Figure 5-9. Chemical slurry feeder controls (right view).
c. Activated Carbon. If the coagulated water has an objectionable color, taste,
or odor, activated carbon is added to the Iimestone slurry compartment at the rate of
1/10 pounds per gallon of water (base charge of 1.4 pounds).
d. Diatomaceous Earth. Diatomaceous earth slurry for precoating the fiIter is
applied directly to the fiIter through the precoat funnel (see para 5-8). Once the fiIter is
in operation, additional diatomite slurry is added to the coagulated water to maintain the
porosity of the fiIter. This diatomite slurry is fed by means of the chemical slurry feeder.
The diatomite slurry compartment, located in the upper left hand section of the chemical
slurry feeder (see figure 5-7), is filled (14-gallon capacity) with fiItered water that is
recirculated from the effluent side of the fiIter. The rate of feed is set on the rate of feed
variator on the left hand side of the slurry compartment (see figures 5-7, 5-9). The
slurry passes through the diatomite dilution tank on the left side of the slurry
compartment where it is diluted with coagulated water from the erdlator assembly. The
diluted diatomite slurry then is piped to the Iine carrying coagulated water from the
erdlator wet well to the fiIter pump (see figure 5-6).
Coagulation of the raw water takes place in the erdlator assembly, or coagulator
(see figure 5-10). The operation is essentially as follows:
a. Raw water is pumped from its source through the aspirators (see figure 5-10,
circle A) into the influent launder (see figure 5-10, circle B) from which it overflows into
the mixing zone (see figure 5-10, circle C) within the down comer tube (see figure 5-10,
circle D). The aspirators aerate the water, which improves coagulation.