25 May 2005
little operator attention required. This does not mean that no attention is required, only
less than that required for medium-sized systems. The treatment program for small
systems is shown in Table 4-12.
Table 4-12. Small Cooling Tower Treatment Program
Do not exceed COC limits for untreated water
Dry slowly soluble phosphate compound
Scale and corrosion program
Dry slowly soluble oxidizing biocide
Filtration and periodic washdowns, as required
Treatment. Small systems can be treated with a low dosage (5 to 10 ppm)
of a slowly soluble phosphate chemical (sodium/calcium polyphosphate) by placing a
nylon mesh bag containing the product into the cooling tower. The product, if applied in
this manner, will usually provide adequate scale and corrosion control. Microbiological
control can be obtained by use of a dry, pelletized, oxidizing biocide, such as bromo-
chlorohydantoin or isocyanuric acid plus sodium bromide (see paragraph 4-4.4.1).
Either of these biocides can be fed continuously via a feeder or suspended in a mesh
bag in the cooling tower water. The cooling tower sump should be kept clean of SS and
other debris by use of a filter and periodic washdowns.
Testing. Testing is usually limited to assurance that the optimum COC
value is being maintained and that the chemical treatment agents are present in the
water. The bag with the chemical treatment should not be allowed to become less than
one-half full. The frequency for refilling the bag will vary; once every 1 to 2 months is
typical. Initially, the treatment level should be checked to assure that adequate, but not
excessive, levels of both phosphate and the biocide are present in the cooling water.
Treatment Program for Medium and Large Cooling Towers. The
chemical treatment program for these cooling tower systems (typically greater than 88
kilowatts [25 tons]) requires sufficient, regular testing as well as water and chemical
control to protect the equipment in contact with the cooling water. Usually treatment
includes control of scale, fouling, microbiological growth, and corrosion. The
composition of an optimum chemical treatment program for cooling towers on a military
installation depends on the quality of water available, the operating conditions of the
cooling system, and the environmental constraints placed on treatment chemicals in the
blowdown water (effluent discharge limitations). Conditions at a particular installation
may require variation of the quantity or mix of the chemicals suggested in Table 4-13.