Culture of microalgae in hatcheries
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Microalgae Microalgae or microphytes are microscopic algae invisible to the naked eye. They are phytoplankton typically found in freshwater and marine systems, living in both the water column and sediment. They are unicellular species which exist indiv ...
or microscopic algae grow in either marine or freshwater systems. They are primary producers in the oceans that convert water and carbon dioxide to
biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
and oxygen in the presence of sunlight. The oldest documented use of microalgae was 2000 years ago, when the Chinese used the
cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...
''
Nostoc ''Nostoc'', also known as star jelly, troll’s butter, spit of moon, fallen star, witch's butter (not to be confused with the fungi commonly known as witches' butter), and witch’s jelly, is the most common genus of cyanobacteria found in vari ...
'' as a food source during a famine. Another type of microalgae, the cyanobacteria ''
Arthrospira ''Arthrospira'' is a genus of free-floating filamentous cyanobacteria characterized by cylindrical, multicellular trichomes in an open left-hand helix. A dietary supplement is made from ''A. platensis'' and ''A. maxima'', known as spirulina. ...
'' ( Spirulina), was a common food source among populations in Chad and Aztecs in Mexico as far back as the 16th century.Whitton, B., and M. Potts. 2000
''The ecology of Cyanobacteria: their diversity in time and space''
p. 506, Kluwer Academic. .
Today cultured microalgae is used as direct feed for humans and land-based farm animals, and as feed for cultured aquatic species such as molluscs and the early larval stages of fish and crustaceans. It is a potential candidate for
biofuel Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. According to the United States Energy Information Administration (E ...
production. Microalgae can grow 20 or 30 times faster than traditional food crops, and has no need to compete for arable land. Since microalgal production is central to so many commercial applications, there is a need for production techniques which increase productivity and are economically profitable.


Commonly cultivated microalgae species


Hatchery production techniques

A range of microalgae species are produced in hatcheries and are used in a variety of ways for commercial purposes. Studies have estimated main factors in the success of a microalgae hatchery system as the dimensions of the container/bioreactor where microalgae is cultured, exposure to light/ irradiation and concentration of cells within the reactor.


Open pond system

This method has been employed since the 1950s across the CONUS. There are two main advantages of culturing microalgae using the
open pond Algaculture is a form of aquaculture involving the farming of species of algae. The majority of algae that are intentionally cultivated fall into the category of microalgae (also referred to as phytoplankton, microphytes, or planktonic algae). Mac ...
system. Firstly, an open pond system is easier to build and operate. Secondly, open ponds are cheaper than closed bioreactors because closed bioreactors require a cooling system. However, a downside to using open pond systems is decreased productivity of certain commercially important strains such as ''Arthrospira sp.'', where optimal growth is limited by temperature. That said, it is possible to use waste heat and from industrial sources to compensate this.


Air-lift method

This method is used in outdoor cultivation and production of microalgae; where air is moved within a system in order to circulate water where microalgae is growing. The culture is grown in transparent tubes that lie horizontally on the ground and are connected by a network of pipes. Air is passed through the tube such that air escapes from the end that rests inside the reactor that contains the culture and creates an effect like stirring.


Closed reactors

The biggest advantage of culturing microalgae within a closed system provides control over the physical, chemical and biological environment of the culture. This means factors that are difficult to control in open pond systems such as evaporation, temperature gradients and protection from ambient contamination make closed reactors favoured over open systems. Photobioreactors are the primary example of a closed system where abiotic factors can be controlled for. Several closed systems have been tested to date for the purposes of culturing microalgae, few important ones are mentioned below:


Horizontal photobioreactors

This system includes tubes laid on the ground to form a network of loops. Mixing of microalgal suspended culture occurs through a pump that raises the culture vertically at timed intervals into a
photobioreactor image:Bioreaktor quer2.jpg, Moss bioreactor, Moss photobioreactor to cultivate mosses like ''Physcomitrella patens'' at the laboratory scale A photobioreactor (PBR) refers to any cultivation system designed for growing Photoautotrophism, photoautotr ...
. Studies have found pulsed mixing at intervals produces better results than the use of continuous mixing. Photobioreactors have also been associated with better production than open pond systems as they can maintain better temperature gradients. An example noted in higher production of ''Arthrospira sp.'' used as a dietary supplement was attributed to higher productivity because of a better suited temperature range and an extended cultivation period over summer months.


Vertical systems

These reactors use vertical polyethylene sleeves hung from an iron frame. Glass tubes can also be used alternatively. Microalgae are also cultured in vertical alveolar panels (VAP) that are a type of
photobioreactor image:Bioreaktor quer2.jpg, Moss bioreactor, Moss photobioreactor to cultivate mosses like ''Physcomitrella patens'' at the laboratory scale A photobioreactor (PBR) refers to any cultivation system designed for growing Photoautotrophism, photoautotr ...
. This photobioreactor is characterised by low productivity. However, this problem can be overcome by modifying the
surface area The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of arc ...
to volume ratio; where a higher ratio can increase productivity. Mixing and deoxygenation are drawbacks of this system and can be addressed by bubbling air continuously at a mean flow rate. The two main types of vertical photobioreactors are the Flow-through VAP and the Bubble Column VAP.


In darkness

By using an electrocatalytic process to produce
acetate An acetate is a salt (chemistry), salt formed by the combination of acetic acid with a base (e.g. Alkali metal, alkaline, Alkaline earth metal, earthy, Transition metal, metallic, nonmetallic or radical Radical (chemistry), base). "Acetate" als ...
from water, electricity and carbon dioxide, which is then used by the algae as food source, sunlight and photosynthesis is no longer required. The method is still at an early stage, but experiments with algae like Chlamydomonas reinhardtii have turned out to be promising.


Flat plate reactors

Flat plate reactors(FPR) are built using narrow panels and are placed horizontally to maximise sunlight input to the system. The concept behind FPR is to increase the surface area to volume ratio such that sunlight is efficiently used. This system of microalgae culture was originally thought to be expensive and incapable of circulating the culture. Therefore, FPRs were considered to be unfeasible overall for the commercial production of microalgae. However, an experimental FPR system in the 1980s used
circulation Circulation may refer to: Science and technology * Atmospheric circulation, the large-scale movement of air * Circulation (physics), the path integral of the fluid velocity around a closed curve in a fluid flow field * Circulatory system, a bio ...
within the culture from a gas exchange unit across horizontal panels. This overcomes issues of circulation and provides an advantage of an open gas transfer unit that reduces oxygen build up. Examples of successful use of FPRs can be seen in the production of ''Nannochloropsis sp.'' used for its high levels of astaxanthin.


Fermentor-type reactors

Fermentor-type reactors (FTR) are bioreactors where
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...
is carried out. FTRs have not developed hugely in the cultivation of microalgae and pose a disadvantage in the surface area to volume ratio and a decreased efficiency in utilizing sunlight. FTR have been developed using a combination of sun and artificial light have led to lowering production costs. However, information available on large scale counterparts to the laboratory-scale systems being developed is very limited. The main advantage is that extrinsic factors i.e. light can be controlled for and productivity can be enhanced so that FTR can become an alternative for products for the pharmaceutical industry.


Commercial applications


Use in aquaculture

Microalgae is an important source of nutrition and is used widely in the
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
of other organisms, either directly or as an added source of basic nutrients. Aquaculture farms rearing larvae of molluscs, echinoderms, crustaceans and fish use microalgae as a source of nutrition. Low bacteria and high microalgal biomass is a crucial food source for shellfish aquaculture. Microalgae can form the start of a chain of further aquaculture processes. For example, microalgae is an important food source in the aquaculture of brine shrimp. Brine shrimp produce dormant eggs, called cysts, which can be stored for long periods and then hatched on demand to provide a convenient form of live feed for the aquaculture of
larval fish Ichthyoplankton (from Greek: ἰχθύς, , "fish"; and πλαγκτός, , "drifter") are the eggs and larvae of fish. They are mostly found in the sunlit zone of the water column, less than 200 metres deep, which is sometimes called the epip ...
and crustaceans. Other applications of microalgae within aquaculture include increasing the
aesthetic Aesthetics, or esthetics, is a branch of philosophy that deals with the nature of beauty and taste, as well as the philosophy of art (its own area of philosophy that comes out of aesthetics). It examines aesthetic values, often expressed th ...
appeal of finfish bred in captivity. One such example can be noted in the aquaculture of salmon, where microalgae is used to make salmon flesh pinker. This is achieved by the addition of natural pigments containing carotenoids such as astaxanthin produced from the microalgae ''Haematococcus'' to the diet of farmed animals. Two microalgae species, ''I. galbana'' and ''C. calcitrans'' are mostly composed of proteins, which are used to brighten the color of salmon and related species.


Human nutrition

The main species of microalgae grown as health foods are '' Chlorella'' and Spirulina (''
Arthrospira platensis ''Arthrospira platensis'' is a filamentous, gram-negative cyanobacterium. This bacterium is non-nitrogen-fixing photoautotroph. It has been isolated in Chenghai Lake, China, soda lakes of East Africa, and subtropical, alkaline lakes. Morpholog ...
''). The main forms of production occur in small scale ponds with artificial mixers. ''Arthrospira platensis'' is a blue-green microalga 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. It 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. The plants produce a variety of nutrients and high amounts of protein, and is often used commercially as a nutritional supplement. ''Chlorella'' has similar nutrition to spirulina, and is very popular in
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
. It is also used as a nutritional supplement, with possible effects on metabolic rate. Production of long chain omega-3 fatty acids important for human diet can also be cultured through microalgal hatchery systems. Australian scientists at
Flinders University Flinders University is a public research university based in Adelaide, South Australia, with a footprint extending across 11 locations in South Australia and the Northern Territory. Founded in 1966, it was named in honour of British navigator ...
in Adelaide have been experimenting with using marine microalgae to produce proteins for human consumption, creating products like " caviar", vegan burgers,
fake meat A meat alternative or meat substitute (also called plant-based meat or fake meat, sometimes pejoratively) is a food product made from vegetarian or vegan ingredients, eaten as a replacement for meat. Meat alternatives typically approximate qua ...
,
jam Jam is a type of fruit preserve. Jam or Jammed may also refer to: Other common meanings * A firearm malfunction * Block signals ** Radio jamming ** Radar jamming and deception ** Mobile phone jammer ** Echolocation jamming Arts and entertai ...
s and other
food spread A spread is a food that is spread, generally with a knife, onto foods such as bread and Cracker (food), crackers. Spreads are added to food to enhance the flavor or texture of the food, which may be considered bland without it. Butter and soft ch ...
s. By manipulating microalgae in a laboratory, the protein and other
nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
contents could be increased, and flavours changed to make them more palatable. These foods leave a much lighter
carbon footprint A carbon footprint is the total greenhouse gas (GHG) emissions caused by an individual, event, organization, service, place or product, expressed as carbon dioxide equivalent (CO2e). Greenhouse gases, including the carbon-containing gases carbo ...
than other forms of protein, as the microalgae absorb rather than produce carbon dioxide, which contributes to the greenhouse gases.


Biofuel production

In order to meet the demands of
fossil fuels A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels ...
, alternative means of fuels are being investigated. Biodiesel and bioethanol are renewable
biofuel Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. According to the United States Energy Information Administration (E ...
s with much potential that are important in current research. However, agriculture based renewable fuels may not be completely sustainable and thus may not be able to replace fossil fuels. Microalgae can be remarkably rich in oils (up to 80% dry weight of
biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
) suitable for conversion to fuel. Furthermore, microalgae are more productive than land based agricultural crops and could therefore be more sustainable in the long run. Microalgae for
biofuel Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. According to the United States Energy Information Administration (E ...
production is mainly produced using tubular
photobioreactors Moss photobioreactor to cultivate mosses like ''Physcomitrella patens'' at the laboratory scale A photobioreactor (PBR) refers to any cultivation system designed for growing Photoautotrophism">photoautotrophic organisms using artificial light sou ...
.


Pharmaceuticals and cosmetics

Novel bioactive chemical compounds can be isolated from microalgae like sulphated
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wa ...
s. These compounds include fucoidans, carrageenans and ulvans that are used for their beneficial properties. These properties are anticoagulants, antioxidants, anticancer agents that are being tested medical research. Red microalgae are characterised by pigments called
phycobiliprotein Phycobiliproteins are water-soluble proteins present in cyanobacteria and certain algae (rhodophytes, cryptomonads, glaucocystophytes). They capture light energy, which is then passed on to chlorophylls during photosynthesis. Phycobiliproteins are ...
s that contain natural colourants used in
pharmaceuticals A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the medical field and rel ...
and/or cosmetics.


Biofertilizer

Blue green alga was first used as a means of fixing nitrogen by allowing
cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...
to multiply in the soil, acting as a biofertilizer. Nitrogen fixation is important as a means of allowing inorganic compounds such as nitrogen to be converted to
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
forms which can then be used by plants. The use of cyanobacteria is an economically sound and environmentally friendly method of increasing productivity. This method has been use for rice production in India and Iran, using the nitrogen fixing properties of free living cyanobacteria to supplement nitrogen content in soils.


Other uses

Microalgae are a source of valuable molecules such as isotopes i.e. chemical variants of an element that contain different neutrons. Microalgae can effectively incorporate isotopes of carbon (13C), nitrogen (15N) and hydrogen (2H) into their biomass. 13C and 15N are used to track the flow of carbon between different trophic levels/food webs. Carbon, nitrogen and
sulphur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
isotopes can also be used to determine disturbances to bottom dwelling communities that are otherwise difficult to study.


Issues

Cell fragility is the biggest issue that limits the productivity from closed
photobioreactors Moss photobioreactor to cultivate mosses like ''Physcomitrella patens'' at the laboratory scale A photobioreactor (PBR) refers to any cultivation system designed for growing Photoautotrophism">photoautotrophic organisms using artificial light sou ...
. Damage to cells can be attributed to the turbulent flow within the
bioreactor A bioreactor refers to any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical reaction, chemical process is carried out which involves organisms or biochemistry, ...
which is required to create mixing so light is available to all cells.


See also

* Algae fuel *
Microbiofuels Microbiofuels are biofuels produced by microorganisms like bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (bi ...


References

{{fishing industry topics, expanded=aquaculture Algaculture