1. GRAVITY THICKENER
(SEDIMENTATION)
Gravity thickener is essentially a sedimentation process similar to the process that
occurs in all settling tanks. It is the most common process currently used for dewatering and for
the concentration of
sludge before digestion.
It is accomplished in a
sedimentation tank in
which solids separate
from liquid phase by
settling. The settled
solid are concentrated
by the action of gravity
by virtue of the weight
of the overlying solid.
First, the feed will enter to the feedwell, as it moves down to the feedwell flocculant is
injected so that as it moves down to the feedwell, flocculation and deaeration occur. Flocculant
causes fine particles to bind together and settled rapidly. The flocculant feed will go down to the
rake arms. The rake arm rotates slowly with the scraper blades on the bottom to push the solids
in the thickener to the deflector cone. The deflector cone is the cone shaped discharged located in
the center of the
thickener. Once
the solids enter
the deflector cone,
they are removed
by
pumps,
pumping
the
concentrated solid
underflow to a
conditioning tank.
The clear water
overflows at the
top
of
the
thickener which
channels the clear
water
to
the
