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  6 - Basins-

Round corners basin
A Rectangular basin with round corners

The big problem about basins is: what material to use for making the waterproof bottoms and side-walls?
There is no single answer.

The basin design which has proven to be the most satisfactory is the rectangular basin with rounded corners having a dividing wall running through the long axis of the basin but terminated one half the width of the basin just before each end so as to create a sort of race track around which the culture can be pushed by paddlewheels. This design can be used for basins of one square meter area up to (and probably exceeding) five hectares in area.
Remember, one needs about one square meter of basin area per child.

A Spirulina culture must be mixed continuously during the daylight hours for several reasons:

A Spirulina culture must be mixed

Prarticularly during Inoculum production step
The culture, during the day, must be mixed
(I) to insure that the nutrients in the culture medium will always be in contact with the algae so that the supply of nutrients wilI not be a factor limiting growth,
(2) to move the algal filaments up into the zone where sunlight penetrates and photosynthesis can take place, but
(3) also to move the filaments downward in the water column to where the diurnishing light cannot cause photolysis (or photon burning) of the photosynthetic pigments in Spirulina, finalIy
(4) so that the algae cannot congregate into dense flocs where the inner filaments are deprived of light and nutrients to the extent that they give off large quantities of polysaccharides and die, thus providing a rich environment for bacteria that eventually can destroy the culture. All this means that the bottom and sides not only be waterproof but also resist being eroded by the moving water

Stirred by muscle energy
Round corners basin
A round basin in Madras (India)

Round basins of the kind used for sewage treatment have been used, chiefly in Taiwan and India. These are stirred by rotating arms like spokes of a wheel ( called a Segner Wheel). However, the stirring paddles near the center of the basin rotate very slowly, resulting in slow growth rate, while those near the perimeter travel so fast that they risk tearing apart the algal filaments (more than 30 centimeters per second). Hence, round basins are limited to about 80 meters in diameter .

Round corners basin
A round basin in Taiwan
On a gentle hillside it is possible to lay narrow concrete basins parallel to the hillside with the head of one basin joining the tail of the basin just above it - like a long snake leisurely descending a large sand dune. This was tried at Casa Grande near Trujillo in Peru in the nineteen eighties. Two problems present themselves. One, you have to pump the culture from the bottom of the hill to the top during the daytime, and, two, there has to be a large reservoir at the bottom to receive the culture for the night in case the pump stops. This can be made simply by raising the side and end walls of the last basin section high enough to contain the entire culture. The pump used, because of the force required, had a tendency to break the algal filaments (this system originally used for culturing Scenedesmus). A solution would be to use a large-diameter Archemedian Screw to lift the culture instead.
Stirred by broom
Credesa basin
A Basin made of polyethylene plastic film (photo: Claude Darcas)

Basins up to about 100 square meters can be made with a roll of black, food grade, polyethylene plastic film one half millimeter thick simply by attaching it to a wooden frame about 40-centimeters high which outlines the basin. The dividing wall to form the racetrack can be of concrete blocks. Larger basins require heavier membranes to resist tearing when entered by persons cleaning out the basins, to give longer service lifetimes as the geo-membranes used for large basins are costly, and to guard against fermentation gases lifting the membrane and causing troublesome "islands" near any small punctures in the membrane. The cost of 0.3 mm polyethylene, which can be used for basins up to about 30 m², is about 1 dollar per square meter. For the half-millimeter films, guaranteed for 15 years against ultra violet damage, the cost is around 5 dollars per square meter. Heavy duty geo-membranes are even more expensive.
The Romans built basins with stone and mortar which hold water to this day - but cost probably was never taken into consideration. Their manpower cost only a minimum amount of food per day and their materials they took from nature. Concrete basins have been constructed recently in Benin, Africa, at a cost of $ 49 per square meter; as opposed to $ 6 per square meter for plastic film construction (film and frame complete). I believe that it is possible to make a 5-centimeter thick concrete slab having 7-centimeter-deep feet on 25-centimeter centers cast on the bottomside for about $ 3.25 per square meter. The cost of the basin walls and center separation would be additional. Of course, one is at the mercy of earth movements, so one could not recommend building concrete algae basins in earthquake or volcanic zones.
- Introduction ] CD-ROM Spirulina for Reducing Malnutrition - Historic of the World ]
- SPIRULINA Composition  ]   [  - Texcoco Lake Story  ]
 [ -  
WHERE SPIRULINA is found ] [  - Basins  ]   [  - Photosynthesis ]  
- SPIRULINA Production  ]  [  - Laboratory ]  [  - Harvesting ]
- Mix-drying SPIRULINA ]   [  - Starting ]  [ Problems and Solutions  ] 
[  -
- Why should we grow SPIRULINA ? : for nutrition and health ]
- Public Information-paper on SPIRULINAuseful links ]


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