SEDIMENTATION Sedimentation is a physical water treatment process using gravity to remove suspended solids from water. Solid particles entrained by the turbulence of moving water may be removed naturally by sedimentation in the still water of lakes and oceans. Settling basins are ponds constructed for the purpose of removing entrained solids by sedimentation. Clarifiers are settling basins built with mechanical means for continuous removal of solids being deposited by sedimentation. The most common form of sedimentation follows coagulation and flocculation and precedes filtration. This type of sedimentation requires chemical addition (in the coagulation/flocculation step) and removes the resulting floc from the water. Sedimentation at this stage in the treatment process should remove 90% of the suspended particles from the water, including bacteria. The purpose of sedimentation here is to decrease the concentration of suspended particles in the water, reducing the load on the filters. Sedimentation can also occur as part of the pre- treatment process, where it is known as pre sedimentation. Pre sedimentation can also be called plain sedimentation because the process depends merely on gravity and includes no coagulation and flocculation. Without coagulation or flocculation, plain sedimentation can remove only coarse suspended matter which will settle rapidly out of the water without the addition of chemicals. This type of sedimentation typically takes place in a reservoir, grit basin, debris dam, or sand trap at the beginning of the treatment process.
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SEDIMENTATION
Sedimentation is a physical water treatment process using gravity to remove suspended solids
from water. Solid particles entrained by the turbulence of moving water may be removed naturally by
sedimentation in the still water of lakes and oceans. Settling basins are ponds constructed for the
purpose of removing entrained solids by sedimentation. Clarifiers are settling basins built with
mechanical means for continuous removal of solids being deposited by sedimentation.
The most common form of sedimentation follows coagulation and flocculation and precedes
filtration. This type of sedimentation requires chemical addition (in the coagulation/flocculation step)
and removes the resulting floc from the water. Sedimentation at this stage in the treatment process
should remove 90% of the suspended particles from the water, including bacteria. The purpose of
sedimentation here is to decrease the concentration of suspended particles in the water, reducing the
load on the filters.
Sedimentation can also occur as part of the pre-treatment process, where it is known as pre
sedimentation. Pre sedimentation can also be called plain sedimentation because the process depends
merely on gravity and includes no coagulation and flocculation. Without coagulation or flocculation,
plain sedimentation can remove only coarse suspended matter which will settle rapidly out of the
water without the addition of chemicals. This type of sedimentation typically takes place in a
reservoir, grit basin, debris dam, or sand trap at the beginning of the treatment process.
While sedimentation following coagulation/flocculation is meant to remove most of the
suspended particles in the water before the water reaches the filters, pre sedimentation removes most
of the sediment in the water during the pre-treatment stage. So pre sedimentation will reduce the load
on the coagulation/flocculation basin and on the sedimentation chamber, as well as reducing the
volume of coagulant chemicals required to treat the water. In addition, pre sedimentation basins are
useful because raw water entering the plant from a reservoir is usually more uniform in quality than
water entering the plant without such a holding basin.
There a four types of sedimentation behaviours. Types 1 sedimentation is discrete settling.
These types will settle of silt in intake and other headwork before coagulation. Besides, it also
softening precipitates in separates softening basin. This type was characterized by particle that settles
discretely at a constant setting velocity. It will settle as individual particles and do not flocculate or
stick to other particles during settling. The type 2 sedimentation is flocculent settling. This type is
being use in settling flocculated water in sedimentation basin. This type was characterized by particles
that flocculate during sedimentation. Since they flocculate, their size is constantly changing; therefore
the settling gravity is changing. Usually it occurs in alum or iron coagulation in primary sedimentation