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 can harbour Legionella and can reduce disinfectant access. The relationship between attached and waterborne counts varies by system and must be assessed by an appropriate sampling plan.
Disinfectant Resistance
Attached organisms can respond differently from free-floating cells. Evidence from one organism, biofilm matrix, surface, concentration and contact time must not be generalised to every system.
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.
Evaluating Chlorine Dioxide for Biofilm Control
Chlorine dioxide (ClO₂) is an oxidising biocide, but biofilm performance cannot be inferred from chemistry alone. Product evidence must identify the organism, EPS and water matrix, surface, concentration, contact time, demand and test conditions. An assessment may consider:
Matrix Transport
Transport through an EPS matrix varies with the biofilm and test conditions. Confirm that the selected product's evidence covers the relevant matrix, concentration and contact time.
Oxidises the EPS
Oxidation may alter EPS under tested conditions. Do not assume complete matrix removal; cleaning and a defined verification method remain necessary.
Organism Control
Any reduction claim must identify the tested organism, matrix, concentration, contact time and conditions. A test result does not establish prevention of recolonisation in a working system.
Prevention vs Remediation
Ongoing Control
Labelled regular dosing may support a monitored biofilm-control programme. It does not guarantee prevention or establish a universal low dose. The programme may include:
- Measuring residual at defined system locations
- Monitoring indicators selected for the specific system
- Managing organic demand, cleaning and hydraulics
- Measure chemical use and cost over time
Remediation (When Needed)
Established biofilm requires a site-specific remediation plan based on product conditions:
- Label-defined concentration and contact time
- Defined treatment stages and acceptance criteria
- May require flushing of dead legs and low-flow areas
- Recording chemical use and programme cost
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. Disruption is not elimination: a 2026 Pseudomonas study investigated dispersal, not chlorine dioxide.
Explore the hub Dispersal, removal and post-treatment verificationWhat is ChloroKlean?
Learn about ChloroKlean products, how chlorine dioxide works, and applications.
Read the guideHospital Case Study
Presentation summaries depict later hospital Legionella SG1 non-detection; original sampling records are unavailable. Non-detection does not establish biofilm removal, Legionella elimination or treatment causation.
Read case study