UV Dose and UV Transmittance in Water Disinfection: What They Mean
Quick answer: what is UV dose?
UV dose is the amount of germicidal ultraviolet energy delivered to water as it passes through a UV reactor. Delivered dose depends on lamp output, reactor design, water flow, UV transmittance, lamp condition and fouling of the quartz sleeve.
What is UV transmittance (UVT)?
UV transmittance describes how much ultraviolet light can pass through a water sample, typically at 254 nm. Water with lower UVT absorbs more UV light, which can reduce the dose reaching microorganisms.
Why flow rate matters
At higher flow, water spends less time inside the UV reactor. If a system is operated beyond its validated or specified flow, delivered dose may fall below the required level.
What can lower delivered UV dose?
- Low UV transmittance
- Excessive flow
- Lamp ageing
- Quartz sleeve fouling
- Low lamp output or electrical faults
- Turbidity or suspended solids that shield microorganisms
What should be checked before selecting a UV system?
- Required flow rate
- UV transmittance or source-water quality
- Target application and required dose
- Reactor validation/specification
- Lamp and sleeve maintenance access
- Upstream filtration and turbidity control
Frequently asked questions
Is UV dose the same as lamp wattage?
No. Lamp wattage alone does not define delivered dose. Reactor design, UVT and flow also matter.
Does clear-looking water always have high UV transmittance?
No. Some dissolved substances can absorb UV even when water looks clear.
Can UV remove TDS or hardness?
No. UV is a disinfection process and does not remove dissolved salts or hardness.
Reference
UV-system selection should follow the UV manufacturer’s validated performance data and water-quality requirements. See ABHIRO’s industrial UV systems and the Knowledge Centre.
