Ozone in Drinking Water Treatment: Applications and Design Criteria
Ensuring safe and high-quality drinking water is becoming increasingly complex. Water utilities must respond not only to conventional microbiological risks, but also to seasonal variations in raw water, algal blooms, natural organic matter, taste and odor events, metals, micropollutants and stricter requirements regarding disinfection by-products.
Conventional treatment processes based on coagulation, clarification, filtration and chlorination remain essential. However, some contaminants are difficult to manage through conventional treatment alone. In these cases, ozone can provide an additional oxidation and disinfection barrier.
Ozone in drinking water treatment is used for microorganism inactivation, taste and odor control, oxidation of iron and manganese, transformation of organic matter and support for downstream biological treatment. Its application must nevertheless be carefully engineered. The required ozone dose, contact time and system configuration depend on the quality of the source water, the treatment objective and the processes located before and after ozonation.
A complete ozone installation involves much more than an ozone generator. It may include oxygen preparation, ozone production, gas–liquid injection, hydraulic contact, residual ozone measurement, off-gas destruction, instrumentation, automation and integration with filtration, biological activated carbon and final disinfection.
Longking EnTech Europe combines more than two decades of experience in ozone, ultraviolet disinfection and Advanced Oxidation Processes with the manufacturing and industrial capacity of Longking Group. Its approach focuses on the design and integration of complete treatment systems adapted to the specific conditions of each plant.
Understanding Ozone as a Water Treatment Technology
Ozone is a molecule composed of three oxygen atoms, O₃. It is a highly reactive gas that decomposes naturally back into oxygen. Because ozone is unstable, it must be generated directly at the treatment plant. The most common industrial method is corona discharge, in which oxygen passes through an electrical field and part of it is converted into ozone.
The feed gas may come from conditioned air, an oxygen concentrator or liquid oxygen. Oxygen-fed systems are frequently used in drinking water applications because they can produce higher ozone concentrations and improve transfer efficiency.
On-site generation eliminates the need to transport and store ozone and allows production to be adjusted to plant flow and treatment demand. However, ozone is also toxic and corrosive, so ventilation, leak detection, compatible materials, automatic shutdown systems and safe residual-gas treatment are essential.
Why Use Ozone in Drinking Water Treatment?
Ozone is a strong oxidizing agent that can react directly with contaminants or indirectly through hydroxyl radicals. The balance between these reaction pathways depends on pH, alkalinity, natural organic matter, temperature and the presence of other substances that consume ozone or radicals.
This versatility allows ozone to address several treatment objectives.
Disinfection
Ozone is effective against bacteria, viruses and certain protozoa. Its performance depends on the target microorganism, dissolved ozone concentration, effective contact time, water temperature, hydraulic conditions and background ozone demand.
The applied dose alone does not demonstrate disinfection performance. The process must be evaluated using the dissolved ozone concentration and the effective hydraulic contact time within the contactor.
Ozone also decays quickly and normally does not maintain a disinfectant residual throughout the distribution network. It is therefore commonly combined with chlorine, chloramine or another secondary disinfectant.
Transformation of Organic Matter
Ozone can alter the structure of natural and synthetic organic compounds. Large molecules may be converted into smaller, more polar and, in some cases, more biodegradable substances.
This transformation can improve downstream biological filtration or biological activated carbon treatment. It should not, however, be described as automatically producing a significant reduction in dissolved organic carbon.
In many applications, ozone transforms organic matter without fully removing it. The actual reduction occurs later through biodegradation, adsorption, filtration or a combination of these processes.
The ozone stage must therefore be designed together with the downstream treatment. Increasing the biodegradability of organic matter without subsequently removing it can reduce the biological stability of the finished water.
Taste and Odor Control
Taste and odor events are often associated with algae, cyanobacteria and the decomposition of natural organic matter.
Geosmin and 2-methylisoborneol, commonly known as MIB, are two of the most frequent odor-causing compounds in surface waters. They can be detected at very low concentrations and may affect public confidence even when the water meets health-related requirements.
Ozone can oxidize these compounds, although the required dose varies according to their concentration and the ozone demand of the water. In more difficult applications, ozonation may be followed by granular activated carbon, biological activated carbon or another complementary treatment.
Iron and Manganese Oxidation
Iron and manganese may cause metallic taste, discoloration, staining and deposits within the treatment plant and distribution system. Ozone converts soluble iron and manganese into oxidized particulate forms. These particles must then be removed by clarification or filtration.
This distinction is important: ozone performs the oxidation, but not the final separation. The filtration stage must be designed to retain the resulting precipitates.
The dose must also be controlled carefully, particularly for manganese. Excessive oxidation may contribute to the formation of soluble permanganate species and cause a pink coloration in the water.
Main Applications of Ozone in Drinking Water Plants
Ozone is normally integrated into a multibarrier treatment process rather than used as an isolated technology. Its main applications include preozonation, intermediate ozonation, primary disinfection, taste and odor treatment, algae management, metal oxidation, micropollutant transformation, reduction of selected disinfection by-product precursors and pretreatment before biological activated carbon.
The most suitable application point depends on the water composition and the treatment objective.
Preozonation
Preozonation is the application of ozone near the beginning of the treatment process, generally before coagulation, clarification or filtration.
Raw surface water may contain suspended particles, organic matter, algae, color, microorganisms, metals and taste and odor substances. Applying ozone at this stage may improve the management of some of these compounds, but raw water often has a high and variable ozone demand.
Effect on Coagulation
Ozone can change the molecular structure and surface properties of natural organic matter. Under certain conditions, this may improve particle destabilization, floc formation and clarification.
This effect is not universal. Depending on the nature of the organic matter, the ozone dose, the application point, pH and the coagulant used, preozonation may improve coagulation, have little effect or make the process more difficult.
Its influence should therefore be confirmed through jar tests, laboratory trials, pilot testing or reliable operational data.
Algae and Cyanobacteria
Ozone can damage or inactivate algae and cyanobacteria, potentially reducing viable cell concentrations, filter clogging and some taste and odor problems.
However, cell damage can also release intracellular organic matter, odor compounds or cyanotoxins into the dissolved phase. The consequences depend on the species, ozone dose, contact time, toxin location and the capacity of the downstream treatment stages.
When cyanobacteria are present, the objective should not simply be to destroy cells. The complete process must also remove or degrade the compounds released after oxidation.
Color Reduction
Ozone can break down the structures responsible for natural water color, particularly those associated with humic substances.
A reduction in color does not necessarily mean an equivalent reduction in organic carbon. Ozone may remove the visible chromophoric structures while leaving much of the carbon in solution.
Intermediate Ozonation and Biological Activated Carbon
Intermediate ozonation is commonly applied after clarification and before filtration or activated carbon treatment. At this stage, much of the suspended matter and part of the initial ozone demand have already been removed. Ozone can therefore act more selectively on dissolved organic compounds.
It may transform natural organic matter, taste and odor substances, pesticides, pharmaceutical residues and other micropollutants into compounds that are easier to biodegrade or adsorb.
This transformation also produces oxidation by-products such as aldehydes, ketones and carboxylic acids. A downstream treatment stage is therefore usually required.
Ozone and Biological Activated Carbon
The combination of ozone and biological activated carbon is widely used in advanced drinking water plants. Ozone increases the biodegradability of part of the organic matter, while the biological activated carbon filter removes the resulting compounds through biological degradation, adsorption and filtration.
The performance of this process depends on the contact time, carbon characteristics, biological activity, temperature, hydraulic loading, backwashing strategy and influent water quality.
The ozone dose should therefore be optimized for the performance of the complete ozone–carbon process, not only for the immediate oxidation result.
Ozone and Disinfection By-Products
Chlorine can react with natural organic matter and bromide to form trihalomethanes, haloacetic acids and other disinfection by-products. Ozone can modify part of the organic precursor pool before final chlorination and may reduce the formation potential of certain chlorinated by-products.
However, the effect is not always positive for every compound. Ozone may also form aldehydes, ketones, carboxylic acids, brominated compounds and bromate.
For this reason, the impact of ozonation must be evaluated across the complete treatment train rather than only at the ozone outlet.
Bromate Formation: A Critical Design Consideration
Bromate is one of the most important issues in drinking water ozonation. Bromide may occur naturally in surface water and groundwater, particularly in coastal areas, waters affected by saline intrusion or sources influenced by industrial discharges. When bromide-containing water is treated with ozone, part of it may be converted into bromate.
The World Health Organization establishes a provisional guideline value of 0.01 mg/L, equivalent to 10 µg/L, although the applicable local regulation must always be checked. Bromate formation depends on several interacting factors.
A higher bromide concentration generally increases the risk. Higher ozone doses and longer exposure can also favor bromate formation, especially after the initial ozone demand has been satisfied.
Higher pH generally increases bromate formation, while temperature affects ozone solubility, decomposition, reaction kinetics and transfer efficiency. Natural organic matter may consume ozone and reduce some bromate-forming reactions, but it can also increase the total ozone dose required.
Alkalinity, ammonia and hydroxyl radical chemistry may also influence the process. Possible control strategies include optimizing the ozone dose, limiting unnecessary residuals, adjusting the application point, reducing pH under controlled conditions, splitting the dose, using ammonia in suitable applications and improving hydraulic and process control.
There is no universal solution. Bromate control should be based on water-specific testing and evaluation of the entire treatment process.
Key Design Criteria for Ozone Drinking Water Systems
Raw Water Characterization
The design process begins with a detailed assessment of the water. Relevant parameters include pH, temperature, turbidity, alkalinity, bromide, ammonia, nitrite, organic carbon, UV absorbance, iron, manganese, algae, cyanotoxins, geosmin, MIB, microbiological indicators and target micropollutants.
Seasonal and event-driven variations are particularly important. A system sized only for average conditions may not provide sufficient treatment during algal blooms, periods of high organic loading or changes in source-water temperature.
Ozone Demand and Treatment Objective
Ozone demand is the amount of ozone consumed before a measurable residual can be established. It may be caused by organic matter, metals, nitrite, sulfur compounds and other reactive substances.
Demand and decay testing can help determine the initial consumption, residual development, reaction time and potential bromate formation.
The treatment objective must also be defined clearly. Disinfection, taste and odor control, metal oxidation, micropollutant removal and pretreatment before biological activated carbon may require different doses, contact conditions and application points.
A dose selected for odor control may not achieve validated disinfection. Conversely, a high disinfection dose may create an unacceptable bromate risk in bromide-rich water.
Determining the Ozone Dose
The applied dose must cover the initial water demand, the ozone consumed in target reactions, transfer losses and any residual exposure required.
It should preferably be established using laboratory studies, pilot trials, demand and decay tests, kinetic modelling and regulatory disinfection criteria.
A single fixed dose is rarely optimal throughout the year. Modern systems should adjust ozone production according to flow, water quality, temperature and dissolved ozone measurements.
Contact Time and Hydraulic Performance
When ozone is used for disinfection, both dissolved concentration and effective contact time must be considered.
The nominal contactor volume does not necessarily represent the effective contact time. Short-circuiting, dead zones, recirculation, variable water levels and inadequate baffling can reduce actual exposure.
Hydraulic performance may be evaluated using tracer tests, baffling factors or Computational Fluid Dynamics. The contactor should maintain adequate transfer, mixing and residence time across the expected operating range.
Feed Gas and Ozone Generation
The gas system may use conditioned air, on-site oxygen generation or liquid oxygen.
Gas purity and dryness directly affect generator performance and reliability. The selected configuration should consider ozone capacity, product gas concentration, energy use, oxygen availability, maintenance requirements and redundancy.
Generator sizing must account for maximum plant flow, maximum ozone dose, transfer efficiency, seasonal demand, operational turndown and future capacity.
Longking EnTech Europe manufactures modular ozone systems for both high-capacity municipal installations and smaller treatment plants. Its systems combine corona discharge technology, high-frequency power supplies, cooling, automation and safety monitoring within integrated configurations.
Injection and Mass Transfer
The ozone produced must be transferred efficiently from the gas phase into the water.
Common systems include fine-bubble diffusers, Venturi injectors, sidestream injection, static mixers and pressurized dissolution.
Transfer efficiency depends on ozone concentration, bubble size, gas-to-water ratio, pressure, water temperature, mixing intensity, water depth and contactor design.
Poor transfer reduces the dissolved dose, increases off-gas losses and raises oxygen and energy consumption. The generator, injection system and contactor must therefore be designed as a coordinated system.
Contactor and Off-Gas Design
The contactor must provide sufficient mass transfer, hydraulic contact and safe gas collection. Its design should consider chamber arrangement, water depth, baffles, gas distribution, flow variation, sampling points, access, sealing and corrosion-resistant materials.
Any ozone not transferred into the water leaves as off-gas and must be collected and destroyed before discharge. Off-gas systems normally include moisture separation, catalytic or thermal destruction, ventilation, monitoring and automatic shutdown interlocks.
Longking EnTech Europe integrates ozone generation, injection, cooling, destruction and automation within complete ozone plants. Its engineering approach may include hydraulic modelling and process simulation to optimize transfer and contact conditions.
Integration with Downstream Treatment
Ozonation must be coordinated with the processes located before and after it. The design should consider its effect on coagulation, filtration, biological activated carbon, membranes, UV treatment, final chlorination and distribution-system biological stability.
For example, an ozone dose that increases biodegradable organic carbon may improve biological activated carbon performance but create regrowth risks if the downstream biological barrier is inadequate.
Residual ozone may also need to decay or be removed before reaching sensitive membranes or biological processes.
Instrumentation and Control
A reliable ozone plant requires coordinated monitoring of water flow, gas flow, oxygen purity, ozone concentration, dissolved ozone, pressure, temperature, cooling conditions, off-gas ozone and ambient ozone. Control may be based on plant flow, raw-water quality, dissolved residuals or a combination of feed-forward and feedback signals.
Safety interlocks should stop ozone generation in the event of gas-supply failure, cooling problems, ventilation failure, high ambient ozone or off-gas destructor malfunction.
Longking systems can incorporate PLC and HMI control, SCADA communication and remote monitoring. This enables the system to adapt production to changing treatment conditions and supports early detection of operational deviations.
Redundancy and Energy Efficiency
Drinking water plants often require continuous operation, so redundancy may be needed for generators, oxygen systems, cooling, pumps, destructors, controls and instrumentation. Modular configurations allow individual units to be isolated for maintenance while the remaining equipment continues to operate.
Energy optimization should consider generator efficiency, oxygen supply, product gas concentration, transfer performance, pressure losses, cooling requirements and operating turndown. The objective is not simply to minimize generator power, but to minimize the energy required to deliver the necessary transferred ozone dose under real operating conditions.
Advanced Oxidation Processes
Some micropollutants react slowly with molecular ozone. In these cases, ozone may be combined with hydrogen peroxide or ultraviolet radiation to increase hydroxyl radical production. Advanced Oxidation Processes can be used for selected pesticides, pharmaceutical residues, endocrine-disrupting compounds and other resistant organic contaminants.
The design must consider ozone dose, peroxide dose, UV dose where applicable, pH, alkalinity, organic matter, radical scavengers and target-compound kinetics. Advanced oxidation does not automatically eliminate bromate risk. Depending on the water chemistry, it may increase or modify the pathways leading to by-product formation.
Longking EnTech Europe has experience in ozone, UV and Advanced Oxidation Processes, allowing these technologies to be integrated when the treatment objective cannot be achieved through conventional ozonation alone.
Longking EnTech Europe: Integrated Ozone Engineering
The performance of an ozone process depends on the interaction between water chemistry, hydraulic design, equipment performance and control.
Longking EnTech Europe works as both a manufacturer and system integrator, covering the main stages required to develop a complete ozone solution.
Its capabilities include process assessment, pilot testing, equipment sizing, ozone generation, gas preparation, injection, off-gas destruction, automation, commissioning and technical support.
The company was founded in 2000 and has more than two decades of experience in ozone, UV and Advanced Oxidation Processes. Since joining Longking Group, it combines European engineering expertise with a broader industrial and manufacturing structure.
This integration allows Longking to adapt the system to the water source and treatment objective instead of applying a standard configuration. Depending on the project, the engineering process may include ozone demand studies, hydraulic assessment, bromate evaluation, equipment redundancy and integration with biological filtration, activated carbon or final disinfection.
Longking also supports plant operation after commissioning through training, remote monitoring, maintenance and spare-parts services. This is particularly important in drinking water installations, where variations in raw water quality may require periodic adjustment of dose and control parameters.
Ozone as Part of a Multibarrier Strategy
Ozone is a powerful treatment technology, but it should not normally be considered a complete drinking water solution by itself.
Its greatest value is achieved when it is integrated with coagulation, clarification, filtration, activated carbon, biological treatment, UV and final residual disinfection.
Each barrier performs a different function. Ozone inactivates microorganisms and transforms contaminants. Clarification and filtration remove particles and oxidized metals. Activated carbon provides adsorption and biodegradation. Final chlorination or chloramination protects the water within the distribution network.
The objective is not to maximize ozone production, but to apply the correct transferred dose, at the correct point, for the necessary contact time, while controlling bromate, energy consumption and downstream effects.
A Complete Engineering Approach to Drinking Water Ozonation
Ozone can address several of the most important challenges in drinking water treatment, including disinfection, taste and odor control, oxidation of iron and manganese, algae-related contaminants, organic matter transformation and micropollutant treatment. Its successful application, however, requires detailed engineering.
Raw water quality, ozone demand, bromide concentration, pH, temperature, contact time, transfer efficiency, contactor hydraulics, off-gas treatment and downstream processes must all be evaluated together.
Particular attention must be given to bromate formation, the absence of a lasting ozone residual in the distribution network and the need to remove oxidation products through filtration or biological treatment.
By combining ozone generation technology with process engineering, system integration, automation and long-term technical support, Longking EnTech Europe can develop solutions that respond to the actual conditions of each drinking water plant.
This integrated approach allows ozone to function not simply as an additional item of equipment, but as a controlled and efficient component of a reliable multibarrier treatment strategy.