas from power plants as a {{chem|CO|2}} source,{{Cite journal | doi = 10.1007/BF02922657| pmid = 1929389| title = Growth of Microalgae in High CO2 Gas and Effects of SOX and NOX| journal = Applied Biochemistry and Biotechnology| volume = 28–29| pages = 877–86| year = 1991| last1 = Negoro | first1 = M. | last2 = Shioji | first2 = N. | last3 = Miyamoto | first3 = K. | last4 = Micira | first4 = Y. | s2cid = 22607146}}{{Cite journal | doi = 10.1007/BF02920589| title = Growth characteristics of microalgae in high-concentration co2 gas, effects of culture medium trace components, and impurities thereon| journal = Applied Biochemistry and Biotechnology| volume = 34–35| pages = 681–692| year = 1992| last1 = Negoro | first1 = M. | last2 = Shioji | first2 = N. | last3 = Ikuta | first3 = Y. | last4 = Makita | first4 = T. | last5 = Uchiumi | first5 = M. | s2cid = 96744279}} an important development for algal biofuel research. Other work focusing on harvesting hydrogen gas, methane, or ethanol from algae, as well as nutritional supplements and pharmaceutical compounds, has also helped inform research on biofuel production from algae.

Following the disbanding of the Aquatic Species Program in 1996, there was a relative lull in algal biofuel research. Still, various projects were funded in the US by the Department of Energy, Department of Defense, National Science Foundation, Department of Agriculture, National Laboratories, state funding, and private funding, as well as in other countries. More recently, rising oil prices in the 2000s spurred a revival of interest in algal biofuels and US federal funding has increased, numerous research projects are being funded in Australia, New Zealand, Europe, the Middle East, and other parts of the world.

In December 2022, ExxonMobil, the last large oil company to invest in algae biofuels, ended its research funding.{{Cite news |last=Westervelt |first=Amy |author-link=Amy Westervelt |date=2023-03-17 |title=Big oil firms touted algae as climate solution. Now all have pulled funding |url=https://www.theguardian.com/environment/2023/mar/17/big-oil-algae-biofuel-funding-cut-exxonmobil |access-date=2023-03-21 |work=The Guardian |language=en-GB |issn=0261-3077}}

In March 2023, researchers said that the commercialization of biofuels would require several billion dollars of funding, plus a long-term dedication to overcoming what appear to be fundamental biological limitations of wild organisms. Most researchers believe that large scale production of biofuels is either "a decade, and more likely two decades, away."

Algal oil is used as a source of fatty acid supplementation in food products, as it contains mono- and polyunsaturated fats, in particular EPA and DHA.{{cite journal|author1=Scott D. Doughman |author2=Srirama Krupanidhi |author3=Carani B. Sanjeevi|s2cid=29591060|title=Omega-3 Fatty Acids for Nutrition and Medicine: Considering Microalgae Oil as a Vegetarian Source of EPA and DHA|journal=Current Diabetes Reviews|volume=3|issue=3|year=2007|pages=198–203|pmid=18220672|doi=10.2174/157339907781368968}} Its DHA content is roughly equivalent to that of salmon based fish oil.{{cite journal|last1=Arterburn|first1=LM|title=Algal-Oil Capsules and Cooked Salmon: Nutritionally Equivalent Sources of Docosahexaenoic Acid|date=July 2008|volume=108|issue=7|pages=1204–1209|url=http://www.andjrnl.org/article/S0002-8223(08)00512-9/abstract|access-date=20 January 2017|doi=10.1016/j.jada.2008.04.020|pmid=18589030|journal=Journal of the American Dietetic Association}}{{cite journal|pmc=3705349|year=2013|last1=Lenihan-Geels|first1=G|title=Alternative Sources of Omega-3 Fats: Can We Find a Sustainable Substitute for Fish?|journal=Nutrients|volume=5|issue=4|pages=1301–1315|last2=Bishop|first2=K. S.|last3=Ferguson|first3=L. R.|doi=10.3390/nu5041301|pmid=23598439|doi-access=free}}

Algae can be converted into various types of fuels, depending on the production technologies and the part of the cells used. The lipid, or oily part of the algae biomass can be extracted and converted into biodiesel through a process similar to that used for any other vegetable oil, or converted in a refinery into "drop-in" replacements for petroleum-based fuels. Alternatively or following lipid extraction, the carbohydrate content of algae can be fermented into bioethanol or butanol fuel.{{cite web

| url= http://www.merinews.com/catFull.jsp?articleID=135399

| title= Biofuels from industrial/domestic wastewater

| access-date= 11 June 2008

| archive-url= https://web.archive.org/web/20090218225448/http://www.merinews.com/catFull.jsp?articleID=135399

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{{Main|Biodiesel}}

Biodiesel is a diesel fuel derived from animal or plant lipids (oils and fats). Studies have shown that some species of algae can produce 60% or more of their dry weight in the form of oil.{{Cite journal | first1 = Anirban |last1=Banerjee |first2=Rohit |last2=Sharma |first3=Yusuf |last3=Chisti |first4=U. C. |last4=Banerjee | year = 2002 | title = Botryococcus braunii: A Renewable Source of Hydrocarbons and Other Chemicals | journal = Critical Reviews in Biotechnology | volume = 22 | issue = 3 | pages = 245–279 | doi = 10.1080/07388550290789513|pmid=12405558 |s2cid=20396446 }} Because the cells grow in aqueous suspension, where they have more efficient access to water, {{chem|CO|2}} and dissolved nutrients, microalgae are capable of producing large amounts of biomass and usable oil in either high rate algal ponds{{Cite web | url=https://www.chemengonline.com/mechanical-co2-sequestration-improves-algae-production/ |title = Mechanical CO2 sequestration improves algae production - Chemical Engineering | Page 1| date=March 2019 }} or photobioreactors. This oil can then be turned into biodiesel which could be sold for use in automobiles. Regional production of microalgae and processing into biofuels will provide economic benefits to rural communities.

{{cite web

|url=http://www.pir.sa.gov.au/__data/assets/pdf_file/0006/77055/microalgal_prod.pdf

|title=Microalgal Production SARDI AQUATIC SCIENCES

|publisher=Government of South Australia

|access-date=3 November 2008

|archive-url=https://web.archive.org/web/20081217093711/http://www.pir.sa.gov.au/__data/assets/pdf_file/0006/77055/microalgal_prod.pdf

|archive-date=17 December 2008

|url-status=dead

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As they do not have to produce structural compounds such as cellulose for leaves, stems, or roots, and because they can be grown floating in a rich nutritional medium, microalgae can have faster growth rates than terrestrial crops. Also, they can convert a much higher fraction of their biomass to oil than conventional crops, e.g. 60% versus 2-3% for soybeans.Tornabene, et al. (1983), Lipid composition of nitrogen starved, green Neochloris oleoabundans The per unit area yield of oil from algae is estimated to be from 58,700 to 136,900 L/ha/year, depending on lipid content, which is 10 to 23 times as high as the next highest yielding crop, oil palm, at 5 950 L/ha/year.{{Cite journal | doi = 10.1016/j.rser.2012.01.003| title = A comprehensive review on biodiesel as an alternative energy resource and its characteristics| journal = Renewable and Sustainable Energy Reviews| volume = 16| issue = 4| pages = 2070–2093| year = 2012| last1 = Atabani | first1 = A. E. | last2 = Silitonga | first2 = A. S. | last3 = Badruddin | first3 = I. A. | last4 = Mahlia | first4 = T. M. I. | last5 = Masjuki | first5 = H. H. | last6 = Mekhilef | first6 = S.| bibcode = 2012RSERv..16.2070A}}

The U.S. Department of Energy's Aquatic Species Program, 1978–1996, focused on biodiesel from microalgae. The final report suggested that biodiesel could be the only viable method by which to produce enough fuel to replace current world diesel usage.{{cite web|url=http://www.eere.energy.gov/biomass/pdfs/biodiesel_from_algae.pdf |title=Biodiesel Production from Algae |publisher=Department of Energy Aquatic Species Program, National Renewable Energy Laboratory |access-date=29 August 2006 |archive-url=https://web.archive.org/web/20060926045050/http://www.eere.energy.gov/biomass/pdfs/biodiesel_from_algae.pdf |archive-date=26 September 2006 |url-status=dead }} If algae-derived biodiesel were to replace the annual global production of 1.1bn tons of conventional diesel then a land mass of 57.3 million hectares would be required, which would be highly favorable compared to other biofuels.{{Cite journal | last1 = Shirvani | first1 = T. | last2 = Yan | first2 = X. | last3 = Inderwildi | first3 = O. R. | last4 = Edwards | first4 = P. P. | last5 = King | first5 = D. A. | s2cid = 111077361 | title = Life cycle energy and greenhouse gas analysis for algae-derived biodiesel | doi = 10.1039/C1EE01791H | journal = Energy & Environmental Science | volume = 4 | issue = 10 | pages = 3773 | year = 2011 | bibcode = 2011EnEnS...4.3773S }}

{{Main|Biodiesel production}}

Algae can be used to produce 'green diesel' (also known as renewable diesel, hydrotreating vegetable oil{{cite journal |last=Knothe |first=Gerhard |year=2010 |title=Biodiesel and renewable diesel: A comparison |url=https://www.sciencedirect.com/science/article/abs/pii/S0360128509000677?via%3Dihub |journal=Progress in Energy and Combustion Science |volume=36 |issue=3 |page=364 |bibcode=2010PECS...36..364K |doi=10.1016/j.pecs.2009.11.004}} or hydrogen-derived renewable diesel){{cite web |title=Alternative & Advanced Fuels |url=http://www.afdc.energy.gov/fuels/emerging_green.html |access-date=7 March 2012 |publisher=US Department of Energy}} through a hydrotreating refinery process that breaks molecules down into shorter hydrocarbon chains used in diesel engines.{{cite web |last1=Brown |first1=Robert |last2=Holmgren |first2=Jennifer |title=Fast Pyrolysis and Bio-Oil Upgrading |url=http://www.ascension-publishing.com/BIZ/HD50.pdf |access-date=15 March 2012}} It has the same chemical properties as petroleum-based diesel meaning that it does not require new engines, pipelines or infrastructure to distribute and use. It has yet to be produced at a cost that is competitive with petroleum. While hydrotreating is currently the most common pathway to produce fuel-like hydrocarbons via decarboxylation/decarbonylation, there is an alternative process offering a number of important advantages over hydrotreating. In this regard, the work of Crocker et al.{{cite journal |last1=Crocker |first1=Mark H. |display-authors=etal |date=21 March 2015 |title=CO₂ Recycling Using Microalgae for the Production of Fuels |journal=Applied Petrochemical Research |volume=4 |pages=41–53 |doi=10.1007/s13203-014-0052-3 |doi-access=free}} and Lercher et al.{{Cite journal |last1=Lercher |first1=Johannes A. |last2=Brück |first2=Thomas |last3=Zhao |first3=Chen |date=21 June 2013 |title=Catalytic deoxygenation of microalgae oil to green hydrocarbons |journal=Green Chemistry |volume=15 |issue=7 |pages=1720–1739 |doi=10.1039/C3GC40558C}} is particularly noteworthy. For oil refining, research is underway for catalytic conversion of renewable fuels by decarboxylation.{{Cite web |title=ACS Presentations on Demand |url=http://presentations.acs.org/common/presentation-detail.aspx/Fall2013/SCHB/SCHB011/20056 |url-status=dead |archive-url=https://web.archive.org/web/20160122074616/https://presentations.acs.org/common/presentation-detail.aspx/fall2013/schb/schb011/20056 |archive-date=22 January 2016 |access-date=2015-06-02 |website=presentations.acs.org}} As the oxygen is present in crude oil at rather low levels, of the order of 0.5%, deoxygenation in petroleum refining is not of much concern, and no catalysts are specifically formulated for oxygenates hydrotreating. Hence, one of the critical technical challenges to make the hydrodeoxygenation of algae oil process economically feasible is related to the research and development of effective catalysts.{{Cite journal |last1=Zhou |first1=Lin |year=2015 |title=Evaluation of Presulfided NiMo/γ-Al2O3 for Hydrodeoxygenation of Microalgae Oil To Produce Green Diesel |journal=Energy & Fuels |volume=29 |pages=262–272 |doi=10.1021/ef502258q}}{{Cite journal |last1=Zhou |first1=Lin |year=2016 |title=Hydrodeoxygenation of microalgae oil to green diesel over Pt, Rh and presulfided NiMo catalysts |url=https://pubs.rsc.org/is/content/articlelanding/2016/cy/c5cy01307k |journal=Catalysis Science & Technology |volume=6 |issue=5 |pages=1442–1454 |doi=10.1039/c5cy01307k}}

{{Main|Butanol fuel}}

Butanol can be made from algae or diatoms using only a solar powered biorefinery. This fuel has an energy density 10% less than gasoline, and greater than that of either ethanol or methanol. In most gasoline engines, butanol can be used in place of gasoline with no modifications. In several tests, butanol consumption is similar to that of gasoline, and when blended with gasoline, provides better performance and corrosion resistance than that of ethanol or E85.{{Cite web|url=http://www.epa.gov/air/caaac/mstrs/March2007/Wolf.pdf|archive-url=https://web.archive.org/web/20081030023008/http://www.epa.gov/air/caaac/mstrs/March2007/Wolf.pdf|url-status=dead|title=Wolf|archive-date=30 October 2008}}

The green waste left over from the algae oil extraction can be used to produce butanol. In addition, it has been shown that macroalgae (seaweeds) can be fermented by bacteria of genus Clostridia to butanol and other solvents.{{cite journal | last1 = Potts | first1 = T. | last2 = Du | first2 = J. | last3 = Paul | first3 = M. | last4 = May | first4 = P. | last5 = Beitle | first5 = R. | last6 = Hestekin | first6 = J. | year = 2012 | title = The Production of Butanol from Jamaica Bay Macro Algae | journal = Environmental Progress & Sustainable Energy | volume = 31 | issue = 1| pages = 29–36 | doi=10.1002/ep.10606| bibcode = 2012EPSE...31...29P | s2cid = 96613555 }} Transesterification of seaweed oil (into biodiesel) is also possible with species such as Chaetomorpha linum, Ulva lactuca, and Enteromorpha compressa (Ulva).{{cite journal |doi=10.3390/en7117194|title=Macroalgae-Derived Biofuel: A Review of Methods of Energy Extraction from Seaweed Biomass|journal=Energies|volume=7|issue=11|pages=7194–7222|year=2014|last1=Milledge|first1=John|last2=Smith|first2=Benjamin|last3=Dyer|first3=Philip|last4=Harvey|first4=Patricia|doi-access=free}}

The following species are being investigated as suitable species from which to produce ethanol and/or butanol:{{Cite web|url=https://theecologist.org/2016/oct/12/biofuels-seaweed|title=Biofuels from seaweed?|website=The Ecologist|date=12 October 2016 }}

• Alaria esculenta
• Laminaria saccharina
• Palmaria palmata{{cite web|url=http://www.renewableenergyworld.com/articles/2013/06/from-the-beach-to-the-pump-is-kelp-a-viable-biofuel.html|title=From the Sea to the Pump: Is Kelp a Viable Biofuel?|date=14 June 2013|website=www.renewableenergyworld.com|access-date=4 May 2018|archive-date=5 May 2018|archive-url=https://web.archive.org/web/20180505070440/https://www.renewableenergyworld.com/articles/2013/06/from-the-beach-to-the-pump-is-kelp-a-viable-biofuel.html|url-status=dead}}

Biogasoline is gasoline produced from biomass. Like traditionally produced gasoline, it contains between 6 (hexane) and 12 (dodecane) carbon atoms per molecule and can be used in internal-combustion engines.{{Cite journal | doi = 10.1002/anie.201308143| title = Hydrodeoxygenation of the Angelica Lactone Dimer, a Cellulose-Based Feedstock: Simple, High-Yield Synthesis of Branched C7-C10Gasoline-like Hydrocarbons| journal = Angewandte Chemie International Edition| volume = 53| issue = 7| pages = 1854–1857| year = 2014| last1 = Mascal | first1 = M. | last2 = Dutta | first2 = S. | last3 = Gandarias | first3 = I. | pmid=24474249}}

{{Main | Biogas}}

Biogas is composed mainly of methane ({{CH4}}) and carbon dioxide ({{CO2}}), with some traces of hydrogen sulphide, oxygen, nitrogen, and hydrogen. Macroalgae has high methane production rate compared to plant biomass. Biogas production from macroalgae is more technically viable compared to other fuels, but it is not economically viable due to the high cost of macroalgae feedstock.{{Cite journal | doi =10.1016/j.energy.2012.05.006 | title = Microalgae: An alternative as sustainable source of biofuels? | journal = Energy | volume = 44 | issue = 1 | pages = 158–166 | year = 2012 | last1 = Amaro | first1 = Helena | last2 = Macedo | first2 = Angela | last3 = Malcata | first3 = F.| bibcode = 2012Ene....44..158A }} Carbohydrate and protein in microalgae can be converted into biogas through anaerobic digestion, which includes hydrolysis, fermentation, and methanogenesis steps. The conversion of algal biomass into methane can potentially recover as much energy as it obtains, but it is more profitable when the algal lipid content is lower than 40%.{{Cite journal | doi =10.1016/j.rser.2013.08.067 | title = Toward a sustainable approach for development of biodiesel from plant and microalgae | journal = Renewable and Sustainable Energy Reviews | volume = 29 | pages = 216–245 | year = 2014 | last1 = Singh | first1 = Bhaskar | last2 = Guldhe | first2 = Abhishek | last3 = Bux | first3 = Faizal| bibcode = 2014RSERv..29..216S }} Biogas production from microalgae is relatively low because of the high ratio of protein in microalgae, but microalgae can be co-digested with high C/N ratio products such as wastepaper.{{Cite journal | doi =10.1016/j.rser.2015.11.026 | title = Macroalgae and microalgae as a potential source for commercial applications along with biofuels production: A biorefinery approach | journal = Renewable and Sustainable Energy Reviews | volume = 55 | pages = 909–941 | year = 2016 | last1 = Suganya | first1 = T. | last2 = Varman | first2 = M. | last3 = Masjuki | first3 = H. | last4 = Renganathan| bibcode = 2016RSERv..55..909S }} Another method to produce biogas is through gasification, where hydrocarbon is converted to syngas through a partial oxidation reaction at high temperature (typically 800 °C to 1000 °C). Gasification is usually performed with catalysts. Uncatalyzed gasification requires temperature to be about 1300 °C. Syngas can be burnt directly to produce energy or used a fuel in turbine engines. It can also be used as feedstock for other chemical productions.{{Cite journal | doi =10.1016/j.rser.2015.03.052 | title = Algae based biorefinery – How to make sense? | journal = Renewable and Sustainable Energy Reviews | volume = 47 | pages = 295–307 | year = 2015 | last1 = Trivedi | first1 = Jayati | last2 = Aila | first2 = Mounika | last3 = Bangwal | first3 = D. | last4 = Garg | first4 = M.| bibcode = 2015RSERv..47..295T }}

Methane,{{cite web | url = http://www.fao.org/docrep/w7241e/w7241e0f.htm#TopOfPage |title = Methane production |publisher = FAO, Agriculture Department | access-date=29 August 2006}} the main constituent of natural gas, can be produced from algae by various methods, namely gasification, pyrolysis and anaerobic digestion. In gasification and pyrolysis methods methane is extracted under high temperature and pressure. Anaerobic digestion[http://www.oilgae.com/algae/pro/met/met.html Methane from algae – Oilgae – Oil from Algae]. Oilgae (2 December 2009). Retrieved 15 April 2012. is a straightforward method involved in decomposition of algae into simple components then transforming it into fatty acids using microbes like acidogenic bacteria followed by removing any solid particles and finally adding methanogenic archaea to release a gas mixture containing methane. A number of studies have successfully shown that biomass from microalgae can be converted into biogas via anaerobic digestion.Eisenberg, D.M., W.J. Oswald, J.R. Benemann, R.P. Goebel, and T.T. Tiburzi. 1979. Methane fermentation of microalgae. In Anaerobic digestion, edited by D. A. Stafford, B. I. Wheatley and D. E. Hughes. London, United Kingdom: Applied Science Publishers LTD.{{cite journal | last1 = Golueke | first1 = C.G. | last2 = Oswald | first2 = W.J. | last3 = Gotaas | first3 = H.B. | year = 1957 | title = Anaerobic digestion of algae | journal = Applied and Environmental Microbiology | volume = 5 | issue = 1| pages = 47–55 | doi = 10.1128/AEM.5.1.47-55.1957 | pmid = 13403639 | pmc = 1057253 | doi-access = free }}{{cite journal | last1 = Rigoni-Stern | first1 = S. | last2 = Rismondo | first2 = R. | last3 = Szpyrkowicz | first3 = L. | last4 = Zilio-Grandi | first4 = F. | last5 = Vigato | first5 = P.A. | year = 1990 | title = Anaerobic digestion of nitrophilic algal biomass from the Venice Lagoon | journal = Biomass | volume = 23 | issue = 3| pages = 179–199 | doi=10.1016/0144-4565(90)90058-r}}{{Cite journal

| last1 = Samson | first1 = R. J.

| last2 = Leduyt | first2 = A.

| doi = 10.1002/bit.260280712

| title = Detailed study of anaerobic digestion of Spirulina maxima algal biomass

| journal = Biotechnology and Bioengineering

| volume = 28

| issue = 7

| pages = 1014–1023

| year = 1986

| pmid = 18555423

| s2cid = 21903205

}}{{Cite journal | last1 = Yen | first1 = H. | last2 = Brune | first2 = D. | doi = 10.1016/j.biortech.2005.11.010 | title = Anaerobic co-digestion of algal sludge and waste paper to produce methane | journal = Bioresource Technology | volume = 98 | issue = 1 | pages = 130–134 | year = 2007 | pmid = 16386894| bibcode = 2007BiTec..98..130Y }} Therefore, in order to improve the overall energy balance of microalgae cultivation operations, it has been proposed to recover the energy contained in waste biomass via anaerobic digestion to methane for generating electricity.Lundquist, T.J., I.C. Woertz, N.W.T. Quinn, and J.R. Benemann, October 2010, [http://www.energybiosciencesinstitute.org/program_project/realistic-technology-and-engineering-assessment-algae-biofuel-production-completed A realistic technology and engineering assessment of algae biofuel production] {{Webarchive|url=https://web.archive.org/web/20130215120851/http://www.energybiosciencesinstitute.org/program_project/realistic-technology-and-engineering-assessment-algae-biofuel-production-completed |date=15 February 2013 }}

The Algenol system which is being commercialized by BioFields in Puerto Libertad, Sonora, Mexico utilizes seawater and industrial exhaust to produce ethanol. Porphyridium cruentum also have shown to be potentially suitable for ethanol production due to its capacity for accumulating large amount of carbohydrates.{{cite journal|title=Effects of nitrogen on growth and carbohydrate formation in Porphyridium cruentum |date=2013-09-21 |doi=10.2478/s11535-013-0248-z |volume=9 |issue=2 |journal=Open Life Sciences | last1 = Razaghi | first1 = Ali|pages=156–162 |doi-access=free }}

{{Main|Aviation biofuel}}

Trials of using algae as biofuel were carried out by Lufthansa and Virgin Atlantic as early as 2008, although there is little evidence that using algae is a reasonable source for jet biofuels.{{cite news |url= http://news.bbc.co.uk/1/hi/uk/7261214.stm |work= BBC News |title= First biofuel flight touches down |access-date=24 February 2008 | date=24 February 2008| archive-url= https://web.archive.org/web/20080229004604/http://news.bbc.co.uk/1/hi/uk/7261214.stm| archive-date= 29 February 2008 | url-status= live}} By 2015, cultivation of fatty acid methyl esters and alkenones from the algae, Isochrysis, was under research as a possible jet biofuel feedstock.{{cite web|last1=Reddy|first1=Chris|last2=O'Neil|first2=Greg|title=Jet Fuel from Algae? Scientists probe fuel potential in common ocean plant|url=https://www.whoi.edu/oceanus/feature/jet-fuel-from-algae|access-date=26 March 2018|date=28 January 2015}}

In May 2022, scientists at University of Cambridge announced they created an algae energy harvester, that uses natural sunlight to power a small microprocessor, initially powering the processor for six months, and then kept going for a full year. The device, which is about the size of AA battery, is a small container with water and blue green algae. The device does not generate a huge amount of power, but it can be used for Internet of Things devices, eliminating the need for traditional batteries such as lithium-ion batteries. The goal is to have more a environmentally friendly power source that can be used in remote areas.{{cite news |last=Irving |first=Michael |url=https://newatlas.com/energy/algae-energy-harvester-electronics/ |title=Algae energy harvester powers electronics for a year on its own |work=New Atlas |date=2022-05-14 |accessdate=2022-05-14 }}

Research into algae for the mass-production of oil focuses mainly on microalgae (organisms capable of photosynthesis that are less than 0.4 mm in diameter, including the diatoms and cyanobacteria) as opposed to macroalgae, such as seaweed. The preference for microalgae has come about due largely to their less complex structure, fast growth rates, and high oil-content (for some species). However, some research is being done into using seaweeds for biofuels, probably due to the high availability of this resource.

{{cite news|last=Lewis|first=Leo|url=http://www.timesonline.co.uk/tol/news/world/article522203.ece|archive-url=https://web.archive.org/web/20090508094022/http://www.timesonline.co.uk/tol/news/world/article522203.ece|url-status=dead|archive-date=8 May 2009|title=Seaweed to breathe new life into fight against global warming|newspaper=The Times Online|access-date=11 February 2008|location=London | date=14 May 2005}}

[https://www.amazon.com/dp/3639153073 Seaweed Biofuels: Production of Biogas and Bioethanol from Brown Macroalgae]. Amazon.com. Retrieved 15 April 2012.

{{As of | 2012}} researchers across various locations worldwide have started investigating the following species for their suitability as a mass oil-producers:{{Cite web|url=http://www.algaefuels.org/algae_FAQ.htm|archive-url=https://web.archive.org/web/20081022031756/http://www.algaefuels.org/algae_FAQ.htm|url-status=dead|title=Algae FAQ|archive-date=22 October 2008}}{{Cite web|url=http://www.unapcaem.org/publication/bioenergy.pdf|title=Bioenergy|access-date=22 October 2008|archive-date=2 October 2018|archive-url=https://web.archive.org/web/20181002214804/http://www.unapcaem.org/publication/bioenergy.pdf|url-status=dead}}{{Cite conference |last1=Ono |first1=Eiichi |last2=Cuello |first2=Joel L. |date=January 2003 |title=Selection of optimal microalgae species for CO 2 sequestration |url=https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=9b8e65993b2a61f6957c9097feba8e369743aaba |conference=Proceedings of Second Annual Conference on Carbon Sequestration |citeseerx= |via=CiteSeerX|s2cid=45589382}}

• Botryococcus braunii
• Chlorella
• Dunaliella tertiolecta
• Gracilaria
• Pleurochrysis carterae (also called CCMP647).

[http://www.ecogenicsresearchcenter.org/prod02.htm Ecogenics Product 2]. Ecogenicsresearchcenter.org. Retrieved 15 April 2012.

• Sargassum, with 10 times the output volume of Gracilaria.{{cite web|url=http://www.taipeitimes.com/News/taiwan/archives/2008/01/12/2003396760|title=Algae eyed as biofuel alternative|date=12 January 2008|work=The Taipei Times |access-date=10 June 2008 |archive-url=https://web.archive.org/web/20080724143536/http://www.taipeitimes.com/News/taiwan/archives/2008/01/12/2003396760|archive-date= 24 July 2008 | url-status= live}}

The amount of oil each strain of algae produces varies widely. Note the following microalgae and their various oil yields:

• Ankistrodesmus TR-87: 28–40% dry weight
• Botryococcus braunii: 29–75% dw
• Chlorella sp.: 29%dw
• Chlorella protothecoides(autotrophic/heterotrophic): 15–55% dw
• Crypthecodinium cohnii: 20%dw
• Cyclotella DI- 35: 42%dw
• Dunaliella tertiolecta : 36–42%dw
• Hantzschia DI-160: 66%dw
• Nannochloris: 31(6–63)%dw
• Nannochloropsis : 46(31–68)%dw
• Nannochloropsis and biofuels
• Neochloris oleoabundans: 35–54%dw
• Nitzschia TR-114: 28–50%dw
• Phaeodactylum tricornutum: 31%dw
• Scenedesmus TR-84: 45%dw
• Schizochytrium 50–77%dw{{cite web|title=Algal Oil Yields|url=http://www.oilgae.com/algae/oil/yield/yield.html|publisher=Oilgae|access-date=13 March 2012}}
• Stichococcus: 33(9–59)%dw
• Tetraselmis suecica: 15–32%dw
• Thalassiosira pseudonana: (21–31)%dw

In addition, due to its high growth-rate, Ulva[http://www.pennenergy.com/index/power/renewable-generation/display/articles/pennenergy/ugc/renewable/seaweed-ulva-photosynthesis-and-zero-emissions-power-generation.html Seaweed Ulva Photosynthesis and Zero Emissions Power Generation] {{Webarchive|url=https://web.archive.org/web/20120305083312/http://www.pennenergy.com/index/power/renewable-generation/display/articles/pennenergy/ugc/renewable/seaweed-ulva-photosynthesis-and-zero-emissions-power-generation.html |date=5 March 2012 }}. Pennenergy.com. Retrieved 15 April 2012. has been investigated as a fuel for use in the SOFT cycle, (SOFT stands for Solar Oxygen Fuel Turbine), a closed-cycle power-generation system suitable for use in arid, subtropical regions.

[http://www.zeitmop.de/pdf/TOWARD_A_LIFE_SEA_NEAR_THE_DEAD_ONE.pdf Toward a live sea near the dead one] {{Webarchive|url=https://web.archive.org/web/20110719115510/http://www.zeitmop.de/pdf/TOWARD_A_LIFE_SEA_NEAR_THE_DEAD_ONE.pdf |date=19 July 2011 }}. (PDF) . Retrieved 15 April 2012.

Other species used include Clostridium saccharoperbutylacetonicum,{{cite web|url=https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/9189/report/F|title=Final Report - Extraction of Sugars from Algae for Direct Conversion to Butanol - Research Project Database - Grantee Research Project - ORD - US EPA|website=cfpub.epa.gov}} Sargassum, Gracilaria, Prymnesium parvum, and Euglena gracilis.{{cite web|url=http://www.oilgae.com/algae/pro/eth/eth.html|title=Ethanol from Algae - Oilgae - Oil from Algae|website=www.oilgae.com}}

{{Main|Algaculture}}

Light is what algae primarily need for growth as it is the most limiting factor. Many companies are investing for developing systems and technologies for providing artificial light. One of them is OriginOil that has developed a Helix BioReactorTM that features a rotating vertical shaft with low-energy lights arranged in a helix pattern.{{Cite web|url=https://lawofalgae.wiki.zoho.com/Chapter-1----Introduction-to-Algae-Biofuels.html|title=Chapter 1 - Introduction to Algae Biofuels - Selecting Algae Species, Algae Production Issues, Harvesting Algae and Extracting Oil, and Converting Algae Oil to Biofuels|website=lawofalgae.wiki.zoho.com|access-date=2016-11-16}} Water temperature also influences the metabolic and reproductive rates of algae. Although most algae grow at low rate when the water temperature gets lower, the biomass of algal communities can get large due to the absence of grazing organisms. The modest increases in water current velocity may also affect rates of algae growth since the rate of nutrient uptake and boundary layer diffusion increases with current velocity.

Other than light and water, phosphorus, nitrogen, and certain micronutrients are also useful and essential in growing algae. Nitrogen and phosphorus are the two most significant nutrients required for algal productivity, but other nutrients such as carbon and silica are additionally required.{{Cite web|url=http://www.krisweb.com/krissheepscot/krisdb/html/krisweb/stream/nutrients.htm|title=Nutrients and Algae|website=www.krisweb.com|access-date=2016-11-16}} Of the nutrients required, phosphorus is one of the most essential ones as it is used in numerous metabolic processes. The microalgae D. tertiolecta was analyzed to see which nutrient affects its growth the most.{{Cite journal|last1=Chen|first1=Meng|last2=Tang|first2=Haiying|last3=Ma|first3=Hongzhi|last4=Holland|first4=Thomas C.|last5=Ng|first5=K. Y. Simon|last6=Salley|first6=Steven O.|date=2011-01-01|title=Effect of nutrients on growth and lipid accumulation in the green algae Dunaliella tertiolecta|journal=Bioresource Technology|volume=102|issue=2|pages=1649–1655|doi=10.1016/j.biortech.2010.09.062|issn=1873-2976|pmid=20947341|bibcode=2011BiTec.102.1649C |s2cid=33867819 }} The concentrations of phosphorus (P), iron (Fe), cobalt (Co), zinc (Zn), manganese (Mn) and molybdenum (Mo), magnesium (Mg), calcium (Ca), silicon (Si) and sulfur (S) concentrations were measured daily using inductively coupled plasma (ICP) analysis. Among all these elements being measured, phosphorus resulted in the most dramatic decrease, with a reduction of 84% over the course of the culture. This result indicates that phosphorus, in the form of phosphate, is required in high amounts by all organisms for metabolism.

There are two enrichment media that have been extensively used to grow most species of algae: Walne medium and the Guillard's F/₂ medium.{{Cite web|url=http://www.fao.org/docrep/003/W3732E/w3732e06.htm|title=2.3. Algal production|website=www.fao.org|access-date=2016-11-16}} These commercially available nutrient solutions may reduce time for preparing all the nutrients required to grow algae. However, due to their complexity in the process of generation and high cost, they are not used for large-scale culture operations. Therefore, enrichment media used for mass production of algae contain only the most important nutrients with agriculture-grade fertilizers rather than laboratory-grade fertilizers.

{{see also|Culture of microalgae in hatcheries}}

File:Photobioreactor PBR 4000 G IGV Biotech.jpg

File:Algal open pond design.jpg commonly used for algal culture]]

Algae grow much faster than food crops, and can produce hundreds of times more oil per unit area than conventional crops such as rapeseed, palms, soybeans, or jatropha. As algae have a harvesting cycle of 1–10 days, their cultivation permits several harvests in a very short time-frame, a strategy differing from that associated with annual crops. In addition, algae can be grown on land unsuitable for terrestrial crops, including arid land and land with excessively saline soil, minimizing competition with agriculture.{{Cite journal | doi = 10.1007/s12155-008-9008-8| title = Second Generation Biofuels: High-Efficiency Microalgae for Biodiesel Production| journal = BioEnergy Research| volume = 1| pages = 20–43| year = 2008| last1 = Schenk | first1 = P. M. | last2 = Thomas-Hall | first2 = S. R. | last3 = Stephens | first3 = E. | last4 = Marx | first4 = U. C. | last5 = Mussgnug | first5 = J. H. | last6 = Posten | first6 = C. | last7 = Kruse | first7 = O. | last8 = Hankamer | first8 = B. | issue = 1| bibcode = 2008BioER...1...20S| s2cid = 3357265}} Most research on algae cultivation has focused on growing algae in clean but expensive photobioreactors, or in open ponds, which are cheap to maintain but prone to contamination.

The lack of equipment and structures needed to begin growing algae in large quantities has inhibited widespread mass-production of algae for biofuel production. Maximum use of existing agriculture processes and hardware is the goal.{{cite web | url= http://www.environmentalgraffiti.com/businesspolitics/will-algae-beat-its-competitors-to-become-the-king-source-of-biofuels/237 | title= Will algae beat its competitors to become the king source of biofuels? | author= Maryking | date= 29 August 2007 | publisher= Environmental Graffiti | access-date= 10 June 2008 | archive-url= https://web.archive.org/web/20101105155515/http://www.environmentalgraffiti.com/businesspolitics/will-algae-beat-its-competitors-to-become-the-king-source-of-biofuels/237 | archive-date= 5 November 2010 | url-status= dead}}

Closed systems (not exposed to open air) avoid the problem of contamination by other

organisms blown in by the air. The problem of a closed system is finding a cheap source of sterile {{chem|CO|2}}.

Several experimenters have found the {{chem|CO|2}} from a smokestack works well for growing algae.{{cite web

| url= http://www.csmonitor.com/2006/0111/p01s03-sten.html | title= Algae – Like a Breath Mint for Smokestacks

| last= Clayton | first= Mark |date= 11 January 2006 |work=The Christian Science Monitor | access-date=10 June 2008 | archive-url= https://web.archive.org/web/20080914134926/http://www.csmonitor.com/2006/0111/p01s03-sten.html| archive-date=14 September 2008| url-status= live}}{{cite web | url= http://www.greenfuelonline.com/gf_files/GreenFuel%20Growth%20Rates.pdf | title= Growth Rates of Emission-Fed Algae Show Viability of New Biomass Crop |date= 26 September 2008 | publisher= Arizona Public Service Company (APS) and GreenFuel Technologies Corporation |url-status=dead |access-date=15 December 2013| archive-url= https://web.archive.org/web/20080521161721/http://www.greenfuelonline.com/gf_files/GreenFuel%20Growth%20Rates.pdf| archive-date=2008-05-21}}

For reasons of economy, some experts think that algae farming for biofuels will have to be done as part of cogeneration, where it can make use of waste heat and help soak up pollution.

To produce micro-algae at large-scale under controlled environment using PBR system, strategies such as light guides, sparger, and PBR construction materials required should be well considered.{{Cite journal| doi = 10.1002/btpr.2628| title = Photobioreactor cultivation strategies for microalgae and cyanobacteria| journal = Biotechnology Progress| volume = 34 | pages = 811–827 | year = 2018 | last1 = Johnson | first1 = Tylor J. | last2 = Katuwal | first2 = Sarmila | last3 = Anderson | first3 = Gary A. | last4 = Ruanbao Zhou | first4 = Liping Gu | last5 = Gibbons | first5 = William R.| issue = 4| pmid = 29516646| doi-access = free | bibcode = 2018BioPr..34..811J}}

Most companies pursuing algae as a source of biofuels pump nutrient-rich water through plastic or borosilicate glass tubes (called "bioreactors" ) that are exposed to sunlight (and so-called photobioreactors or PBR).{{Cite journal |last1=Huesemann |first1=M. |last2=Williams |first2=P. |last3=Edmundson |first3=Scott J. |last4=Chen |first4=P. |last5=Kruk |first5=R. |last6=Cullinan |first6=V. |last7=Crowe |first7=B. |last8=Lundquist |first8=T. |date=September 2017 |title=The laboratory environmental algae pond simulator (LEAPS) photobioreactor: Validation using outdoor pond cultures of Chlorella sorokiniana and Nannochloropsis salina |journal=Algal Research |volume=26 |pages=39–46 |doi=10.1016/j.algal.2017.06.017 |osti=1581797 |issn=2211-9264|doi-access=free |bibcode=2017AlgRe..26...39H }}

Running a PBR is more difficult than using an open pond, and costlier, but may provide a higher level of control and productivity. In addition, a photobioreactor can be integrated into a closed loop cogeneration system much more easily than ponds or other methods.

Open pond systems consist of simple in ground ponds, which are often mixed by a paddle wheel. These systems have low power requirements, operating costs, and capital costs when compared to closed loop photobioreactor systems.{{Cite journal |doi = 10.1089/dst.2012.0013|title = Life Cycle Assessment for Microalgae Oil Production|journal = Disruptive Science and Technology|volume = 1|issue = 2|pages = 68–78|year = 2012|last1 = Benemann|first1 = John|last2 = Woertz|first2 = Ian|last3 = Lundquist|first3 = Tryg}} Nearly all commercial algae producers for high value algal products utilize open pond systems.{{cite journal |url=https://digitalcommons.calpoly.edu/cenv_fac/188/ |title=A Realistic Technology and Engineering Assessment of Algae Biofuel Production |journal=Energy Biosciences Institute |pages=1–178 |date=October 2010 |last1=Lundquist |first1=T. |last2=Woertz |first2=I. |last3=Quinn |first3=N. |last4=Benemann |first4=J. }}

File:ATSHydromentia.jpg

The Algae scrubber is a system designed primarily for cleaning nutrients and pollutants out of water using algal turfs. An algal turf scrubber (ATS) mimics the algal turfs of a natural coral reef by taking in nutrient rich water from waste streams or natural water sources, and pulsing it over a sloped surface.{{Cite web|url=http://www.algalturfscrubber.com/|title=最新のF-01α 歌舞伎モデル一覧製品は今、人気のUT通販サイトで探す。新作のその他, イベント＆特集続々入荷！お買い物マラソンはこちらへ！全品送料無料!|website=www.algalturfscrubber.com}} This surface is coated with a rough plastic membrane or a screen, which allows naturally occurring algal spores to settle and colonize the surface. Once the algae has been established, it can be harvested every 5–15 days,{{cite conference | url=http://www.physicsegypt.org/epc08/epc823.pdf | title=Algal Turf Scrubbers: Cleaning Water while Capturing Solar Energy for Bio fuel Production | date=2008 | access-date=4 November 2016 | author=Jeffrey Bannon, J.|author2=Adey, W. | pages=19–23 | conference=Proceedings of the Fourth Environmental Physics Conference (EPC'10)}} and can produce 18 metric tons of algal biomass per hectare per year.{{cite journal|title=Algal Turf Scrubbing: Cleaning Surface Waters with Solar Energy while Producing a Biofuel|first1=Walter H.|last1=Adey|first2=Patrick C.|last2=Kangas|first3=Walter|last3=Mulbry|date=1 June 2011|journal=BioScience|volume=61|issue=6|pages=434–441|via=bioscience.oxfordjournals.org|doi=10.1525/bio.2011.61.6.5|doi-access=free}} In contrast to other methods, which focus primarily on a single high yielding species of algae, this method focuses on naturally occurring polycultures of algae. As such, the lipid content of the algae in an ATS system is usually lower, which makes it more suitable for a fermented fuel product, such as ethanol, methane, or butanol. Conversely, the harvested algae could be treated with a hydrothermal liquefaction process, which would make possible biodiesel, gasoline, and jet fuel production.{{cite web | url=http://www.pnl.gov/main/publications/external/technical_reports/PNNL-22314.pdf | title=Whole Algae Hydrothermal Liquefaction Technology Pathway | publisher=National Renewable Energy Laboratory | access-date=4 November 2016 | last1=Biddy | first1=Mary |last2=Davis|first2=Ryan|last3=Jones|first3=Susanne|last4=Zhu|first4=Yunhua}}

There are three major advantages of ATS over other systems. The first advantage is documented higher productivity over open pond systems.{{cite web | url=http://www.hydromentia.com/End-Products/NREL-Biodiesel-Algae-1998.pdf | title=A Look Back at the U.S. Department of Energy's Aquatic Species Program: Biodiesel from Algae | publisher=U.S. Department of Energy's Office of Fuels Development | date=July 1998 | access-date=4 November 2016 | last1=Sheehan| first1=John|last2=Dunahay|first2=Terri|last3=Benemann|first3=John|last4=Roessler|first4=Paul}} The second is lower operating and fuel production costs. The third is the elimination of contamination issues due to the reliance on naturally occurring algae species. The projected costs for energy production in an ATS system are $0.75/kg, compared to a photobioreactor which would cost $3.50/kg. Furthermore, due to the fact that the primary purpose of ATS is removing nutrients and pollutants out of water, and these costs have been shown to be lower than other methods of nutrient removal, this may incentivize the use of this technology for nutrient removal as the primary function, with biofuel production as an added benefit.{{Cite web|url=https://hydromentia.com/technologies/algal-turf-scrubber/features-and-benefits-cost-effective/|title=Cost Effective|website=Hydromentia|date=30 November 2015 }}File:Algae ATS harvest.jpg

After harvesting the algae, the biomass is typically processed in a series of steps, which can differ based on the species and desired product; this is an active area of research and also is the bottleneck of this technology: the cost of extraction is higher than those obtained. One of the solutions is to use filter feeders to "eat" them. Improved animals can provide both foods and fuels. An alternative method to extract the algae is to grow the algae with specific types of fungi. This causes bio-flocculation of the algae which allows for easier extraction.{{cite journal|last1=Mackay|first1=S.|last2=Gomes|first2=E.|last3=Holliger|first3=C.|last4=Bauer|first4=R.|last5=Schwitzguébel|first5=J.-P.|title=Harvesting of Chlorella sorokiniana by co-culture with the filamentous fungus Isaria fumosorosea: A potential sustainable feedstock for hydrothermal gasification|journal=Bioresource Technology|volume=185|year=2015|pages=353–361|issn=0960-8524|doi=10.1016/j.biortech.2015.03.026|pmid=25795450|bibcode=2015BiTec.185..353M }}

Often, the algae is dehydrated, and then a solvent such as hexane is used to extract energy-rich compounds like triglycerides from the dried material.{{cite journal |last1=Ajayebi |first1=Atta |title=Comparative life cycle assessment of biodiesel from algae and jatropha: A case study of India |journal=Bioresource Technology |date=2013 |volume=150 |pages=429–437 |doi=10.1016/j.biortech.2013.09.118 |pmid=24140355 |bibcode=2013BiTec.150..429A |url=https://www.sciencedirect.com/science/article/pii/S0960852413015502#!}} Then, the extracted compounds can be processed into fuel using standard industrial procedures. For example, the extracted triglycerides are reacted with methanol to create biodiesel via transesterification. The unique composition of fatty acids of each species influences the quality of the resulting biodiesel and thus must be taken into account when selecting algal species for feedstock.

An alternative approach called Hydrothermal liquefaction employs a continuous process that subjects harvested wet algae to high temperatures and pressures—{{convert|350|C|F}} and {{convert|3000|psi}}.{{cite web

utes in the lab |publisher=Gizmag.com |access-date=2013-12-31}}{{YouTube|id=Qs0QZJ0rea0|title=Fuel extracation video}}{{Cite journal | last1 = Elliott | first1 = D. C. | last2 = Hart | first2 = T. R. | last3 = Schmidt | first3 = A. J. | last4 = Neuenschwander | first4 = G. G. | last5 = Rotness | first5 = L. J. | last6 = Olarte | first6 = M. V. | last7 = Zacher | first7 = A. H. | last8 = Albrecht | first8 = K. O. | last9 = Hallen | first9 = R. T. | last10 = Holladay | first10 = J. E. | doi = 10.1016/j.algal.2013.08.005 | title = Process development for hydrothermal liquefaction of algae feedstocks in a continuous-flow reactor | journal = Algal Research | volume = 2 | issue = 4 | pages = 445–454 | year = 2013 | bibcode = 2013AlgRe...2..445E | url = https://zenodo.org/record/1258702 }}

Products include crude oil, which can be further refined into aviation fuel, gasoline, or diesel fuel using one or many upgrading processes.{{cite journal|last1=Ramirez|first1=Jerome|last2=Brown|first2=Richard|last3=Rainey|first3=Thomas|title=A Review of Hydrothermal Liquefaction Bio-Crude Properties and Prospects for Upgrading to Transportation Fuels|journal=Energies|date=1 July 2015|volume=8|issue=7|pages=6765–6794|doi=10.3390/en8076765|doi-access=free}} The test process converted between 50 and 70 percent of the algae's carbon into fuel. Other outputs include clean water, fuel gas and nutrients such as nitrogen, phosphorus, and potassium.

{{Main|Algal nutrient solutions}}

Nutrients like nitrogen (N), phosphorus (P), and potassium (K), are important for plant growth and are essential parts of fertilizer. Silica and iron, as well as several trace elements, may also be considered important marine nutrients as the lack of one can limit the growth of, or productivity in, an area.{{cite web

| url= http://www.marinebio.net/marinescience/02ocean/swcomposition.htm

| title= Seawater Composition

| last= Anderson | first= Genny

|date= 18 December 2004 | access-date=18 June 2008 | archive-url= https://web.archive.org/web/20080610043809/http://www.marinebio.net/marinescience/02ocean/swcomposition.htm| archive-date= 10 June 2008 | url-status= live}}

Bubbling {{chem|CO|2}} through algal cultivation systems can greatly increase productivity and yield (up to a saturation point). Typically, about 1.8 tonnes of CO2 will be utilised per tonne of algal biomass (dry) produced, though this varies with algae species.{{cite web|url=http://www.globalccsinstitute.com/publications/accelerating-uptake-ccs-industrial-use-captured-carbon-dioxide/online/28426#c25|title=Accelerating the uptake of CCS: Industrial use of captured carbon dioxide|publisher=Global CCS Institute|access-date=25 February 2012|archive-url=https://web.archive.org/web/20120916011508/http://www.globalccsinstitute.com/publications/accelerating-uptake-ccs-industrial-use-captured-carbon-dioxide/online/28426#c25|archive-date=16 September 2012|url-status=dead}} The Glenturret Distillery in Perthshire percolate CO2 made during the whisky distillation through a microalgae bioreactor. Each tonne of microalgae absorbs two tonnes of {{chem|CO|2}}. Scottish Bioenergy, who run the project, sell the microalgae as high value, protein-rich food for fisheries. In the future,{{When|date=January 2025|reason=14 years have passed since}} they will use the algae residues to produce renewable energy through anaerobic digestion.{{cite web | url= http://www.theecologist.org/blogs_and_comments/commentators/other_comments/609556/forget_palm_oil_and_soya_microalgae_is_the_next_big_biofuel_source.html | title= Forget palm oil and soya, microalgae is the next big biofuel source | last= Aylott | first= Matthew | date= September 2010 }}

Nitrogen is a valuable substrate that can be utilized in algal growth. Various sources of nitrogen can be used as a nutrient for algae, with varying capacities. Nitrate was found to be the preferred source of nitrogen, in regards to amount of biomass grown. Urea is a readily available source that shows comparable results, making it an economical substitute for nitrogen source in large scale culturing of algae.{{Cite journal | last1 = Arumugam | first1 = M. | last2 = Agarwal | first2 = A. | last3 = Arya | first3 = M. C. | last4 = Ahmed | first4 = Z. | title = Influence of nitrogen sources on biomass productivity of microalgae Scenedesmus bijugatus | doi = 10.1016/j.biortech.2012.12.159 | journal = Bioresource Technology | volume = 131 | pages = 246–249 | year = 2013 | pmid = 23353039| bibcode = 2013BiTec.131..246A }} Despite the clear increase in growth in comparison to a nitrogen-less medium, it has been shown that alterations in nitrogen levels affect lipid content within the algal cells. In one study{{Cite journal | last1 = Moellering | first1 = E. R. | last2 = Benning | first2 = C. | doi = 10.1128/EC.00203-09 | title = RNA Interference Silencing of a Major Lipid Droplet Protein Affects Lipid Droplet Size in Chlamydomonas reinhardtii | journal = Eukaryotic Cell | volume = 9 | issue = 1 | pages = 97–106 | year = 2009 | pmid = 19915074| pmc =2805299 }} nitrogen deprivation for 72 hours caused the total fatty acid content (on a per cell basis) to increase by 2.4-fold. 65% of the total fatty acids were esterified to triacylglycerides in oil bodies, when compared to the initial culture, indicating that the algal cells utilized de novo synthesis of fatty acids. It is vital for the lipid content in algal cells to be of high enough quantity, while maintaining adequate cell division times, so parameters that can maximize both are under investigation.

{{Main|Wastewater treatment facility}}

A possible nutrient source is wastewater from the treatment of sewage, agricultural, or flood plain run-off, all currently major pollutants and health risks. However, this waste water cannot feed algae directly and must first be processed by bacteria, through anaerobic digestion. If waste water is not processed before it reaches the algae, it will contaminate the algae in the reactor, and at the very least, kill much of the desired algae strain. In biogas facilities, organic waste is often converted to a mixture of carbon dioxide, methane, and organic fertilizer. Organic fertilizer that comes out of the digester is liquid, and nearly suitable for algae growth, but it must first be cleaned and sterilized.{{Cite journal | doi = 10.1016/j.biortech.2010.06.035| pmid = 20594826| title = The potential of sustainable algal biofuel production using wastewater resources| journal = Bioresource Technology| volume = 102| issue = 1| pages = 17–25| year = 2011| last1 = Pittman | first1 = J. K. | last2 = Dean | first2 = A. P. | last3 = Osundeko | first3 = O. | bibcode = 2011BiTec.102...17P}}

The utilization of wastewater and ocean water instead of freshwater is strongly advocated due to the continuing depletion of freshwater resources. However, heavy metals, trace metals, and other contaminants in wastewater can decrease the ability of cells to produce lipids biosynthetically and also impact various other workings in the machinery of cells. The same is true for ocean water, but the contaminants are found in different concentrations. Thus, agricultural-grade fertilizer is the preferred source of nutrients, but heavy metals are again a problem, especially for strains of algae that are susceptible to these metals. In open pond systems the use of strains of algae that can deal with high concentrations of heavy metals could prevent other organisms from infesting these systems. In some instances it has even been shown that strains of algae can remove over 90% of nickel and zinc from industrial wastewater in relatively short periods of time.{{Cite journal | doi = 10.1016/S0045-6535(99)00418-X| pmid = 10819208| title = Performance of different microalgal species in removing nickel and zinc from industrial wastewater| journal = Chemosphere| volume = 41| issue = 1–2| pages = 251–7| year = 2000| last1 = Chong | first1 = A. M. Y. | last2 = Wong | first2 = Y. S. | last3 = Tam | first3 = N. F. Y. | bibcode = 2000Chmsp..41..251C}}

In comparison with terrestrial-based biofuel crops such as corn or soybeans, microalgal production results in a much less significant land footprint due to the higher oil productivity from the microalgae than all other oil crops.{{Cite journal | last1 = Smith | first1 = V. H. | last2 = Sturm | first2 = B. S. M. | last3 = Denoyelles | first3 = F. J. | last4 = Billings | first4 = S. A. | title = The ecology of algal biodiesel production | doi = 10.1016/j.tree.2009.11.007 | journal = Trends in Ecology & Evolution | volume = 25 | issue = 5 | pages = 301–309 | year = 2010 | pmid = 20022660| bibcode = 2010TEcoE..25..301S }} Algae can also be grown on marginal lands useless for ordinary crops and with low conservation value, and can use water from salt aquifers that is not useful for agriculture or drinking.{{cite web | url= http://www.worldwatch.org/node/5391 | title= Better Than Corn? Algae Set to Beat Out Other Biofuel Feedstocks | last= Herro | first= Alana | date= 8 October 2007 | publisher= Worldwatch Institute | access-date= 10 June 2008 | archive-url= https://web.archive.org/web/20080621101938/http://www.worldwatch.org/node/5391 | archive-date= 21 June 2008 | url-status= dead }}{{cite web|last=Bullis |first=Kevin |url=http://www.technologyreview.com/news/407268/algae-based-fuels-set-to-bloom/ |title=Algae-Based Fuels Set to Bloom | MIT Technology Review |publisher=Technologyreview.com |date=2007-02-05 |access-date=29 November 2013}} Algae can also grow on the surface of the ocean in bags or floating screens.{{cite web|title=NASA OMEGA Project|url=http://www.nasa.gov/centers/ames/research/OMEGA/index.html|access-date=8 May 2012}} Thus microalgae could provide a source of clean energy with little impact on the provisioning of adequate food and water or the conservation of biodiversity.{{Cite journal | doi = 10.1111/j.1523-1739.2007.00879.x| pmid = 18261147| title = Biofuels and Biodiversity: Principles for Creating Better Policies for Biofuel Production| journal = Conservation Biology| volume = 22| issue = 3| pages = 602–9| year = 2008| last1 = Groom | first1 = M. J. | last2 = Gray | first2 = E. M. | last3 = Townsend | first3 = P. A. | bibcode = 2008ConBi..22..602G| s2cid = 26350558}} Algae cultivation also requires no external subsidies of insecticides or herbicides, removing any risk of generating associated pesticide waste streams. In addition, algal biofuels are much less toxic, and degrade far more readily than petroleum-based fuels.{{cite web|url=http://www.epa.gov/oem/docs/oil/fss/fss09/hollebonebiofuels.pdf|title=Emergency Response|first=US|last=EPA, OSWER, OEM|date=13 March 2013}}{{cite web | url=http://www.inchem.org/documents/sids/sids/71363.pdf | title=n-Butyl Alcohol CAS N°: 71-36-3 | publisher=OECD SIDS | date=9 November 2001 | access-date=4 November 2016 | archive-url=https://web.archive.org/web/20150924051939/http://www.inchem.org/documents/sids/sids/71363.pdf | archive-date=24 September 2015 | url-status=dead }}{{cite web|url=http://www.ethanolrfa.org/pages/ethanol-facts-environment |title=RFA: Renewable Fuels Association |access-date=22 February 2015 |url-status=dead |archive-url=https://web.archive.org/web/20100523101843/http://www.ethanolrfa.org/pages/ethanol-facts-environment |archive-date=23 May 2010 }} However, due to the flammable nature of any combustible fuel, there is potential for some environmental hazards if ignited or spilled, as may occur in a train derailment or a pipeline leak.{{cite web | url=http://www.mass.gov/eopss/docs/dfs/emergencyresponse/special-ops/ethanol-spill-impacts-and-response-7-11.pdf | title=Large Volume Ethanol Spills – Environmental Impacts and Response Options | date=July 2011 | access-date=4 November 2016}} This hazard is reduced compared to fossil fuels, due to the ability for algal biofuels to be produced in a much more localized manner, and due to the lower toxicity overall, but the hazard is still there nonetheless. Therefore, algal biofuels should be treated in a similar manner to petroleum fuels in transportation and use, with sufficient safety measures in place at all times.

Studies have determined that replacing fossil fuels with renewable energy sources, such as biofuels, have the capability of reducing {{chem|CO|2}} emissions by up to 80%.{{Cite journal | last1 = Acién Fernández | first1 = F. G. | last2 = González-López | first2 = C. V. | last3 = Fernández Sevilla | first3 = J. M. | last4 = Molina Grima | first4 = E. | title = Conversion of CO2 into biomass by microalgae: How realistic a contribution may it be to significant CO2 removal? | doi = 10.1007/s00253-012-4362-z | journal = Applied Microbiology and Biotechnology | volume = 96 | issue = 3 | pages = 577–586 | year = 2012 | pmid = 22923096| s2cid = 18169368 }} An algae-based system could capture approximately 80% of the {{chem|CO|2}} emitted from a power plant when sunlight is available. Although this {{chem|CO|2}} will later be released into the atmosphere when the fuel is burned, this {{chem|CO|2}} would have entered the atmosphere regardless. The possibility of reducing total {{chem|CO|2}} emissions therefore lies in the prevention of the release of {{chem|CO|2}} from fossil fuels. Furthermore, compared to fuels like diesel and petroleum, and even compared to other sources of biofuels, the production and combustion of algal biofuel does not produce any sulfur oxides or nitrous oxides, and produces a reduced amount of carbon monoxide, unburned hydrocarbons, and reduced emission of other harmful pollutants.{{Cite journal | last1 = Hemaiswarya | first1 = S. | last2 = Raja | first2 = R. | last3 = Carvalho | first3 = I. S. | last4 = Ravikumar | first4 = R. | last5 = Zambare | first5 = V. | last6 = Barh | first6 = D. | doi = 10.1007/s00253-012-4487-0 | title = An Indian scenario on renewable and sustainable energy sources with emphasis on algae | journal = Applied Microbiology and Biotechnology | volume = 96 | issue = 5 | pages = 1125–1135 | year = 2012 | pmid = 23070650| s2cid = 14763431 }} Since terrestrial plant sources of biofuel production simply do not have the production capacity to meet current energy requirements, microalgae may be one of the only options to approach complete replacement of fossil fuels.

Microalgae production also includes the ability to use saline waste or waste {{chem|CO|2}} streams as an energy source. This opens a new strategy to produce biofuel in conjunction with waste water treatment, while being able to produce clean water as a byproduct. When used in a microalgal bioreactor, harvested microalgae will capture significant quantities of organic compounds as well as heavy metal contaminants absorbed from wastewater streams that would otherwise be directly discharged into surface and ground-water. Moreover, this process also allows the recovery of phosphorus from waste, which is an essential but scarce element in nature – the reserves of which are estimated to have depleted in the last 50 years.{{Cite journal | last1 = Kumar | first1 = A. | last2 = Ergas | first2 = S. | last3 = Yuan | first3 = X. | last4 = Sahu | first4 = A. | last5 = Zhang | first5 = Q. | last6 = Dewulf | first6 = J. | last7 = Malcata | first7 = F. X. | last8 = Van Langenhove | first8 = H. | doi = 10.1016/j.tibtech.2010.04.004 | title = Enhanced CO2 fixation and biofuel production via microalgae: Recent developments and future directions | journal = Trends in Biotechnology | volume = 28 | issue = 7 | pages = 371–380 | year = 2010 | pmid = 20541270}} Another possibility is the use of algae production systems to clean up non-point source pollution, in a system known as an algal turf scrubber (ATS). This has been demonstrated to reduce nitrogen and phosphorus levels in rivers and other large bodies of water affected by eutrophication, and systems are being built that will be capable of processing up to 110 million liters of water per day. ATS can also be used for treating point source pollution, such as the waste water mentioned above, or in treating livestock effluent.{{cite web | url=http://www.alachuacounty.us/Depts/epd/WaterResources/GroundwaterAndSprings/SFRSBWG%20Presentations/110216_Algae%20Turf%20Scrubbers.pdf | title=Algae Based Water Treatment Systems – Cost-Effective Nutrient Pollution Control and for Point and Nonpoint Source Applications | date=16 February 2010 | access-date=4 November 2016 | author=Mark J. Zivojnovich | archive-date=1 December 2016 | archive-url=https://web.archive.org/web/20161201030318/http://www.alachuacounty.us/Depts/epd/WaterResources/GroundwaterAndSprings/SFRSBWG%20Presentations/110216_Algae%20Turf%20Scrubbers.pdf | url-status=dead }}{{cite web | url=http://www.tvrl.lth.se/fileadmin/tvrl/files/vvrf05/CharlottaD_Application_of_Algal_Turf_Scrubber_Technique.pdf | title=Application of Algal Turf Scrubber Technique to remove nutrient from a eutrophic reservoir in the Jiulong River watershed, Southeast China | publisher=International Summer Water Resources Research School | date=2013-07-20 | access-date=4 November 2016 | last=Dixner | first=Charlotta | archive-date=13 October 2016 | archive-url=https://web.archive.org/web/20161013232904/http://www.tvrl.lth.se/fileadmin/tvrl/files/vvrf05/CharlottaD_Application_of_Algal_Turf_Scrubber_Technique.pdf | url-status=dead }}

Nearly all research in algal biofuels has focused on culturing single species, or monocultures, of microalgae. However, ecological theory and empirical studies have demonstrated that plant and algae polycultures, i.e. groups of multiple species, tend to produce larger yields than monocultures.{{cite journal | last1 = Downing | first1 = A. L. | last2 = Leibold | first2 = M. A. | year = 2002 | title = Ecosystem consequences of species richness and composition in pond food webs | journal = Nature | volume = 416 | issue = 6883| pages = 837–841 | doi=10.1038/416837a | pmid=11976680| bibcode = 2002Natur.416..837D | s2cid = 4374059 }}{{cite journal | last1 = Cardinale | first1 = B. J. | last2 = Srivastava | first2 = D. S. | last3 = Duffy | first3 = J. E. | last4 = Wright | first4 = J. P. | last5 = Downing | first5 = A. L. | last6 = Sankaran | first6 = M. | last7 = Jouseau | first7 = C. | year = 2006 | title = Effects of biodiversity on the functioning of trophic groups and ecosystems | journal = Nature | volume = 443 | issue = 7114| pages = 989–992 | doi=10.1038/nature05202| pmid = 17066035 | bibcode = 2006Natur.443..989C | s2cid = 4426751 }}{{cite journal | last1 = Tilman | first1 = D. | last2 = Wedin | first2 = D. | last3 = Knops | first3 = J. | year = 1996 | title = Productivity and sustainability influenced by biodiversity in grassland ecosystems | journal = Nature | volume = 379 | issue = 6567| pages = 718–720 | doi=10.1038/379718a0| bibcode = 1996Natur.379..718T | s2cid = 4347014 }}{{Cite journal | doi = 10.1126/science.286.5442.1123| pmid = 10550043| title = Plant Diversity and Productivity Experiments in European Grasslands| journal = Science| volume = 286| issue = 5442| pages = 1123–7| year = 1999| last1 = Hector | first1 = A.| last2 = Schmid| first2 = B| last3 = Beierkuhnlein| first3 = C| last4 = Caldeira| first4 = M. C.| last5 = Diemer| first5 = M| last6 = Dimitrakopoulos| first6 = P. G.| last7 = Finn| first7 = J. A.| last8 = Freitas| first8 = H| last9 = Giller| first9 = P. S.| last10 = Good| first10 = J| last11 = Harris| first11 = R| last12 = Hogberg| first12 = P| last13 = Huss-Danell| first13 = K| last14 = Joshi| first14 = J| last15 = Jumpponen| first15 = A| last16 = Korner| first16 = C| last17 = Leadley| first17 = P. W.| last18 = Loreau| first18 = M| last19 = Minns| first19 = A| last20 = Mulder| first20 = C. P.| last21 = O'Donovan| first21 = G| last22 = Otway| first22 = S. J.| last23 = Pereira| first23 = J. S.| last24 = Prinz| first24 = A| last25 = Read| first25 = D. J.| last26 = Et| first26 = al| s2cid = 1899020}} Experiments have also shown that more diverse aquatic microbial communities tend to be more stable through time than less diverse communities.{{cite journal | last1 = Ptacnik | first1 = R. | last2 = Solimini | first2 = A. G. | last3 = Andersen | first3 = T. | last4 = Tamminen | first4 = T. | last5 = Brettum | first5 = P. | last6 = Lepisto | first6 = L. | last7 = Willen | first7 = E. | last8 = Rekolainen | first8 = S. | year = 2008 | title = Diversity predicts stability and resource use efficiency in natural phytoplankton communities | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 105 | issue = 13| pages = 5134–5138 | doi=10.1073/pnas.0708328105 | pmid=18375765 | pmc=2278227| bibcode = 2008PNAS..105.5134P | doi-access = free }}{{cite journal | last1 = McGrady-Steed | first1 = J. | last2 = Harris | first2 = P. | last3 = Morin | first3 = P. | year = 1997 | title = Biodiversity regulates ecosystem predictability | journal = Nature | volume = 390 | issue = 6656| pages = 162–165 | bibcode = 1997Natur.390..162M | doi = 10.1038/36561 | s2cid = 4302617 }}{{cite journal | last1 = Naeem | first1 = S. | last2 = Li | first2 = S. | year = 1997 | title = Biodiversity enhances ecosystem reliability | journal = Nature | volume = 390 | issue = 6659| pages = 507–509 | bibcode = 1997Natur.390..507N | doi = 10.1038/37348 | s2cid = 4420940 }}{{cite journal | last1 = Steiner | first1 = C. F. | last2 = Long | first2 = Z. | last3 = Krumins | first3 = J. | last4 = Morin | first4 = P. | year = 2005 | title = Temporal stability of aquatic food webs: partitioning the effects of species diversity, species composition and enrichment | journal = Ecology Letters | volume = 8 | issue = 8| pages = 819–828 | doi=10.1111/j.1461-0248.2005.00785.x| bibcode = 2005EcolL...8..819S }} Recent studies found that polycultures of microalgae produced significantly higher lipid yields than monocultures.{{Cite journal | doi = 10.1007/s10811-010-9644-1| title = The effect of species diversity on lipid production by micro-algal communities| journal = Journal of Applied Phycology| volume = 24| pages = 45–54| year = 2011| last1 = Stockenreiter | first1 = M. | last2 = Graber | first2 = A. K. | last3 = Haupt | first3 = F. | last4 = Stibor | first4 = H. | s2cid = 17272043}}{{Cite journal | doi = 10.1111/jpy.12092| pmid = 27007310| title = Functional group richness: Implications of biodiversity for light use and lipid yield in microalgae| journal = Journal of Phycology| volume = 49| issue = 5| pages = 838–47| year = 2013| last1 = Stockenreiter | first1 = M. | last2 = Haupt | first2 = F. | last3 = Graber | first3 = A. K. | last4 = Seppälä | first4 = J. | last5 = Spilling | first5 = K. | last6 = Tamminen | first6 = T. | last7 = Stibor | first7 = H. | bibcode = 2013JPcgy..49..838S| s2cid = 206146808}} Polycultures also tend to be more resistant to pest and disease outbreaks, as well as invasion by other plants or algae.{{Cite journal | doi = 10.1038/nature11148| pmid = 22678280| title = Biodiversity loss and its impact on humanity| journal = Nature| volume = 486| issue = 7401| pages = 59–67| year = 2012| last1 = Cardinale | first1 = B. J. | last2 = Duffy | first2 = J. E. | last3 = Gonzalez | first3 = A. | last4 = Hooper | first4 = D. U. | last5 = Perrings | first5 = C. | last6 = Venail | first6 = P. | last7 = Narwani | first7 = A. | last8 = Mace | first8 = G. M. | last9 = Tilman | first9 = D. | last10 = Wardle | first10 = D. A. | last11 = Kinzig | first11 = A. P. | last12 = Daily | first12 = G. C. | last13 = Loreau | first13 = M. | last14 = Grace | first14 = J. B. | last15 = Larigauderie | first15 = A. | last16 = Srivastava | first16 = D. S. | last17 = Naeem | first17 = S. | bibcode = 2012Natur.486...59C | s2cid = 4333166| url = https://pub.epsilon.slu.se/10240/7/wardle_d_etal_130415.pdf| type = Submitted manuscript}} Thus culturing microalgae in polyculture may not only increase yields and stability of yields of biofuel, but also reduce the environmental impact of an algal biofuel industry.

{{Update|part=section|date=January 2025|updated=2017|reason=most sources are over a decade old}}

There is clearly a demand for sustainable biofuel production, but whether a particular biofuel will be used ultimately depends not on sustainability but cost efficiency. Therefore, research is focusing on cutting the cost of algal biofuel production to the point where it can compete with conventional petroleum.{{cite journal |last1=Stephens |first1=E. |last2=Ross |first2=I.L. |last3=Mussgnug |first3=J.H. |last4=Wagner |first4=L.D. |last5=Borowitzka |first5=M.A. |last6=Posten|first6=C. |last7=Kruse |first7=O. |last8=Hankamer |first8=B. |date=October 2010 |title=Future prospects of microalgal biofuel production systems |journal=Trends in Plant Science |volume=15 |issue=10 |pages=554–564 |doi=10.1016/j.tplants.2010.06.003|pmid=20655798 |bibcode=2010TPS....15..554S }} The production of several products from algae has been mentioned{{weasel inline|date=August 2015}} as the most important factor for making algae production economically viable. Other factors are the improving of the solar energy to biomass conversion efficiency (currently 3%, but 5 to 7% is theoretically attainableNote that for biofuel crops it is only 0,5%) and making the oil extraction from the algae easier.NewScientist, March 2014

In a 2007 report{{Cite journal | last1 = Chisti | first1 = Y. | title = Biodiesel from microalgae | doi = 10.1016/j.biotechadv.2007.02.001 | journal = Biotechnology Advances | volume = 25 | issue = 3 | pages = 294–306 | year = 2007 | pmid = 17350212| s2cid = 18234512 }} a formula was derived estimating the cost of algal oil in order for it to be a viable substitute to petroleum diesel:

::C_{(algal oil)} = 25.9 × 10⁻³ C_(petroleum)

where: C_{(algal oil)} is the price of microalgal oil in dollars per gallon and C_(petroleum) is the price of crude oil in dollars per barrel. This equation assumes that algal oil has roughly 80% of the caloric energy value of crude petroleum.Organization of the Petroleum Exporting Countries: [http://www.opec.org/opec_web/en/data_graphs/40.htm?selectedTab=daily Basket Prices]. (accessed 01/29, 2013)

The IEA estimated in 2017 that algal biomass can be produced for a little as $0.54/kg in open pond in a warm climate to $10.20/kg in photobioreactors in cooler climates.{{Cite web |last=Laurens |first=Lieve |date=31 January 2017 |title=State of Technology Review - Algae Bioenergy |url=https://www.ieabioenergy.com/wp-content/uploads/2017/02/IEA-Bioenergy-Algae-report-update-Final-template-20170131.pdf |access-date=28 February 2023 |website=IEA Bioenergy}} Assuming that the biomass contains 30% oil by weight, the cost of biomass for providing a liter of oil would be approximately $1.40 ($5.30/gal) and $1.81 ($6.85/gal) for photobioreactors and raceways, respectively. Oil recovered from the lower cost biomass produced in photobioreactors is estimated to cost $2.80/L, assuming the recovery process contributes 50% to the cost of the final recovered oil. If existing algae projects can achieve biodiesel production price targets of less than $1 per gallon, the United States may realize its goal of replacing up to 20% of transport fuels by 2020 by using environmentally and economically sustainable fuels from algae production.{{Cite journal |last1=Ghasemi |first1=Y. |last2=Rasoul-Amini |first2=S. |last3=Naseri |first3=A. T. |last4 =Montazeri-Najafabady |first4=N. |last5=Mobasher |first5=M. A. |last6=Dabbagh |first6=F. |doi=10.1134/S0003683812020068 |title=Microalgae biofuel potentials (Review) |journal=Applied Biochemistry and Microbiology |volume=48 |issue=2 |pages=126–144 |year=2012 |pmid=22586908 |s2cid=11148888 }}

Whereas technical problems, such as harvesting, are being addressed successfully by the industry, the high up-front investment of algae-to-biofuels facilities is seen by many as a major obstacle to the success of this technology. As of 2007, only few studies on the economic viability were publicly available, and must often rely on the little data (often only engineering estimates) available in the public domain. Dmitrov{{cite web |url=http://www.nanostring.net/Algae/CaseStudy.pdf |title=GreenFuel Technologies: A Case Study for Industrial Photosynthetic Energy Capture |last=Dmitrov |first=Krassen |date=March 2007 }} examined the GreenFuel's photobioreactor and estimated that algae oil would only be competitive at an oil price of $800 per barrel. A study by Alabi et al.{{cite web |url=http://www.bcic.ca/media-and-press/publications/life-sciences-publications |title=Microalgae Technologies and Processes for Biofuels/Bioenergy Production in British Columbia |last=Alabi |first=Yomi |date=14 January 2009 |publisher=British Columbia Innovation Council |display-authors=etal |url-status=dead |archive-url=https://web.archive.org/web/20091207120202/http://www.bcic.ca/media-and-press/publications/life-sciences-publications |archive-date=7 December 2009}} examined raceways, photobioreactors and anaerobic fermenters to make biofuels from algae and found that photobioreactors are too expensive to make biofuels. Raceways might be cost-effective in warm climates with very low labor costs, and fermenters may become cost-effective subsequent to significant process improvements. The group found that capital cost, labor cost and operational costs (fertilizer, electricity, etc.) by themselves are too high for algae biofuels to be cost-competitive with conventional fuels. Similar results were found by others,{{cite news |title=Biofuels' cost explosion necessitates adaptation of process concepts. Algae as alternative raw materials. (slide presentation). Paper presented at the European White Biotechnology Summit, 21–22 May 2008, Frankfurt, Germany |last= Steiner |first= U.}}{{cite journal |title= Commercial applications of algae: opportunities and constraints |last=Radmer |first= R.J. |journal=Journal of Applied Phycology |year= 1994 |volume=6 |issue=2 |page=93 |publisher= Journal of Applied Phycology, 6(2), 93–98 |doi=10.1007/BF02186062 |bibcode=1994JAPco...6...93R }}{{cite web |url=http://carbontrust.co.uk/NR/rdonlyres/62511FB9-A701-48F4-BDA2-5ADD41CEDC27/0/FAQs.pdf |archive-url=http://webarchive.nationalarchives.gov.uk/20081023182450/carbontrust.co.uk/NR/rdonlyres/62511FB9-A701-48F4-BDA2-5ADD41CEDC27/0/FAQs.pdf |url-status=dead |archive-date=23 October 2008 |title=Algae biofuels challenge- frequently asked questions |last=Carbon Trust (UK) |year=2008 |access-date=14 November 2008 }} suggesting that unless new, cheaper ways of harnessing algae for biofuels production are found, their great technical potential may never become economically accessible. In 2012, Rodrigo E. Teixeira{{cite journal |last1=Teixeira |first1=R. E. |s2cid=96149136 |title=Energy-efficient extraction of fuel and chemical feedstocks from algae |doi=10.1039/C2GC16225C |journal=Green Chemistry |volume=14 |issue=2 |pages=419–427 |year=2012 }} demonstrated a new reaction and proposed a process for harvesting and extracting raw materials for biofuel and chemical production that requires a fraction of the energy of current methods, while extracting all cell constituents.

A 2022 study stated that selling fuel from commercially refining biofuel was not feasible due to technological limitations and high costs. The study found that byproducts would require a selling price of $899/ton of residual solids in order to support a competitive price of $2.50 per gallon gasoline equivalent, using the method of converting proteins and carbohydrates into mixed alcohols. Comparatively, the study found converting proteins and carbohydrates into hydrocarbons to require a higher selling price $1033/ton of residual solids in order to be economically feasible.{{Cite journal |last1=Wiatrowski |first1=Matthew |last2=Klein |first2=Bruno C. |last3=Davis |first3=Ryan W. |last4=Quiroz-Arita |first4=Carlos |last5=Tan |first5=Eric C. D. |last6=Hunt |first6=Ryan W. |last7=Davis |first7=Ryan E. |date=2022-01-18 |title=Techno-economic assessment for the production of algal fuels and value-added products: opportunities for high-protein microalgae conversion |journal=Biotechnology for Biofuels and Bioproducts |volume=15 |issue=1 |pages=8 |doi=10.1186/s13068-021-02098-3 |doi-access=free |issn=2731-3654 |pmc=8764804 |pmid=35418157|bibcode=2022BBB....15....8W }}

Many of the byproducts produced in the processing of microalgae can be used in various applications, many of which have a longer history of production than algal biofuel. Some of the products not used in the production of biofuel include natural dyes and pigments, antioxidants, and other high-value bio-active compounds.{{Cite journal | last1 = Mata | first1 = T. M. | last2 = Martins | first2 = A. N. A. | last3 = Caetano | first3 = N. S. | title = Microalgae for biodiesel production and other applications: A review | doi = 10.1016/j.rser.2009.07.020 | journal = Renewable and Sustainable Energy Reviews | volume = 14 | pages = 217–232 | year = 2010 | issue = 1 | bibcode = 2010RSERv..14..217M | url = http://recipp.ipp.pt/bitstream/10400.22/10059/1/ART_NidiaCaetano_DEQ_2009.pdf | type = Submitted manuscript | hdl = 10400.22/10059 | s2cid = 15481966 | hdl-access = free }}{{cite journal | last1 = Pulz | first1 = O. | last2 = Gross | first2 = W. | year = 2004 | title = Valuable Products from Biotechnology of Microalgae | doi = 10.1007/s00253-004-1647-x | pmid = 15300417 | journal = Applied Microbiology and Biotechnology | volume = 65 | issue = 6| pages = 635–648 | s2cid = 42079864 }}{{cite journal | last1 = Singh | first1 = S. | last2 = Kate | first2 = B.N. | last3 = Banerjee | first3 = U.C. | year = 2005 | title = Bioactive Compounds from Cyanobacteria and Microalgae: An Overview | journal = Critical Reviews in Biotechnology | volume = 25 | issue = 3| pages = 73–95 | doi=10.1080/07388550500248498| pmid = 16294828 | s2cid = 11613501 }} These chemicals and excess biomass have found numerous use in other industries. For example, the dyes and oils have found a place in cosmetics, commonly as thickening and water-binding agents.Sporalore, P., C.Joannis-Cassan, E. Duran, and A. Isambert, "Commercial Applications of Microalgae", Journal of Bioscience and Bioengineering, 101(2):87-96, 2006. Discoveries within the pharmaceutical industry include antibiotics and antifungals derived from microalgae, as well as natural health products, which have been growing in popularity over the past few decades. For instance Spirulina contains numerous polyunsaturated fats (Omega 3 and 6), amino acids, and vitamins,{{Cite journal | last1 = Tokuşoglu | first1 = O. | last2 = Uunal | first2 = M. K. | doi = 10.1111/j.1365-2621.2003.tb09615.x | title = Biomass Nutrient Profiles of Three Microalgae: Spirulina platensis, Chlorella vulgaris, and Isochrisis galbana | journal = Journal of Food Science | volume = 68 | issue = 4 | pages = 1144–1148 | year = 2003 }} as well as pigments that may be beneficial, such as beta-carotene and chlorophyll.Vonshak, A. (ed.). Spirulina platensis (Arthrospira): Physiology, Cell-biology and Biotechnology. London: Taylor & Francis, 1997.

One of the main advantages that using microalgae as the feedstock when compared to more traditional crops is that it can be grown much more easily.{{Cite journal | last1 = Demirbas | first1 = A. | last2 = Fatih Demirbas | first2 = M. | doi = 10.1016/j.enconman.2010.06.055 | title = Importance of algae oil as a source of biodiesel | journal = Energy Conversion and Management | volume = 52 | pages = 163–170 | year = 2011 | issue = 1 | bibcode = 2011ECM....52..163D }} Algae can be grown in land that would not be considered suitable for the growth of the regularly used crops. In addition to this, wastewater that would normally hinder plant growth has been shown to be very effective in growing algae. Because of this, algae can be grown without taking up arable land that would otherwise be used for producing food crops, and the better resources can be reserved for normal crop production. Microalgae also require fewer resources to grow and little attention is needed, allowing the growth and cultivation of algae to be a very passive process.

Many traditional feedstocks for biodiesel, such as corn and palm, are also used as feed for livestock on farms, as well as a valuable source of food for humans. Because of this, using them as biofuel reduces the amount of food available for both, resulting in an increased cost for both the food and the fuel produced. Using algae as a source of biodiesel can alleviate this problem in a number of ways. First, algae is not used as a primary food source for humans, meaning that it can be used solely for fuel and there would be little impact in the food industry.{{Cite journal | last1 = Vasudevan | first1 = P. T. | last2 = Briggs | first2 = M. | doi = 10.1007/s10295-008-0312-2 | title = Biodiesel production—current state of the art and challenges | journal = Journal of Industrial Microbiology & Biotechnology | volume = 35 | issue = 5 | pages = 421–430 | year = 2008 | pmid = 18205018| s2cid = 2860212 | doi-access = free }} Second, many of the waste-product extracts produced during the processing of algae for biofuel can be used as a sufficient animal feed. This is an effective way to minimize waste and a much cheaper alternative to the more traditional corn- or grain-based feeds.{{Cite journal | last1 = Demirbaş | first1 = A. | title = Production of Biodiesel from Algae Oils | doi = 10.1080/15567030701521775 | journal = Energy Sources, Part A: Recovery, Utilization, and Environmental Effects | volume = 31 | issue = 2 | pages = 163–168 | year = 2008 | s2cid = 97324232 }}

Growing algae as a source of biofuel has also been shown to have numerous environmental benefits, and has presented itself as a much more environmentally friendly alternative to current biofuels. For one, it is able to utilize run-off, water contaminated with fertilizers and other nutrients that are a by-product of farming, as its primary source of water and nutrients. Because of this, it prevents this contaminated water from mixing with the lakes and rivers that currently supply our drinking water. In addition to this, the ammonia, nitrates, and phosphates that would normally render the water unsafe actually serve as excellent nutrients for the algae, meaning that fewer resources are needed to grow the algae. Many algae species used in biodiesel production are excellent bio-fixers, meaning they are able to remove carbon dioxide from the atmosphere to use as a form of energy for themselves. Because of this, they have found use in industry as a way to treat flue gases and reduce GHG emissions.

The process of microalgae cultivation is highly water-intensive. Life cycle studies estimated that the production of 1 liter of microalgae based biodiesel requires between 607 and 1944 liters of water.{{Citation|last1=Pishvaee|first1=Mir Saman|title=Chapter 4 - Uncertainties in biofuel supply chain|date=2021-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780128206409000040|work=Biomass to Biofuel Supply Chain Design and Planning Under Uncertainty|pages=65–93|publisher=Academic Press|doi=10.1016/b978-0-12-820640-9.00004-0|isbn=978-0-12-820640-9|access-date=2021-01-12|last2=Mohseni|first2=Shayan|last3=Bairamzadeh|first3=Samira|s2cid=230592922}} That said, abundant wastewater and/or seawater, which also contain various nutrients, can theoretically be used for this purpose instead of freshwater.

Algae biodiesel is still a fairly new technology. Despite the fact that research began over 30 years ago, it was put on hold during the mid-1990s, mainly due to a lack of funding and a relatively low petroleum cost.{{Cite journal | last1 = Pienkos | first1 = P. T. | last2 = Darzins | first2 = A. | doi = 10.1002/bbb.159 | title = The promise and challenges of microalgal-derived biofuels | journal = Biofuels, Bioproducts and Biorefining | volume = 3 | issue = 4 | pages = 431–440 | year = 2009 | s2cid = 10323847 | url = https://zenodo.org/record/1229121 }} For the next few years algae biofuels saw little attention; it was not until the gas peak of the early 2000s that it eventually had a revitalization in the search for alternative fuel sources.

Increasing interest in seaweed farming for carbon sequestration, eutrophication reduction and production of food has resulted in the creation of commercial seaweed cultivation since 2017.{{Cite web |last=Fisheries |first=NOAA |date=2020-09-28 |title=Seaweed Aquaculture {{!}} NOAA Fisheries |url=https://www.fisheries.noaa.gov/national/aquaculture/seaweed-aquaculture |access-date=2023-02-28 |website=NOAA |language=en}} Reductions in the cost of cultivation and harvesting as well as the development of commercial industry will improve the economics of macroalgae biofuels. Climate change has created a proliferation of brown macroalgae mats, which wash up on the shores of the Caribbean. Currently these mats are disposed of but there is interest in developing them into a feedstock for biofuel production.{{Cite journal |last1=Orozco-González |first1=Jorge Gabriel |last2=Amador-Castro |first2=Fernando |last3=Gordillo-Sierra |first3=Angela R. |last4=García-Cayuela |first4=Tomás |last5=Alper |first5=Hal S. |last6=Carrillo-Nieves |first6=Danay |date=2022 |title=Opportunities Surrounding the Use of Sargassum Biomass as Precursor of Biogas, Bioethanol, and Biodiesel Production |journal=Frontiers in Marine Science |volume=8 |doi=10.3389/fmars.2021.791054 |issn=2296-7745|doi-access=free |bibcode=2022FrMaS...891054O }}

The biodiesel produced from the processing of microalgae differs from other forms of biodiesel in the content of polyunsaturated fats. Polyunsaturated fats are known for their ability to retain fluidity at lower temperatures. While this may seem like an advantage in production during the colder temperatures of the winter, the polyunsaturated fats result in lower stability during regular seasonal temperatures.

{{Overly detailed|section|nosplit=y|date=April 2023}}

Numerous policies have been put in place since the 1975 oil crisis in order to promote the use of Renewable Fuels in the United States, Canada and Europe. In Canada, these included the implementation of excise taxes exempting propane and natural gas which was extended to ethanol made from biomass and methanol in 1992. The federal government also announced their renewable fuels strategy in 2006 which proposed four components: increasing availability of renewable fuels through regulation, supporting the expansion of Canadian production of renewable fuels, assisting farmers to seize new opportunities in this sector and accelerating the commercialization of new technologies. These mandates were quickly followed by the Canadian provinces:

Policies in the United States have included a decrease in the subsidies provided by the federal and state governments to the oil industry which have usually included $2.84 billion. This is more than what is actually set aside for the biofuel industry. The measure was discussed at the G20 in Pittsburgh where leaders agreed that "inefficient fossil fuel subsidies encourage wasteful consumption, reduce our energy security, impede investment in clean sources and undermine efforts to deal with the threat of climate change". If this commitment is followed through and subsidies are removed, a fairer market in which algae biofuels can compete will be created. In 2010, the U.S. House of Representatives passed a legislation seeking to give algae-based biofuels parity with cellulose biofuels in federal tax credit programs. The algae-based renewable fuel promotion act (HR 4168) was implemented to give biofuel projects access to a $1.01 per gal production tax credit and 50% bonus depreciation for biofuel plant property. The U.S Government also introduced the domestic Fuel for Enhancing National Security Act implemented in 2011. This policy constitutes an amendment to the Federal property and administrative services act of 1949 and federal defense provisions in order to extend to 15 the number of years that the Department of Defense (DOD) multiyear contract may be entered into the case of the purchase of advanced biofuel. Federal and DOD programs are usually limited to a 5-year periodG20. [http://www.canadainternational.gc.ca/g20/summit-sommet/g20/declaration_092509.aspx?view=d G20 Leaders' Statement] {{Webarchive|url=https://web.archive.org/web/20130310100805/http://www.canadainternational.gc.ca/g20/summit-sommet/g20/declaration_092509.aspx?view=d |date=10 March 2013 }} - 2009 Pittsburgh Summit. 2009.

The European Union (EU) has also responded by quadrupling the credits for second-generation algae biofuels which was established as an amendment to the Biofuels and Fuel Quality Directives.[http://www.biofuelstp.eu/funding.html European biofuels technology platform. R&D&D funding] {{Webarchive|url=https://web.archive.org/web/20130518225250/http://www.biofuelstp.eu/funding.html |date=18 May 2013 }} (accessed 28 January 2013)

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• {{annotated link|Cyanotoxin}}
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• {{annotated link|List of algal fuel producers}}
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{{Reflist}}

• {{Cite book|last=Worldwatch Institute|title=Biofuels for Transport: Global Potential and Implications for Sustainable Agriculture and Energy in the 21st century|publisher=Earthscan|year=2007|isbn=978-1-84407-422-8|url=http://www.worldwatch.org/node/530}}
• {{Cite book|last=McKay|first=David JC|title=Sustainable Energy-Without Hot Air|publisher=UIT Cambridge Ltd|date=3 November 2008|series=3.5.2|isbn=978-0-9544529-3-3|url=http://www.withouthotair.com/}}
• {{cite web|url=http://www.renewableenergyworld.com/rea/news/article/2010/04/salt-water-the-tangy-taste-of-energy-freedom|title=Salt Water: The Tangy Taste of Energy Freedom|last=Lane|first=Jim|date=18 April 2010|publisher=Renewable Energy World|access-date=21 April 2010}}
• {{cite book | title=Algae biofuel | publisher=Studium Press (India) Pvt. Ltd. | editor=Bhatnagar, S.K. |editor2=Atul Saxena |editor3=Stefan Kraan | year=2011 | location=New Delhi | isbn=978-93-8001-244-5| url=https://books.google.com/books?id=AEcntwAACAAJ }}
• {{cite book|last1=Darzins|first1=Al|last2=Pienkos|first2=Philip|last3=Edye|first3=Les|title=Current status and potential for algal biofuels production|date=2010|publisher=IEA Bioenergy Task 39|url=http://task39.org/files/2013/05/IEA-Task-39-Current-Status-and-Potential-of-Algal-biofuels0.pdf}}

{{Commons category|Algae fuel}}

• [http://www.oilgae.com/ref/report/Report_Sample.pdf A Report on Commercial Usage and Production of Algal Oil]
• [http://www.biodieselmagazine.com/article.jsp?article_id=3313 A Sober Look at Biofuels from Algae (Biodiesel Magazine)]
• [http://www.nrel.gov/publications US National Renewable Energy Laboratory Publications]
• [http://task39.org/files/2013/05/IEA-Task-39-Current-Status-and-Potential-of-Algal-biofuels0.pdf Current Status and Potential for Algal Biofuels Production]

{{Bioenergy}}

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