The goal of a good water treatment program should be to ensure that the water has constant contact with heat exchange surfaces and is free of biological fouling. Biological growth, scale deposition, and corrosion can force equipment to work harder because of reduced ability of the water to contact these surfaces. In order to increase the effectiveness of a water treatment plan, water treatment professionals recommend a dual alternating biocide program.

Oxidizing Biocides

Biocides are chemicals used to eliminate bacteria and algae found in cooling towers and other recirculating cooling systems. All biocides can be divided into two major classes- oxidizing and non-oxidizing. Each type of biocide approaches biological organisms in a different way.

Oxidizing biocides take a “shot gun” approach to destroying bacteria and biological growth. These biocides attack the cell structure of the organism to destroy the cell and ultimately kill the organism. Oxidizing biocides are effective because of the speed and nature of their approach and organisms are unable to build up a resistance to the chemicals used to treat the water.

However, there are a few drawbacks with the use of oxidizing biocides. These chemicals can increase the corrosiveness of water. Some oxidizing chemicals used in water treatment programs can also create undesirable byproducts that are bad for the environment.

All water treatment programs require consistent monitoring of water conditions and chemical levels. Oxidizing biocides can increase the need for observation because they can interact with other corrosion control chemicals used in the program, and render them less effective.

Non- Oxidizing Biocides

A non-oxidizing biocide attacks biological growth in a different way, by interrupting the organism’s metabolism, and effectively poisoning the cells to kill them. This class of biocides targets specific organisms and specific cellular processes, taking a “rifle” approach to treatment.

An added benefit of non-oxidizing biocides is that they can have little to no impact on other chemicals used to treat corrosion and scale. Unfortunately, due to the vast number of microorganisms that could exist in any recirculating cooling system, as a non-oxidizing biocide is used the organisms can become resistant to that particular chemical are not affected and continue to grow in the water and require the attention of a water treatment technician.

How Does A Dual Alternating Biocide Program Work?

Continuous use of one single biocide in a water treatment program can lead to resistant flora and damaging conditions in the water, making a dual alternating approach ideal to control the biological growth. In a dual alternating biocide program, both oxidizing and non-oxidizing biocides are fed into the system on an alternating slug dosage based off of the continued monitoring of water conditions. Often times, to increase the effectiveness of non-oxidizing biocides, a dispersant is added to loosen and penetrate bio-films attached to metal surfaces in a system which allows the biocide to be more effective.

If you are interested in learning more about a dual alternating biocide program and how it can improve water conditions in your facility’s cooling system, visit or call (800) 849-1915.

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