Sodium hypochlorite
Sodium hypochlorite is very effective against all types of micro-organism (including spores). It is inexpensive in comparison to other disinfectants and it is unaffected by hard water. The efficacy of a solution is dependent on its pH.
Care should be taken with storage and stock rotation of sodium hypochlorite. The product will naturally lose available chlorine (by conversion to sodium chloride – not chlorine gas) and should generally be used within 3 months of manufacture. If stored in direct sunlight the rate of loss of available chlorine increases. It should also be stored separate from other chemicals, particularly acids, as lethal chlorine gas will be released if these two products are mixed.
Ideally Sodium hypochlorite should be automatically dosed via a chlorine compatible dosing unit to ensure that it is used at the correct strength.
Chlorine dioxide
Chlorine dioxide is mainly used for the disinfection of water systems but is also being utilised for surface disinfection in CIP. It is produced by mixing under controlled conditions:
Chlorine with chlorite
Acid with hypochlorite and chlorite
Acid with chlorite
Or using a stabilised form of chlorine dioxide
All the above methods must be carried out using specialised dosing systems with safety precautions built in. The main advantages that chlorine dioxide has as a disinfectant are: Broad spectrum of activity at low concentrations, rapid microbiological killing action, dosing is reliably and automatically controlled, it does not readily react with organics to form ecotoxic and bio accumulative by-products and it is much less tainting than chlorine.
It is approved for potable water use (0.5mg/l causes no objectionable taste, whereas the same concentration of chlorine would). It will typically be used at 0.3mg/l in water treatment and at 5 to 15 mg/l (ppm) for surface disinfection.
Hydrogen peroxide
Hydrogen peroxide works in the same manner as sodium hypochlorite but is not as broad spectrum. It is used predominantly in the beverage sector for disinfection of product packs prior to aseptic filling.
Typically, a 0.03% solution will give 100 ppm hydrogen peroxide, at this level of concentration it may not require rinsing from the surface. Used at elevated temperatures, hydrogen peroxide becomes more effective. It is not safe to use on aluminium, zinc, tin or their alloys.
Peracetic acid
Peracetic acid (PAA) products are used mainly in the dairy, beverage and brewing sectors as they are low foaming, effective against all types of bacteria and can be used at very low concentrations and temperatures. Typically, two concentrations are commercially available; these have activities of 5% and 15% peracetic acid.
Used at the recommended concentration (e.g. 0.1 - 0.4%) a 5% active product will give 50-200 ppm PAA which would not typically be rinsed off but allowed to slowly decompose to acetic acid, oxygen and water.
As with other oxidising disinfectants PAA should not be used on soft metals. Some PAA formulations are approved by DEFRA for use against specific animal diseases.
Iodophors
Iodophors are expensive but incredibly effective disinfectants having both detergent and disinfectant properties. They are produced by dissolving iodine in an acid medium together with surfactants. Iodophors have several advantages including: The ability to kill a wide range of organisms at low temperatures, short contact time and the ability to cope with soiling/hard water.
Iodophors are now only approved for agricultural applications such as farm gate foot baths and drive-over disinfectant blankets and have DEFRA approvals for many farm based diseases.