A technical overview of ozone in water treatment, including disinfection, oxidation of iron and manganese, taste and odor control, micropollutant removal, bromate risk management, ozone generator design, and safe operation.

Abstract

Ozone is one of the most powerful oxidants used in modern water treatment. It can inactivate a wide range of microorganisms, improve taste, odor and color, oxidize iron and manganese, transform many organic micropollutants, and support advanced water reuse schemes. At the same time, ozonation is not a simple plug-and-play technology. Its performance depends on ozone dose, contact time, water quality, mass transfer efficiency, pH, temperature, bromide concentration, organic matter, and downstream treatment. The main regulatory and design concern is bromate formation when bromide-containing waters are ozonated. For industrial and municipal applications, the best practice is to treat ozone as a controlled oxidation process, not only as a disinfectant. This article explains how ozone works, where it is most useful, how to design an ozone system, and what new trends are shaping ozonation in water treatment.

1. Why Ozone Matters in Modern Water Treatment

Water treatment is moving from simple clarification and chlorination toward multi-barrier systems capable of removing pathogens, controlling taste and odor, managing industrial contaminants, reducing chemical residuals, and enabling water reuse. Ozone has become increasingly important in this transition because it combines strong disinfection with broad oxidative capability. In drinking water and process water systems, ozone can improve taste, odor, and color, oxidize iron and manganese, and inactivate microorganisms that are more resistant to conventional disinfectants [1,2].

Unlike chlorine, ozone is generated on site from dry air or oxygen and does not require the storage of large volumes of chemical disinfectant. It reacts rapidly and then decomposes back to oxygen. This is a major operational advantage in facilities that want high oxidation strength with minimal long-term residual chemical in the treated water. However, the same short lifetime means ozone does not provide persistent disinfectant residual in a distribution network; when residual protection is required, a secondary disinfectant may still be necessary [3].

2. How Ozone Treats Water

Ozone works through two main pathways. The first is direct molecular ozone reaction, where O3 reacts selectively with electron-rich compounds such as phenols, amines, reduced sulfur compounds, some pesticides, and many odor-causing molecules. The second is indirect oxidation, where ozone decomposes in water and forms hydroxyl radicals. These radicals are much less selective and can attack many compounds that react slowly with molecular ozone. The balance between these pathways depends on pH, alkalinity, dissolved organic matter, carbonate/bicarbonate concentration, temperature, and oxidant dose.

In practical engineering terms, ozone treatment is controlled by four linked parameters: ozone generation, ozone dissolution, contact time, and off-gas destruction. A high-capacity ozone generator alone does not guarantee performance. If the gas-liquid transfer is poor, a significant portion of ozone leaves the contactor as off-gas instead of reacting in water. Efficient injectors, diffusers, static mixers, contact tanks, pressure conditions and real-time monitoring are therefore central to a successful system.

3. Main Applications of Ozone in Water Treatment

In wastewater and reuse applications, ozone is especially valuable as a polishing step after biological treatment. It can transform many trace organic compounds, reduce UV absorbance, improve color, and enhance downstream biological activated carbon or granular activated carbon performance. Recent studies continue to evaluate ozone combined with activated carbon because this hybrid approach can improve micropollutant removal while reducing the risk of unwanted transformation products [4,5].

4. Ozone for Micropollutants and Emerging Contaminants

A major recent driver for ozonation is the removal or transformation of micropollutants such as pharmaceuticals, personal care products, endocrine-active compounds, pesticides, industrial additives, and odorants. Many of these compounds pass through conventional biological treatment. Ozone can react rapidly with some of them, while others require hydroxyl radical pathways or combined advanced oxidation processes such as O3/H2O2.

However, modern design should not evaluate ozonation only by parent-compound removal. Ozone can produce oxidation transformation products, and some may require downstream polishing. This is why the current best practice for reuse and advanced treatment is often an integrated sequence: ozonation followed by biological activated carbon, granular activated carbon, membrane filtration, or another polishing barrier. A 2025 risk-driven study comparing ozone and GAC for pharmaceutical remediation highlighted the importance of evaluating risk and transformation products, not concentration reduction alone [5].

5. Bromate: The Critical Control Point

The most important regulatory and design issue in ozonation is bromate formation. Bromate can form when ozone is applied to water containing bromide. The U.S. drinking water maximum contaminant level for bromate is 0.010 mg/L, or 10 micrograms per liter [1,2]. For any drinking water or potable reuse project, bromide in the feed water must be measured before ozone is selected and before final design is completed.

Bromate formation is influenced by bromide concentration, ozone dose, pH, alkalinity, ammonia, natural organic matter, temperature, contactor hydraulics, and hydroxyl radical exposure. Higher pH generally increases bromate risk because ozone decomposition and radical pathways become more active. Recent research has focused on bromate control using staged or multi-point ozone dissolution, hydrogen peroxide, pH management, ammonia or monochloramine strategies, and careful balancing of disinfection/oxidation targets with by-product control [7].

Practical bromate control measures include:

• Measure bromide in raw water, concentrate streams, blended water and seasonal sources before design.
• Avoid over-ozonation; dose ozone to a measurable treatment objective, not to a fixed generic number.
• Optimize pH, because bromate formation often increases at higher pH.
• Use staged ozone contact or multi-point dissolution where appropriate to control peak ozone exposure.
• Consider O3/H2O2 or other bromate control strategies only after bench or pilot testing.
• Provide downstream biological activated carbon or GAC when oxidation by-products or biodegradable organic carbon are concerns.
• Monitor bromate routinely in regulated drinking water and potable reuse applications.

6. Design Criteria for Industrial Ozone Systems

A reliable ozone system is an integrated process unit. It includes a feed gas system, ozone generator, cooling system, power supply, gas flow control, injection or diffusion equipment, contactor, off-gas ozone destructor, instrumentation and safety controls. Industrial systems normally use corona discharge ozone generation because it is efficient and suitable for continuous operation. Oxygen-fed systems generally provide higher ozone concentration and better energy efficiency than air-fed systems, while air-fed systems require excellent drying because moisture reduces ozone output and damages generator components.

Key design parameters are:

• Water flow rate and peak flow variation.
• Ozone demand of the water, including natural organic matter, nitrite, iron, manganese, sulfide and industrial contaminants.
• Target treatment objective: disinfection, color removal, odor control, micropollutant transformation, or oxidation before filtration.
• Required ozone dose and transferred ozone dose, not only generator nameplate capacity.
• Mass transfer efficiency of injector, diffuser, static mixer and contactor.
• Contact time and hydraulic performance of the contact tank.
• Feed gas purity, dew point, cooling water or air cooling conditions.
• Monitoring points for ORP, dissolved ozone, off-gas ozone, flow, pressure, temperature and alarms.
• Materials compatibility, because ozone attacks many elastomers and plastics.

7. Ozone Is Not Always the Best Stand-Alone Technology

Ozone is powerful, but it is not universal. It is generally not an efficient stand-alone method for removing dissolved salts, hardness, nitrate, most metals after they are already dissolved in stable forms, or PFAS. For these objectives, ozone must be combined with other processes such as filtration, activated carbon, ion exchange, nanofiltration, reverse osmosis, advanced oxidation, or adsorption. This is especially important for industrial customers: if the target is TDS reduction, RO is the primary technology; if the target is microbial control or oxidation, ozone may be appropriate; if the target is reuse polishing, ozone may be one barrier in a larger treatment train.

8. Safety and Operation

Ozone is a hazardous gas and must never be treated as a harmless “green” disinfectant. It is toxic by inhalation and can irritate the respiratory system at low concentrations. OSHA lists an ozone permissible exposure limit of 0.1 ppm as an 8-hour time-weighted average, with additional short-term exposure values shown in its ozone chemical data [8]. Any industrial ozone installation should include leak prevention, ventilation, off-gas destruction, interlocks, shutdown alarms, safe access, compatible piping and seals, and operator training.

Operational records should include generator output, feed gas flow, power consumption, water flow, dissolved ozone, ORP, contact tank conditions, off-gas ozone, bromate where relevant, and routine maintenance. A well-designed ozone plant is not only equipment; it is a monitored oxidation process.

9. Emerging Trends for 2026 and Beyond

The strongest market trend is the expansion of water reuse. EPA released Water Reuse Action Plan 2.0 in April 2026, emphasizing beneficial reuse of wastewater and the need for appropriate treatment for specific end uses [9]. In this context, ozone is gaining attention as a flexible oxidation barrier for reuse systems, especially when combined with biological activated carbon, granular activated carbon, membranes, UV/H2O2, or other polishing steps.

Another trend is smarter process control. Instead of dosing ozone at a fixed value, modern systems increasingly use online measurements such as UV254, TOC/DOC, dissolved ozone, ORP, flow-paced control, and surrogate parameters for micropollutant removal. For industrial systems, this can reduce energy cost, limit over-oxidation, improve safety, and reduce by-product formation.

Microbubble and nanobubble ozone systems are also being explored to improve gas-liquid transfer and extend contact efficiency. These technologies can be promising, but they should be validated by site-specific testing because water chemistry and contactor design still control the final treatment result.

10. Conclusion

Ozone is one of the most versatile technologies in modern water treatment. It can disinfect, oxidize, deodorize, decolorize and support advanced treatment trains for reuse. Its value is highest when it is engineered as a controlled oxidation process with clear objectives, accurate dosing, efficient mass transfer, monitoring, by-product control and safety systems. For Noor & Hayat Khalij Fars, ozone technology is best positioned as part of an integrated engineering solution: water analysis, process design, ozone generator selection, contactor design, safety system design, commissioning, operator training and ongoing performance optimization.

Technical Checklist for Customers

Before selecting an ozone generator, customers should prepare the following information:

• Application: drinking water, process water, wastewater polishing, reuse, odor control, cooling water or food industry use.
• Water flow rate, peak flow and operating hours.
• Water analysis including pH, temperature, TDS, alkalinity, bromide, TOC/DOC, UV254, iron, manganese, turbidity, COD/BOD where relevant.
• Target performance: microbial reduction, color reduction, odor control, Fe/Mn oxidation, micropollutant removal or reuse quality.
• Available oxygen supply or compressed dry air infrastructure.
• Available space, ventilation, drainage and electrical conditions.
• Regulatory requirements and monitoring obligations.
• Need for downstream filtration, BAC, GAC, UV, membrane treatment or residual disinfectant.

Frequently Asked Questions

 ?Can ozone replace chlorine completely

In some closed or point-of-treatment systems, ozone may replace chlorine for primary disinfection. In distribution systems, ozone usually does not provide a long-lasting residual, so a secondary disinfectant may still be needed.

?Does ozone remove TDS or hardness

No. Ozone is an oxidant and disinfectant, not a desalination process. TDS and hardness reduction usually require reverse osmosis, nanofiltration, ion exchange or softening.

?Is ozone effective against micropollutants

It can be highly effective for many compounds, especially ozone-reactive molecules. More resistant compounds may require hydroxyl radical pathways such as O3/H2O2 or another advanced oxidation process, followed by downstream polishing.

?What is the main risk of ozonation in drinking water

The main regulatory risk is bromate formation when bromide-containing water is ozonated. Bromide testing and bromate control must be part of the design.

?Is ozone safe for operators

Ozone systems can be operated safely when properly designed with ventilation, ozone destructors, leak monitoring, interlocks and training. Ozone gas exposure must be controlled because it is harmful by inhalation.

Call to Action

Noor & Hayat Khalij Fars provides engineering support for ozone generator selection, water quality evaluation, treatment train design, ozone injection and contactor design, bromate risk review, commissioning and operator training. For project assessment, send your water analysis, flow rate and treatment objective to the technical team.

References

[1] TCEQ. Ozone and Bromate in Drinking Water. Updated March 18, 2026. https://www.tceq.texas.gov/drinkingwater/chemicals/dbp/ozone-and-bromate.html

[2] U.S. EPA. National Primary Drinking Water Regulations: Bromate MCL 0.010 mg/L. https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations

[3] CDC. How Water Treatment Works. Ozone and UV can disinfect at the treatment plant but do not provide continuing residual in pipes. https://www.cdc.gov/drinking-water/about/how-water-treatment-works.html

[4] Zhang T. et al. Combining ozonation and powdered activated carbon adsorption for organic micropollutants removal in municipal wastewater treatment plants. Water Research, 2025. https://www.sciencedirect.com/science/article/abs/pii/S0043135425009431

[5] Davey C.J.E. et al. Wastewater remediation of pharmaceuticals with ozone and granular activated carbon: a risk-driven approach. Environmental Science: Water Research & Technology, 2025. https://doi.org/10.1039/D5EW00600G

[6] Morrison C.M. et al. Critical Review on Bromate Formation during Ozonation and Control Options for Its Minimization. Environmental Science & Technology, 2023. https://doi.org/10.1021/acs.est.3c00538

[7] Pearce R., Hogard S., Bott C. Multi-point ozone dissolution for enhanced bromate control with hydrogen peroxide in potable reuse. Environmental Science: Water Research & Technology, 2025. https://doi.org/10.1039/D4EW00627E

[8] OSHA. Ozone Chemical Data. Last updated January 22, 2024. https://www.osha.gov/chemicaldata/9

[9] U.S. EPA. Water Reuse Action Plan 2.0. Released April 16, 2026. https://www.epa.gov/waterreuse/water-reuse-action-plan-20