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Circular clarifiers

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Circular Clarifiers for the treatment of waste water

Published in: Engineering
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Circular clarifiers

  1. 1. Clarifiers Presented By: Ghulam Murtaza Presented To: Engr. Waqas Qamar Roll No: 12063123-046
  2. 2. Contents……  What is clarifier???  Types of Clarifier  Working Principle  Primary Clarifier  Sludge Process
  3. 3. Continu…..  Secondary Clarifier  Designing Parameters (Calculations)
  4. 4. What is clarifier???  Clarifiers are settling tanks built for continuous removal of solids being deposited by sedimentation.  A clarifier is generally used to remove solid particulates or suspended solids from liquid for clarification.
  5. 5. Types of Clarifiers There are two types of Clarifiers  Rectangular Clarifiers  Circular Clarifiers  Inclined Plate Clarifiers
  6. 6. Effluent Launder Effluent Weir Scum Trough Flights Drive Unit Drive Chain Drive Gear Idler Sprockets Sludge Withdrawal Pipe Sludge Trough Inlet Baffle Inlet Rectangular Clarifier
  7. 7. Overflow Box Clarifier Influent Sludge Discharge Clarifier Effluent Sludge Hopper Flocculation Tank Flash Mix Tank Coagulant Feed Feed Box Discharge FlumesDistribution Orifice Inclined Plates Inclined Plate Clarifier (Lamella)
  8. 8. Circular Clarifiers Operation  Circular clarifiers use slowly rotating rake arms to separate solid particulate.  A liquid feed with suspended solids is fed into a tank with a diameter of 5 to 500 feet.  As the particles settle, angled rake arms move the concentrated slurry toward the center of the tank, where it is removed.
  9. 9. Primary Clarifier  Primary clarification is the physical treatment process of removing solids before biological treatment.  Floatable material (scum) are removed from the surface by skimmers and settle able solids (sludge) are collected on the bottom by a rakes.  The expected range for percent removal in a primary clarifier is 90%-95% settle able solids, 40%-60% suspended solids
  10. 10. Activated sludge Process  The activated sludge process is widely used for biological wastewater treatment all over the world.  An activated sludge wastewater treatment system always has an aeration tank and secondary clarifier, which function as a unit to remove organic matter and suspended solids from the wastewater.
  11. 11. Secondary Clarifier  Microorganisms such as bacteria and protozoa can use the small particles and dissolved organic matter not removed in primary clarifier as food.  In a secondary clarifier which operates in the same manner as the primary clarifier described previously. Some of the solids collected in the secondary clarifier (return activated sludge) are sent back to the aeration tank.
  12. 12. Cont….  secondary clarifier effectively separates the biological floc and colloidal solids to produce wastewater with very low levels of organic material and suspended matter.
  13. 13. Efficiency of solid Removal related to Characteristics of solid  Stokes law VF = Fall Velocity (ρ - ρo) = Density difference between particle and water n = viscosity of water g = gravitational acceleration constant d = diameter of the particle
  14. 14. Particle Size versus Settling Time Particle Size mm Order of Size Time to Settle 1.0 Coarse Sand 3 Seconds 0.1 Fine Sand 38 Seconds 0.01 Silt 33 Minutes 0.001 Bacteria 55 Hours 0.0001 Colloidal 230 Days 0.00001 Colloidal 6.3 Years
  15. 15. Calculations (Designing Parameters)  Hydraulic Loading  Solid Loading
  16. 16. Hydraulic Loading  Detention Time (DT) The time it takes for a water to travel from inlet to outlet. Typical Design Value = 2 – 3 Hours
  17. 17. Calculate the Detention Time in HOURS for a clarifier with a volume of 25,000 gallons that receives a flow of 310,000 gal/day. Detention Time = Volume Flow = 25,000 gallons 310,000 gallons/day = 0.08 Days 0.08 Days X 24 hours/days = 1.9 Hours
  18. 18. Hydraulic Loading  Surface Overflow Rate The flow in gallons per day into the clarifier per square foot of surface area.
  19. 19. Continu…….. SOR, gpd/ft2 = Flow, gallons/day Surface Area, ft2 Typical Design Value = 400 - 800 gal/day/ft2
  20. 20. SOR, gpd/ft2 = Flow, gallons/day Surface Area, ft2 Calculate the Surface Overflow Rate for a clarifier that is 50 ft long, 15 ft wide, 12 ft deep, and receives a flow of 338,000 gallons per day. = 50 ft. X 15 ft. = 750 ft2Surface Area, ft2 338,000 gallons per day 750 ft2 SOR, gpd/ft2 = = 451 gpd/ft2
  21. 21. Solid Loading The pounds per day of solids in the clarifier influent per square foot of surface area. Typical Design Value = Max 30 lbs./d/ft2
  22. 22. Pounds = Concentration Of STUFF In the Water Conc. x Flow (or Volume) x 8.34 Lbs./gallon X Quantity Of Water The STUFF Is In Weight Of The Water X “Pounds Equation”
  23. 23. SLR, lbs./d/ft2 = Solids, lbs./day Surface Area, ft2 Calculate the Solids Loading Rate for a clarifier with a 50 ft diameter and a depth of 12 feet, and receives a flow of 2.4 MGD with a suspended solids concentration of 1800 mg/L. SA = 3.14 X 25 ft. X 25 ft. = 1962.5 ft2 1800 mg/L X 2.4 MGD X 8.34 lbs./gal = 36,029 lbs./d 36,029 lbs./day 1962.5 ft2 = 18.4 lbs./d/ft2 Solids, lbs./day = SLR, lbs./d/ft2 =

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