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4.1.2 Grit Chambers
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4.1.2 Grit Chambers

Description:
Description:
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Grit Chamber

Grit chamber is a long narrow or circular tank to remove inorganic particles, such as sand, gravel, and other solid materials with greater specific gravity than those of the organic matters in wastewater. The removal is achieved through physical settlement by: (i) controlling the velocity of influent flow (horizontal flow chambers); (ii) utilizing centrifugal force in the flow vortices formed by aeration (aerated chambers); or (iii) using a mechanically induced vortex to capture grit solids (vortex chambers).

 

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Figure 4.2 Schematic diagram of an aerated grit chamber

(Source: Tilley et al, 2014)

 

Grit chambers can protect the downstream equipment from abrasion and abnormal wear. The horizontal-flow grit chambers are well suited for village wastewater systems to remove sand and grit from the wastewater. The designed flow velocity in a grit chamber will enable most organic particles pass through the chamber channel and grit particles retained in the chamber.

 

Design Criteria:

 

  • The grit chamber should be designed with at least two parallel channels so that one may be closed for maintenance or cleaning.
  • The hydraulic residence time (HRT) should between 45 to 90 seconds, typically 60 seconds.
  • The horizontal velocity should be maintained between 0.25 to 0.4 m/s, typically 0.3 m/s.
  • Head loss through a downstream control section of 30 to 40% is required to create backflow conditions, typically 35%.
  • The overall length of the grit chamber shall be added to reduce inlet and outlet turbulence. Typically, 25 to 50% of additional length is added at both the inlet and outlet of the grit chamber.
  • The minimum depth of the chamber should be 0.5 m to provide adequate freeboard.
  • The minimum width of the channels should be 0.6 m to allow for easy access and cleaning.
  • The grit chamber can be covered with a steel or fiberglass cover that can be opened or removed for routine cleaning.

 

Operation and Maintenance:

 

  • Required regular inspection and cleaning to avoid unpleasant odor from the degradation of accumulated materials.

The screenings shall be disposed in an environmentally sound wa

 

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