Ozonation for Wastewater Treatment
On-site ozone generation for colour removal, COD reduction, and disinfection of industrial wastewater — leaving no added salts or disinfection byproducts behind
Overview
About Ozonation for Wastewater Treatment
Ozonation uses ozone (O3), one of the strongest oxidants available in water treatment, generated on-site most commonly via corona discharge (electrical) ozone generators fed with ambient air or purified oxygen. Ozone is applied for colour removal, COD reduction, disinfection, and degradation of recalcitrant micropollutants that resist conventional biological or chemical treatment. Because ozone is unstable, it must be generated continuously at the point of use and dosed directly into the wastewater through a contactor or diffuser column.
Colour removal is a particularly strong application for ozone: it oxidatively cleaves the chromophore double bonds in dye molecules, making it highly effective on azo dyes that are common in textile dyeing operations. Typical ozone dose for industrial effluent colour removal is 5–20 mg/L depending on dye load, applied with a contact time of 10–30 minutes in an ozone contactor. The required dose and contact time scale with the strength and complexity of the colour load being treated.
Ozone can also be combined with hydrogen peroxide (the peroxone process) or with UV light (UV/O3) for advanced oxidation. These combinations generate hydroxyl radicals (OH•), a far more powerful and less selective oxidant species, enabling more complete mineralisation of organic compounds that are resistant to ozone alone. This makes advanced oxidation a valuable polishing step for recalcitrant COD that survives biological treatment and would otherwise persist in the final discharge.
A key advantage of ozone is that it decomposes back to oxygen after reacting, leaving no added salts or disinfection byproducts in the treated water — a meaningful difference from chlorine-based oxidants. However, because ozone gas is toxic at low ambient concentrations, an off-gas ozone destruction unit (catalytic or thermal) is required before venting to atmosphere. Ozone generation is also energy-intensive, typically consuming 8–12 kWh per kg of O3 produced, making capital and power costs higher than chemical oxidation alternatives. Common applications include textile dyeing effluent colour removal, tertiary polishing for water reuse schemes, and removal of recalcitrant COD that survives biological treatment.
Specifications
Technical Specifications
| Ozone Generation Method | Corona discharge (air-fed or oxygen-fed) |
| Typical Colour Removal Dose | 5–20 mg/L |
| Contact Time | 10–30 minutes (ozone contactor/diffuser column) |
| Energy Consumption | 8–12 kWh per kg O3 produced |
| Advanced Oxidation Options | UV/O3, Peroxone (O3 + H2O2) |
| Off-Gas Treatment | Catalytic or thermal ozone destruction unit |
| Typical COD Reduction | Process and dose dependent, polishing stage |
| Flow Capacity Range | 1 m³/hr to 500+ m³/hr per system |
Process
How Ozonation Works
On-Site Ozone Generation
Ambient air or purified oxygen is fed into a corona discharge ozone generator, producing ozone gas on demand since ozone cannot be stored or transported.
Ozone Dosing via Contactor
Generated ozone gas is injected into the wastewater stream through a diffuser or venturi injector inside an ozone contactor column, sized for the required dose, typically 5–20 mg/L for colour removal.
Oxidative Reaction with Contaminants
Ozone reacts with dye molecules, organics, and pathogens over a contact time of 10–30 minutes, cleaving chromophore double bonds in dyes and oxidising COD-contributing compounds.
Optional Advanced Oxidation Enhancement
For recalcitrant organics resistant to ozone alone, hydrogen peroxide (peroxone process) or UV light (UV/O3) is added to generate hydroxyl radicals for more complete mineralisation.
Off-Gas Destruction
Unreacted ozone gas exiting the contactor is routed through a catalytic or thermal ozone destruction unit, converting it back to oxygen before safe venting to atmosphere.
Treated Water Discharge
Treated water, now decolourised and oxidised, proceeds to further polishing, discharge, or reuse — with no added salts or disinfection byproducts remaining from the ozone treatment itself.
Benefits
Key Advantages
Highly Effective Colour Removal
Oxidatively cleaves chromophore double bonds in dye molecules, making ozone particularly effective on azo dyes common in textile dyeing effluent.
No Disinfection Byproducts or Added Salts
Ozone decomposes to oxygen after reacting, leaving no chlorinated byproducts or added salts in the treated water, unlike chlorine-based oxidation.
Degrades Recalcitrant Micropollutants
Effective against complex organic compounds and micropollutants that survive biological treatment and resist simpler chemical oxidation.
Combinable for Advanced Oxidation
Can be paired with hydrogen peroxide (peroxone) or UV light (UV/O3) to generate hydroxyl radicals for near-complete mineralisation of resistant organics.
Dual Function: Oxidation and Disinfection
Simultaneously achieves colour/COD reduction and disinfection in a single process step, reducing the need for separate treatment stages.
Generated On-Site, No Storage Risk
Ozone is produced on demand from air or oxygen, eliminating the need to store hazardous oxidant chemicals on site.
No Residual Chemical Sludge from Oxidant
Unlike chemical coagulant-based decolourisation, ozone oxidation does not itself generate additional chemical sludge.
Applications
Industries & Use Cases
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