Settling Basin Theoretical Design  For any clay-sized or larger
particle in suspension in a fluid, the settling rate is a
function of the gravitational force (downward) and the
frictional resistance (opposite). Because the mass of a particle
increases with the cube of the radius, but drag surface area
only increases with the square of the radius, larger particles
settle more quickly than small particles. Very small particles
(such as the colloidal particles in milk), can be kept in
solution indefinately by static charges and brownian motion, so
settling basins are ineffective at removing these particles. The
essence of the design process is to determine a specific
residence time, dependent on a particle size removal goal. The
sediment removal will include all particles with a velocity >
Vc, plus that fraction of the slower (smaller) particles that
enter low enough in the column to also settle to the sludge
layer before passing out of the basin.   In order to
theoretically calculate the critical velocity of th