TM 5-813-3/AFM 88-10, Vol 3
type combine rapid-mixing, flocculation, sedimenta-
tion, and sludge removal in a single unit. Coagulation
and flocculation take place in the presence of a slurry
of previously formed precipitates which are cycled
back to the mixing and reaction zone. Upflow rates at
the point of slurry separation should not exceed about
1.0 gpm per square foot for units used as clarifiers fol-
lowing coagulation and approximately 1.5-1.75 gpm
per square foot for units used in conjunction with lime
softening.
2-6. Filtration.
Filtration of water is defined as the separation of col-
loidal and larger particles from water by passage
through a porous medium, usually sand, granular coal,
b. Flocculation-sedimentation basins. Units of this
type, usually circular, combine the functions of floc-
culation, sedimentation and sludge removal, Floccula-
tion is accomplished in a circular center well, Sedimen-
tation occurs in the annular space between the floc-
culation section and the perimeter effluent weir. De-
sign criteria are generally similar to those applicable
--
to separate units.
c. Suspended solids contact basins, Basins of this
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