Screening – Type of screening in water treatment plant
The process involving water treatment plants is screening, sedimentation, coagulation, filtration, disinfection(Chlorination) and distribution. First process of a water treatment plant is screening.
Screening in water treatment plant
Screening is the first unit operation of a water treatment plant. Screening is the process to remove the big floating particles having size that lies between approx 10 mm to 150 mm depending upon the types of screen used in the screening process. In this process generally paper, wooden pieces, Plastic bottles, Glass bottles etc. are removed.
Screening is done with the help of a device known as screen. Screen is a device having uniform spacing with uniform size of rod. The working principle of screen is; If the particles whose size is greater than the clear spacing of the screen get particles are retained over there and manually retained particles are removed.[Principle of sedimentation – Type of sedimentation]
Generally the screen fitted in a water treatment plant is 30° – 60° angle from the horizontal, and the approach velocity of water lies between 0.6 – 1.2 m/s.
Type of screening used in water treatment plants.
Screening are classified on the basis of clear spacing of the rod, generally three types of screening are available in the screening process in water treatment plant.
- Coarse screening
- Medium screening
- Fine screening
| Sl No. | Type of Screening | Retained Particles in mm |
|---|---|---|
| 01. | Coarse Screen | 50 mm – 150 mm |
| 02. | Medium Screen | 20 mm – 50 mm |
| 03. | Fine Screen | less than 20 mm |
Coarse screening
Coarse screening – In coarse screening, Clear spacing between the rod is lies between 50mm – 150mm. In this type of screen only big floating particles are retained whose width lies between 50mm – 150mm.[Type of chlorination – Residual chlorine]
Medium screening
Medium screening – In this type of screening, Clear spacing between the rod lies between 20mm – 50mm. In the medium screen only medium floating particles are retained whose width lies between 20mmm – 50mm.
Fine screening
Fine screening – In fine screening, the clear spacing between rod lies 20 mm. and in this type of screen very fine floating particles are retained in the water treatment plant. The arrangement of screens in the water treatment plant is coarse screening, medium screening and then the last fine screening is arranged.
Note – Width of screen is calculated by following formula
B = n ɸ + ( n + 1 ) S
n = no of rod
ɸ = diameter of rod
Screening in water treatment plant Important Information
- First process of a water treatment plant is screening.
- Screening is the first unit operation of a water treatment plant.
- Generally three types of screening are available in the screening process in water treatment plant.
FAQs
Q1. What is the screening in a water treatment plant?
Answer – Screening is the first unit operation of a water treatment plant. Screening is the process to remove the big floating particles having size that lies between approx 10 mm to 150 mm depending upon the type of screen.
Q2. What are the types of screening?
Answer – Screen are classified on the basis of clear spacing of the rod, generally three types of screen are available in the screening process in water treatment plants.
- Coarse screen
- Medium screen
- Fine screen
Q3. What is the function of screening?
Answer – The main function of screening is removing the big floating particles. In this process generally paper, wooden pieces, Plastic bottles, Glass bottles etc. are removed.
Q4. The arrangement of screening in water treatment plant
Answer – The arrangement of screens in the water treatment plant is coarse screening, medium screening and then the Last fine screening is arranged.
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