What is a Ozonation?
Ozonation: Ozone disinfection and oxidation
Ozonation is the dosing of ozone gas, generated on site from oxygen or air by electrical discharge, into water to disinfect it and oxidise dissolved contaminants. Ozone is a stronger oxidant than chlorine, leaves no persistent residual and breaks down taste, odor and colour compounds, pharmaceuticals and other micropollutants, which is why it is common in drinking-water plants and in water reuse schemes, and why it is spreading to wastewater effluent where micropollutant limits are being introduced. Among the 11,783 US wastewater plants Klarifi tracks, ozone disinfection is rare compared with the 417 plants using UV and 333 using chlorine; the 189 disinfection line items in city capital plans show where conversions are planned.
How ozonation works
An ozone generator passes dry oxygen or air through a corona discharge, producing a few percent ozone by weight. The gas is dissolved in the water through fine-bubble diffusers or side-stream injectors in a contact tank sized for a few minutes of contact time. Off-gas is destroyed catalytically because ozone is toxic at low concentrations. Ozone decays within minutes, so it provides no residual in a distribution system; drinking-water plants add chlorine or chloramine afterwards.
Ozone versus UV and chlorine
Chlorine is cheapest and provides a residual, but forms chlorinated by-products and needs dechlorination before discharge to a river. UV disinfects without chemicals but does not oxidise anything. Ozone does both, at the highest capital and energy cost, and can form bromate in bromide-rich water. In wastewater it is chosen where effluent is reused, where colour or micropollutants must be removed, or as part of an advanced oxidation process combining ozone with peroxide or UV.
Where ozonation is growing
Potable reuse projects in the western US use ozone followed by biologically active filtration or membranes. In Europe, Switzerland requires micropollutant removal at larger plants and many have chosen ozonation; similar rules are arriving under the revised EU urban wastewater directive. In the US, disinfection projects in capital plans are mostly chlorine-to-UV or gas-to-hypochlorite conversions, with ozone concentrated in reuse schemes.