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Sedimentation Tank Configurations and Design for Effective Particle Settling

Learn about sedimentation tank configurations, four zones (inlet, settling, outlet, sludge), particle settling types, Stoke's Law, overflow rates, and design considerations for efficient particle removal in water treatment processes.

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Sedimentation Tank Configurations and Design for Effective Particle Settling

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  1. Sedimentation Tank Configurations • Four Zones • Inlet, Settling, Outlet, Sludge • Outlet zone has weirs for slow exit of water • Rectangular Clarifiers • most common • Circular clarifiers • Center feed • Peripheral feed • Flocculator-Clarifiers

  2. Particle Settling Settling Type • Type 1-Discrete (Single) • Type 2-Floc (Multiple forming a larger particle) • Type 3-Blanket: Cannot distinguish particles Stoke’s Law Assumes spherical shape Provides particle settling velocity vs ρ density of fluid ρp density of particle vs>vo for all particles to settle

  3. Overflow Rate; Surface Loading RateTanks are designed based on overflow rateParticle settling velocity vs has to be greater than vo Vo = Q/As H Outlet Zone Inlet Zone Sludge Zone vo=The overflow rate

  4. Design Typical design overflow rates for settling tanks are: 500-1000 gpd/ft2 All particles with a settling velocity greater than or equal to the overflow rate will be 100% removed. Particles with a lesser settling velocity will be removed to a fractional extent. Those that happen to enter the settling zone near the bottom will be completely removed and those that enter near the top will not.

  5. Sedimentation Tank Design • Side water depth: about 12 ft. • settling velocities: 2-6 ft/hr • retention time: 4-8 hr • overflow rates: 500-1000 gpd/ft2 or 0.3-0.7 gpm/ft2 • linear velocities: less than 0.5 ft/min

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