9
operation
6. Continue pump operation for about 15 minutes, after which it is rec-
ommended that the water system be drained, flushed, and refilled in
order to clean the system.
7. While operating the pump(s) and prior to operating the cooling tower
fan, execute one of the two alternative biocidal treatment programs
described in the following:
• Resume treatment with the biocide which had been used prior to shut-
down. Utilize the services of the water treatment supplier. Maintain the
maximum recommended biocide residual (for the specific biocide) for
a sufficient period of time (residual and time will vary with the biocide)
to bring the system under good biological control
or
• Treat the system with sodium hypochlorite to a level of 4 to 5 mg/L
free chlorine residual at a pH of 7.0 to 7.6. The chlorine residual must
be held at 4 to 5 mg/L for six hours, measurable with standard com-
mercial water test kits.
If the cooling tower has been in operation and then shut down for a duration
of time and not drained, perform one of the two previous biocidal treatment
programs directly to the cooling water storage vessel (cooling tower sump,
drain down tank, etc.) without circulating stagnant water over the cooling
tower fill or operating the cooling tower fan.
After biocidal pretreatment has been successfully completed, cooling
water may be circulated over the tower fill with the fan off.
When biocidal treatment has been maintained at a satisfactory level for
at least six hours, the fan may be turned on and the system returned to
service. Resume the standard water treatment program, including biocidal
treatment.
