What is the Difference Between Secondary Disinfection and Supplemental Disinfection?

Both secondary disinfection and supplemental disinfection are terms used in Legionella disinfection discussions. There is some ambiguity in the usage of the terms, so it is helpful to consider some of the differences.

• In general, secondary disinfection tends to denote a higher level of disinfection than supplemental disinfection.
• Secondary disinfection may also infer a residual disinfectant presence. This is important because the level of disinfectant is a risk factor for Legionella. Using this distinction, here are two examples:
  • Monochloramine treatment provides a long-lasting residual effect, so it would be considered secondary disinfection.
  • Ultraviolet light treatment can be an effective treatment for waterborne pathogens but does not provide residual disinfection, so it would be considered supplemental disinfection.
• Secondary disinfection in some applications carries a specific requirement of a 99.99% reduction in certain microorganisms, while supplemental disinfection may provide a reduction at a lower or non-specific level.
• Some organizations may refer to primary and secondary disinfection as that which occurs at the municipal level while supplemental disinfection occurs in your facility.
• Some define supplemental disinfection as an additional disinfectant of the same type. For instance, if the municipality adds chlorine, supplemental disinfection would consist of adding more chlorine locally. Secondary disinfection would only be a different modality (method) to disinfect the water. Copper-silver ionization on top of the existing chlorine would be a secondary disinfectant.

Here are some waterborne pathogen and Legionella disinfection options that tend to fall in one category or another:

Secondary Disinfection Methods

• Chlorination
• Monochloramines
• Chlorine Dioxide
• Mixed Oxidant Solution (MOS)
• Ozonation
• Advanced Oxidation Process (AOP)
• Copper-Silver Ionization

Supplemental Disinfection Methods

• Ultraviolet (UV) Light
• Nanobubbles
• Dissolved Oxygen Removal

Given the possible ambiguity in the terms secondary disinfection versus supplemental disinfection, it is important to check your specific requirements to ensure you are providing the proper level of disinfection for your application. You can reach us at info@legionellacontrolsystems.com or 888-416-8626 right now if you would like assistance with keeping your water safe with either secondary or supplemental disinfection.