Ozone (O3) is a powerful disinfectant that disinfects by reacting with the of the cell and is particularly effective against Giardia and cryptosporidium. It has the very desirable quality that it is unstable and leaves no residual. Additionally, ozone does not form disinfection byproducts. The extra oxygen atom binds in a split second to all the organic matter it contacts. After this oxidation process, all that remains is the pure and stable oxygen molecule.
An ozonation system consists of the ozone generator, an air dryer or oxygen source, a means of adding the ozone into the wastewater, a mixing/contact chamber, and a ventilation device. Ozone is produced by discharging electricity in very dry (desiccated) air. A high voltage (6,000-20,000V) is applied to two electrodes to create a continuous arc (corona) and the high voltage converts O2 to O3. The feed gas for the ozone generator may be air or pure oxygen.
For ozone to be effective, it must be added to the effluent and dispersed as finely as possible. This is accomplished either by using a fine bubble diffuser or a venturi configuration. The mixing/contact chamber must be configured so that there is adequate contact time for disinfection.
The amount of interference any constituent exerts on the effectiveness of ozone disinfection is minimal. This is especially apparent when compared to the decrease in effectiveness of other forms of disinfection due to interferences.
Ozone has an acute toxicity associated with it. It is important when utilizing this technology to demonstrate extra caution. Ozone is a toxic gas and can cause illness if inhaled in sufficient quantity. Some ozone generators are equipped with ozone monitors and a safety system which shuts down the generator at 0.3 ppm. It is best also to set an alarm at 0.1 ppm, so people can take action in time to avoid problems.
Ozonation equipment for the onsite wastewater treatment industry is not as readily available as other forms of disinfection.