Even though the bacteria counts in a well-designed water treatment plant may be very low, in most cases, disinfection of closed systems is still necessary. This is especially the true when a system is not continually replenished with fresh make-up water, such as overnight or weekends, when the water is stagnant in a tank or circulates in a system. At those times during periods of low or no flow, disinfection is essential to avoid the proliferation of bacteria colonies.

There are several processes that can be used for the disinfection of pure water systems, however, each of these have distinct limitations or disadvantages when compared to ozonation with an electrolytic process:

Shock disinfeciton with chemicals

Disadvantages:

• Interruption of operation
• Work intensive
• Waste chemical problems
• Water quality fluctuations
• Chemical traces

Shock sterilization with steam

Disadvantages:

• Interruption of operation
• Costly installation
• Uncontaminated steam required
• Water quality fluctuations

Ultraviolet irradiation

Limitations:

• Disinfection not always 100 percent
• Only localized effect
• Sterile filter required

Sterile filtration

Disadvantages:

• Bacteria
• Sterilization and replacement required
• Danger of bursting
• Expensive

Ozone itself is a virtually colorless gas with an acrid odor. It is one of the strongest known oxidants with an electrochemical oxidation potential of 2.08 V. The ozone molecule is only moderately stable and has a half life time of some 20 minutes in pure water at service conditions.

In the absence of oxidiziale substances ozone decomposes to form oxygen - in the presence of oxidizable substances traces of CO2 will also form.

Used for a broad range of applications the advantages of ozone are numerous, however, the most important of these are:

• There are no objectionable by-products or residues when water is disinfected with ozone.
• No chemical traces.
• The transport and storage of potentially dangerous chemicals is not necessary because ozone is produced on site where and when it is necessary.
• The ozone production rate can be controlled by the process parameters, i.e. the required amounts of ozone are generated in order to avoid under or over dosing.
• Experience, gained over many years, shows that an average ozone concentration of ca 0.1 to 0.2 mg/l. is sufficient to keep the germ count in pure water systems below 1 per 100ml.