Ozone Sterilization

Ozone provides many significant advantages over other conventional treatments when applied properly. Ozone can be a quick and thorough disinfectant and an effective remover of particulates (through flocculation), metals, colour, and taste. As it is a very unstable gas, ozone cannot be stored. Thus it must be generated at point of use when needed. It can be detected at low concentration levels as having a ‘fresh’ odour. At high concentrations it becomes acrid and very unpleasant.

Oxygen, from which ozone is generated, is normally found in its stable form in a two atom bond (O2). In the ozone form it takes on a three atom or triatomic form. This unstable bond is formed by passing oxygen through a high voltage corona discharge (CD) or by subjecting oxygen to ultraviolet radiation at specific wavelengths. Most commercial ozone generators use the high voltage corona discharge process as it renders higher concentrations of ozone by weight in the resulting gas flow. However the UV based ozone systems are considerably cheaper, in small water treatment plants, both to purchase and maintain.

The most common use for ozone is in water polishing and/or disinfection. Since ozone is so reactive, any existing level of suspended solids, dissolved organics, metals and other will affect the rate of reaction and the level of residual ozone available for disinfection. Where the water is clean having passed through some form of filtration such as RO, Ultra filtration or other, relatively short contact times are required to achieve meaningful disinfection. In relatively ‘dirty’ water ozone demand is usually quite high. It is also often difficult to maintain a measurable level of ozone residual. Demand can be so high that the desired disinfection effect can be achieved before any residual ozone level can be achieved hence why at times it is better to measure the overall quality of the water (using ORP in mV) rather than specific ozone residuals (in ppm).

Ozone can clear some turbid waters as suspended solids flocculate and settle. Water with a high concentration of similarly charged particles however, which repel each other and do not flocculate, tend to remain turbid. If positively-charged particles predominate, ozone will cause the surface charges of some colloidal particles to become negative. The oppositely charged particles are attracted to each other and form larger particles (flocculate) that settle out, reducing turbidity. When the suspended solids are primarily organic, ozone should prove to be a beneficial treatment for their removal. It’s very effective in the removal of many algae species.

Removal of colour, taste, and odour from water can also be achieved through the use of ozonation. Colour in water is usually an aesthetic problem associated with tannins in the water source such as from a river. However it could also be metals originating from a borehole. Odour such as those found in grey water and other waste water can be broken down and the smell reduced or eliminated.