Design Manual › Disinfection › Ozone
FREE ENGINEERING TOOL · DISINFECTION

Ozone Disinfection

Ozone is the strongest oxidant in municipal practice — it kills, decolourises, destroys odour and attacks trace organics, and it leaves no chlorinated byproducts. It also leaves no residual at all, and it can turn bromide in the water into bromate. This tool sizes the generator and the contactor, then tells you plainly whether those two trade-offs bite on your water.

1Duty & treatment objective

The dose is set by the objective, not by the flow. Plain disinfection is simple; decolourisation costs twice as much, and trace-organic oxidation three times as much again.

2Generator & contactor

Ozone is generated on site from oxygen or air, and it must be transferred into the water — never completely. The gap between what you generate and what dissolves is the off-gas you have to destroy.

Results — generator & energy

Generator duty
—kg/h
Ozone produced
—kg/d
Energy
—kWh/m³
ItemValueBasis

3Contactor & off-gas

Whatever does not dissolve has to be destroyed before it leaves the building. Off-gas handling is not an accessory — it is a permit condition and an operator safety issue.
ItemValueBasis

4Bromate & the residual gap

The two things that decide whether ozone is the right answer. Bromate is a carcinogen with a 10 µg/L guideline; and ozone leaves nothing behind to protect the outfall.
ItemValueBasis

Where ozone wins, and where it does not

ItemValueBasis

5Instrument schedule

Ozone needs more instrumentation than any other disinfection option: gas phase, dissolved phase, and off-gas — plus the safety interlocks.
PointInstrumentWhy here

Quote the ozonation instruments at factory price

Ozone monitoring, ORP, turbidity and flow — all mappable to our catalogue and supplied at the manufacturer's ex-works price (our margin is the export rebate, not a markup on the device).

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Sources & parameter basis

[1]METCALF & EDDY / EPA — ozonation of municipal effluent: contact 10–30 min at peak flow, multi-cell contactors in series to approach plug flow.
[2]Transferred dose by objective: disinfection 3–8 mg/L; disinfection with colour removal 8–15 mg/L; trace organic oxidation 15–25 mg/L. COD and colour are the main ozone scavengers and raise the demand.
[3]Generator: oxygen feed 6–10 kWh/kg O₃ (typ. 8) at 8–14 wt% ozone; air feed 12–20 kWh/kg (typ. 16) at 1–3 wt%. Oxygen consumption ≈7–10 kg O₂ per kg O₃ on an oxygen-fed system.
[4]Contactor: 2–4 cells in series, depth 4–6 m, transfer efficiency 80–95 % with fine-bubble diffusers or injectors. Ozone half-life in secondary effluent is roughly 10–30 min and shortens as temperature rises.
[5]Bromate: formed when ozone oxidises bromide. Risk becomes material above roughly 50 µg/L Br⁻ with doses above 5 mg/L. WHO guideline value for bromate is 10 µg/L.
[6]Turbidity shields organisms and consumes ozone; keep effluent below about 2 NTU ahead of an ozone contactor.
[7]ORP is used as a continuous proxy for oxidative disinfection strength; ozonation typically runs 600–800 mV. It is a surrogate and needs periodic calibration against a direct measurement.
Full derivation and worked example: Ozone-Disinfection-Calculation-Sheet.md. Change the objective from "disinfection only" to "trace organic oxidation" and watch the generator duty and the energy per cubic metre both roughly triple — that is the real cost of going after micropollutants.
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