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{{short description|Aquaculture involving the farming of algae}}
[[File:Seaweed farm uroa zanzibar.jpg|thumb|A seaweed farm in [[Uroa]], Zanzibar]]
[[File:Algoculture au kibboutz Ketura.JPG|thumb|Algaculture in [[Ketura, Israel|Kibbutz Ketura]], [[Israel]]]]
'''Algaculture''' is a form of [[aquaculture]] involving the farming of species of [[algae]].<ref name=":1">{{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 }}</ref>

The majority of algae that are intentionally cultivated fall into the category of [[microalgae]] (also referred to as [[phytoplankton]], [[microphytes]], or [[planktonic algae]]). [[Macroalgae]], commonly known as [[seaweed]], also have many commercial and industrial uses, but due to their size and the specific requirements of the environment in which they need to grow, they do not lend themselves as readily to cultivation (this may change, however, with the advent of newer seaweed cultivators, which are basically [[algae scrubber]]s using upflowing air bubbles in small containers).{{Citation needed|date=March 2023}}

Commercial and industrial algae cultivation has numerous uses, including production of [[nutraceutical]]s such as [[omega-3 fatty acids]] (as algal oil)<ref>{{cite journal |last1=Lane |first1=Katie |last2=Derbyshire |first2=Emma |last3=Li |first3=Weili |last4=Brennan |first4=Charles |title=Bioavailability and Potential Uses of Vegetarian Sources of Omega-3 Fatty Acids: A Review of the Literature |journal=Critical Reviews in Food Science and Nutrition |date=January 2014 |volume=54 |issue=5 |pages=572–579 |doi=10.1080/10408398.2011.596292|pmid=24261532 |s2cid=30307483 }}</ref><ref>{{cite book |last1=Winwood |first1=R.J. |chapter=Algal oil as a source of omega-3 fatty acids |title=Food Enrichment with Omega-3 Fatty Acids |date=2013 |series=Woodhead Publishing Series in Food Science, Technology and Nutrition |pages=389–404 |doi=10.1533/9780857098863.4.389|isbn=978-0-85709-428-5 }}</ref><ref>{{cite journal |last1=Lenihan-Geels |first1=Georgia |last2=Bishop |first2=Karen |last3=Ferguson |first3=Lynnette |title=Alternative Sources of Omega-3 Fats: Can We Find a Sustainable Substitute for Fish? |journal=Nutrients |date=18 April 2013 |volume=5 |issue=4 |pages=1301–1315 |doi=10.3390/nu5041301|pmid=23598439 |pmc=3705349 |doi-access=free }}</ref> or natural food [[colorants]] and [[dyes]], [[food]], [[fertilizer]]s, [[bioplastics]], chemical feedstock (raw material), protein-rich animal/[[Commercial fish feed|aquaculture]] feed, [[pharmaceuticals]], and [[algal fuel]],<ref name="10.1007/s43615-021-00084-3">{{cite journal |last1=Venkatesh |first1=G. |title=Circular Bio-economy—Paradigm for the Future: Systematic Review of Scientific Journal Publications from 2015 to 2021 |journal=Circular Economy and Sustainability |date=1 March 2022 |volume=2 |issue=1 |pages=231–279 |doi=10.1007/s43615-021-00084-3 |s2cid=238768104 |language=en |issn=2730-5988|doi-access=free |bibcode=2022CirES...2..231V }}</ref> and can also be used as a means of [[pollution control]] and [[Nature-based solutions|natural]] [[Carbon sequestration#Seaweed farming and algae|carbon sequestration]].<ref name="10.3389/fnut.2022.1029841" />

Global production of farmed aquatic plants, overwhelmingly dominated by seaweeds, grew in output volume from 13.5 million tonnes in 1995, to just over 30 million tonnes in 2016 and 37.8 million tonnes in 2022.<ref name=":12">{{Cite book |url=https://openknowledge.fao.org/handle/20.500.14283/cd0683en |title=The State of World Fisheries and Aquaculture 2024 |date=2024-06-07 |publisher=FAO |isbn=978-92-5-138763-4 |language=en |doi=10.4060/cd0683en}}</ref><ref name=":0">{{Cite book|url=http://www.fao.org/3/ca0191en/ca0191en.pdf|title=In brief, The State of World Fisheries and Aquaculture, 2018|publisher=FAO|year=2018}}</ref> This increase was the result of production expansions led by China, followed by Malaysia, the Philippines, the United Republic of Tanzania, the Russian Federation.<ref name=":12" />

Cultured microalgae already contribute to a wide range of sectors in the emerging [[bioeconomy]].<ref>{{cite journal |last1=Verdelho Vieira |first1=Vítor |last2=Cadoret |first2=Jean-Paul |last3=Acien |first3=F. Gabriel |last4=Benemann |first4=John |title=Clarification of Most Relevant Concepts Related to the Microalgae Production Sector |journal=Processes |date=January 2022 |volume=10 |issue=1 |pages=175 |doi=10.3390/pr10010175 |language=en |issn=2227-9717|doi-access=free |hdl=10835/13146 |hdl-access=free }}</ref> Research suggests there are large potentials and benefits of algaculture for the development of a future [[healthy diet|healthy]] and [[sustainable food system]].<ref name="10.5670/oceanog.2022.213">{{cite journal |last1=Greene |first1=Charles |last2=Scott-Buechler |first2=Celina |last3=Hausner |first3=Arjun |last4=Johnson |first4=Zackary |last5=Lei |first5=Xin Gen |last6=Huntley |first6=Mark |title=Transforming the Future of Marine Aquaculture: A Circular Economy Approach |journal=Oceanography |date=2022 |pages=26–34 |doi=10.5670/oceanog.2022.213 |issn=1042-8275|doi-access=free}}
*News article about the study: {{cite news |title=Nutrient-rich algae could help meet global food demand: Cornell researchers |url=https://www.ctvnews.ca/sci-tech/nutrient-rich-algae-could-help-meet-global-food-demand-cornell-researchers-1.6117300 |access-date=17 November 2022 |work=CTVNews |date=20 October 2022 |language=en}}</ref><ref name="10.3389/fnut.2022.1029841">{{cite journal |last1=Diaz |first1=Crisandra J. |last2=Douglas |first2=Kai J. |last3=Kang |first3=Kalisa |last4=Kolarik |first4=Ashlynn L. |last5=Malinovski |first5=Rodeon |last6=Torres-Tiji |first6=Yasin |last7=Molino |first7=João V. |last8=Badary |first8=Amr |last9=Mayfield |first9=Stephen P. |title=Developing algae as a sustainable food source |journal=Frontiers in Nutrition |date=2023 |volume=9 |doi=10.3389/fnut.2022.1029841 |pmid=36742010 |pmc=9892066 |issn=2296-861X|doi-access=free}}</ref>
{{toclimit|3}}

== Uses of algae ==

=== Food ===
{{Further|Edible seaweed}}
[[File:Dulse.JPG|thumb|right|Dulse is one of many edible algae.]]
[[File:Land and freshwater footprints for protein production from various sources.jpg|thumb|Algaculture may become an important part of a [[healthy diet|healthy]] and [[sustainable food system]]<ref name="10.5670/oceanog.2022.213" />]]
Several species of algae are raised for food. While algae have qualities of a sustainable food source, "producing highly digestible proteins, lipids, and carbohydrates, and are rich in essential fatty acids, vitamins, and minerals" and e.g. having a high protein productivity per acre, there are several challenges "between current biomass production and large-scale economic algae production for the food market".<ref name="10.3389/fnut.2022.1029841" />

* Micro-algae can be used to create [[Microbial food cultures#Microbial protein|microbial protein]] used as a powder or in a variety of products.<ref name="mprot">{{cite web |title=Microbial Protein: a promising and sustainable food and feed ingredient – North-CCU-hub |url=https://northccuhub.eu/microbial-protein-a-promising-and-sustainable-food-and-feed-ingredient/ |access-date=1 July 2022}}</ref>
* Purple laver (''[[Porphyra]]'') is perhaps the most widely domesticated marine algae.<ref name="Mumford 88">Mumford, T.F. and Miura, A. 4.''Porphyra'' as food: cultivation and economics. in Lembi, C.A. and Waaland, J.R. 1988. ''Algae and Human Affairs.'' Cambridge University Press, Cambridge. {{ISBN|0-521-32115-8}}</ref> In Asia it is used in [[nori]] ([[Japan]]) and [[gim (food)|gim]] ([[Korea]]). In [[Wales]], it is used in [[laverbread]], a traditional food, and in [[Ireland]] it is collected and made into a [[Gel|jelly]] by [[stewing]] or [[boiling]]. Preparation also can involve frying or heating the [[frond]]s with a little water and beating with a fork to produce a pinkish jelly. Harvesting also occurs along the west coast of [[North America]], and in [[Hawaii]] and [[New Zealand]].{{citation needed|date=January 2021}}
* [[Algae fuel#Food supplementation|Algae oil]] is used as a [[dietary supplement]] as the plants also produce [[Omega-3]] (and [[Omega-6]]) [[fatty acids]], which are commonly also found in [[fish oils]], and which have been shown to have positive health benefits, including [[nootropic|for cognition]] and against [[brain aging]].<ref name="ISBNews">{{cite web | url = http://www.isb.vt.edu/news/2004/artspdf/jul0403.pdf |title = Transgenic Plants Produce Omega-3 and Omega-6 Fatty Acids |publisher = School of Biology and Biochemistry, [[University of Bath]], England, UK| access-date = 2006-08-29| archive-url= https://web.archive.org/web/20060828040031/http://www.isb.vt.edu/news/2004/artspdf/jul0403.pdf| archive-date= 28 August 2006 <!--DASHBot-->| url-status= live}}</ref><ref>{{cite journal |last1=Arterburn |first1=Linda M. |last2=Oken |first2=Harry A. |last3=Bailey Hall |first3=Eileen |last4=Hamersley |first4=Jacqueline |last5=Kuratko |first5=Connye N. |last6=Hoffman |first6=James P. |title=Algal-Oil Capsules and Cooked Salmon: Nutritionally Equivalent Sources of Docosahexaenoic Acid |journal=Journal of the American Dietetic Association |date=1 July 2008 |volume=108 |issue=7 |pages=1204–1209 |doi=10.1016/j.jada.2008.04.020 |pmid=18589030 |language=en |issn=0002-8223}}</ref><ref>{{cite journal |last1=Ryan |first1=Lisa |last2=Symington |first2=Amy M. |title=Algal-oil supplements are a viable alternative to fish-oil supplements in terms of docosahexaenoic acid (22:6n-3; DHA) |journal=Journal of Functional Foods |date=1 December 2015 |volume=19 |pages=852–858 |doi=10.1016/j.jff.2014.06.023 |language=en |issn=1756-4646}}</ref><ref name="10.3389/fnut.2022.1029841" />
* Dulse (''[[Palmaria palmata]]'') is a red species sold in [[Ireland]] and Atlantic [[Canada]]. It is eaten raw, fresh, dried, or cooked like [[spinach]].{{citation needed|date=January 2021}}
* [[Spirulina (dietary supplement)|Spirulina]] (''Arthrospira platensis'') is a blue-green microalgae with a long history as a food source in East Africa and pre-colonial Mexico. Spirulina is high in protein and other nutrients, finding use as a [[food supplement]] and for malnutrition. Spirulina thrives in open systems and commercial growers have found it well-suited to cultivation. One of the largest production sites is [[Lake Texcoco]] in central Mexico.<ref name="KickingImp">{{cite web | url = http://www.cnn.tv/ASIANOW/asiaweek/98/0731/feat_2.html |title = The Imp With a Mighty Kick | website =Asia Week |publisher = CNN.tv|author = Yenni Kwok}}</ref> The plants produce a variety of nutrients and high amounts of [[protein]]. Spirulina is often used commercially as a nutritional supplement.<ref name="sbalgae">{{cite web|url=http://www.sbgalgae.com/afa.htm |title=Aphanizomenon Flos-Aquae Blue Green Algae |publisher=Energy For Life Wellness Center |access-date=2006-08-29 |url-status=dead |archive-url=https://web.archive.org/web/20060426144221/http://www.sbgalgae.com/afa.htm |archive-date=2006-04-26 }}</ref><ref name="microalgaenutrition">{{cite web | url = http://www.fao.org/DOCREP/003/W3732E/w3732e07.htm |title = Nutritional value of micro-algae |publisher = United States Fisheries Department| access-date = 2006-08-29| archive-url= https://web.archive.org/web/20060826055621/http://www.fao.org/DOCREP/003/W3732E/w3732e07.htm| archive-date= 26 August 2006 <!--DASHBot-->| url-status= live}}</ref>
* '' [[Chlorella]]'', another popular microalgae, has similar nutrition to spirulina. ''Chlorella'' is very popular in [[Japan]]. It is also used as a nutritional supplement with possible effects on metabolic rate.<ref>{{Cite web|url=https://naturalways.com/chlorella-growth-factor.htm|title=Chlorella Growth Factor|website=Naturalways.com|access-date=29 January 2022}}</ref>
* Irish moss (''[[Chondrus crispus]]''), often confused with ''[[Mastocarpus stellatus]]'', is the source of [[carrageenan]], which is used as a stiffening agent in instant puddings, sauces, and dairy products such as ice cream. Irish moss is also used by beer brewers as a [[finings|fining]] agent.{{citation needed|date=January 2021}}
* [[Sea lettuce]] (''[[Ulva lactuca]]''), is used in [[Scotland]], where it is added to soups and salads.{{citation needed|date=January 2021}}
* Dabberlocks or badderlocks (''[[Alaria esculenta]]'') is eaten either fresh or cooked in [[Greenland]], [[Iceland]], Scotland and Ireland.{{citation needed|date=January 2021}}
* ''[[Aphanizomenon flos-aquae]]'' is a [[cyanobacteria]] similar to spirulina, which is used as a nutritional supplement.
* Extracts and oils from algae are also used as additives in various food products.<ref name="algaeicecream">{{cite web|url=http://ift.confex.com/ift/2005/techprogram/paper_31527.htm |title=Sensory properties of strawberry- and vanilla-flavored ice cream supplemented with an algae oil emulsion |publisher=Dept. of Food Science, [[Pennsylvania State University]] |access-date=2006-08-29 |url-status=dead |archive-url=https://web.archive.org/web/20070506011358/http://ift.confex.com/ift/2005/techprogram/paper_31527.htm |archive-date=2007-05-06 }}</ref>
*''Sargassum'' species are an important group of seaweeds. These algae have many [[phlorotannin]]s.
*  Cochayuyo (''[[Durvillaea antarctica]]'') is eaten in salads and ceviche in Peru and Chile.
*Both microalgae and macroalgae are used to make [[agar]] (see below), which is used as a [[gelling agent]] in foods.<ref name="SeaweedUses" /><ref name="SeaweedInEurope" />

==== Lab manipulation ====
Australian scientists at [[Flinders University]] in [[Adelaide]] have been experimenting with using marine microalgae to produce proteins for human consumption, creating products like "[[caviar]]", [[vegan]] burgers, [[fake meat]], [[jam]]s and other [[food spread]]s. By manipulating microalgae in a [[laboratory]], the [[protein]] and other [[nutrient]] contents could be increased, and flavours changed to make them more palatable. These foods leave a much lighter [[carbon footprint]] than other forms of protein, as the microalgae absorb rather than produce [[carbon dioxide]], which contributes to the [[greenhouse gases]].<ref>{{cite web | last=Leckie | first=Evelyn | title=Adelaide scientists turn marine microalgae into 'superfoods' to substitute animal proteins | website=ABC News |publisher=[[Australian Broadcasting Corporation]] | date=14 Jan 2021 | url=https://www.abc.net.au/news/2021-01-14/marine-microalgae-could-be-the-solution-to-protein-shortage/13054084 | access-date=17 Jan 2021}}</ref>

=== Fertilizer and agar ===
For centuries [[seaweed]] has been used as [[fertilizer]]. It is also an excellent source of [[potassium]] for manufacture of [[potash]] and [[potassium nitrate]]. Some types of microalgae can be used this way as well.<ref>{{cite web|url= https://www.fao.org/3/i0424e/i0424e00.pdf |title = A Review on Culture, Production and Use of Spirulina as Food for Humans and Feeds for Domestic Animals and Fish|publisher = Food and Agriculture Organization of the United Nations |date = 2008}}</ref>

Both microalgae and macroalgae are used to make [[agar]].<ref name="SeaweedUses">{{cite book| title=Seaweeds and their Uses | publisher=Chapman and Hall Ltd. |location = London |first1= V.J.|last1= Chapman|first2 = D.J.|last2= Chapman|date = 1980|url = |isbn =  978-94-009-5808-1 |doi = 10.1007/978-94-009-5806-7}}</ref><ref name="PorphyraAsfood">{{cite book |author1=Mumford, T.F.  |author2=Miura, A | chapter=Porphyra as food: cultivation and economics | editor=Lembi, C.A. |editor2=Waaland, J.R. |title=Algae and Human Affairs | year=1988 | pages= 87–117}}</ref><ref name="SeaweedInEurope">{{cite book |author1=Guiry, M.D.  |author2=Blunden, G. | title=Seaweed Resources in Europe: Uses and Potential | publisher=John Wiley and Sons | year=1991 |isbn=978-0-471-92947-5}}</ref>

=== Pollution control ===
With concern over [[global warming]], new methods for the thorough and efficient [[Carbon capture and storage|capture of CO<sub>2</sub>]] are being sought out. The carbon dioxide that a carbon-fuel burning plant produces can feed into open or closed algae systems, fixing the CO<sub>2</sub> and accelerating algae growth. Untreated [[sewage]] can supply additional nutrients, thus turning two pollutants into valuable commodities.<ref name="SmokestackGasTank">{{cite journal
| last = McKenna
| first = Phil
| title = From smokestack to gas tank
| journal = New Scientist
| volume = 192
| issue = 2572
| pages = 28–29
| date = 7 October 2006
| doi =10.1016/S0262-4079(06)60667-2
| id = 1233
}}</ref>

Waste high-purity {{CO2}} as well as sequestered carbon from the atmosphere can be used, with potential significant benefits for [[climate change mitigation]].<ref>{{cite journal |last1=Ou |first1=Longwen |last2=Banerjee |first2=Sudhanya |last3=Xu |first3=Hui |last4=Coleman |first4=André M. |last5=Cai |first5=Hao |last6=Lee |first6=Uisung |last7=Wigmosta |first7=Mark S. |last8=Hawkins |first8=Troy R. |title=Utilizing high-purity carbon dioxide sources for algae cultivation and biofuel production in the United States: Opportunities and challenges |journal=Journal of Cleaner Production |date=25 October 2021 |volume=321 |pages=128779 |doi=10.1016/j.jclepro.2021.128779 |s2cid=238739590 |language=en |issn=0959-6526|doi-access=free }}</ref><ref>{{cite news |title=Brilliant Planet is running algae farms to pull carbon out of the air |url=https://techcrunch.com/2022/04/07/brilliant-planet-series-a/ |access-date=12 June 2022 |work=TechCrunch}}</ref><ref>{{cite journal |last1=Moreira |first1=Diana |last2=Pires |first2=José C.M. |title=Atmospheric CO2 capture by algae: Negative carbon dioxide emission path |journal=Bioresource Technology |date=September 2016 |volume=215 |pages=371–379 |doi=10.1016/j.biortech.2016.03.060|pmid=27005790 }}</ref>

Algae cultivation is under study for uranium/plutonium sequestration and purifying fertilizer runoff.

=== Energy production ===
{{Further|Algae fuel}}
Business, academia and governments are exploring the possibility of using algae to make gasoline, bio-diesel, [[biogas]] and other fuels. Algae itself may be used as a biofuel, and additionally be used to create hydrogen.

Microalgae are also researched for [[biohydrogen|hydrogen production]] – e.g. micro-droplets for algal cells or synergistic algal-bacterial multicellular [[spheroid]] [[microreactor|microbial reactors]] capable [[Hydrogen fuel#Production|of producing]] oxygen as well as hydrogen via photosynthesis in daylight under air.<ref name="phys-droplets">{{cite news |title=Research creates hydrogen-producing living droplets, paving way for alternative future energy source |url=https://phys.org/news/2020-11-hydrogen-producing-droplets-paving-alternative-future.html |access-date=9 December 2020 |work=phys.org |language=en |archive-date=16 December 2020 |archive-url=https://web.archive.org/web/20201216151601/https://phys.org/news/2020-11-hydrogen-producing-droplets-paving-alternative-future.html |url-status=live }}</ref><ref>{{cite journal |last1=Xu |first1=Zhijun |last2=Wang |first2=Shengliang |last3=Zhao |first3=Chunyu |last4=Li |first4=Shangsong |last5=Liu |first5=Xiaoman |last6=Wang |first6=Lei |last7=Li |first7=Mei |last8=Huang |first8=Xin |last9=Mann |first9=Stephen |title=Photosynthetic hydrogen production by droplet-based microbial micro-reactors under aerobic conditions |journal=Nature Communications |date=25 November 2020 |volume=11 |issue=1 |pages=5985 |doi=10.1038/s41467-020-19823-5 |pmid=33239636 |pmc=7689460 |bibcode=2020NatCo..11.5985X |url=|language=en |issn=2041-1723}}</ref>

==== Microgeneration ====
{{Excerpt|Algae bioreactor|Microgeneration}}

=== Carbon sequestration ===
{{Excerpt|Carbon sequestration|Seaweed farming and algae}}

=== Other uses ===
''Chlorella'', particularly a transgenic strain which carries an extra mercury [[reductase]] [[gene]], has been studied as an agent for [[environmental remediation]] due to its ability to reduce {{chem|Hg|2+}} to the less toxic elemental mercury.<ref>{{cite journal |author =Huang C |title=Expression of mercuric reductase from Bacillus megaterium MB1 in eukaryotic microalga Chlorella sp. DT: an approach for mercury phytoremediation |journal=Appl Microbiol Biotechnol |volume=72 |issue=1 |pages=197–205 |year=2006 |pmid=16547702 |doi=10.1007/s00253-005-0250-0 |last2=Chen |first2=MW |last3=Hsieh |first3=JL |last4=Lin |first4=WH |last5=Chen |first5=PC |last6=Chien |first6=LF|s2cid=9693543 }}</ref>

Cultured strains of a common coral microalgal [[endosymbiont]]s are researched as a potential way to increase corals' thermal tolerance for [[climate resilience]] and [[coral bleaching|bleaching tolerance]].<ref>{{cite news |title=Scientists successfully develop 'heat resistant' coral to fight bleaching |url=https://phys.org/news/2020-05-scientists-successfully-resistant-coral.html |access-date=12 June 2020 |work=phys.org |language=en}}</ref><ref>{{cite journal |last1=Cornwall |first1=Warren |title=Lab-evolved algae could protect coral reefs |journal=Science |date=13 May 2020 |doi=10.1126/science.abc7842 |s2cid=219408415 }}</ref><ref>{{cite journal |last1=Buerger |first1=P. |last2=Alvarez-Roa |first2=C. |last3=Coppin |first3=C. W. |last4=Pearce |first4=S. L. |last5=Chakravarti |first5=L. J. |last6=Oakeshott |first6=J. G. |last7=Edwards |first7=O. R. |last8=Oppen |first8=M. J. H. van |title=Heat-evolved microalgal symbionts increase coral bleaching tolerance |journal=Science Advances |date=1 May 2020 |volume=6 |issue=20 |pages=eaba2498 |doi=10.1126/sciadv.aba2498 |pmid=32426508 |pmc=7220355 |bibcode=2020SciA....6.2498B |doi-access=free }}</ref>

Cultured microalgae is used in research and development for potential medical applications, in particular for [[microbot]]s<ref>{{cite journal |last1=Xie |first1=Shuangxi |last2=Jiao |first2=Niandong |last3=Tung |first3=Steve |last4=Liu |first4=Lianqing |title=Controlled regular locomotion of algae cell microrobots |journal=Biomedical Microdevices |date=June 2016 |volume=18 |issue=3 |pages=47 |doi=10.1007/s10544-016-0074-y|pmid=27206511 |s2cid=254278019 }}</ref> such as [[Biohybrid microswimmer#Biomedical applications|biohybrid microswimmers]] for [[targeted drug delivery]].

Cultivated algae serve many other purposes, including cosmetics,<ref name=Flanders>Starckx, Senne (31 October 2012) [http://www.flanderstoday.eu/content/place-sun A place in the sun – Algae is the crop of the future, according to researchers in Geel] {{webarchive |url=https://web.archive.org/web/20130905074520/http://www.flanderstoday.eu/content/place-sun |date=September 5, 2013 }} Flanders Today, Retrieved 8 December 2012</ref>{{explain|date=March 2023}} animal feed,<ref name = Flanders />{{explain|date=March 2023}} bioplastic production, dyes and colorant production, chemical [[feedstock]] production, and pharmaceutical ingredients.{{explain|date=March 2023}}

== Growing, harvesting, and processing algae ==
=== Monoculture ===
{{More citations needed|section|date=January 2022}}
Most growers prefer [[monocultural]] production and go to considerable lengths to maintain the purity of their cultures. However, the [[Contamination#Contaminated samples|microbiological contaminants]] are still under investigation.<ref>{{cite web|url=https://open.uct.ac.za/bitstream/item/26426/thesis_ebe_2016_mogale_motlalekgomo.pdf?sequence=1|title=Identification and quantification of bacteria associated with cultivated Spirulina and impact of physiological factors|website=Open.uct.ac.za|access-date=29 January 2022}}</ref>

With mixed cultures, one species comes to dominate over time and if a non-dominant species is believed to have particular value, it is necessary to obtain pure cultures in order to cultivate this species. Individual species cultures are also much needed for research purposes.

A common method of obtaining pure cultures is [[serial dilution]]. Cultivators dilute either a wild sample or a lab sample containing the desired algae with filtered water and introduce small aliquots (measures of this solution) into a large number of small growing containers. Dilution follows a microscopic examination of the source culture that predicts that a few of the growing containers contain a single cell of the desired species. Following a suitable period on a light table, cultivators again use the microscope to identify containers to start larger cultures.

Another approach is to use a special medium which excludes other organisms, including invasive algae.  For example, ''[[Dunaliella]]'' is a commonly grown genus of microalgae which flourishes in extremely salty water that few other organisms can tolerate.

Alternatively, mixed algae cultures can work well for larval [[mollusks]]. First, the cultivator filters the sea water to remove algae which are too large for the [[larva]]e to eat. Next, the cultivator adds nutrients and possibly [[Aerated waters|aerates]] the result. After one or two days in a greenhouse or outdoors, the resulting thin soup of mixed algae is ready for the larvae. An advantage of this method is low maintenance.

=== Growing algae ===
{{See also|Seaweed cultivator|Culture of microalgae in hatcheries}}
[[File:Microalgae cultivation facility along the Kona Coast of the Big Island of Hawai’i.jpg|thumb|A microalgae cultivation facility<ref name="10.5670/oceanog.2022.213" />]]
[[File:Brine shrimp cyst.jpg|thumb|Microalgae is used to culture [[brine shrimp]], which produce dormant eggs (pictured). The eggs can then be hatched on demand and fed to cultured fish larvae and crustaceans.]]
Water, [[carbon dioxide]], minerals and light are all important factors in cultivation, and different algae have different requirements. The basic reaction for algae growth in water is carbon dioxide + light energy + water = glucose + oxygen + water.<ref>{{Cite web |url=http://www.coolclassroom.org/cool_projects/lessons/biology/resources.html |title=Biology Resources |access-date=2008-06-17 |archive-url=https://web.archive.org/web/20081208163406/http://www.coolclassroom.org/cool_projects/lessons/biology/resources.html |archive-date=2008-12-08 |url-status=dead }}</ref>  This is called ''[[autotrophic]]'' growth.  It is also possible to grow certain types of algae without light, these types of algae consume sugars (such as glucose). This is known as ''[[heterotrophic]]'' growth.

==== Temperature ====
The water must be in a temperature range that will support the specific algal species being grown mostly between 15˚C and 35˚C.

==== Light and mixing ====
In a typical algal-cultivation system, such as an open pond, light only penetrates the top {{convert|3|to(-)|4|in}} of the water, though this depends on the algae density. As the algae grow and multiply, the culture becomes so dense that it blocks light from reaching deeper into the water. Direct sunlight is too strong for most algae, which can use only about {{frac|10}} the amount of light they receive from direct sunlight; however, exposing an algae culture to direct sunlight (rather than shading it) is often the best course for strong growth, as the algae underneath the surface is able to utilize more of the less intense light created from the shade of the algae above.

To use deeper ponds, growers agitate the water, circulating the algae so that it does not remain on the surface. [[Paddlewheel aerator|Paddle wheels]] can stir the water and [[compressed air]] coming from the bottom lifts algae from the lower regions. Agitation also helps prevent over-exposure to the sun.

Another means of supplying light is to place the light ''in'' the system. [[Glow plate]]s made from sheets of plastic or glass and placed within the [[Water tank|tank]] offer precise control over light intensity, and distribute it more evenly.  They are seldom used, however, due to high cost.

==== Odor and oxygen ====
The odor associated with [[bogs]], [[swamps]], and other stagnant waters can be due to oxygen depletion caused by the decay of deceased [[algal bloom]]s. Under [[Anoxic waters|anoxic]] conditions, the bacteria inhabiting algae cultures break down the organic material and produce [[hydrogen sulfide]] and [[ammonia]], which causes the odor. This [[hypoxia (environmental)|hypoxia]] often results in the death of aquatic animals. In a system where algae is intentionally cultivated, maintained, and harvested, neither [[eutrophication]] nor hypoxia are likely to occur.

Some living algae and bacteria also produce odorous chemicals, particularly certain [[cyanobacteria]] (previously classed as blue-green algae) such as ''[[Anabaena]]''. The most well known of these odor-causing chemicals are MIB ([[2-methylisoborneol]]) and [[geosmin]]. They give a musty or earthy odor that can be quite strong. Eventual death of the cyanobacteria releases additional gas that is trapped in the cells. These chemicals are detectable at very low levels – in the parts per billion range – and are responsible for many "taste and odor" issues in [[drinking water]] treatment and distribution.<ref>"A Guide to Geosmin and MIB-producing Cyanobacteria in the United States", Izaguirre and Taylor, Water Science Technology, 2004, 49(9): pp. 19-24</ref> Cyanobacteria can also produce chemical toxins that have been a problem in drinking water.

==== Nutrients ====
Nutrients such as [[nitrogen]] (N), [[phosphorus]] (P), and [[potassium]] (K) serve as fertilizer for algae, and are generally necessary for growth. 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, a given area.  Carbon dioxide is also essential; usually an input of CO<sub>2</sub> is required for fast-paced algal growth. These elements must be dissolved into the water, in bio-available forms, for algae to grow.

=== Methods ===
'''Farming of macroalgae'''
{{Excerpt|Seaweed farming}}

==== Open system cultivation ====
[[File:Microalgenkwekerij te Heure bij Borculo.jpg|thumb|300px|right|[[Raceway pond]] used to cultivate microalgae. The water is kept in constant motion with a powered [[Paddlewheel aerator|paddle wheel]].]]

An open system of algae cultivation involves the growth of algae in shallow water streams which could originate from a natural system or artificially prepared. In this system, algae can be cultivated in natural water bodies like lakes, rivers, and in oceans, as well as artificial ponds made up of concrete, plastic, pond liners or variety of materials. The open system of algae cultivation is simple and cost-effective, making it an attractive option for commercial production of algae-based products.

Open ponds are highly vulnerable to contamination by other microorganisms, such as other algal species or bacteria. Thus cultivators usually choose closed systems for monocultures. Open systems also do not offer control over temperature and lighting. The growing season is largely dependent on location and, aside from tropical areas, is limited to the warmer months.<ref name=":1" />

Open pond systems are cheaper to construct, at the minimum requiring only a trench or pond. Large ponds have the largest production capacities relative to other systems of comparable cost. Also, open pond cultivation can exploit unusual conditions that suit only specific algae. For instance, ''[[Dunaliella salina]]'' grow in extremely salty water; these unusual media exclude other types of organisms, allowing the growth of pure cultures in open ponds. Open culture can also work if there is a system of harvesting only the desired algae, or if the ponds are frequently re-inoculated before invasive organisms can multiply significantly.  The latter approach is frequently employed by [[Chlorella]] farmers, as the growth conditions for Chlorella do not exclude competing algae.

The former approach can be employed in the case of some chain [[diatom]]s since they can be filtered from a stream of water flowing through an [[wikt:outflow|outflow]] [[water pipe|pipe]]. A "[[pillow case]]" of a fine [[mesh]] cloth is tied over the outflow pipe allowing other algae to escape. The chain diatoms are held in the bag and feed [[wikt:shrimp|shrimp]] larvae (in Eastern [[hatchery|hatcheries]]) and [[inoculation|inoculate]] new tanks or ponds.

Enclosing a pond with a transparent or translucent barrier effectively turns it into a greenhouse. This solves many of the problems associated with an open system. It allows more species to be grown, it allows the species that are being grown to stay dominant, and it extends the growing season – if heated, the pond can produce year round. Open race way ponds were used for removal of lead using live ''Spirulina (Arthospira) sp''.<ref>{{cite journal | last1 = Siva Kiran | first1 = RR | last2 = Madhu | first2 = GM | last3 = Satyanarayana | first3 = SV | last4 = Kalpana | first4 = P | last5 = Bindiya | first5 = P | last6 = Subba Rangaiah | first6 = G | year = 2015 | title = Equilibrium and kinetic studies of lead biosorption by three ''Spirulina (Arthrospira) species'' in open raceway ponds | journal = Journal of Biochemical Technology | volume = 6 | issue = 1| pages = 894–909 }}</ref>

===== Water lagoons =====
A [[lagoon]] is a type of aquatic ecosystem that is characterized by a shallow body of water that is separated from the open ocean by natural barriers such as sandbars, barrier islands, or coral reefs. The Australian company Cognis Australia is a well-known company that specializes in producing β-carotene from ''Dunaliella salina'' harvested from hypersaline extensive ponds located in [[Hutt Lagoon]] and [[Whyalla]]. These ponds are primarily used for wastewater treatment, and the production of ''D. salina'' is a secondary benefit.<ref>Spolaore, Pauline; Joannis-Cassan, Claire; Duran, Elie; Isambert, Arsène (2006-02). "Commercial applications of microalgae". ''Journal of Bioscience and Bioengineering''. '''101''' (2): 87–96. [[Doi (identifier)|doi]]:10.1263/jbb.101.87. [[ISSN (identifier)|ISSN]] 1389-1723</ref>

===== Open sea =====
[[Open sea]] cultivation is a method of cultivating seaweed in the open ocean, as well as on a costal line in shallow water. Seaweed farming industry serves commercial needs for various products such as food, feed, pharma chemicals, cosmetics, [[biofuel]]s, and bio-stimulants. Seaweed extracts act as bio-stimulants, reducing biotic stress and increasing crop production. Additionally, it presents opportunities for creating animal and human nutrition products that can improve immunity and productivity. Open ocean seaweed cultivation is an eco-friendly technology that doesn't require land, fresh water, or chemicals. It also helps mitigate the effects of climate change by sequestering CO<sub>2</sub>.

Open sea cultivation method involves the use of rafts or ropes anchored in the ocean, where the seaweed grows attached to them. This method is widely used for commercial seaweed farming, as it allows for large-scale production and harvesting. The process of open sea cultivation of seaweed involves several steps. First, a suitable site in the ocean is identified, based on factors such as water depth, temperature, salinity, and nutrient availability. Once a site is chosen, ropes or rafts are anchored in the water, and the seed pieces of seaweed are attached to them using specialized equipment. The seaweed is then left to grow for several months, during which it absorbs nutrients from the water and sunlight through photosynthesis.<ref>Peteiro, César; Sánchez, Noemí; Dueñas-Liaño, Clara; Martínez, Brezo (2013-08-07). "Open-sea cultivation by transplanting young fronds of the kelp Saccharina latissima". ''Journal of Applied Phycology''. '''26''' (1): 519–528. [[Doi (identifier)|doi]]:10.1007/s10811-013-0096-2. [[ISSN (identifier)|ISSN]] 0921-8971</ref>

===== Raceway ponds =====
[[Raceway pond|Raceway-type ponds]] and lakes are open to the elements.<ref name=":02">{{Cite journal |last1=Khawam |first1=George |last2=Waller |first2=Peter |last3=Gao |first3=Song |last4=Edmundson |first4=Scott J. |last5=Wigmosta |first5=Mark S. |last6=Ogden |first6=Kimberly |date=May 2019 |title=Model of temperature, evaporation, and productivity in elevated experimental algae raceways and comparison with commercial raceways |journal=Algal Research |volume=39 |pages=101448 |doi=10.1016/j.algal.2019.101448 |osti=1581776 |s2cid=92558441 |issn=2211-9264|doi-access=free |bibcode=2019AlgRe..3901448K }}</ref> They are one of the most common and economic methods of large-scale algae cultivation, and offer several advantages over other cultivation methods. An open raceway pond is a shallow, rectangular-shaped pond used for the cultivation of algae. Because it is designed to circulate water in a continuous loop or raceway, allowing algae to grow in a controlled environment. Open system is a low-cost method of algae cultivation, and it is relatively easy to construct and maintain. The pond is typically lined with a synthetic material, such as polyethylene (HDPE) or polyvinyl chloride, to prevent the loss of water and nutrients. The pond is also equipped with paddlewheels or other types of mechanical devices to provide mixing and aeration.<ref>Klein, Bruno; Davis, Ryan (2022-04-05). "Algal Biomass Production via Open Pond Algae Farm Cultivation: 2021 State of Technology and Future Research</ref>

===== HRAPs =====
High-Rate Algal Ponds (HRAPs) are a type of open algae cultivation system that has gained popularity in recent years due to their efficiency and low cost of operation. HRAPs are shallow ponds, typically between 0.1 to 0.4 meters deep, that are used for the cultivation of algae. The ponds are equipped with a paddlewheel or other type of mechanical agitation system that provides mixing and aeration, which promotes algae growth. HRAP system is also recommended in wastewater treatment using algae.<ref>SA, Local Government Association of (2020-06-19). "High Rate Algal Ponds (HRAP)". ''LGA South Australia''. Retrieved 2023-03-23.</ref>

==== Photobioreactors ====
Algae can also be grown in a [[photobioreactor]] (PBR). A PBR is a [[bioreactor]] which incorporates a light source. Virtually any [[translucent]] container could be called a PBR; however, the term is more commonly used to define a closed system, as opposed to an open tank or pond.

Because PBR systems are closed, the cultivator must provide all nutrients, including {{chem|CO|2}}.

A PBR can operate in "[[Batch production|batch]] mode", which involves restocking the reactor after each harvest, but it is also possible to grow and harvest continuously. Continuous operation requires precise control of all elements to prevent immediate collapse. The grower provides sterilized water, nutrients, air, and carbon dioxide at the correct rates. This allows the reactor to operate for long periods. An advantage is that algae that grows in the "[[Bacterial growth|log phase]]" is generally of higher nutrient content than old "[[senescent]]" algae. Algal culture is the culturing of algae in ponds or other resources. Maximum productivity occurs when the "exchange rate" (time to exchange one volume of liquid) is equal to the "doubling time" (in mass or volume) of the algae.

PBRs can hold the culture in suspension, or they can provide a substrate on which the culture can form a [[biofilm]]. Biofilm-based PBRs have the advantage that they can produce far higher yields for a given water volume, but they can suffer from problems with cells separating from the substrate due to the water flow required to transport gases and nutrients to the culture.

===== Flat panel PBRs =====
Flat panel PBRs consist of a series of flat, transparent panels that are stacked on top of each other, creating a thin layer of liquid between them. Algae are grown in this thin layer of liquid, which is continuously circulated to promote mixing and prevent stagnation. The panels are typically made of glass or plastic and can be arranged in various configurations to optimize light exposure. Flat panel PBRs are generally used for low-to-medium density cultivation and are well-suited for species that require lower light intensity and maximum surface area for optimum light exposure. The temperature control in Flat panel PBR system is carried out by cooling down the culture in reservoir chamber using chilled water jacket as well as by sprinkling cold water on the flat panel surface.<ref>Sierra, E.; Acién, F.G.; Fernández, J.M.; García, J.L.; González, C.; Molina, E. (2008-05). "Characterization of a flat plate photobioreactor for the production of microalgae". ''Chemical Engineering Journal''. '''138''' (1–3): 136–147. [[Doi (identifier)|doi]]:10.1016/j.cej.2007.06.004</ref>

===== Tubular PBRs =====
Tubular PBRs consist of long, transparent tubes that are either vertically or horizontally oriented. Algae are grown inside the tubes, which are typically made of glass or plastic. The tubes are arranged in a helical or serpentine pattern to increase surface area for light exposure. The tubing can be either continuously or intermittently circulated to promote mixing and prevent stagnation. Tubular PBRs are generally used for high-density cultivation and are well-suited for species that require high light intensity. The temperature control in tubular PBR is a difficult task which is generally achieved by external sprinkling of deionized water which allow cooling of the tubes and subsequently reduces the temperature of culture circulating inside the tubes.<ref>Torzillo, Giuseppe; Chini Zittelli, Graziella (2015), "Tubular Photobioreactors", ''Algal Biorefineries'', Cham: Springer International Publishing, pp. 187–212, {{ISBN|978-3-319-20199-3}}, retrieved 2023-03-23</ref>

===== Biofilm PBRs =====
Biofilm PBRs include packed bed and porous substrate PBRs. Packed bed PBRs can be different shapes, including flat plate or tubular. In Porous Substrate Bioreactors (PSBRs), the biofilm is exposed directly to the air and receives its water and nutrients by capillary action through the substrate itself. This avoids problems with cells becoming suspended because there is no water flow across the biofilm surface. The culture could become contaminated by airborne organisms, but defending against other organisms is one of the functions of a biofilm.

===== Plastic bag PBRs =====
V-shaped plastic bags are commonly used in closed systems of algae cultivation for several reasons. These bags are made from high-density polyethylene (HDPE) and are designed to hold algae cultures in a closed environment, providing an ideal environment for algae growth. V-shaped plastic bags are effective for growing a variety of algae species, including ''Chlorella'', ''Spirulina'', and ''Nannochloropsis''.<ref>Chen, Yu Pei; Huang, Yao Hsin; Huang, Hsiang Chin (2021-03-01). "Different plastic-bag type photobioreactor for biomass production of Chlorella species". ''IOP Conference Series: Materials Science and Engineering''. '''1113''' (1): 012004. [[Doi (identifier)|doi]]:10.1088/1757-899x/1113/1/012004. [[ISSN (identifier)|ISSN]] 1757-8981.</ref> The growth rate and biomass yield of ''Chlorella vulgaris'' in V-shaped plastic bags was found to be higher than any other shaped plastic bags. Different designs of plastic bags based PBR is developed from sealing the plastic bags at different places that generated, flat bottom hanging plastic bags, V-shaped hanging plastic bags, horizontally laying plastic bags that serves kind of flat PBR system, etc. Many plastic bag-based designs are proposed but few are utilized on commercial scale due to their productivities. Operation of plastic bags is tedious as they need to be replaced after every use to maintain the sterility, which is a laborious task for large scale facility.<ref>Wang, Bei; Lan, Christopher Q.; Horsman, Mark (2012-07). "Closed photobioreactors for production of microalgal biomasses". ''Biotechnology Advances''. '''30''' (4): 904–912. [[Doi (identifier)|doi]]:10.1016/j.biotechadv.2012.01.019. [[ISSN (identifier)|ISSN]] 0734-9750</ref><ref>Huang, Qingshan; Jiang, Fuhua; Wang, Lianzhou; Yang, Chao (2017-06). "Design of Photobioreactors for Mass Cultivation of Photosynthetic Organisms". ''Engineering''. '''3''' (3): 318–329. [[Doi (identifier)|doi]]:10.1016/j.eng.2017.03.020. [[ISSN (identifier)|ISSN]] 2095-8099</ref>

=== {{anchor|autoflocculation}} Harvesting ===
Algae can be harvested using microscreens, by [[centrifugation]], by [[flocculation]]<ref name="FlocculationMicroalgae">{{cite journal |author1=D. Bilanovic |author2=A. Sukenik |author3=G. Shelef |year=1988 |doi = 10.1016/0144-4565(88)90071-6 |title=Flocculation of microalgae with cationic polymers. Effects of medium salinity |publisher=Elsevier Ltd |journal = Biomass|volume = 17 |issue = 1 |pages=65–76 }}</ref> and by [[froth flotation]].

Interrupting the [[carbon dioxide]] supply can cause algae to flocculate on its own, which is called "autoflocculation".

"[[Chitosan]]", a commercial [[flocculant]], more commonly used for water purification, is far more expensive. The powdered shells of [[crustaceans]] are processed to acquire [[chitin]], a [[polysaccharide]] found in the shells, from which chitosan is derived via [[deacetylation]]. Water that is more [[brackish]], or saline requires larger amounts of flocculant. Flocculation is often too expensive for large operations.

[[Alum]] and [[ferric chloride]] are used as chemical flocculants.

In [[froth]] flotation, the cultivator [[Aerated waters|aerates]] the water into a froth, and then skims the algae from the top.<ref name="FrothingAlgaeHarvest">{{cite journal|author1=Gilbert V. Levin |author2=John R. Clendenning |author3=Ahron Gibor |author4=Frederick D. Bogar |year=1961 |url=http://aem.asm.org/content/10/2/169.full.pdf |title=Harvesting of Algae by Froth Flotation |journal=Applied Microbiology |volume=10 |issue=2 |pages=169–175 |publisher = Research Resources, Inc, Washington, D.C. |doi=10.1128/am.10.2.169-175.1962 |pmid=14464557 |pmc=1057831 |access-date=2006-08-28 }}</ref>

[[Ultrasound]] and other harvesting methods are currently under development.<ref name="UltrasoundAlgaeHarvest">{{cite journal |last1=Bosma |first1=Rouke |last2=Van Spronsen |first2=Wim A |last3=Tramper |first3=Johannes |last4=Wijffels |first4=René H |date=March 2003 |title=Ultrasound, a new separation technique to harvest microalgae |journal=Journal of Applied Phycology |volume=15 |issue=2–3 |pages=143–153 |doi=10.1023/A:1023807011027|bibcode=2003JAPco..15..143B |s2cid=11377093 }}</ref><ref name="AlgaeHarvestNewMethods">{{cite web | url = http://www.freepatentsonline.com/6524486.html |title = Microalgae separator apparatus and method, United States Patent 6524486 |publisher = United States Patent Department | access-date = 2006-08-28}}</ref>

=== Oil extraction ===
{{Main|Algae fuel}}

Algae oils have a variety of commercial and industrial uses, and are extracted through a  variety of methods. Estimates of the cost to extract oil from microalgae vary, but are likely to be around three times higher than that of extracting [[palm oil]].<ref name="chisti">{{cite journal |last = Chisti |first = Y. |title = Biodiesel from microalgae |journal = Biotechnology Advances |volume = 25 |pages = 294–306 |year = 2007 |doi = 10.1016/j.biotechadv.2007.02.001 |pmid = 17350212 |issue = 3|s2cid = 18234512 }}</ref>

==== Physical extraction ====
In the first step of extraction, the oil must be separated from the rest of the algae. The simplest method is mechanical [[crusher|crushing]]. When algae is dried it retains its oil content, which then can be "pressed" out with an [[oil press]]. Different [[strain (biology)|strains]] of algae warrant different methods of oil pressing, including the use of screw, expeller and piston. Many commercial manufacturers of vegetable oil use a combination of mechanical pressing and chemical solvents in extracting oil. This use is often also adopted for algal oil extraction.

Osmotic shock is a sudden reduction in [[osmotic pressure]], this can cause cells in a solution to rupture. Osmotic shock is sometimes used to release cellular components, such as oil.

[[Ultrasound|Ultrasonic]] extraction, a branch of [[sonochemistry]], can greatly accelerate extraction processes. Using an ultrasonic reactor, ultrasonic waves are used to create [[cavitation]] bubbles in a solvent material.  When these bubbles collapse near the cell walls, the resulting [[shock waves]] and liquid jets cause those cells walls to break and release their contents into a solvent.<ref name="Sonochemistry">{{cite web | url = http://www.gov.pe.ca/ftc/index.php3?number=1024819&lang=E |title = Sonochemistry |publisher = Prince Edward Island Government Food Technology Centre | access-date = 2006-08-28}}</ref>  [[Sonication|Ultrasonication]] can enhance basic enzymatic extraction.

==== Chemical extraction ====
[[Chemical solvents]] are often used in the extraction of the oils.  The downside to using solvents for oil extraction are the dangers involved in working with the chemicals. Care must be taken to avoid exposure to vapors and skin contact, either of which can cause serious health damage. Chemical solvents also present an explosion hazard.<ref name="HexaneRisks">{{cite web|url=http://www.healthfromthesun.com/HexaneFreePg.htm |title=Essential Fatty Acids and Herb FAQ's: What are the hazards of Hexane? |publisher=Health From The Sun |access-date=2006-08-28 |url-status=dead |archive-url=https://web.archive.org/web/20060620174335/http://www.healthfromthesun.com/HexaneFreePg.htm |archive-date=2006-06-20 }}</ref>

A common choice of [[chemical solvent]] is [[hexane]], which is widely used in the food industry and is relatively inexpensive. [[Benzene]] and [[diethyl ether|ether]] can also separate oil.  Benzene is classified as a [[carcinogen]].

Another method of chemical solvent extraction is [[Soxhlet]] extraction.  In this method, oils from the algae are extracted through repeated washing, or [[percolation]], with an organic solvent such as [[hexane]] or [[petroleum ether]], under [[reflux]] in a special glassware.<ref name="AutoSoxhletExtraction">{{cite web| url= http://www.cyberlipid.org/extract/extr0010.htm| title= Automatic soxhlet extraction| publisher= cyberlipid.org| access-date= 2006-08-28| archive-url= https://web.archive.org/web/20060927163406/http://www.cyberlipid.org/extract/extr0010.htm| archive-date= 27 September 2006| url-status= dead}}</ref>  The value of this technique is that the solvent is reused for each cycle.

[[Enzymatic]] extraction uses enzymes to degrade the cell walls with water acting as the solvent. This makes [[fractionation]] of the oil much easier. The costs of this extraction process are estimated to be much greater than hexane extraction.<ref name="EnzymaticExtraction">{{cite web | url = http://www.p2pays.org/ref/10/09365.htm |title = Aqueous Enzymatic Extraction of Oil from Rapeseeds |publisher = Institute for Applied Environmental Economics | access-date = 2006-08-28}}</ref>

[[Supercritical fluid|Supercritical]] CO<sub>2</sub> can also be used as a solvent.  In this method, [[carbon dioxide|CO<sub>2</sub>]] is liquefied under pressure and heated to the point that it becomes supercritical (having properties of both a liquid and a gas), allowing it to act as a solvent.<ref name="supercriticalfluids1">{{cite web|url=http://www.supercriticalfluids.com/faqs.htm |archive-url=https://web.archive.org/web/20041215012744/http://www.supercriticalfluids.com/faqs.htm |url-status=dead |archive-date=2004-12-15 |title=How Do Supercritical Fluids Work? |publisher=Supercritical Fluid Technologies |access-date=2006-08-28 }}</ref><ref name="supercriticalfluids2">{{cite web| url= http://www.phasex4scf.com/supercritical_markets/supercritical_fluids_nutraceuticals.htm| title= Nutraceuticals and Supercritical Fluid Applications: Production of Astaxanthin Concentrate| publisher= Phasex| access-date= 2006-08-28| archive-url= https://web.archive.org/web/20060827192259/http://www.phasex4scf.com/supercritical_markets/supercritical_fluids_nutraceuticals.htm| archive-date= 27 August 2006| url-status= dead}}</ref>

Other methods are still being developed, including ones to extract specific types of oils, such as those with a high production of long-chain highly unsaturated fatty acids.<ref name="UltrasoundAlgaeHarvest" /><ref name="AlgaeHarvestNewMethods" />

== Algal culture collections ==
Specific algal strains can be acquired from algal culture collections, with over 500 culture collections registered with the World Federation for Culture Collections.<ref>{{cite web|url=http://wdcm.nig.ac.jp/hpcc.html|title=Home Pages of Culture Collections in the World|date=10 December 2009|access-date=10 December 2009|archive-url=https://web.archive.org/web/20091121031600/http://wdcm.nig.ac.jp/hpcc.html|archive-date=21 November 2009|url-status=dead}}</ref>

== See also ==
{{div col}}
* {{annotated link|Algal bloom}}
* {{annotated link|Algal nutrient solution}}
* {{annotated link|Aquatic Species Program}}
* {{annotated link|Biological hydrogen production (Algae)}}
* {{annotated link|Biofuel}}
* {{annotated link|Bio Fuel Systems}}
* {{annotated link|Biotechnology}}
* {{annotated link|Carrageenan}}
* {{annotated link|Photobioreactor}}
* {{annotated link|Seaweed farming}}
* {{annotated link|SERI microalgae culture collection}}
* {{annotated link|Vitamin B12}}
{{div col end}}

== Sources ==
{{Free-content attribution
| title = In brief, The State of World Fisheries and Aquaculture, 2018
| author = FAO
| publisher = FAO
| page numbers = 
| source = 
| documentURL = http://www.fao.org/3/ca0191en/ca0191en.pdf
| license statement URL = https://commons.wikimedia.org/wiki/File:In_brief,_The_State_of_World_Fisheries_and_Aquaculture,_2018.pdf
| license = CC BY-SA 3.0 IGO
}}

== References ==
{{Reflist|30em}}

== External links ==
* {{cite journal |last1=Greene |first1=Charles |display-authors=et al. |title=Transforming the Future of Marine Aquaculture: A Circular Economy Approach |journal=Oceanography |date=2022 |pages=26–34 |doi=10.5670/oceanog.2022.213 |doi-access=free}}
* {{cite journal |last1=Diaz |first1=Crisandra J. |display-authors=et al. |title=Developing algae as a sustainable food source |journal=Frontiers in Nutrition |date=2023 |volume=9 |doi=10.3389/fnut.2022.1029841 |pmid=36742010 |pmc=9892066 |doi-access=free}}
* {{Cite journal |last1=Greene |first1=Charles |display-authors=et al. |date=2016-12-04 |title=Marine Microalgae: Climate, Energy, and Food Security from the Sea |url=https://tos.org/oceanography/article/marine-microalgae-climate-energy-and-food-security-from-the-sea |journal=Oceanography |volume=29 |issue=4 |doi=10.5670/oceanog.2016.91 |doi-access=free |hdl=11250/2436441 |hdl-access=free }}
* [https://web.archive.org/web/20060504040833/http://www.sas.org/tcs/weeklyIssues/2004-10-15/feature2/ www.sas.org] How to Rear a Plankton Menagerie (home grow micro algae in soda bottles)
* [https://web.archive.org/web/20060427082806/http://io.uwinnipeg.ca/~simmons/ysesp/contents.htm io.uwinnipeg.ca] breeding algae in batch and continuous flow systems on small scale
* [http://www.teachingboxes.org/upwelling/lessons/lesson2_activity1.jsp Making Algae Grow] {{Webarchive|url=https://web.archive.org/web/20090704080054/http://www.teachingboxes.org/upwelling/lessons/lesson2_activity1.jsp |date=2009-07-04 }}
* [http://www.unu.edu/unupress/unupbooks/80434e/80434E0f.htm www.unu.edu] {{Webarchive|url=https://web.archive.org/web/20070216113653/http://www.unu.edu/unupress/unupbooks/80434e/80434E0f.htm |date=2007-02-16 }} Indian experience with algal ponds
* [https://web.archive.org/web/20121003075521/http://www.renewableenergyworld.com/rea/u/gerd-kloeck-141049/blog Blog Posts | gerd-kloeck-141049 | Renewable Energy World] List of companies involved in microalgae production.
* [http://library.wur.nl/wda/dissertations/dis3423.pdf Photobioreactors : Scale-up and optimisation] PhD thesis Wageningen UR.
* [http://www.algae.wur.nl/uk/ Research on algae within Wageningen UR]
* [http://www.malawicichlidhomepage.com/aquainfo/greenwater1.JPG Photobioreactor using polyethylene and chicken wire] {{Webarchive|url=https://web.archive.org/web/20091225204454/http://www.malawicichlidhomepage.com/aquainfo/greenwater1.JPG |date=2009-12-25 }}.
* [https://archive.today/20130126070713/http://www.instructables.com/id/Simple_Algae_Home_CO2_Scrubber_Part_II_Culturing Instructables.com – Simple Home Algae Culture and Breeding]
* [http://www.microphyt.eu/en/ Microphyt – Microalgae Production and Photobioreactor Design] {{Webarchive|url=https://web.archive.org/web/20200221192135/http://www.microphyt.eu/en |date=2020-02-21 }}
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