Design fundamentals of sedimentation tanks

 

What is sedimentation and sedimentation tank???

Sedimentation is a process used for various stages within a wastewater treatment plant to reduce the concentration of settleable and suspended matter. Sedimentation tanks, commonly referred to as clarifiers, are described as primary, intermediate and final clarifiers dependent upon the process stage. Primary clarifiers are installed to reduce organic loadings and floatables to the downstream treatment processes. Intermediate and/or final clarifiers are utilized after biological treatment processes to separate chemical and/or biological floc from the treatment process.

Types of settling patterns:

  1. Discrete settling
  2. Flocculent settling
  3. Hindered  or zone settling
  4. Compression settling

General design considerations:

  • Multiple units capable of independent operation shall be provided for plants having an average design capacity greater than 0.1 MGD unless temporary removal of a single unit from service for repairs will not result in an adverse effect to the quality of the receiving stream.
  • Clarifiers shall be arranged to facilitate operating flexibility and maintenance, assure continuity of treatment, and ease of installation of future units.
  • Provision shall be made for dewatering and bypassing each unit independently process units.
  • Effective flow measurement devices and controls shall be provided to permit proper flow distribution to each unit.
  • The anticipated flow pattern should be considered in the selection of clarifier configuration and location and type of inlets and outlets
  • Due consideration shall be given to the possible need for hydrostatic pressure relief devices to prevent structure flotation.

Types of sedimentation tanks:

Classification based on nature of working:

  • Fill and draw type
  • Continuous flow type

Classification based on location

  • Primary tank
  • Secondary tank

Classification based on shape

  • Rectangular tank
  • Circular tank
  • Hopper bottom type

Design Considerations:

sedimentation tank

 

 

 

 

 

 

 

 

 

 

 

 

 

  • Detention Time
  • Flow Velocity (camp formula)
  • Surface Loading rate and depth consideration
  • Inlets
  • Weir Loading
  • Proportioning of tank
  • Free board
  • Removal Efficiency of tank
  • Sludge Handling and Withdrawal

 

 

Power Point Presentation has been embedded below for better understanding.

 

 

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