Water treatment by UV is a physical disinfection process: UV-C photons at around 254 nm are absorbed by the nucleic acids of bacteria, viruses and protozoa, forming pyrimidine dimers that block replication. Because no chemicals are added, no disinfection by-products are formed and the taste of the water is unchanged. UV is normally the final barrier after filtration and, where needed, reverse osmosis.
UV-C radiation is absorbed by DNA and RNA. Thymine dimers prevent the micro-organism from replicating, so it is inactivated even though it may still be detectable by culture-independent methods. Inactivation follows first-order kinetics with the applied UV dose.
The effective dose is the product of UV intensity and residence time (mJ/cm2). Annular reactors with a quartz sleeve and a defined flow profile are used so that every parcel of water receives the required dose; the sleeve must be cleaned because fouling attenuates UV.
UV does not remove particles, dissolved solids or colour, and micro-organisms shielded inside particles are protected. UV therefore works best after filtration, and its effect leaves no residual disinfectant in the distribution network.
| Low-pressure mercury | 254 nm monochromatic, high efficiency | Municipal and industrial water disinfection |
|---|---|---|
| Low-pressure mercury | 254 nm monochromatic, high efficiency | Municipal and industrial water disinfection |
| Medium-pressure mercury | Broad spectrum, high power density | Large plants, photochemical oxidation |
| UV-LED | Mercury-free, instant on/off, compact | Point-of-use and small systems |
UV water treatment is used wherever water must be disinfected without adding chemicals.
Final barrier after filtration
Ultrapure and rinse water loops
Disinfection before discharge or reuse
Recirculating systems without residual chemicals
Filling lines and CIP water
Reducing chloramine load
UV water treatment only works if the lamp output stays within specification, so the UV dose delivered to the water is a measurement problem.
| UV dose (mJ/cm2) | The quantity that must be verified to prove inactivation | UV-int140 / UV-int150 |
|---|---|---|
| UV dose (mJ/cm2) | The quantity that must be verified to prove inactivation | UV-int140 / UV-int150 |
| UV intensity (mW/cm2) | Monitored to detect lamp ageing and sleeve fouling | UV-int150 / UV-intM |
| Lamp output drift | Detected by routine measurement, not by the lamp's rated life | UV-intS / UV-int159 |
It adds nothing: the process is photonic and leaves no chemical residue.
Dose depends on intensity at the water, residence time and quartz transmission - a fouled sleeve can cut it in half.