TM 5-4610-218-12
(c) The water is pumped from the wet well
(c) The sludge concentrator tank permits
tank through valve CV-34 (fig. 2-3), valve SCV-35
settling of slurry in the bottom of the tank for con-
tinuous or intermittent drainage to waste. It also
the FILTER position, and up into the influent sec-
permits the skimming of clear coagulated water at
tion (fig. 2-5) of the filter. The water rises until it
the top of the tank for return to the wet well from
starts escaping through valve CV-38 (fig. 2-3)
where it is pumped to the filter.
which now must be closed.
(d) The draining of slurry to waste and the
(d) Air is trapped and compressed in each
return flow to the wet well is manually controlled,
of the plastic cups (fig. 2-5) of the elements and in
depending upon the amount of slurry produced in
the dome of the filter housing cover. The air is pre-
the erdlator tank.
vented from escaping through the air release valve
(4) Chemical solution feeder. The chemical
ARV-49 (fig. 2-1) since it is closed in the FILTER
solution feeder (fig. 1-5) pumps ferric chloride and
position.
calcium hypochlorite solutions into the downcomer
(e) As the water is filtered through the ele-
or mixing zone (fig. 1-4). The pump discharge rate is
ment membranes the diatomaceous earth and sus-
adjustable, but delivers a fixed constant rate of feed
pended matter are deposited on the elements and
with each pump stroke at any one setting.
the water enters the effluent section through the
(5) Chemical slurry feeder (limestone com-
two pipes from each element.
partment).
(f) The water then goes through valves CV-
(a) The chemical slurry feeder tank (fig. 1-
40, CV-45, and CV-46, (fig. 2-3), which is in the RE-
5) supplies pulverized limestone (coagulation aid)
CIRCULATION position and back to the wet well
to the mixing zone of the erdlator tank.
tank. The water is recirculated through the filter
(b) Raw water is continuously added to a
until it appears clear when viewed through the fil-
collection trough on the back of the compartment. A
ter window.
portion of this water flows through a constant head-
(2) Filtering.
fixed orifice into the limestone slurry compartment
(a) Filtering removes the remaining sus-
and the remainder overflows to a weir for dilution of
pended matter and organisms from the water.
the slurry discharge from the feeder. This diluted
slurry flows by gravity into the downcomer.
(b) The flow of the water from the wet well
and through the filter is the same as during pre-
(c) The limestone slurry is kept in sus-
coating, until it reaches valve CV-46 which is now
pension by agitators within the limestone slurry
in the FILTER position to allow the water to flow
compartments.
through the filter water hose to the storage tanks.
(d) Since 65 percent of the initial charge of
(c) Diatomite slurry is discharged from the
slurry is fed during a period of one hour, therefore
diatomite slurry compartment of the chemical
the feeder requires recharging with dry chemicals
slurry feeder (fig. 1-5) to the water line of the suc-
every hour. The limestone compartment remains
tion side of the filter pump.
full of liquid slurry but becomes more diluted dur-
ing the hour until recharged with the dry chem-
(d) The flow of water carries the diatomite
icals.
slurry to the filter where it is deposited on the filter
elements. The continuous feed of diatomite slurry
c. Filter Process. The filtering process further
maintains the porosity of the filter cake and per-
reduces the suspended matter by use of a di-
mits longer filter runs. As water is pumped through
atomaceous earth filtering aid. The filtering pro-
the diatomite filter cake, the suspended matter in
cess consists of three steps; precoating, filtering,
the water will gradually plug the filter cake and in-
and backwashing.
crease the pressure differential across the filter ele-
(1) Precoating.
ments. When the effluent pressure gage PG-3 (fig.
(a) Before the water can be filtered, it is
2-1) indicates a pressure of 5 psi the filter is ready
necessary to precoat the filter elements with di-
to be backwashes. The filter cycle is the time the fil-
atomaceous earth.
ter is in operation, from the time the precoat has
been added until the filter elements must be
(b) Diatomaceous earth slurry is added to
backwashes.
the water line through the precoat funnel (fig. 1-3),
and valve CV-38 (fig. 2-3).
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