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Algaculture is a form of aquaculture involving the farming of species of algae for purposes of producing food or other products that can be extracted from the cultivated species. The focus of this article is on the cultivation and uses of microalgae, (also known as phytoplankton, microphytes, or planktonic algae), and cyanobacteria.

Cultivation

Algae can be cultured in raceway-type ponds and lakes * Due to the fact that these systems are "open" to the elements, sometimes called "open-pond" systems, they are much more vulnerable to being invaded by other algal species and bacteria. The number of species that have been successfully cultivated for a given purpose, (ie: as a food source, for oil production, or for pigments.), in an outdoor system, are relatively small. In open systems you do not have control over water temperature, and you have little control over lighting conditions. The growing season is largely dependent on location and, aside from tropical areas, is limited to the warmer months. Some of the benefits of this type of system are that it is one of the cheaper ones to produce - at the most basic you only need to dig a trench or pond. It also has one of the largest production capacities compared to other systems, and depending on how large it's made. A variation on the basic "open-pond" system is to close it off, to cover a pond or pool with a greenhouse. While this usually results in a smaller system, (for economic reasons), it does take care of many of the problems associated with an open system. It allows more species to be able to be grown, it allows the species that are being grown to stay dominant, and it extends the growing season, only slightly if unheated, and if heated it can produce year round.

Algae can be grown in a photobioreactor. A photobioreactor is basically a bioreactor which incorporates some type of light source. While almost anything that it would be possible to grow algae in could technically be called a photobioreactor, the term is more commonly used to define a closed system, as opposed to an open tank, or pond. Because these systems are closed, when used to cultivate algae, everything that the algae need to grow, (carbon dioxide, nutrient-rich water and light), all must be introduced into the system. A pond covered with a greenhouse could be considered a photobioreactor.

Different types of photobioreactors include:

  • Tanks provided with a light source.
  • Polyethylene sleeves or bags.
  • Glass or plastic tubes.

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In most algal-cultivation systems, light only penetrates the top 3-4 inches of the water. This is because as the algae grow and multiply they become so dense that they block light from reaching deeper into the pond or tank. Algae only need about 1/10 the amount of light they receive from direct sunlight. Direct sunlight is often too strong for algae. In order to have ponds that are deeper than 4 inches algae growers use various methods to agitate the water in their ponds, exposing the algae below to light and keeping algae on the surface from being over-exposed.

  • Paddle wheels can be used to circulate the water in a pond.
  • Compressed air can be introduced into the bottom of a pond or tank, bringing algae from the lower levels up to the top to receive its share of light.

Aside from agitation, another means of supplying light to algae is to place the light in the system.

  • Glow plates are sheets of plastic or glass that can be submerged into the water of a tank, providing light directly to the algae at the right concentration.

The odour that many people assosciate with bogs or swamps, or stagnant ponds that have been taken over by algae is due to the depletion of oxygen in the water caused by the death of algal blooms that have been left to decay. Often the oxygen is depleted to the point where it kills all the fish, resulting in an even worse smell. In a system where algae is intentionally cultivated, maintained, and harvested, this situation shouldn't arise, the air around an algal pond should actually be very fresh from all the oxygen produced.

Harvesting

Algae can be harvested using microscreens, by centrifugation, or by flocculation.

Alum and ferric chloride are chemical flocculants used to harvest algae.

Chitosin can be used as a flocculant. The shells of crustaceans are ground into powder and processed to acquire chitin, a polysaccharide found in the shells, from which Chitosin is derived. Chitosin is commonly used for water purification.

The more brackish, or saline the water that the algae is being grown in, the more chemical flocculant will be required to induce flocculation. Harvesting by chemical flocculation is a method that is often too expensive for large operations.

Autoflocculation Interrupting the CO2 supply to an algal system can cause algae in it to flocculate.

  • www.bemidjistate.edu Flocculation of microalgae with cationic polymers. Effects of medium salinity.(pdf)
  • www.pubmedcentral.gov harvesting of algae by froth flotation(pdf)
  • www.lapes.ufrgs.br Overview of flotation as a wastewater treatment technique (pdf)
  • www.ajol.info dissolved air flotation for algae removal (pdf)
  • www.dep.state.fl.us Large-Scale Algal Turf Scrubber® Pollutant Recovery System (pdf)
  • www.bom.hik.se Removal of Prymnesium parvum (Haptophyceae) cells under different nutrient conditions by clay (pdf)
  • ospt.tnw.utwente.nl ULTRASOUND-A new technique to harvest microalgae ? (pdf)
  • * patent for microalgae separator apparatus and method

Oil Extraction

  • Chemical solvents-Algal oil can be extracted using chemicals. Benzene and ether have been used, oil can also be separated by hexane extraction, which is widely used in the food industry and is relatively inexpensive. 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 direct contact with the skin, either of which can cause serious damage. Benzene is classified as a carcinogen. Chemical solvents also present the problem of being an explosion hazard. *
  • Enzymatic extraction-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. [http://www.emcentre.com/unepweb/tec_case/food_15/process/p16.htm
  • Expression/Expeller press-When algae is dried it retains its oil content, which then can be "pressed" out with an oil press. Many commercial manufacturers of vegetable oil use a combination of mechanical pressing and chemical solvents in extracting oil.
  • Osmotic shock-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.
  • Supercritical fluid-In supercritical fluid/CO2 extraction, CO2 is liquefied under pressure and heated to the point that it has the properties of both a liquid and a gas, this liquified fluid then acts as the solvent in extracting the oil. [http://www.phasex4scf.com/supercritical_markets/supercritical_fluids_nutraceuticals.htm
  • Ultrasonic-assisted extraction- 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, it creates shock waves and liquid jets that causes those cells walls to break and release their contents into the solvent.*
  • www.cyberlipid.org Soxhlet extraction
  • * U.S. patent: Process for extracting lipids with a high production of long-chain highly unsaturated fatty acids

Algae as an energy source

Biodiesel production

www.eere.energy.govDepartment of Energy Aquatic Species Program; Biodiesel Production from Algae. (pdf)

Currently most research into efficient algal-oil production is being done in the private sector, but if predictions from small scale production experiments bear out then using algae to produce biodiesel may be the only viable method by which to produce enough automotive fuel to replace current world gasoline usage. Microalgae have much faster growth-rates than terrestrial crops. The per unit area yield of oil from algae,(estimated to be from between 5,000 to 20,000 gallons per acre, per year), is 7 to 31 times greater than the next best crop, palm oil(635gal). Algal-oil processes into biodiesel as easily as oil derived from land-based crops. The difficulties in efficient biodiesel production from algae lie not in the extraction of the oil, which can be done using methods common to the food-industry such as hexane extraction, but in finding an algal strain with a high lipid content and fast growth rate that isn't too difficult to harvest, and a cost-effective cultivation system (ie, type of photobioreactor) that is best suited to that strain. Open-pond systems for the most part have been given up for the cultivation of algae with high-oil content. Many believe that a major flaw of the Aquatic Species Program was the decision to focus their efforts exclusivly on open-ponds, this makes the entire effort dependent upon the hardiness of the strain chosen, requiring it to be unnecessarily resiliant in order to withstand wide swings in temperature and pH, and competition from invasive algae and bacteria. The energy that a high-oil strain invests into the production of oil is energy that is not invested into the production of proteins or carbohydrates, usually resulting in the species being less hardy, or having a slower growth rate. Algal species with a lower oil content, not having to divert their energies away from growth, have an easier time in the harsher conditions of an open system. Research into algae for the mass-production of oil is mainly focused on microalgae, (which is a term generally referred to as organisms capable of photosynthesis that are less than 2 mm in diameter, including the diatoms and cyanobacteria), as opposed to macroalgae, (ie. seaweed). This preference towards microalgae is due largely to its less complex structure, fast growth rate, and high oil content- (for some species). Some commercial interests into large scale algal-cultivation systems are looking to tie-in to existing infrastructures, such as coal power plants or sewage treatment facilities. This approach not only provides for the needs of the system, such as CO2 and nutrients, which, if the facility were built independently, would have to be otherwise acquired, but in addition it remediates waste.

SVO

The algal-oil feedstock that is used to produce biodiesel can also be used for fuel directly as "Straight Vegetable Oil",(SVO). While using the oil in this manner does not require the additional energy needed for transesterification,(processing the oil with an alcohol and a catalyst to produce biodiesel), it does require a special engine designed for its use, or modifications to a normal diesel engine, whereas biodiesel can be run in any modern diesel engine, unmodified, that is designed to use ultra-low sulfur diesel, the new diesel fuel standard for the United States that goes into effect in the fall of 2006.

Hydrogen production

Algae can be grown to produce hydrogen. In 1939 a German researcher named Hans Gaffron, while working at the University of Chicago, observed that the algae he was studying, Chlamydomonas reinhardtii (a green-algae), would sometimes switch from the production of oxygen to the production of hydrogen.Gaffron never discovered the cause for this change and for many years other scientists failed in their attempts at its discovery. In the late 1990's professor Anastasios Melis a researcher at the University of California at Berkeley discovered that by depriving the algae of sulfur it will switch from the production of oxygen (normal photosynthesis), to the production of hydrogen. He found that the enzyme responsible for this reaction is hydrogenase, but that the hydrogenase will not cause this switch in the presence of oxygen. Melis found that depleting the amount of sulfur available to the algae interrupted its internal oxygen flow, allowing the hydrogenase an environment in which it can react, causing the algae to produce hydrogen. Chlamydomonas moewusii is also a good strain for the production of hydrogen. [http://www.yale.edu/rosenbaum/green_yeast.html" target="_blank" >*

Biomass

Algae can be grown to produce biomass, which can then be harvested and burned in the same manner as wood, to produce heat and electricity. *

Ethanol

Methane

*

Industrial Uses

Dyes and Colorants

www.dunaliella.org Xanthophylls in Microalgae: From Biosynthesis to Biotechnological Mass Production and Application (pdf)

Feedstock

Algae can be dried and used as a feed for livestock, or fresh as food for fish and crustaceans.

Medicinal

  • www.ansinet.org Chemoprevention of Penzo*pyrene-induced Carcinogen and Lipid Peroxidation in Mice by Lipophilic Algae Extracts (pdf)
  • * Antioxidant Activity of Algal Extracts on Lipid Peroxidation (pdf)
  • www.nutraingredients.com DHA may suppress colon cancer growth

Nutritional

There are many algae that are cultivated for their nutritional value, either for supplemental use, or as a food source. Spirulina(Arthrospira platensis) is a blue-green algae(cyanobacteria) that is quite nutritious, this species does very well in open systems and commercial growers have found it well-suited to cultivation. One of the largest production sites for Spriulina is Lake Texcoco in central Mexico.
  • *
  • *
  • * Nutritional value of micro-algae
  • *

  • www.isb.vt.edu TRANSGENIC PLANTS PRODUCE OMEGA-3 AND OMEGA-6 FATTY ACIDS(pdf)

Astaxanthin

Overexposing the algal-species Haematococcus pluvialis to direct sunlight will cause it to produce astaxanthin in defense. Astaxanthin is a carotenoid that has the ability to pass between the blood and the brain, carotenoids such as lycopene and beta-carotene can not. There are companies setting up large scale bioreactors for producing Astaxanthin.

"Astaxanthin is an antioxidant pigment found in microalgae such as Haematococcus algae. Its strong antioxidant action is linked to anti-inflammatory activity, and may have a role in strengthening immunity, slowing the aging of skin (age spots and wrinkles) and alleviating muscle fatigue. It is attracting a great deal of attention, not only in the health food market, but in the sports and beauty markets as well. "

Beta-carotene

Dunaliella, (Dunaliella salina)

Cantaxanthin

Chlorella

Algal-oil

Algal-oil is very high in unsaturated fatty acids. Some UFA's found in different algal-species include:

___________________________________________________________________________________________

Plastics production from algae

Rowell et al. "Emerging Technologies for Materials and Chemicals from Biomass" American Chemical Society Symposium Series, vol. 476, Chapters 3, 12, 13 and 18, Aug. 1990.

Pollution control

Much of the carbon dioxide that is released into the atmosphere is from the burning of fossil fuels for the production of energy. Coal power plants are a major source of carbon dioxide emissions. With concerns over global warming, new methods for the thorough and efficient sequestration of CO2 are being sought out. Algae can be used to reduce coal power plant emmissions. By attaching an algae pond, or photobioreactor to a coal burning plant, the carbon dioxide produced during combustion can be fed into the algae system.
  • pepei.pennnet.com Beta Test Set for Emission-Fighting Algae Bioreactor
  • www.usatoday.com Algae — like a breath mint for smokestacks
  • www.unh.edu The Controlled Eutrophication Process: Using Microalgae for CO2 Utilization and Agricultural Fertilizer Recycling. (pdf)
  • www.idrc.ca Piggery Waste Treatment (Singapore)
www.irccm.de Greenhouse Gas Mitigation Project at the International University Bremen

Algal cultures available for purchase

External links

Algal cultivation

General

Phycology groups

  • http://www.intphycsoc.org/ International Phycological Society
  • http://www.psaalgae.org/ Phycological Society of America
  • http://www.schweizerbart.de/j/algological-studies/ Algological Studies is an international journal of phycology which publishes peer reviewed scientific papers of international significance from the entire field of algology (phycology)

See also

Algae | High_lipid_content_microalgae

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Algaculture".

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