Biofilm: what it is, where it grows, and what it costs.

What biofilm is

Biofilm is a community of microorganisms attached to a surface and wrapped in a slimy matrix they produce, called extracellular polymeric substance (EPS). The matrix protects the cells inside from drying out, from cleaning and from disinfectants. That is why biofilm is harder to remove than free-floating microorganisms, and why it comes back after a surface is cleaned.

How it forms

1. Attachment. Free-floating microorganisms land on a wet surface and stick.
2. Matrix. They multiply and produce EPS, which anchors and shields the colony.
3. Maturation. Layers build up and more species join, making the film thicker and tougher.
4. Dispersion. Pieces break off and seed new surfaces downstream.

Where it costs you

• Cooling coils and drain pans

  Biofilm on the coil raises airside pressure drop and insulates the fins, so fans work harder and capacity falls. Drain pans add odors.

  Cognituv Grid →

• Ducts and plenums

  Dark, damp duct sections hold growth that the airstream passes over on its way to occupied rooms.

  In-duct UV-C →

• Cooling towers and building water

  Biofilm in fill, basins and piping reduces heat transfer, drives corrosion and shelters Legionella. ASHRAE Standard 188 covers how to manage the risk.

  Cooling tower UV-C →

• Pipelines and gas systems

  Sulfate-reducing bacteria in biofilm produce H₂S, sour gas and drive microbially influenced corrosion.

  Oil & gas →

• Food contact surfaces

  Listeria and other pathogens persist in biofilm in cold, wet areas such as drains, coolers and conveyors.

  Industrial UV-C →

Common culprits

Where UV-C fits

UV-C is most useful against biofilm when it runs continuously on the surfaces where biofilm forms, such as cooling coils and drain pans, so a new film can’t get established. It is less effective on thick, established biofilm, which shields the cells underneath, so heavily fouled surfaces are usually cleaned first and then kept clean.

The research is candid about the limits. A 2024 review of 58 UV and biofilm studies found that methods vary widely, which makes results hard to compare. Food-safety studies report that UV-C combined with sanitizers works better than either alone, and that the surface material matters. UV-C is a tool to keep surfaces clean between cleanings, not a replacement for cleaning.

Proving it

Biofilm control is easy to claim and hard to see, so Cognituv measures it. On HVAC systems, coil pressure drop and supply-air temperatures show whether a coil is fouling. UV-C sensors confirm the lamps are delivering output. Swabs before and after show what’s on the surface. Cognituv Connect keeps those readings together, measured against a baseline agreed for your site.

Cognituv Connect → Book an assessment →

Research