Key Components of a Cooling Tower System Biocide Program

Cooling tower systems can be ideal environments for unwanted microbiological activity to flourish. They offer warm, wet conditions with food sources coming from the air and sometimes even process contamination. This microbiological activity can lead to corrosion, reduced heat transfer, blockages, and even illness.

Choosing the correct biocide program is crucial to maintaining efficiently operating systems to maximize energy efficiency and reduce public health risks. Key items to consider when selecting a biocide program for your cooling tower include:

Evaluate System Characteristics

• Consider factors such as water quality, pH, temperature, and the presence of contaminants or nutrients that can affect biocide performance.
• Determine the water volume of the system you are treating. Non-oxidizing biocides are commonly fed based on volume. You need to feed the correct amount for a toxic dose.
• Assess the cooling tower system’s metallurgy and potential corrosion issues. Some biocides may be more corrosive than others under the right conditions.
• Evaluate the system’s holding time index (aka, half-life or retention time). Some biocides require a longer contact time of a toxic dose to be effective.
• Review system design to identify and eliminate areas with low or no flow (dead legs). Without flow, the water in dead legs does not receive biocide treatment.
• Determine if there are any discharge limits or toxicity concerns that may restrict the use of certain biocides.

Assess Microbial Loa

• Evaluate the types and levels of microorganisms present, including bacteria (IRBs, SRBs, & slime formers), algae, fungi, and viruses, since different biocides may be more effective against specific microbes.
• Understand the oxidizing biocide demand and potential for process contamination. This can significantly impact biocide selection and dosage.
• Assess cooling tower cleanliness. It is important to routinely clean and disinfect cooling tower systems. No biocide program can provide good microbial control in a dirty system.

Determine the Type of Biocide

• Oxidizing biocides (e.g., chlorine, bromine, chlorine dioxide) kill microorganisms by destroying their cell walls through oxidation. They are fast-acting and often cost-effective.
• Non-oxidizing biocides (e.g., glutaraldehyde, isothiazoline, DBNPA) kill microorganisms through various “poisoning” mechanisms. They can be more expensive and require longer retention times.
• A dual-biocide program is a common practice that uses both an oxidizing AND non-oxidizing biocide to utilize the advantages of each.

Implement and Monitor

• Implement a controlled dosing system to maintain the optimal biocide concentration (e.g., pumps, brominators, timers) and proper frequency of application. The feed point and time of each biocide application can be critically important to its effectiveness and impact on the rest of the water treatment program and the system.
• Biocides need to be added to the system quickly enough to be effective. Ideally, non-oxidizing biocides need to be dosed within 60 minutes (which may require a higher output chemical dosing pump), and oxidizing biocides dosed over a 1-to-4 hour timeframe (followed up with free halogen residual testing 1 hour after feed).
• Regularly monitor the system to ensure effective microbiological control. This can include testing (e.g., dipslides, plate counts, ATP), monitoring biocidal concentrations (e.g., free chlorine, ORP), and using online microbiological monitoring (e.g., bioDART™).

By considering factors such as system characteristics, microbial load, and biocide properties, you can select the most appropriate biocide for your cooling water system to help ensure its efficient and safe operation. Contact Chem-Aqua today for help with your cooling system’s microbiological needs.

*It is a violation of Federal law to use a biocide in a manner inconsistent with the label instructions.