TM 5-814-3/AFM 88-11, Volume III
(a) Process description. After sludge feeding is stopped, the centrifuge begins to decelerate and a
special skimmer nozzle moves into position to skim the relatively soft and low solids concentration sludge
on the inner periphery of the sludge mass. These skimmings are typically returned to the plant headworks or
the digesters. After the skimming operation, the centrifuge slows further; to about 70 revolutions per minute,
and a plowing knife moves into position to cut the sludge away from the walls; the sludge cake then drops
through the open bottom of the basket. After plowing terminates, the centrifuge begins to accelerate and feed
sludge is again introduced. At no time does the centrifuge actually stop rotating.
(b) Application. The cake solids concentration produced by the basket machine is typically not as dry
as that achieved by the solid bowl centrifuge. However, the basket centrifuge is especially suitable for
dewatering biological or fine solids sludges that are difficult to dewater, for dewatering sludges where the
nature of the solids varies widely, and for sludges containing significant grit. The basket centrifuge is most
commonly used for thickening waste activated sludge. A basket centrifuge can be a good application in small
plants with capacities in the range of 1 to 2 million gallons per day where thickening is required before or
after stabilization or where dewatering to 10 to 12 percent solids is adequate. The basket centrifuge is
sometimes used in larger plants.
(c) Advantages and disadvantages. Advantages and disadvantages of a imperforate basket centrifuge
compared to other dewatering processes are presented in table 16-7.