Reviewed by
Gavin Owen
Managing Director, ChloroKlean
What is Biofilm?
Biofilm is a community of microorganisms-bacteria, fungi, algae-that attach to surfaces and produce a protective matrix called extracellular polymeric substances (EPS). This slimy coating allows microorganisms to survive in conditions that would otherwise be inhospitable.
In water systems, biofilm forms on pipe walls, tank surfaces, cooling tower fill, and any other wetted surfaces. The EPS matrix provides:
- Protection from disinfectants: The matrix acts as a barrier, reducing biocide penetration
- Nutrient trapping: Organic matter accumulates, providing food for continued growth
- Shelter for pathogens: Harmful bacteria like Legionella can survive within biofilm even when the surrounding water is treated
- Resistance to flow: Biofilm can survive high flow rates that would dislodge individual cells
Why Biofilm is a Concern
Legionella Harbour
Biofilm provides an ideal environment for Legionella bacteria to multiply, protected from routine water treatment. Studies show Legionella concentrations within biofilm can be 1,000 times higher than in surrounding water.
Disinfectant Resistance
Bacteria within biofilm can be up to 1,000 times more resistant to disinfectants than free-floating (planktonic) bacteria. This means standard disinfection may appear effective while biofilm remains.
Water Quality Issues
Biofilm can cause taste and odour problems, discoloured water, increased chlorine demand, and accelerated corrosion of pipework. Sloughed biofilm can contaminate downstream processes.
How Chlorine Dioxide Controls Biofilm
Chlorine dioxide (ClO₂) is particularly effective against biofilm due to its unique chemical properties. Unlike chlorine, which reacts quickly with organic matter at the biofilm surface, chlorine dioxide:
Penetrates the Matrix
As a dissolved gas, chlorine dioxide diffuses through the EPS matrix rather than reacting only at the surface. This allows it to reach bacteria deep within the biofilm structure.
Oxidises the EPS
Chlorine dioxide oxidises the polysaccharide bonds that hold the biofilm matrix together, breaking down the protective structure and exposing the bacteria within.
Kills Exposed Bacteria
Once the biofilm is disrupted, chlorine dioxide kills the released bacteria through oxidation of cell membranes. This dual action prevents recolonisation.
Prevention vs Remediation
Prevention (Preferred)
Regular, low-dose chlorine dioxide treatment prevents biofilm from establishing by:
- Maintaining residual disinfectant throughout the system
- Inhibiting microbial attachment to surfaces
- Controlling organic matter accumulation
- Lower chemical usage and cost over time
Remediation (When Needed)
Removing established biofilm requires more intensive treatment:
- Higher initial dosing concentrations
- Extended treatment periods (weeks to months)
- May require flushing of dead legs and low-flow areas
- Higher overall cost than prevention
Important Safety Information
ChloroKlean products are biocidal products. Always read the product label and Safety Data Sheet before use. Use biocides safely. For biofilm remediation programmes, consult our technical team for guidance on appropriate dosing and monitoring.
Related Information
Biofilm Learning Hub
Explore evidence-led guides on EPS, disinfectant tolerance and biofilm in managed water systems.
Explore the hubWhat is ChloroKlean?
Learn about ChloroKlean products, how chlorine dioxide works, and applications.
Read the guideHospital Case Study
See how chlorine dioxide eliminated Legionella and biofilm in a hospital water system.
Read case study