Sedimentation and Other Clarification Processes - Public Water Systems - page 319

Basic Systems Available Two basic types of shallow-depth settling systems avail-
able from several manufacturers are illustrated in Figure 11-11: essentially horizontal
tube settlers, and steeply inclined tube or plate settlers.

Essentially Horizontal. The operation of essentially horizontal tube settlers is coordi-
nated with that of the downstream filter (see Fig. 11-11). The tubes essentially fill
with sludge before any significant amount of floc escapes. Solids leaving the tubes are
captured by the filter. Each time the filter backwashes, the settler is completely drained.
The tubes are inclined only slightly in the direction of normal flow (5 ) to promote
the drainage of sludge during the backwash cycle. The rapidly falling water surface
scours the sludge deposits from the tubes and carries them to waste. The water drained
from the tubes is replaced with the last portion of the filter backwash water so that no
additional water is lost in the tube-draining procedure. This tube configuration is ap-

Essentially Horizontal Tube Settler

Chemical
Coagulants

Last Portion of Filter
Backwash Refill Tubes

First Portion of
Backwash to Waste

Raw Water

Tube Settler

Flocculator

Filter

o

5

Tube Contents Drained
During Filter Backwash

Steeply Inclined Tube Settler (or Plate Settler)

Chemical
Coagulants

Backwash to Waste

Raw Water

Flocculator

Filter

o

60

Sludge Drawoff

Fig. 11-11. Two shallow-depth settling systems (From Culp, Gordon, and Williams, Robert,
Handbook of Public Water Systems. Copyright 1986 by John Wiley & Sons, Inc. Reprinted by
permission of John Wiley & Sons, Inc.)