The great dissolved oxygen debate and trial update

The long term dissolved oxygen technology comparison is now in its 18th month. To recap two dissolved oxygen monitors are installed on an aeration lane at a UK Waste water treatment works.

Both systems feature the ATi air blast AutoClean system, the only difference is that one used the tried and tested galvanic sensor with a Teflon (tm) membrane while the other has our optical sensor.

After 17 months of maintenance free operation it can be seen from the attached data there is still nothing between the monitors. To emphasise, the sensors on these monitors have still never been manually cleaned. The calibration values were checked in December 2010 and the pre calibration and post calibration values for both sensors were less than 1% apart.

In summary, if a comparison is made between efficiently auto cleaned sensors the cost of ownership for optical systems is around 20 times that of galvanic system for no major performance improvement. ATi can supply both systems so ultimately the choice will be down to the end user.

In December 2010 both sensors after 17 months of running with zero manual intervention are still clean and still in calibration.

There seems to be confusion over the term fluorescence and luminescence with various claims being made about the advantages of one technique over another. To clear this up lluminescence is the emission of visible light without heat. It is contrasted with incandescence where visible light is emitted as a result of heat. Fluorescence falls under the category of luminescent light.

Other types of luminescent light include phosphorescence or bioluminescence. These types of luminescence are distinguished by the source of energy that produces the release of electromagnetic radiation and by the decay time duration.

It is misleading to say that a fluorescent sensor will give better performance than a luminescent one; a fluorescent sensor is a luminescent sensor.

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