31.2 Historical usesof ozone
31.2.1 Water treatment
Someof the earliest recordedindustrial usesof ozoneare in the treatmentof
watersupplies. Thereare many municipal drinking waterfacilities in France that
haveemployedozoneas the primarydisinfectantsince 1906(Gurley1985).The
abilityof ozoneto retainits highoxidation potential when dissolvedin wateris
necessary for waterdisinfectionas ozonedisinfects by oxidizingmicrobialcells.
The ozonemoleculeand otherspeciespresentwill react withany organic
molecules and will ultimately be oxidized to carbon dioxideand water. Different
sourcesof waterwill contain varyingamountsof organic matter and the waterto
be disinfectedwill,therefore,havea specificozonedemand. Thisis the amount
of ozoneconsumed by a givenvolumeof waterin oxidizingthe organicmatter
and mustbe satisfiedbeforethereis any antimicrobialeffect. The ozonedemand
and the concentration of dissolved ozone are the two major factors that
determine the degreeof disinfection.Theremust be a residual concentrationof
ozoneto act as an antimicrobialagent.
A studyby Broadwateret al.(1973)indicatedthat ozonedisinfectsby an `all or
nothing'actionin water.If the applieddosageis high enoughto oxidizethe organic
matterand the microorganisms,all the microorganismswill be inactivated.When
the dosageof ozoneis too low,it is quicklyexhaustedby oxidationof the organic
matterand a significantnumberof microorganismswill survive.
Ozoneis also usedto disinfectwatercontainingnatural organic matter (Cho
et al.2003)and has proved effective againsta numberof organisms,including
Cryptosporidium parvumoocysts andClostridiumperfringensspores, whichare
relatively resistantto chlorine (Finchet al.1993;Venczelet al.1997).
31.2.2 Thefoodindustry
The use of ozoneas an antimicrobialagentin the foodprocessing industry has
excited interestdue to a number of factors. Ozonewas approved for use by the
US Food and DrugAdministrationon 26 June 2001 for use as an antimicrobial
agentfor the treatment,storageand processingof foodsin the gaseousand
aqueous phases.
It has beeninvestigatedfor use as a decontaminantof actualfoodproducts
but also has a majorrole to playin the decontaminationof equipmentand the
foodprocessing environment. Ozone gas has beenfoundto be effectiveat
reducingthe levels of viableorganismsattachedto stainlesssurfaces(Mooreet
al.2000).As it leavesno residueon the surface,it may havepotentialfor use as
a terminalsanitizer for foodcontact surfaces.It must, however, be employed
following cleaning, as ozoneis highlyreactive and its microbicidal effectsare
lost uponcontactwithany other organic material, suchas fooddebris.It is not,
therefore, a replacementfor goodhygienepracticessuchas cleaningbut can
enhance the efficiencyof a good cleaningpolicyif usedcorrectly.Casestudies
concerningthe effects of ozoneas a terminalsanitizer in the foodindustry, for
boththe environmentand equipment,are presentedin section 31.5.1.
Ozone decontamination in hygiene management 509