A cooling tower is an ideal environment for the development and growth of microorganisms. Algae can develop in the tower where sunlight is present while slime can develop in almost any part of the system. These deposits can cause local corrosion as well as plugging and reduction of heat transfer.
Growth of the microorganisms can be controlled by using chlorine, chlorinated phenols, organometallic salts, quaternary ammonium compounds, and various other biocides.
Chlorination is probably the most widely used control method. A chlorine residual of 0.3 to 1.0 ppmw is usually effective. The most appropriate treatment is best determined experimentally. Proprietary compounds of several biocides have frequently
been found to be more effective than any single material. These compounds are sometimes used alternately with chlorine. Chlorination programs may be either continuous or intermittent. A generally successful program has been to chlorinate daily until a 1 ppmw free chlorine residual has been maintained for one hour. Chlorine can cause deterioration of cooling tower wood, so prolonged exposure to concentrations over 1 ppmw should be avoided. Limitations on chlorine concentrations in effluent waters have necessitated closer control of chlorine dosage. Several techniques have been employed to reduce chlorine residuals in cooling tower blowdown. The chlorine can be removed by reaction with reducing agents such as sulfur dioxide or sodium bisulfite, or blowdown can be discontinued until the chlorine residual of the circulating water has fallen to an acceptable level. In the latter technique, it is usually necessary to blowdown at a somewhat higher rate prior to the initiation of chlorination to ensure that cycles of concentration do not exceed control levels when blowdown is shut off.
been found to be more effective than any single material. These compounds are sometimes used alternately with chlorine. Chlorination programs may be either continuous or intermittent. A generally successful program has been to chlorinate daily until a 1 ppmw free chlorine residual has been maintained for one hour. Chlorine can cause deterioration of cooling tower wood, so prolonged exposure to concentrations over 1 ppmw should be avoided. Limitations on chlorine concentrations in effluent waters have necessitated closer control of chlorine dosage. Several techniques have been employed to reduce chlorine residuals in cooling tower blowdown. The chlorine can be removed by reaction with reducing agents such as sulfur dioxide or sodium bisulfite, or blowdown can be discontinued until the chlorine residual of the circulating water has fallen to an acceptable level. In the latter technique, it is usually necessary to blowdown at a somewhat higher rate prior to the initiation of chlorination to ensure that cycles of concentration do not exceed control levels when blowdown is shut off.