Figure 2-12. Circular Imhoff tank.
2-6. SLUDGE REMOVAL
a. Methods of Removal.
(1) Scum may be run to sludge digesters at the treatment plant, drained
and hauled to the sanitary landfill or incinerator, or buried under at least two feet of
earth. Another way of dealing with scum is to spray it with final effluent, causing it to
settle with the sludge in the primary settling tank.
(2) Sludge is removed from primary settling tanks either by means of
sludge pumps or by gravity. Figure 2-7 shows a tank with a gravity-flow sludge pipe,
while Figures 2-8 and 2-9 illustrate tanks, which require pumps. Reciprocating pumps