Definition
A slimy layer formed by bacteria, fungi and algae on the inner surfaces of water systems within a polysaccharide matrix; it provides nutrients + protection for Legionella and is up to 1,000× more resistant to disinfectants than free-floating cells.
Detailed Explanation
Biofilm is a slimy layer that bacteria and microorganisms form on the inner surfaces of wet systems in four stages: (1) Attachment — free bacteria stick to the surface (24–72 h); (2) Colonisation — surface colonies form (1–2 weeks); (3) Maturation — a protected 3D structure embedded in a polysaccharide matrix (EPS) (2–4 weeks); (4) Dispersion — fragments break off and seed new biofilm elsewhere. The biofilm layer is 100–500 μm thick, resists flow, and renders most chemical disinfectants 95%+ ineffective.
Why It Matters
Biofilm creates three critical problems in humidification hygiene: (1) DISINFECTANT RESISTANCE — UV cannot reach into the shadow, chlorine does not penetrate the matrix, antibiotic resistance forms under the layer. Legionella is 1,000× more resistant inside biofilm. (2) HEAT-TRANSFER LOSS — biofilm on a heat-exchanger or tank wall acts as insulation, lowering thermal efficiency. (3) PRESSURE DROP + FLOW REDUCTION — pipe ID narrows under biofilm, system pressure drops, nozzle flow suffers. The only effective measure is prevention: continuous flow + RO pre-treatment + UV + periodic chemical cleaning (acid + alkali rotation).
Practical Example
A textile plant in Kayseri saw UV-disinfection efficacy drop from 99% to 70% after 18 months in its evaporative tank; microbiology returned 250 CFU/L of Legionella. NKT inspection found a 2 mm biofilm layer on the inner tank wall. The fix: 2% citric-acid wash + 1% sodium-hypochlorite disinfection + in-tank polish. UV recovered to 99.9% and microbiology returned to zero. A yearly chemical-clean protocol was added.
Engineering Note
Biofilm-prevention protocol: (1) Surface quality — AISI 316L electropolished interior Ra < 0.4 μm; biofilm attaches poorly; (2) Flow velocity > 1.5 m/s — shrinks the laminar layer and adds mechanical shear; (3) Chemical regime — semi-annual acid + alkali rotation (2% citric + 1% sodium hydroxide); (4) Online monitoring — ATP bioluminescence test (10 min) for on-site quick checks; PCR microbiology twice a year. Modern UV reactors integrate ATP sensors for real-time biofilm risk monitoring.
NKT Application Link
For this application NKT – Nem Kontrol Teknolojileri supplies the Neptronic SKH high-pressure atomisation system and the Neptronic SKVF evaporative cooler. Unit-selection support is based on space conditions, humidification load and the feed-water analysis; technical service and spare parts are provided. Design and installation of water treatment, as well as engineering design, installation and commissioning, remain within the scope of the facility's designer, contractor and water-treatment specialist.
