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Unwanted Microorganisms
Evaporative cooling systems are a hospitable environment for the growth of unwanted microorganisms. The evaporative cooling tower environment is warm, wet and contains nutrients – the perfect atmosphere for biological growth. Regardless of the type of water that’s used, biogrowth can cause serious biofouling in any recirculating cooling system. Biofouling can lead to equipment clogging and higher energy consumption, and will eventually damage the equipment. Fortunately, biogrowth can be controlled easily through proper monitoring and the use of appropriate antimicrobials.

Managing Bio-fouling
SBWR recycled water is delivered with some chlorine residual, which can help manage the effects of biofouling. Additionally, the State Water Resources Control Board - Division of Drinking Water (SWRCB - Division of Drinking Water) requires use of biocides in all evaporative cooling towers that use recycled water. Oxidative biocides such as bromine or chlorine are commonly used to meet this requirement. Some facilities use formulated biocides, such as glutaraldehyde or tetrakis (hydroxymethyl) phosphonium sulfate (THPS).

This table illustrates relationships between water quality and biofouling, and includes methods of control.

Water Quality Parameter(1)

Level of Concern

Operating Range(2)

SBWR (2010 avg)


Method of Control

Ammonia (N) 2 0-2 <0.7 mg/L - Promotes biofilm.
- Combines with chloride to negate disinfecting effect of chlorine.
Use bromine as a biocide if ammonia is present
BOD 4 <4 <3.0 mg/L Contributes to biofouling Use organic or inorganic biocide
Iron (Fe) 0.1 107 ug/L Can combine with phosphate to form foulants. Use corrosion inhibitors
Organics Note(3) Note(3) Note(3) Promotes growth of microorganisms. Utilize chlorine or bromine disinfectant