Supplemental (or secondary) disinfection refers to additional water treatment techniques used beyond what is typically provided by municipal systems. These measures are essential for mitigating the risk of waterborne pathogens, especially Legionella, the primary cause of Legionnaires’ disease.

Maintaining appropriate disinfectant levels is a critical factor in preventing Legionella growth. Effective supplemental disinfection must tackle biofilm formation, complex plumbing networks, and specific water chemistry issues. Below is a summary of available secondary disinfection options.

Oxidizing Chemical Disinfection Systems

Chlorination

Chlorination introduces chlorine, commonly sodium hypochlorite,into the water supply to maintain a disinfectant residual.

Pros:

  • Well-documented effectiveness against various pathogens
  • Economical and widely available
  • Offers moderate biofilm prevention

Cons:

  • Limited efficacy against established biofilms (where most Legionella exist)
  • Can produce by-products like trihalomethanes (THMs)
  • Potential pipe corrosion if mismanaged

Monochloramines

Created by combining chlorine and ammonia, monochloramines offer a more stable disinfectant compared to free chlorine.

Pros:

  • Persistent residual, ideal for extensive plumbing systems
  • Better biofilm penetration than chlorine
  • Generates fewer harmful by-products

Cons:

  • Slower to disinfect compared to other oxidants
  • Can lead to nitrification in the system
  • Possible link to higher levels of nontuberculous mycobacteria (NTM)

Chlorine Dioxide

Chlorine Dioxide is a powerful oxidant introduced as a dissolved gas in water.

Pros:

  • Rapid action on biofilms and Legionella
  • Effective against a wide range of pathogens
  • Strong biofilm control

Cons:

  • Less stable in hot water; dosing is limited by the EPA
  • Requires specific precursor chemicals
  • By-products must be monitored frequently

Mixed Oxidant Solution (MOS)

MOS involves generating a mix of oxidants on-site for enhanced performance.

Pros:

  • Effective against Legionella and biofilms
  • Rapid disinfection
  • Safer precursor materials (typically just salt and water)
  • Broad antimicrobial activity

Cons:

  • Requires specialized equipment
  • Potential for pipe corrosion
  • Can produce THMs

Ozonation

Ozonation dissolves ozone gas in water to oxidize pathogens, including Legionella.

Pros:

  • Potent disinfectant
  • No residual chemical by-products if managed properly

Cons:

  • Short-lived residual effect limits reach
  • Not effective against distant or protected biofilm
  • High installation and operational costs
  • Risk of bromate formation in certain waters

Advanced Oxidation Processes (AOP)

AOP combines agents like ozone, hydrogen peroxide, and UV light to generate hydroxyl radicals.

Pros:

  • Highly effective on Legionella and biofilms
  • Leaves no harmful residuals

Cons:

  • Expensive and energy-intensive
  • Very short-lived disinfectant effect
  • Not suitable for long-term residual protection

Non-Oxidizing Chemical Disinfection Systems

Copper-Silver Ionization

Releases copper and silver ions to disrupt bacterial cell structures and biofilms.

Pros:

  • Long-lasting residual for biofilm and Legionella control
  • No hazardous chemicals or by-products
  • Effective regardless of water temperature

Cons:

  • Higher upfront installation cost
  • Less research available on efficacy for non-Legionella pathogens
  • Slower action than oxidative treatments

Other Non-Chemical Supplemental Disinfection Methods

Ultraviolet (UV) Light

Uses UV rays to deactivate microbial DNA, rendering pathogens harmless.

Pros:

  • Immediate microbial inactivation
  • No chemical by-products
  • Effective against resistant organisms like NTM and protozoa

Cons:

  • No residual effect; only disinfects water that passes through the UV system
  • Does not affect biofilms
  • Requires clear water to function efficiently

Nanobubbles

Nanobubbles are tiny gas bubbles that enhance microbial disruption and improve water quality.

Pros:

  • Can break into biofilms to neutralize Legionella
  • Environmentally friendly with no chemical residues

Cons:

  • Low or no residual disinfection
  • Emerging technology with limited long-term performance data

Dissolved Oxygen Removal

Dissolved Oxygen Removal reduces oxygen levels to create conditions unsuitable for aerobic pathogens like Legionella.

Pros:

  • Effective in reducing Legionella growth
  • Can minimize corrosion risks
  • No chemical precursors needed

Cons:

  • High implementation costs
  • Limited data on biofilm control
  • Still a relatively new approach in this application

Key Considerations for Selecting a Disinfection Strategy

Because Legionella and other waterborne pathogens have unique survival mechanisms, choosing the right solution often requires expert, unbiased input. Secondary Disinfection Systems offers this independent expertise and can tailor recommendations to your facility’s design, water chemistry, and budget.

When developing a plan, we consider:

  • Biofilm Control: Technologies like copper-silver ionization, chlorine dioxide, monochloramines, and MOS are particularly effective.
  • Residual Effect: Long-lasting solutions like monochloramines and copper-silver ionization reduce the chance of recolonization.
  • Water Chemistry: Adjusting pH, hardness, and conductivity is crucial for optimizing disinfection outcomes.

In many cases, a multi-layered approach yields the best protection. For example, point-of-use treatments (UV, AOP, or POE filtration) can be paired with system-wide disinfectants like copper-silver ionization or monochloramines.

Contact Secondary Disinfection Systems today at 888-416-8626 or info@secondarydisinfectionsystems.com to determine the most effective secondary disinfection strategy for your building.

We can help you with all of your water treatment needs. Contact a Secondary Disinfection Systems expert today.

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