Factors affecting UV

Reduction Levels

•         SANITIZATION

–        Defined as 50 – 99% reduction (2-log)

•         DISINFECTION

–        Defined as 99.99% reduction (4-log)

•         STERILIZATION

–        Defined as 99.9999% reduction (6-log)

•         DOSAGE is the product of Intensity & Time

•         DOSAGE

•         = INTENSITY X TIME

•         = microW/cm² X time

•         = microWsec/cm²

•         Note: 1000 microWsec/cm² = 1 mJ/cm²

Factors Affecting UV

•    UV can only be effective if it is absorbed by the target:

•     UV absorption in water is almost entirely caused by dissolved substances. Certain organic substances such as humic or fumic acids (tannins), and certain inorganic substances such as iron and manganese absorb UV.

•     Suspended solids shield microorganism and need filtration.

•     Hardness causes the formation of scale on the quartz sleeve surface and therefore prevents transmissibility.

•     Iron causes the staining of the quartz sleeve thereby impeding UV transmission

•     Lamp operating temperature levels is an important factor. The optimum being 40oC. The increase or decrease of temperature will affect UV energy levels. Quartz sleeves will minimize temperature fluctuations.

•     Good flow rate design does take into account energy level fluctuations.

Water Quality Effects

•         ABSORPTION

–        This varies according to the dissolved substances in water(mainly due to iron, humic acids and tannins)

•         TURBIDITY

–        This has an effect on scattering of light, absorption and light penetration

•         FOULING

–        Due to chemical and biological deposits (mainly inorganic scale: iron, magnesium, calcium, aluminum, manganese, sodium, and anionic carbonate, phosphate, sulphate and organic biofilms)

pretreatment required

•    Iron                < 0.3 ppm

•    Manganese          < 0.05 ppm

•    Hydrogen Sulphide      < 0.05 ppm

•    Hardness              < 7 gpg

•    Suspended Solids        < 10 ppm

•    Excessive colour, turbidity, iron or organics, require additional treatment

NSF Standard 55

•         CLASS A SYSTEMS

•    systems capable of producing an ultraviolet dose at the alarm setpoint equivalent to a UV dose of 40 mJ/cm² (40,000 microWsec/cm² ) at 254 nm

•     challenge organism is MS-2 Coliphage

•     must have a 254nm UV sensor to monitor UV transmission (set at 70%)

•     must have a flow control device

•     must have either a visual alarm, audible alarm or shut-off device (solenoid)

•     must have a NSF 53 turbidity filter for a general cyst claim (crypto & giardia are allowed)

•     must pass applicable structural integrity tests (eliminates Teflon)