Algaculture is a form of
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 ...
involving the farming of species of
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...
.
The majority of algae that are intentionally cultivated fall into the category of
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 ...
(also referred to as
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
...
,
microphytes
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 individ ...
, or
planktonic algae
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning ' plant', and (), meaning 'wanderer' or 'drifter'. ...
).
Macroalgae
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
, commonly known as
seaweed
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and '' Chlorophyta'' (green) macroalgae. Seaweed species such as ...
, 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 scrubbers using upflowing air bubbles in small containers).
Commercial and industrial algae cultivation has numerous uses, including production of
nutraceutical
A nutraceutical or bioceutical is a pharmaceutical alternative which claims physiological benefits. In the US, "nutraceuticals" are largely unregulated, as they exist in the same category as dietary supplements and food additives by the FDA, un ...
s such as
omega-3 fatty acids
Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chem ...
(as algal oil) or natural food
colorants and
dyes
A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution an ...
,
food
Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is in ...
,
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s,
bioplastics
Bioplastics are plastic materials produced from renewable biomass sources, such as vegetable fats and oils, corn starch, straw, woodchips, sawdust, recycled food waste, etc. Some bioplastics are obtained by processing directly from natural bi ...
, chemical feedstock (raw material), protein-rich animal/
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 ...
feed,
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 re ...
, and
algal fuel,
and can also be used as a means of
pollution control
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...
.
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.
Cultured microalgae already contribute to a wide range of sectors in the emerging
bioeconomy. Research suggests there are large potentials and benefits of algaculture for the development of a future
healthy
Health, according to the World Health Organization, is "a state of complete physical, mental and social well-being and not merely the absence of disease and infirmity".World Health Organization. (2006)''Constitution of the World Health Organiz ...
and
sustainable food system.
Growing, harvesting, and processing algae
Monoculture
Most growers prefer monocultural production and go to considerable lengths to maintain the purity of their cultures. However, the microbiological contaminants are still under investigation.
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
A serial dilution is the stepwise dilution of a substance in solution. Usually the dilution factor at each step is constant, resulting in a geometric progression of the concentration in a logarithmic fashion. A ten-fold serial dilution could be ...
. 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
''Dunaliella'' is a single-celled, photosynthetic green alga, that is characteristic for its ability to outcompete other organisms and thrive in hypersaline environments. It is mostly a marine organism, though there are a few freshwater species ...
'' 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
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...
. First, the cultivator filters the sea water to remove algae which are too large for the
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
...
e to eat. Next, the cultivator adds nutrients and possibly
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
Water,
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
, 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. 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
A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
'' 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 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 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.
Paddle wheel
A paddle wheel is a form of waterwheel or impeller in which a number of paddles are set around the periphery of the wheel. It has several uses, of which some are:
* Very low-lift water pumping, such as flooding paddy fields at no more than a ...
s can stir the water and
compressed air
Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, an ...
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 plates made from sheets of plastic or glass and placed within the
tank
A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and good battlefield mobility provided by tracks and a powerful ...
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
A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg; a ...
,
swamps
A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...
, and other stagnant waters can be due to oxygen depletion caused by the decay of deceased
algal bloom
An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompass ...
s. Under
anoxic
The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts:
* Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...
conditions, the bacteria inhabiting algae cultures break down the organic material and produce
hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...
and
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
, which causes the odor. This
hypoxia often results in the death of aquatic animals. In a system where algae is intentionally cultivated, maintained, and harvested, neither
eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phyt ...
nor hypoxia are likely to occur.
Some living algae and bacteria also produce odorous chemicals, particularly certain
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, bl ...
(previously classed as blue-green algae) such as ''
Anabaena
''Anabaena'' is a genus of filamentous cyanobacteria that exist as plankton. They are known for nitrogen-fixing abilities, and they form symbiotic relationships with certain plants, such as the mosquito fern. They are one of four genera of cyan ...
''. The most well known of these odor-causing chemicals are MIB (
2-methylisoborneol) and
geosmin
Geosmin ( ) is an irregular sesquiterpenoid, produced from the universal sesquiterpene precursor farnesyl pyrophosphate (also known as farnesyl diphosphate), in a two-step -dependent reaction. Geosmin, along with the irregular monoterpene 2-met ...
. 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
Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, ...
treatment and distribution. Cyanobacteria can also produce chemical toxins that have been a problem in drinking water.
Nutrients
Nutrients such as
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
(N),
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
(P), and
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...
(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
2 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
Open ponds
Raceway-type ponds and lakes are open to the elements.
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.
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
''Chlorella'' is a genus of about thirteen species of single-celled green algae belonging to the division Chlorophyta. The cells are spherical in shape, about 2 to 10 μm in diameter, and are without flagella. Their chloroplasts contain th ...
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
A diatom ( Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising se ...
s since they can be filtered from a stream of water flowing through an
outflow pipe
Pipe(s), PIPE(S) or piping may refer to:
Objects
* Pipe (fluid conveyance), a hollow cylinder following certain dimension rules
** Piping, the use of pipes in industry
* Smoking pipe
** Tobacco pipe
* Half-pipe and quarter pipe, semi-circular ...
. A "
pillow case
A pillow is a support of the body at rest for comfort, therapy, or decoration. Pillows are used in different variations by many species, including humans. Some types of pillows include throw pillows, body pillows, decorative pillows, and man ...
" of a fine
mesh
A mesh is a barrier made of connected strands of metal, fiber, or other flexible or ductile materials. A mesh is similar to a web or a net in that it has many attached or woven strands.
Types
* A plastic mesh may be extruded, oriented, exp ...
cloth is tied over the outflow pipe allowing other algae to escape. The chain diatoms are held in the bag and feed
shrimp
Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are ref ...
larvae (in Eastern
hatcheries
A hatchery is a facility where eggs are hatched under artificial conditions, especially those of fish, poultry or even turtles. It may be used for ex-situ conservation purposes, i.e. to breed rare or endangered species under controlled condi ...
) and
inoculate
Inoculation is the act of implanting a pathogen or other microorganism. It may refer to methods of artificially inducing immunity against various infectious diseases, or it may be used to describe the spreading of disease, as in "self-inoculati ...
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''.
Photobioreactors
Algae can also be grown in a
photobioreactor Moss photobioreactor to cultivate Physcomitrella_patens.html"_;"title="mosses_like_''Physcomitrella_patens">mosses_like_''Physcomitrella_patens''_at_the_laboratory_scale
A_photobioreactor_(PBR)_refers_to_any_cultivation_system_designed_for_growin ...
(PBR). A PBR is a
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 process is carried out which involves organisms or biochemically active substance ...
which incorporates a light source. Virtually any
translucent
In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable scattering of light. On a macroscopic scale (one in which the dimensions ...
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 .
A PBR can operate in "
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 "
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.
Different types of suspended culture PBRs include:
*
Tank
A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and good battlefield mobility provided by tracks and a powerful ...
s
*
Polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including b ...
sleeves or bags
* Glass or plastic
tubes.
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.
Harvesting
Algae can be harvested using microscreens, by
centrifugation
Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The denser components of the mixture migrate ...
, by
flocculation
Flocculation, in the field of chemistry, is a process by which colloidal particles come out of suspension to sediment under the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from ...
and by
froth flotation
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in mineral processing, paper recycling and waste-water treatment industries. Historically this was first used in the mining industry, wher ...
.
Interrupting the
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
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
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean g ...
are processed to acquire
chitin
Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
, a
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 w ...
found in the shells, from which chitosan is derived via
deacetylation
:
In organic chemistry, acetylation is an organic esterification reaction with acetic acid. It introduces an acetyl group into a chemical compound. Such compounds are termed ''acetate esters'' or simply '' acetates''. Deacetylation is the oppo ...
. Water that is more
brackish
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estua ...
, or saline requires larger amounts of flocculant. Flocculation is often too expensive for large operations.
Alum
An alum () is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula , where is a monovalent cation such as potassium or ammonium. By itself, "alum" often refers to potassium alum, with the ...
and
ferric chloride
Iron(III) chloride is the inorganic compound with the formula . Also called ferric chloride, it is a common compound of iron in the +3 oxidation state. The anhydrous compound is a crystalline solid with a melting point of 307.6 °C. The col ...
are other chemical flocculants.
In
froth flotation, the cultivator
aerates the water into a froth, and then skims the algae from the top.
Ultrasound
Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies ...
and other harvesting methods are currently under development.
Oil extraction
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
Palm oil is an edible vegetable oil derived from the mesocarp (reddish pulp) of the fruit of the oil palms. The oil is used in food manufacturing, in beauty products, and as biofuel. Palm oil accounted for about 33% of global oils produced fr ...
.
Physical extraction
In the first step of extraction, the oil must be separated from the rest of the algae. The simplest method is mechanical
crushing. When algae is dried it retains its oil content, which then can be "pressed" out with an
oil press. Different
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
Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane.
It is also defined as the measure of the tendency of a solution to take in a pure ...
, this can cause cells in a solution to rupture. Osmotic shock is sometimes used to release cellular components, such as oil.
Ultrasonic extraction, a branch of
sonochemistry, can greatly accelerate extraction processes. Using an ultrasonic reactor, ultrasonic waves are used to create
cavitation
Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, ca ...
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.
Ultrasonication
image:Sonicator.jpg, A sonicator at the Weizmann Institute of Science during sonicationSonication is the act of applying sound energy to agitate particles in a sample, for various purposes such as the extraction of multiple compounds from plants, m ...
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.
A common choice of
chemical solvent is
hexane
Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14.
It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relative ...
, which is widely used in the food industry and is relatively inexpensive.
Benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
and
ether
In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again ...
can also separate oil. Benzene is classified as a
carcinogen
A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive sub ...
.
Another method of chemical solvent extraction is
Soxhlet extraction. In this method, oils from the algae are extracted through repeated washing, or
percolation
Percolation (from Latin ''percolare'', "to filter" or "trickle through"), in physics, chemistry and materials science, refers to the movement and filtering of fluids through porous materials.
It is described by Darcy's law.
Broader applicatio ...
, with an organic solvent such as
hexane
Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14.
It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relative ...
or
petroleum ether
Petroleum ether is the petroleum fraction consisting of aliphatic hydrocarbons and boiling in the range 35–60 °C, and commonly used as a laboratory solvent. Despite the name, petroleum ether is not classified as an ether; the term is used ...
, under
reflux in a special glassware.
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.
Supercritical CO
2 can also be used as a solvent. In this method,
CO2 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.
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.
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.
Uses of algae
Food
Several species of algae are raised for food. Micro-algae can be used to create
microbial protein.
* Purple laver (''
Porphyra
''Porphyra'' is a genus of coldwater seaweeds that grow in cold, shallow seawater. More specifically, it belongs to red algae phylum of laver species (from which comes laverbread), comprising approximately 70 species.Brodie, J.A. and Irvine, ...
'') is perhaps the most widely domesticated marine algae.
[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. ] In Asia it is used in
nori
Nori is a dried edible seaweed used in Japanese cuisine, made from species of the red algae genus '' Pyropia'', including ''P. yezonesis'' and '' P. tenera''. It has a strong and distinctive flavor, and is often used to wrap rolls of sushi or ...
(
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 n ...
) and
gim (
Korea
Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic ...
). In
Wales
Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...
, it is used in
laverbread
Laverbread (; cy, bara lafwr or '; ga, sleabhac) is a food product made from laver, an edible seaweed (littoral alga) consumed mainly in Wales as part of local traditional cuisine. The seaweed is commonly found around the west coast of Great ...
, a traditional food, and in
Ireland
Ireland ( ; ga, Éire ; Ulster-Scots: ) is an island in the North Atlantic Ocean, in north-western Europe. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the s ...
it is collected and made into a
jelly by
stewing or
boiling
Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere. Th ...
. Preparation also can involve frying or heating the
frond
A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...
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
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
, and in
Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
and
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
.
* Dulse (''
Palmaria palmata
''Palmaria palmata'', also called dulse, dillisk or dilsk (from Irish/Scottish Gaelic '/'), red dulse, sea lettuce flakes, or creathnach, is a red alga (Rhodophyta) previously referred to as ''Rhodymenia palmata''. It grows on the northern coast ...
'') is a red species sold in
Ireland
Ireland ( ; ga, Éire ; Ulster-Scots: ) is an island in the North Atlantic Ocean, in north-western Europe. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the s ...
and Atlantic
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...
. It is eaten raw, fresh, dried, or cooked like
spinach
Spinach (''Spinacia oleracea'') is a leafy green flowering plant native to central and western Asia. It is of the order Caryophyllales, family Amaranthaceae, subfamily Chenopodioideae. Its leaves are a common edible vegetable consumed either f ...
.
*
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
A dietary supplement is a manufactured product intended to supplement one's diet by taking a pill, capsule, tablet, powder, or liquid. A supplement can provide nutrients either extracted from food sources or that are synthetic in order ...
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
Lake Texcoco ( es, Lago de Texcoco) was a natural lake within the "Anahuac" or Valley of Mexico. Lake Texcoco is best known as where the Aztecs built the city of Tenochtitlan, which was located on an island within the lake. After the Spanish con ...
in central Mexico.
The plants produce a variety of nutrients and high amounts of
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
. Spirulina is often used commercially as a nutritional supplement.
* ''
Chlorella
''Chlorella'' is a genus of about thirteen species of single-celled green algae belonging to the division Chlorophyta. The cells are spherical in shape, about 2 to 10 μm in diameter, and are without flagella. Their chloroplasts contain th ...
'', another popular microalgae, has similar nutrition to spirulina. ''Chlorella'' 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 n ...
. It is also used as a nutritional supplement with possible effects on metabolic rate.
* Irish moss (''
Chondrus crispus
''Chondrus crispus''—commonly called Irish moss or carrageen moss (Irish ''carraigín'', "little rock")—is a species of red algae which grows abundantly along the rocky parts of the Atlantic coast of Europe and North America. In its fres ...
''), often confused with ''
Mastocarpus stellatus
''Mastocarpus stellatus,'' commonly known as carrageenan moss or false Irish moss, is a species in the Rhodophyceae division, a red algae seaweed division, and the Phyllophoracea family. ''M. stellatus'' is closely related to Irish Moss (''Cho ...
'', is the source of
carrageenan
Carrageenans or carrageenins ( ; ) are a family of natural linear sulfated polysaccharides that are extracted from red edible seaweeds. Carrageenans are widely used in the food industry, for their gelling, thickening, and stabilizing properties. T ...
, 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
fining agent.
*
Sea lettuce
The sea lettuces comprise the genus ''Ulva'', a group of edible green algae that is widely distributed along the coasts of the world's oceans. The type species within the genus ''Ulva'' is ''Ulva lactuca'', wikt:lactuca, ''lactuca'' being Latin ...
(''
Ulva lactuca
''Ulva lactuca'', also known by the common name sea lettuce, is an edible green alga in the family Ulvaceae. It is the type species of the genus ''Sea lettuce, Ulva''. A synonym is ''U. fenestrata'', referring to its "windowed" or "holed" appeara ...
''), is used in
Scotland
Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to ...
, where it is added to soups and salads.
* Dabberlocks or badderlocks (''
Alaria esculenta'') is eaten either fresh or cooked in
Greenland
Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...
,
Iceland
Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its ...
, Scotland and Ireland.
* ''
Aphanizomenon flos-aquae'' is a
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, bl ...
similar to spirulina, which is used as a nutritional supplement.
* Extracts and oils from algae are also used as additives in various food products.
The plants also produce
Omega-3 and
Omega-6
Omega-6 fatty acids (also referred to as ω-6 fatty acids or ''n''-6 fatty acids) are a family of polyunsaturated fatty acids that have in common a final carbon-carbon double bond in the ''n''-6 position, that is, the sixth bond, counting from ...
fatty acids
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an B ...
, which are commonly found in
fish oils, and which have been shown to have positive health benefits.
*''Sargassum'' species are an important group of seaweeds. These algae have many
phlorotannins.
* Cochayuyo (''
Durvillaea antarctica'') is eaten in salads and ceviche in Peru and Chile.
*Both microalgae and macroalgae are used to make
agar
Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from ogonori (''Gracilaria'') and "tengusa" (''Gelidiaceae''). As found in nature, agar i ...
(see below), which is used as a
gelling agent
A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state, although the liquid phase may still dif ...
in foods.
Lab manipulation
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 M ...
in
Adelaide
Adelaide ( ) is the capital city of South Australia, the state's largest city and the fifth-most populous city in Australia. "Adelaide" may refer to either Greater Adelaide (including the Adelaide Hills) or the Adelaide city centre. The dem ...
have been experimenting with using marine microalgae to produce proteins for human consumption, creating products like "
caviar
Caviar (also known as caviare; from fa, خاویار, khâvyâr, egg-bearing) is a food consisting of salt-cured roe of the family Acipenseridae. Caviar is considered a delicacy and is eaten as a garnish or a spread. Traditionally, the te ...
",
vegan
Veganism is the practice of abstaining from the use of animal product—particularly in diet—and an associated philosophy that rejects the commodity status of animals. An individual who follows the diet or philosophy is known as a vegan. ...
burgers,
fake meat,
jams and other
food spread
A spread is a food that is spread, generally with a knife, onto foods such as bread and 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 cheeses are typic ...
s. By manipulating microalgae in a
laboratory
A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physi ...
, the
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
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 excre ...
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
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
, which contributes to the
greenhouse gases
A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), methane ...
.
Fertilizer and agar
For centuries
seaweed
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and '' Chlorophyta'' (green) macroalgae. Seaweed species such as ...
has been used as
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
. It is also an excellent source of
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...
for manufacture of
potash
Potash () includes various mined and manufactured salts that contain potassium in water- soluble form. and
potassium nitrate
Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and ...
. Also some of microalgae can be used like this.
Both microalgae and macroalgae are used to make
agar
Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from ogonori (''Gracilaria'') and "tengusa" (''Gelidiaceae''). As found in nature, agar i ...
.
Pollution control
With concern over
global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
, new methods for the thorough and efficient
capture of CO2 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
2 and accelerating algae growth. Untreated
sewage
Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from reside ...
can supply additional nutrients, thus turning two pollutants into valuable commodities.
[
]
Waste high-purity as well as sequestered carbon from the atmosphere can be used, with potential significant benefits for
climate change mitigation
Climate change mitigation is action to limit climate change by reducing emissions of greenhouse gases or removing those gases from the atmosphere. The recent rise in global average temperature is mostly caused by emissions from fossil fuels bu ...
.
Algae cultivation is under study for uranium/plutonium sequestration and purifying fertilizer runoff.
Energy production
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. See
Algae fuel
Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels that uses algae as its source of energy-rich oils. Also, algae fuels are an alternative to commonly known biofuel sources, such as corn and sugarcane. When made fr ...
.
Microalgae are also researched for
hydrogen production
Hydrogen production is the family of industrial methods for generating hydrogen gas. As of 2020, the majority of hydrogen (∼95%) is produced from fossil fuels by steam reforming of natural gas and other light hydrocarbons, partial oxidation of ...
– e.g. micro-droplets for algal cells or synergistic algal-bacterial multicellular
spheroid
A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. A spheroid has ...
microbial reactors capable
of producing oxygen as well as hydrogen via photosynthesis in daylight under air.
Microgeneration
Other uses
''Chlorella'', particularly a transgenic strain which carries an extra mercury
reductase
A reductase is an enzyme that catalyzes a reduction reaction.
Examples
* 5α-Reductase
* 5β-Reductase
* Dihydrofolate reductase
* HMG-CoA reductase
* Methemoglobin reductase
* Ribonucleotide reductase
* Thioredoxin reductase
* ''E. coli' ...
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
, has been studied as an agent for
environmental remediation
Environmental remediation deals with the removal of pollution or contaminants from environmental media such as soil, groundwater, sediment, or surface water. Remedial action is generally subject to an array of regulatory requirements, and may al ...
due to its ability to reduce to the less toxic elemental mercury.
Cultured strains of a common coral microalgal
endosymbiont
An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.
(The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...
s are researched as a potential way to increase corals' thermal tolerance for
climate resilience
Climate resilience is defined as the "capacity of social, economic and ecosystems to cope with a hazardous event or trend or disturbance".IPCC, 2022Summary for Policymakers .-O. Pörtner, D.C. Roberts, E.S. Poloczanska, K. Mintenbeck, M. Tignor, ...
and
bleaching tolerance.
Cultured microalgae is used in research and development for potential medical applications, in particular for
microbot
''MicroBot'' is a twin-stick shooter video game developed by Naked Sky Entertainment and published by Electronic Arts. It was released on the Xbox 360 via Xbox Live Arcade on December 29, 2010, and on PlayStation 3 via the PlayStation Netwo ...
s
such as
biohybrid microswimmers
A biohybrid microswimmer can be defined as a microswimmer that consist of both biological and artificial constituents, for instance, one or several living microorganisms attached to one or various synthetic parts.
In recent years nanoscopic and m ...
for
targeted drug delivery.
Cultivated algae serve many other purposes, including cosmetics,
[Starckx, Senne (31 October 2012]
A place in the sun - Algae is the crop of the future, according to researchers in Geel
Flanders Today, Retrieved 8 December 2012 animal feed,
[ bioplastic production, dyes and colorant production, chemical ]feedstock
A raw material, also known as a feedstock, unprocessed material, or primary commodity, is a basic material that is used to produce goods, finished goods, energy, or intermediate materials that are feedstock for future finished products. As feeds ...
production, and pharmaceutical ingredients.
See also
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
Sources
References
External links
*
www.sas.org
How to Rear a Plankton Menagerie (home grow micro algae in soda bottles)
breeding algae in batch and continuous flow systems on small scale
Making Algae Grow
Indian experience with algal ponds
Blog Posts , gerd-kloeck-141049 , Renewable Energy World
List of companies involved in microalgae production.
Photobioreactors : Scale-up and optimisation
PhD thesis Wageningen UR.
Research on algae within Wageningen UR
Photobioreactor using polyethylene and chicken wire
.
Instructables.com - Simple Home Algae Culture and Breeding
Microphyt - Microalgae Production and Photobioreactor Design
*
{{plankton