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Plain sedimentation tanks ,Types & Design considerations
The document discusses plain sedimentation tanks, their theory, design, and types, explaining the sedimentation process and its role in water treatment. It describes four major zones in sedimentation tanks and classifies tanks based on operation methods, shape, and location. Different types of sedimentation tanks, such as intermittent, continuous, rectangular, and circular, are compared in terms of their functions, advantages, and applications.
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Plain sedimentation tanks ,Types & Design considerations
- 1. Plain sedimentation tanks -Theorydesign & types of tanks By : ANSHIKA SAXENA B.Tech (FPE)2015027006 INDIAN INSTITUE OF FOOD PROCESSING TECHNOLOGY TAMIL NADU
- 2. Sedimentation • The processof settling or being deposited as a sediment. • Physical water treatment process • Uses gravity to remove suspended solids from water.
- 3. Sedimentation tanks Waste water Filled Storedfor some time Settled sludge (SS)OR (SP) Clear Water (SS removed) • Settled suspended solids are removed by using scrapers. • May be continuous / intermittent. • NOTE - If the suspended particles have low specific gravity than water, they settle at the top of the tank. • Clarifiers are tanks built with mechanical means for continuous removal of solids being deposited by sedimentation.
- 4. 4 major zonesin sedimentation tank • I. Inlet zone II. Outlet zone III. Settling zone IV. Sludge zone
- 6. • The settlementof a particle iis obstructed or opposed by following 3 forces : • Velocity of flow • Size & shape of par66ticles • Viscosity of water
- 7. Stokes’ law • Applicableto the discrete particles (which donot change in size,shape or mass during settling). • 𝑉 = − ∗ 𝐷2 ∗ + / • for particle dia < 0.1mm • Where • d=diameter of discrete particles • T= temperature(deg. Celsius) • V=velocity of settlement (mm/sec) • S=specific gravity of particle s1=sp. Gr. Of water
- 8. Types of sedimentationtanks • Depending upon various factors sedimentation tanks are classified as follows : Based on methods of operation Intermittent / Quiescent type Continuous type Based on shape Circular tank Rectangular tank Hopper bottom tank Based on location Primary tank Secondary tank
- 9. Intermittent / QuiescentType • The intermittent tanks also called quiescent type tanks • They are those which store water for a certain period and keep it in complete rest.
- 10. Continuous Flow Type •Only the flow velocity is reduced. • Water is keeps running. • Settling basins may be either long rectangular or circular in plan. *Long narrow rectangular tanks with horizontal flow are generally preferred to the circular tanks with radial or spiral flow(depends upon requirement)
- 11. Fill and DrawType Sedimentation Tank
- 12. Fill and DrawType Sedimentation Tank • Water from inlet is stored for some time. • The time may be 24 hours. In that time, the suspended particles are settled at the bottom of the tank. • After 24 hours, the water is discharged through outlet. • Then settled particle are removed. This removal action requires 6-12 hours. • Here 1 complete action of sedimentation requires 30-40 hours.
- 13. Continuous Flow TypeSedimentation Tank • water is not allowed to rest. • Flow has very small velocity. • During this flow, suspended particles are settle at the bottom of the tank. • The flow may be either in horizontal direction or vertical direction.
- 14. Horizontal flow typesedimentation tank • Generally rectangular in shape. • They have more length twice its width. (Because they need to flow more distance to settle all suspended particles) • Maximum permissible velocity in this case is 0.3m/sec.
- 15. Vertical flow typesedimentation tank • The vertical flow type sedimentations tanks are generally in circular shape • Flow takes place in vertical direction. • Hopper bottom is provided at the bottom of the tank to dispose the collected sludge.
- 16. 3 Types oftanks Rectangular- large Circular- small & medium Square(similar to rectangular) High-Rate Tube Settlers Water inlet with baffles Lamellar separators
- 17. Rectangular Sedimentation Tank Easyto operate. Low maintenance costs. Large capacity plants. Used in municipal & industrial applications. Sometimes baffle walls are provided to prevent short circuiting.
- 18. Hopper Bottom Tank •A deflector box is located at the top which deflects the influent coming from central pipe downwards. • Sludge is collected at the bottom • It is disposed through sludge pump.
- 19. Circular Sedimentation Tank Easysludge removal. High clarification efficiency. Small to medium sized applications. For plants with constant flow rates & quality. Uneconomical as compared to rectangular tanks. high clarification efficiency.
- 20. Design & Technology •Detention period : 1 – 3 hours • Velocity of flow : Not greater than 30 cm/min (horizontal flow) • Tank dimensions : L:W = 3:1 to 5:1 • Depth : 2.5 to 5.0 m (3 m). • Slopes : Rectangular 1% towards inlet and circular 8% (For plain sedimentation tank)
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- 22. • Very largesurface area onto which particles may fall and become stabilized • Flow is temporarily accelerated between the plates and then immediately slows down • this helps to aggregate very fine particles that can settle as the flow exits the plates High-Rate Tube Settlers Water inlet with baffles Lamellar separators WORKING of
- 23. Primary Sedimentation Tank •Primary sedimentation tank is a normal sedimentation tank in which water is stored at rest for some time . • Sludge collected at bottom • Oily matter collected at top are removed. • After primary sedimentation process the wastewater is discharged into aerobic filter where activated sludge process take place.
- 24. Secondary Sedimentation Tank •After activated sludge process the wastewater enters secondary sedimentation tank in which suspended particles containing microbes are removed. • Then are reflected towards aerobic filter to maintain high microbe concentration in aerobic filter.
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