In an ozone water treatment system, a very high percentage of ozone is transferred to the water and used. A small part
passes through the ozone water mixing system and leaves the process. In some ozone water treatment systems the vent
gas must be treated with a vent gas treatment system using an ozone destroyer. In these situations, it may be required
to know the ozone in the vent gas for regulatory purposes. The ozone concentration in the vent gas should be less than
0.1 ppm. So a low concentration ozone monitor would be needed.
Low concentration monitors can be made using UV photometers similar to the high concentration monitors or can employ electrochemical sensors as used in the some ambient ozone monitors. In either case a sample of the gas is taken to be measured. As with the other monitors, alarm relays can be supplied to alert operators that the vent gas is no longer in specification.
The need for such monitors depends on the air pollution regulations under which the ozone water treatment system is operating. In the US, the Clean air Act requires that in large scale gas releases that ozone levels be kept under 0.1 ppm. In some cases, the amount of ozone is so low that it does not require any treatment. In more sensitive areas, outputs below 0.08 ppm must be maintained. The ozone destroyers are highly reliable devices that work by simple principles. Thus continuous monitoring may not be necessary.