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Satish Lele

Cultivation of Algae

Cultivating Algae for Biodiesel Production: With the increasing interest in biodiesel as an alternative to petroleum diesel, many have looked at the possibility of growing more oilseed crops as a solution to the problem of peak oil. There are two problems with the approach: first, growing more oilseed crops would displace the food crops grown to feed mankind. Second, traditional oilseed crops are not the most productive or efficient source of vegetable oil. Micro-algae are 8 to 25 times productive than palm and 40 to 120 times than rapeseed, the highest potential energy yield temperate vegetable oil crop.

    The advantages of culturing microalgae as a source of biomass are many.

  • Microalgae are considered to be a very effective biological system for harvesting solar energy for the production of organic compounds via the photosynthetic process.

  • Microalgae are nonvascular plants lacking complex reproductive organs, making the entire biomass available for harvest and use.

  • Many species of microalgae can be induced to produce particularly high concentrations of chosen, commercially valuable compounds such as proteins carbohydrates, lipids and pigments.

  • Microalgae undergo a simple cell division that enables them to complete their lifecycle faster compared to higher plants. This allows a more rapid development and demonstration of production processes than with agricultural crops.

  • For many regions suffering low productivity due to poor soils or shortage of sweet water, farming of microalgae that can be grown using sea or brackish water may be almost the only way to increase productivity securing a basic protein supply.

Cultivation of Algae Strains for oil: The ponds in which the algae are cultivated are usually what are called the raceway ponds. In these ponds, the algae, water & nutrients circulate around a racetrack. With paddle wheels providing the flow, algae are kept suspended in water, and are circulated back to the surface on a regular frequency. The ponds are usually kept shallow because the algae need to be exposed to sunlight, and sunlight can only penetrate the pond water to a limited depth. The ponds are operated in a continuous manner, with CO2 and nutrients being constantly fed to the ponds, while algae-containing water is removed at the other end.
Open Algae Pond: In case of a large algae pond, the pond depth is 20 cm corresponding to a volume of 200 m3 or 200,000 liters, it is not lined and powered entirely by electricity. Many ponds of this size fit into a small area along with larger settling ponds and a pumping centrifuge station in order to produce algae on a large scale. The pond surface area corresponding to a volume of 200 m3 or 200,000 liters is 1,000 m2.
Pond Operation: Algae pond operations are very simple. The algae are introduced into the pond and allowed to grow until they occupy 1% of the volume of the pond. Very high growth rates are achieved because the pond is constantly mixed by the paddle wheel and it is infused with an ample amount of CO2 and fertilizer. The paddle wheel rotates providing a current of 20 cm/sec around the pond. The mixing is required to ensure that all of the algae receive the necessary amounts of solar radiation, CO2, and fertilizer required for optimal growth. The CO2 is injected into the algae pond in the form of flume gas from a nearby coal fired electricity generation plant. The bubblers are spaced around the pond so that the CO2 is evenly dispersed throughout the pond.

Photo BioReactors: In case of Photo Bioreactors made of Flat glass fixed in steel frame, the depth is 10 cm corresponding to a volume of 0.1440 m3 or 140 liters. Many such BioReactors of this size would fit into a small area along with settling tanks and a pumping centrifuge station in order to produce algae on a large scale. The surface area of each unit is 2.42 m2.
In a transparent tank, tube system or algal bag system for growing algae, the organisms pick up light whilst in the few centimeters near the tank wall or surface where they react with carbon dioxide and nutrients and photosynthesis occurs. Once they move away from that surface then light cannot penetrate and photosynthesis ceases. However, this dark area allows more complex protein building to occur within the algae. By the very nature of a tank the ratio of light to dark area is small and so algae growth is limited. These reactors get around this problem by using transparent compartments that allow the light to penetrate to the center of the liquid. This maximizes the surface area available for photosynthesis. Because there is still a requirement for algae to spend time away from the light the reactor is so constructed, that the algae is constantly recalculated from a light to a dark area.

    Key benefits of bio-reactor are as follows:
  • It offers maximum efficiency in using light and therefore greatly improves productivity. Typically the culture density of algae produced is 10 to 20 times greater than bag culture and can be even greater.

  • Space saving. Can be mounted vertically, horizontally or at an angle, indoors or outdoors.

  • Dramatically reduces labor requirements and eliminates handling problems.

  • Systems can be operated for long periods without culture crashes, or currying.

  • Easy self-cleaning system can dramatically reduce fouling.

  • They are closed, controlled, usually automated systems and therefore cultures may be more easily kept hygienically. Environmental parameters are simply controlled.

  • Hundreds of these can be mounted together.

  • No big and expensive pump needed with this system. A pump will act like a liquidizer on many algae species.

  • Design enables the system to be run for extended periods without culture crashes or cleaning.

  • Oxygen poisoning can't occur. System automatically releases all Oxygen.

  • Reactor stimulates rapid algae growth.

  • Because the system is automatically controlled and delivers algae either continuously or at set intervals, the equipment requires little attention. A cell count once a day should suffice. In addition, the algae can be delivered either directly to where it will be used or into easily handled containers.

Extraction of Algae Oil: There are two well-known methods to extract the oil from oilseeds, and these methods should apply equally well for algae too. These are Expeller or Press and Solvent extraction.