Harvesting by filtration | Harvesting is done by passing the culture
over a fine filter screen - polyester cloth
with 30-micron diameter holes. The filter
screen is inclined slightly so that the accumulating
Spirulina filter cake moves gradually toward
the lower edge of the filter screen, where
it is rinsed, collected, and then sent to
a dewatering station where water is extracted
by vacuum, by pressing, or by gravity through
a vibrating screen. The filter cake, or paste,
now can be cut with a knife and it will retain
its shape; but it still contains 70 to 80%
water .
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If the Spirulina is left in this state, because
it is such a good food it will be invaded
by bacteria and fermented into an unapproachable
stinking mass within a few hours - depending
upon the temperature. This is why the Aztecs
and the Kanembous poured the Spirulina concentrate
into shallow basins they hollowed out of
the sand. The sand allowed the water to filter
down through to the ground and the hot sunshine
dried it in 4 or 5 hours, which stopped any
fermenting action by bacteria.
However, exposure to direct sunlight bleaches
and destroys the green pigment, chlorophyll,
and degrades the B-vitamin content of Spirulina.
So, artisanal and small-scale Spirulina farms
use solar dryers which avoid direct contact
between the algae and the sunlight - a black-painted
metal box which allows air to pass over and
under the algae cake. |
drying spirulina on the
sand | |
Extruding Spirulina Cake | This is done by extruding fine (about 2-mm
diameter) "noodles" of the algae
cake onto plastic screens (about l-mm diameter
holes) ...screens which are stretched tightly
over wood or metallic frames that are nested
inside the dryer box ...the dryer box having
equal sized inlet and outlet holes to allow
an unobstructed passage of air .
One can improve efficiency by heating the
air under glass or plastic before it enters
the dryer box. This creates a draft which
pulls a greater quantity of air through the
box. Bear in mind that it is not the heat
that dries the algae but the capacity of
a lot of air to absorb moisture as it passes
across the algae cake.
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When producing several kilograms of dried
algae per day it is much more convenient
to create a black plastic walk-in sized tunnel
equipped with a large diameter evacuation
fan. Many "noodle" trays can be
stacked one over the other in wood or metal
racks. The advantages of extruding "noodles"
onto the drying screens instead of just spreading
a thin layer of algae cake on top are, first,
that air circulates around all sides of a
"noodle" and hence the cake dries
more quickly. Second, it is much easier to
remove "noodles" from a screen
than to scrape and chip away at a smooth-surfaced
dry product. Third, spreading a film of algae
cake onto a screen pushes it into the mesh
of the screen where, when it dries, it is
gripped tightly by the screen. |
Spirulina solar drier system | |
WEBMASTER Site'' http://Spirulina.online.fr
'' mailto:''Webmaster'' (Updated: November 2005)
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