Air in water - effect on UV dose

[mazee]

Hi,

Imagine UV unit used for disinfection of potable water. The turbidity of water is ~0.2 NTU – measured in lab. However at times the on-line analyser for the unit reads above detection limit (>30 NTU) – due to air presence – lots of small air bubbles which clear if sample is left for ~15 minutes.

I understand why the sample of this “super aerated” water appears white (visible light refraction through multiple air-water and water-air inter-phases) and why on-line turbidity instrument has spurious readings (scatter instrument).

My concern is whether the presence of these air bubbles affects UV dose and absorbance?
In my understanding UV waves would just simply change direction multiple times inside the unit but the absorbance should not be increased (or increase would be negligible) similarly the dose would not change (much).

The unit is also equipped with UV dose sensor and this did not detect any significant changes when the air was present in the water which would confirm my thinking was correct.

Any advice on the issue would be appreciated. Thanks.

 

[DixitDominus]

I would prefer to have no bubbles at all.

UV penetration as water flows through the unit is calculated only through absorption from water, no reflections / refractions are taken into account when sizing and flow rating such units.

 

[mazee]

so are reflections/refractions not accounted for because their effect is negligible or undesired?