Over the years, manufactures have grown increasingly aware of the importance of water purify and its effect on the quality of the final product. One of the largest problems that confront pure water system operators is bacterial recontamination shortly after the water purification equipment has done its job. There are several recommended methods of either preventing or removing such contamination but most have inherent disadvantages. The most innovative and effective method adopted by leading pharmaceutical, biotech, cosmetics and semiconductor manufacturers, involves ozonation of the water in the system and reducing this prior to the first point of use with ultraviolet (UV) irradiation.

An efficient way of producing ozone is with an electrolytic ozone generator that actually produces ozone from the water being treated. Ozone, and particularly electrolytically generated ozone, is ideally suited for pure water loops because only low concentrations are necessary to sanitize the system and there are no objectionable by products or residue after the ozone has decomposed back to oxygen.

Irrespective of how well a plant has been designed and constructed, when no special measures have been taken, it’s virtually impossible to avoid microbial contamination in a pure water network. This is especially true when a system isn’t continually replenished with fresh makeup water such as overnight or over the weekend when production is shut down and the water stands in a tank or circulates in a closed loop.

Of the above-mentioned standard methods, shock disinfections with chemicals or shock sterilization with steam seem to produce the best result provided services interruptions and fluctuating water quality can be tolerated. An innovative and alternative method of disinfections of pure water loops, without any of the mentioned drawbacks, is by introducing ozone to the circulation flow. The advantages of using ozone are manifold:
There are no objectionable by products or residues when water is disinfected with ozone. In the absence of oxidizable substances, ozone decomposes to form oxygen; as soon as oxidizable substances are present, traces of carbon dioxide will form. These substances do not pose a major problem in connection with water quality.
Because the ozone does ultimately decay to form oxygen – the ozone molecule is only moderately stable and has a half-life of something like 30 to 60 minutes at normal service conditions – there are no lasting problems with traces of disinfections chemicals.
Experience gained in the pharmaceutical industry has shown very low ozone concentrations in the magnitude of 0.1 to 0.2 mg/L are sufficient to keep germ counts below 1 colonyforming units (CFU) per 100 milliliters (ml).
Disinfections with ozone are a continual process and in most cases, can be regulated by simple means. If required, however, the ozone production rate can be controlled by the process parameters in order to avoid incorrect dosing and to ensure optimized efficiency.
As the feed gas. Synthetic ozone produced by these generators is ideal for drinking water disinfections, wastewater treatment, pulp bleaching etc., but does have limitations when dealing with pure water systems. For example, fluctuations in water pH and resistivity can occur if feed gas preparation (oxygen) isn’t properly maintained.

Ozone is a very strong oxidizing agent with powerful disinfecting properties. It’s bactericidal, viricidal, fungicidal and sporicidal – furthermore, it’s active against yeasts, parasites, etc. One of the important factors to be taken into consideration when calculating the ozone dose is the organic content of the water being disinfected. That’s because, if this is high, the ozone demand will be correspondingly high and the ozone also will be used to reduce the organic content rather than just destroying microorganisms. During periods when ozone is being used to oxidize both microorganisms and organics, the kill rate will be slow. Once the total organic carbon (TOC) has been reduced to a minimum, the kill rate will increase accordingly. It should be kept in mind, however, that because cell death is caused by lyses and catoplasmic dispersion, i.e., it ruptures the cell wall and attacks the RNA, this will continually supplement the organic content of the water.
In order to simulate the effect of electrolytically produced ozone on normal water contamination, a 1988 study2 carried out tests on a mixed culture of staphylococcus albus, Pseudomonas diminuta, Flavobacterium deevorans and Croyneybacterium pyrogenes which were seeded into a tank prior to ozonation. A count was taken for the total quantity of bacteria killed rather than the kill for each particular species