contactwiththe disinfectant. The strengthof the disinfectantused can be
affectedby decompositionof soil, and bacteria that survive owingto insufficient
disinfectioncan multiplyin soil residues and contaminatethe product.Lower
soil concentrations permit the use of combined cleaningand disinfectionagents.
Thermaldisinfection
Thermaldisinfection is effectiveonlyif all plantcomponents are subjectedto
the required temperatureand time.Thermaldisinfectionkillsbacteria,but does
not removethemfromthe system± `sterilesoil'is formed.
Methodsof thermal disinfectionincludehot water(preferablywithdirect
flowthroughequipment and pipes), steamat a temperature between 70 ÎC and
80 ÎC, maintained for 15 minutes(for productionplantswith a largevolume,e.g.
tanks),and hot pressurizedwater. Sporesof somebacteriophages and some
mouldfungiare killed only if keptat temperaturesof 130±140ÎC for at least 20
minutes. It is importantto preventthe intakeof contaminatedair duringthe
coolingphaseafterthermal disinfection.
Chemicaldisinfection
Theeffectivenessof the variousdifferentchemical disinfectantsdepends on
concentration, temperature, reaction timeand soil load. Activated chlorine
decomposes rapidly withincreasing temperature,and thereforecan only be used
coldand without collection.It cannotbe usedfor standingdisinfectionbecause
of its corrosive effect on stainlesssteel.Peroxidecompounds, suchas hydrogen
peroxide and peracetic acid, are alsosuitable as additivesto acidcleaning
solutions. Peracetic acid can be usedas a colddisinfectantat low temperatures.
Iodophorshavegoodbactericidal and sporicidaleffects,but thereare problems
withflushingthemout and a risk of reaction withplasticpartsor corrosion
effects. They are not suitable for temperatures above 40 ÎC. Quaternary
ammonia compounds have good wetting properties and surface activity.
Disadvantagesincluderesidueformation and a strongtendencyto foaming.
They are rarely used in CIP processes. Halo acids have comprehensive
biological effectsand are usedin combination withacid carriers.Theyare
completely free of foamand havegoodflushingproperties.
The top diagramin Fig. 27.3 shows a pocket-free designfor processpipelines
and all integratedcomponentsin a functionalsystem, describedas a hygienic
design.By comparisonwith the standard installation(the lowerdiagramin Fig.
27.3),the hygienicdesignreduces cleaning timesignificantly, whichmeansthat
production timecan be extended.
27.3 Factors determiningthe effectivenessof a CIP system
27.3.1 Typeof CIPsystem
The cleaning parameters can be optimized by selectingthe rightCIP system.
The fourmostcommonlyusedCIP systemsare described below.
Improving cleaning-in-place (CIP) 429