Before I start about types of sedimentation, Sedimentation is the removal of suspended particles by gravitational settling. Sedimentation is an important water treatment process for water purification.
The purpose of sedimentation tanks is to reduce the velocity of water flow so as to permit suspended particles to settle in a tank under the action of gravity.
Our primary aim of sedimentation water treatment is to purify water. Surface water comes from various sources contains large amounts of suspended particles and debris. If you directly pass these water to water treatment machines, finally it leads to deteriorating of machines.
So in order to prevent these causes, at the beginning of water treatment itself, you need to remove the suspended particles by sedimentation process. The sedimentation process can be done with help of sedimentation tanks. There are different types of sedimentation tanks used for this process.
Types of Sedimentation process
As you have studied, what is sedimentation and why you need sedimentation in your water treatment process? Next, you can study what are the types of sedimentation process.
There are two types of sedimentation process, the first one is plain sedimentation and the second one is sedimentation with coagulation( clarification).
When the suspended solids (impurities) are settled out by the action of natural forces alone, by gravitation is called plain sedimentation.
2.Sedimentation with coagulation( Clarification)
When chemicals or other substances are used to hasten and settling of finely divided suspended matter or colloids, this operation or types of sedimentation is called as clarification or sedimentation with coagulation.
You know that the suspended matter may be in finely solid or dissolved state. In a simple logic, you know that any substance whose specific gravity less than water will float on the surface of the water.
Here, the suspended matter having less specific gravity than water will float on the surface of water or will not settle under gravity.
Here we use chemicals to increase the weight of these suspended particles by attracting with each other. Thus the weight of suspended particles can be increased.
The efficiency of the sedimentation tank is proportional to its surface area and length, not its depth. That is if you have two tanks, one is having large surface area and other is having a larger depth. The larger tank having more surface area is more suitable for sedimentation process even if the volume of two tanks are same.
However, when you design a sedimentation tank, you should provide at least 3-metre depth for the proper removal of suspended particles.
Now you have studied about various types of sedimentation. Next, you need to study what are various types of sediments(suspended particles).
Types of Sediments (Settlings)
There are various types of sediments in runoff or suspended water. These sediments will settle in various layers of water in the sedimentation tank. The settling of suspended particles takes place according to their specific gravity.
That is denser particle will settle in the deeper area of the tank than the surface of the water. Types of settlings are divided into four.
Discrete settling refers to when suspended particles having low concentration settles at the top layer of the water as shown in the above figure. If you don’t know the meaning of discrete, they are individually separate and distinct particles.
Discrete settling is also called as free settling because they have the little chances for flocculating. Flocculate means they these small particles ( discrete particles) have a tendency to form or unite and lead to the formation of small masses.
Hindered settling particles which are seen below the discrete settling particles as shown in the above figure.
They are formed by flocculation during the sedimentation process. The hindered setlling particles will be larger than discrete settling particles.
The flocculation process can increase the mass of the sediments and can promote the rate of sedimentation at a faster rate.
The zone settling comes under the third category. They have intermediate concentration. The interparticle forces are high and they can unite each other and can form large groups.
Compression settling particles have a high concentration and they are wool like structures. They are merged and growth into one body.
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