31.1 Introduction
Discovered in 1840 by German chemist Christian Scho»nbein, ozone is an
allotrope of oxygen, naturally present as a colourless gas with a distinctive
odour. It is produced in the upper atmosphere by the action of ultraviolet
radiation on oxygen molecules and at ground level as a by-product of
photochemical reactions involving oxygen, nitrogen and hydrocarbons (Graham
1997).
Ozone is an effective antimicrobial agent due to its high oxidizing potential
(+0.27 volts) compared with oxidizing agents such as hypochlorous acid
(HOCl), the active chlorine species in aqueous solution, which has an oxidation
potential of +1.49 volts. The only substances with a higher oxidation potential
are fluorine, fluorine dioxide and the oxygen radical (Gurley 1985).
31.1.1 Chemical characteristics and production of ozone
Because of its highly reactive nature, ozone autodecomposes over a relatively
short time to produce oxygen. This means that ozone does not persist in the
environment and will only be present for a short period of time after its
application. It cannot, therefore, be stored and must be producedin situ.The
concentration of ozone is quoted as either parts per million (ppm) or milligrams
per litre (mg Lˇ^1 ). 1 ppm is equivalent to 0.00196 mg Lˇ^1 (the equivalent of
1.96 10 ˇ^6 mg mˇ^3 ).
Ozone can be used as an antimicrobial agent in two forms, either in the
gaseous state or dissolved in purified water to produce ozonated water. Gaseous
31 Ozone decontaminationin hygienemanagement...
L. Fielding and R. Bailey, University of Wales Institute Cardiff,
UK