Grit chambers are designed to separate the intended heavier inorganic material (specific gravity about 2.65) and to pass forward the lighter organic materials. They are similar to the sedimentation tanks but, the flow velocity in grit chambers is neither too low as to cause the settling of lighter organic matter nor too high as not to cause the settlement of the silt and grit present in the sewage.
This tool is useful in determining the dimensions of a grit chamber.
Horizontal velocity (m/s)
Detention Time (Sec)
The particle diameter assumed in this calculation is 200 microns.
Specific density (d) = 2.65
Vertical velocity range = 0.016-0.021 m/s for 0.2 mm particles
Horizontal velocity limit = 0.15-0.30 m/s usually 0.2 m/s
Detention time (at peak flow) =30-90sec usually 60s
Depth range = 1-1.5 m
Length range = 3-25 m
Allowance for inlet and outlet turbulence = 25% to 50% (based on theoretical length)