18-20 April 2023
Ozone is an effective means for sanitising PW (purified water), HPW (highly purified water) and WFI (water for injection) systems. But how high should the concentration of ozone be so that the sanitisation effect (i. e. germ reduction) is sufficient?
Basically, the use of ozone only makes sense in systems that store and distribute the water cold or at room temperature. The usual use is up to max. 35°C.
In hot-stored PW or WFI systems, the half-life of ozone shortens so significantly from 40°C that sufficient effectiveness is questionable. In addition, hot storage itself inactivates germs, so that the additional use of ozone does not make sense anyway.
Water storage and distribution systems that are operated at room temperature generally have an increased risk of germination - compared to hot systems. For these cold systems, the decisive question is whether the ozone is used for a short time (1-2 h) or for a long time (>6 h) to prevent microbiological growth. For short periods, ozone values of > 50 ppb are usually required. For long exposure times, lower values are sufficient. There, it should be at least 20 ppb ozone.
In cosmetics or drinking water treatment, values above 300 ppb are also used. Such high values are unusual in the area of pharmaceutical GMP water qualities, because there the ozone usually has to be reduced to below the detection limit (5 ppb) for critical applications. For PW and WFI systems there is still a requirement that they must contain "no added substances", which is why in the loops the ozone is typically catalytically degraded by UV light before the water is used.
The needed ozone concentration may be higher in large systems or in hard-to-reach locations with poorer flow. The above-mentioned ozone values should therefore be achieved in the return flow of the distribution system. The ozone concentration to be achieved should be determined as part of the DQ (design qualification) of the water system.