31.3 The effectof ozoneon microorganisms
31.3.1 Vegetative bacteria
Vegetativebacterialcellsin watertend to be verysusceptible to ozone.Amounts
ranging from 106 to 10^7 cfu/ml can be reducedto undetectablelevelsafter5 min
when exposedto ozoneconcentrationsrangingfrom0.01 to 1.0 mg LĖ^1 (Haufele
and von Sprockhoff1973; Venosa1972).
Mooreet al.(2000)foundgaseous ozoneto be effectiveagainst a rangeof
Gram-positive and Gram-negativeorganismsat levels of 0.05to 2 ppm.The
effects werealso proven to be timedependent. Thisstudyalso investigatedthe
effects of organic soil on ozoneefficacyand concludedthat its presencereduces
the antimicrobialeffects.The studyconfirmsthat ozoneis onlyan effective
sanitizerwhenthe surfaces are cleanand free fromorganic soil.
31.3.2 Bacterialendospores
Bacterialsporesare muchmore resistant to ozone,owingto the presenceof the
sporecoat and the extraprotectionthis providesto the protoplast.Broadwateret
al.(1973)foundthat spores ofBacillusspp. were up to 15 timesmoreresistant
than theirvegetativecells.A study by Ishizakiet al.(1986)foundthat increasing
the relativehumidityincreasedthe effectiveness of ozoneas a sporicidalagent
and that no significant inactivation of sporesoccurredat humidities of less than
50%.
31.3.3 Fungiand fungal spores
Mooreet al.(2000)foundthat 2 ppmozonesignificantlyreducedthe numberof
fungiattachedto stainlesssteel couponswhileFoardeet al.(1997)determined
that levelsin excessof 6 ppmwererequired(9 ppmwhen attached to a surface).
31.3.4 Viruses
Viruses havean extremely low tolerance to ozonein low ozonedemand waters.
The ozoneinactivationof virusesin wateris limitedby the rate of diffusion
throughthe protein coatinto the nucleicacidcore,resultingin damageto the
viral RNA.Komanapalliand Lau (1998)found that bacteriophage was
completelyinactivatedby 600 ppmozonein phosphate buffer solutionafter 10
minutes.
31.4 Undesirableeffects of ozone
31.4.1 Constructionmaterials
The reactivenatureof ozonemeansthat it reactswithmanymaterialsincluding
textiles, organicdyes,metals, manyplastics,paints and naturalrubber.It can
also reactexplosivelywith grease and oils (Anon1998a).The rate of degrada-
tion of natural rubber can be reduced by the additionof anti-ozonants.Thiscan,
510 Handbookof hygiene controlin the foodindustry