Definition
A method of inactivating bacteria, viruses and fungi by exposing water to ultraviolet-C (UV-C, 254 nm) light; the primary disinfection layer for Legionella control in adiabatic humidification systems.
Detailed Explanation
UV disinfection works by forming dimers in DNA thymine bases, halting cellular replication. UV-C at 254 nm is the peak biocidal wavelength; low-pressure mercury or high-pressure amalgam lamps emit it. Dosage is mJ/cm² (millijoules/cm²): 10 mJ/cm² gives 99% kill for Legionella, 30 mJ/cm² 99.99% (FDA + EPA guidance). A standard UV reactor uses an AISI 316L stainless shell with quartz lamp sleeve, 1–5 s contact time, capacity 100–5,000 L/h. Lamp life 9,000–12,000 h (≈ 12 months of continuous operation).
Why It Matters
UV is the most effective layer in adiabatic humidification hygiene architecture: no chemicals, no waste, instant action (seconds), 99.99% of bacteria inactivated at a 30 mJ/cm² dose. But it is not sufficient alone — biofilm shadows the light, turbid water absorbs UV (below 85% transmission, efficacy drops 50%), and non-circulating water nurtures bacteria far from the lamp. So UV is always combined with filtration + RO + continuous circulation. Capex €1,500–8,000 (by capacity); annual lamp €200–800. ROI: the most economical technology that zeros a single Legionella incident risk.
Practical Example
A hotel SPA in Bursa runs evaporative humidification + a recirculating water bath. The original design lacked UV; after 6 months a microbiological test found 850 CFU/L of Legionella (control limit 10 CFU/L). The system was shut down and a UV-C reactor delivering a dose of ≥ 30 mJ/cm² plus tank recirculation were added. The next test came back zero, and every 6-month re-test for 4 years has stayed at zero. Lamp life 11 months, annual maintenance €350.
Engineering Note
UV sizing: dose (mJ/cm²) = UV intensity (mW/cm²) × exposure time (s); exposure time is set by the flow rate through the reactor. For critical applications, target ≥ 40 mJ/cm² (EPA Long Term 1 enhanced). A bypass alarm is mandatory — when the lamp fails, water must divert or the system stops. Maintenance: lamp swap every 12 months or when the UV-intensity sensor reports a 70% drop, quartz sleeve cleaning every 3 months (acid wash), full overhaul annually. Typical labour 30 min/year.
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.
