Ozone Water Treatment System — Generation, Contacting and Off-gas Destruction

An ozone system generates ozone on site from dry air or oxygen, dissolves it into water, contacts it long enough to oxidise the target compounds, and destroys the ozone left in the vent gas. Ozone is produced by corona discharge across a dielectric inside a stainless reactor. It cannot be stored, so generation is matched to demand.

A complete train is feed-gas preparation, generator, injector, contact vessel, off-gas destructor, and controls that read ORP or dissolved ozone. Ozone is an oxidant, not a filter: it converts dissolved iron, manganese, colour and taste compounds into forms that filtration or carbon can remove.

Commercial generators range from about 10 g/h for a small drinking point to several kg/h for a plant. The rating is always stated at a defined oxygen concentration, dew point and cooling temperature, so compare quotations on the same basis.

Ozone must dissolve, not bubble through. A venturi injector creates a vacuum that draws gas into the water stream, and a static mixer or contact tower gives the bubbles time to transfer. Counter-current towers with a diffuser at the bottom and water entering at the top reach high transfer efficiency; bubble columns are simpler but taller. Transfer depends on bubble size, water depth and temperature; the undissolved fraction goes to the destructor.

Contact time is usually 5–15 minutes for drinking water, longer for iron and manganese oxidation. The vessel must be vented to an ozone destructor, and the water should be degassed before it reaches a storage tank or carbon bed. The injector is sized for peak water flow and gas-to-liquid ratio; too much gas at low flow creates foam and poor transfer.

Generator output in grams per hour equals water flow in cubic metres per hour multiplied by the ozone dose in milligrams per litre, then divided by the transfer efficiency. One cubic metre per hour at 1 mg/L requires 1 g/h before losses. A 10 m³/h stream at 2 mg/L therefore needs 20 g/h at 100% transfer, or about 22–25 g/h at 80–90% transfer.

The dose must be based on the ozone demand of the water, not only the target residual. Demand is measured by a bench test: dose a sample, wait the contact time, and measure the residual. High iron, manganese, colour or nitrite consumes ozone before disinfection begins. Add the demand to the target residual before selecting the generator.

Ozone decays to oxygen, with a half-life of roughly 20–30 minutes in clean water at 20 °C and much less in water carrying organics or metals. It leaves no persistent residual in the distribution network, so it protects the contact vessel and the tank but not a long loop. UV acts only while water passes the lamp and also leaves no residual.

Ozone is an oxidant and can remove colour, taste and metals; UV is a photochemical disinfectant and removes none of those. Ozone can form bromate where bromide is present; UV at 254 nm does not. Use ozone before filtration and storage, UV at the point of use.

Maintenance centres on the feed gas and the destructor. Replace the dryer desiccant and filters on schedule, keep the dew point low, clean the generator cooling circuit, and calibrate the ozone or ORP sensor. Replace the destructor catalyst or check the heater annually. Keep spare fuses, solenoid valves and sensor membranes: most shutdowns are feed-gas or instrument faults, not generator failure.