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Algaculture

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Image:Chlorella.jpg 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.

Macroalgae, (commonly know as seaweed), also have many commercial and industrial uses, but due to their size and the specific requirements of the environment in which they need to grow, they do not lend themselves as readily to cultivation on a large scale as microalgae and are most often harvested wild from the ocean.

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[edit] History and uses of algae

Presumably, the first use of algae was food. One example is the wrapper on a sushi roll. Other species are edible as well. Spirulina, and dulse (Palmaria palmata). Dulse is a red species sold particularly in Ireland and Atlantic Canada. It is eaten raw, fresh, dried, or cooked like spinach. Image:Dulce.JPG Purple laver (Porphyra) is also collected and used in a variety of ways (for example "laverbread" in the British Isles). In Ireland it is collected and made into a jelly by stewing or boiling. Preparation also involves frying or converting to a pinkish jelly by heating the fronds with a little water and beating with a fork. It is also harvested along western coast of North America, from California to British Columbia and by Native Hawaiians and the Māori of New Zealand.

Irish moss (Chondrus crispus), often confused with Mastocarpus stellatus, is used as "carrageen" for the stiffening of milk and dairy products, such as ice cream. It also finds uses in instant puddings, and sauces. Irish moss is also used by brewers as a fining agent; the addition of Irish moss to the wort 15 minutes before the end of the boil produces a clearer beer.

Sea lettuce (Ulva lactuca), is used in Scotland where it is added to soups and salads. Alaria esculenta or dabberlocks is used either fresh or cooked, in Greenland, Iceland, Scotland and Ireland.

For centuries seaweed has been used as fertilizer: "This kind of ore they often gather and lay in heaps where it heteth and rotteth, and will have a strong and loathsome smell; when being so rotten they cast it on the land, as they do their muck, and thereof springeth good corn, especially barley." It is also an excellent source of Potassium for manufacture of potash and potassium nitrate.

There are commercial uses of algae, such as agar.<ref name="SeaweedUses">"Seaweeds and their Uses". Methuen & Co. Ltd., London.</ref><ref name="PorphyraAsfood">Mumford, T.F. and Miura, A (1988). "Porphyra as food: cultivation and economics". In Lembi, C.A. and Waaland, J.R. (Ed.) Algae and Human Affairs: 87-117.</ref><ref name="SeaweedInEurope">Guiry, M.D. and Blunden, G. (1991). "Seaweed Resources in Europe: Uses and Potential.". John Wiley and Sons Ltd..</ref>

[edit] Growing, harvesting, and processing algae

[edit] Growing algae

Image:Spirulina farm.jpg

When cultivating algae, several factors must be considered, and different algae have different requirements. The water must be in a temperature range that will support the specific algal species being grown. Nutrients must be controlled so algae will not be "starved" and so that nutrients will not be wasted. Light must not be too strong nor too weak.

Algae can be cultured in raceway-type ponds and lakes.<ref name="spirulina1">How spirulina is ecologically grown. spirulinasource. Retrieved on 2006-08-28.</ref> Because these systems are open to the elements, sometimes called "open-pond" systems, they are much more vulnerable to contamination by other microorganisms, such as invasive algal species or bacteria. Because of these factors, the number of species successfully cultivated in an "open-pond" system for a specific purpose (such as for food, for the production of oil, or for pigments) are relatively limited. In open systems one does not have control over water temperature and lighting conditions. The growing season is largely dependent on location and, aside from tropical areas, is limited to the warmer months. A major benefit to this type of system are that it is one of the cheaper ones to construct, in the very least only a trench or pond needs to be dug. It can also have some of the largest production capacities relative to other systems of comparable size and cost.

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 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 also 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.
Image:Spirulina drying.jpg

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 1/10th 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 to agitate the water, bringing algae from the lower levels up with it as it makes its way to the surface.

Apart 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 a tank, providing light directly to the algae at the right concentration.

The odor associated with bogs, swamps, or any stagnant waters that have been taken over by algae is from oxygen depletion in the water caused by the death of algal blooms that have been left to decay. This condition, called hypoxia, often results in the death of all aquatic animals, and an even worse smell. In a system where algae is intentionally cultivated, maintained, and harvested, neither eutrophication nor aquatic hypoxia are likely to occur. The air around an algal pond should actually be very fresh from the oxygen produced.

[edit] Harvesting of algae

Algae can be harvested using microscreens, by centrifugation, or by flocculation.<ref name="FlocculationMicroalgae">D. Bilanovic, A. Sukenik, G. Shelef (PDF) (1988). Flocculation of microalgae with cationic polymers. Effects of medium salinity.. Elsevier Science Publishers Ltd, England. Retrieved on 2006-08-28.</ref> Froth flotation is another method to harvest algae whereby the water and algae are aerated into a froth, with the algae then removed from the water.<ref name="FrothingAlgaeHarvest">Gilbert V. Levin, John R. Clendenning, Ahron Gibor, and Frederick D. Bogar. (PDF) (1961). Harvesting of Algae by Froth Flotation. Research Resources, Inc, Washington, D.C.. Retrieved on 2006-08-28.</ref> Alum and ferric chloride are chemical flocculants used to harvest algae. Chitosin, a commercial product commonly used for water purification, can also 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. 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. Interrupting the carbon dioxide supply to an algal system can cause algae in it to flocculate on its own, which is called autoflocculation. Ultrasound based methods of algae harvesting are currently under development, and other, additional methods are currently being developed.<ref name="UltrasoundAlgaeHarvest">Rouke Bosma, Prof. dr.ir J.Tramper, Dr. ir. R.H. Wijffels (PDF) (1961). ULTRASOUND A new technique to harvest microalgae?. Universiteit Twente. Retrieved on 2006-08-28.</ref><ref name="AlgaeHarvestNewMethods">Microalgae separator apparatus and method, United States Patent 6524486. United States Patent Department. Retrieved on 2006-08-28.</ref>

[edit] Oil Extraction

Algae oils have a variety of commercial and industrial uses, and are extracted through a wide variety of scientific methods.

  • 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.<ref name="HexaneRisks">Essential Fatty Acids and Herb FAQ's: What are the hazards of Hexane?. Health From The Sun. Retrieved on 2006-08-28.</ref>
Soxhlet extraction is an extraction method that uses chemical solvents. Oils from the algae are extracted through repeated washing, or percolation, with an organic solvent such as hexane or petroleum ether, under reflux in a special glassware.<ref name="AutoSoxhletExtraction">AUTOMATIC SOXHLET EXTRACTION. cyberlipid.org. Retrieved on 2006-08-28.</ref>
  • 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.<ref name="EnzymaticExtraction">Aqueous Enzymatic Extraction of Oil from Rapeseeds. Institute for Applied Environmental Economics. Retrieved on 2006-08-28.</ref>
  • 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.<ref name="supercriticalfluids1">How Do Supercritical Fluids Work?. Supercritical Fluid Technologies. Retrieved on 2006-08-28.</ref><ref name="supercriticalfluids2">Nutraceuticals and Supercritical Fluid Applications: Production of Astaxanthin Concentrate. Phasex. Retrieved on 2006-08-28.</ref>
  • 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.<ref name="Sonochemistry">Sonochemistry. Prince Edwards Island Government Food Technology Centre. Retrieved on 2006-08-28.</ref>

Other methods are still being developed, including ones to extract specific types of oils, such as those with a high production of long-chain highly unsaturated fatty acids.<ref name="UltrasoundAlgaeHarvest">Rouke Bosma, Prof. dr.ir J.Tramper, Dr. ir. R.H. Wijffels (PDF) (1961). ULTRASOUND A new technique to harvest microalgae?. Universiteit Twente. Retrieved on 2006-08-28.</ref><ref name="AlgaeHarvestNewMethods">Microalgae separator apparatus and method, United States Patent 6524486. United States Patent Department. Retrieved on 2006-08-28.</ref>

[edit] Algae as an energy source

[edit] Biodiesel production

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.<ref name="BiodieselFromAlgae">Biodiesel Production from Algae. Department of Energy Aquatic Species Program, National Renewable Energy Laboratory. Retrieved on 2006-08-29.</ref>

Microalgae have much faster growth-rates than terrestrial crops. The per unit area yield of oil from algae is estimated to be from between 5,000 to 20,000 gallons per acre, per year; this is 7 to 31 times greater than the next best crop, palm oil (635 gallons).

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 exclusively on open-ponds; this makes the entire effort dependent upon the hardiness of the strain chosen, requiring it to be unnecessarily resilient 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; organisms capable of photosynthesis that are less than 2 mm in diameter, including the diatoms and cyanobacteria; as opposed to macroalgae, e.g. 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 the raw materials for the system, such as CO2 and nutrients; but it changes those wastes into resources.

[edit] Hydrogen production

Main article: Biological hydrogen production (Algae)

Algae can be used as a biological source for the production of 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.<ref name="WiredAlgae1">Algae: Power Plant of the Future?. Wired News. Retrieved on 2006-08-29.</ref> Gaffron never discovered the cause for this change and for many years other scientists failed in their attempts at its discovery. In the late 1990s 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.

[edit] 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.<ref name="ENERGYFROMALGAE">ENERGY FROM ALGAE. Access To Energy, Cave Junction, Oregon. Retrieved on 2006-08-29.</ref>

[edit] Methane

Through the use of algaculture grown organisms and cultures, various polymeric materials can be broken down into methane.<ref name="MethanProductionFromAlgae">Methane production. FAO, Agriculture Department. Retrieved on 2006-08-29.</ref>

[edit] 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 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 of America that goes into effect in the fall of 2006.

[edit] Hydrocracking to traditional transport fuels

The oil of algae strain Botryococcus braunii is different than other algal oils, in that it contains a class of oils which can be chemically reduced to chemicals traditionally extracted from petroleum and used for transport fuels, such as octane (gasoline, a.k.a. petrol), diesel, and aviation-grade kerosene. <ref name="Hydrocracking of the oils of Botryococcus braunii to transport fuels">Hydrocracking of the oils of Botryococcus braunii to transport fuels. Biotechnology and BioEngineering (1981). Retrieved on 2006-11-05.</ref>

[edit] Commercial and industrial uses

Algae are cultivated to serve many commercial and industrial uses.

  • CO2 sequestration
  • Fertilizer Runoff reclamation
  • Sewage treatment

[edit] 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 thrives 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.<ref name="KickingImp">The Imp With a Mighty Kick. Asia Week. Retrieved on 2006-08-29.</ref> The plants themselves produce a variety of nutrients and high amounts of protein, and is often used commercially as a nutritional supplement.<ref name="sbalgae">Aphanizomenon Flos-Aquae Blue Green Algae. Energy For Life Wellness Center. Retrieved on 2006-08-29.</ref><ref name="microalgaenutrition">Nutritional value of micro-algae. United States Fisheries Department. Retrieved on 2006-08-29.</ref> Extracts and oils from algae are also used as additives in various food products.<ref name="algaeicecream">Sensory properties of strawberry- and vanilla-flavored ice cream supplemented with an algae oil emulsion. Dept. of Food Science, Pennsylvania State University. Retrieved on 2006-08-29.</ref> The plants also produce Omega-3 and Omega-6 fatty acids, which are commonly found in fish oils, and which have been shown to have positive medical benefits to humans.<ref name="ISBNews">Transgenic Plants Produce Omega-3 and Omega-6 Fatty Acids. School of Biology and Biochemistry, University of Bath, England, UK. Retrieved on 2006-08-29.</ref>

[edit] 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. 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.

[edit] Algal Culture Collections

Specific algal strains can be acquired from algal culture collections.

Main article: List of algal culture collections

[edit] See also

[edit] References

<references/>

[edit] External links

Alternative Fuel

Algal cultivation

Harvesting

  • 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)
  • [1] patent for microalgae separator apparatus and method

General

Photobioreactors

Phycology groups

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