a. Principles of Operation. Raw water enters at the top through aspirator type
orifices, which provide aeration of the influent to reduce tastes and odors caused by
organic decomposition, to remove hydrogen sulfide, and to reduce certain chemical
agents of war. The water overflows from the pre-aeration tank into the mixing
compartment, where it is thoroughly mixed with ferric chloride, pulverized limestone,
calcium hypochlorite, and when necessary, activated carbon. These chemicals act as
coagulants, remove colors and dissolved minerals, adjust pH, prechlorinate the water,
and remove or reduce many poisons, including chemical agents of war. The water
flows downward through the mixing zone, where it is rotated at high speed. A reverse
rotation is imparted to the water when it enters the slurry energizing section. This slurry
is a thin, watery paste comprised of suspended floc and other solids. Rotation of the
slurry prevents a short-circuiting of the water flowing upward through it and improves
flocculation. The slurry level in the clarifying chamber is maintained by a continuous
withdrawal of slurry at the time of separation into a sludge concentrator that acts as a
small auxiliary clarifier. The slurry can be discharged to waste from near the bottom of
the sludge concentrator. The clear water is pumped to diatomite filters for further
treatment.
Figure 5-2. Continuous-flow coagulation assembly.
b. Mobile Units. Standard purification units, both mobile and base mounted,
utilize the continuous flow equipment. Two mobile units, of 1,500 gallons per hour (gph)
and 3,000 gph output, are truck mounted (figure 5-3). A raw water pump, chemical
feeders, filter pump, either one or two diatomite filters, and an electrical control panel
are located in the truck body with the coagulator assembly. A gasoline engine driven
generator, trailer mounted, provides the required electric power for the pumps, chemical
feeders, and all other powered components, including the illumination needed for night
operation. Figure 5-4 shows a typical layout for the mobile unit. A scaled down model
of the mobile unit is trailer mounted and has a capacity of 600 gph. It is powered by a
MD0008
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