O3 in Water
The Principles, Applications, and Technical Practices of Ozone in Water Introduction
In modern water treatment technologies, “O3 in water” (ozone in water) has become a highly discussed and important topic. Ozone (O₃), a highly reactive gas composed of three oxygen atoms, plays a significant role in various applications such as drinking water disinfection, wastewater treatment, and the preparation of ultrapure water for industrial use — all thanks to its strong oxidizing power.But why do we apply ozone in water? How exactly does it work? And what are the technical challenges and potential safety concerns associated with its use?This article will provide a systematic explanation of the relationship between ozone and water — from fundamental principles to practical applications — helping readers gain a comprehensive understanding of this essential water treatment technology.
What is Ozone (O₃)?
Ozone, with the chemical formula O₃, is a pale blue gas that has a distinctive, pungent odor. Unlike the common diatomic oxygen molecule O₂, ozone consists of three oxygen atoms. This unique structure gives ozone extremely strong oxidizing properties, with an oxidation-reduction potential as high as +2.07 V. It is the second most powerful oxidant known in nature, second only to fluorine, and is considered one of the strongest natural oxidizers.In the Earth’s atmosphere, ozone is primarily concentrated in the stratosphere, where it plays a critical role by absorbing ultraviolet (UV) radiation and protecting living organisms on the planet. However, near the Earth’s surface, ozone is often regarded as an air pollutant due to its reactivity and potential health effects.Nevertheless, in controlled water treatment environments, ozone transforms into a highly effective tool for disinfection and purification.
Why Use Ozone in Water?
– Key Advantages and Application Scenarios
The widespread application of “O3 in water” is primarily due to ozone’s strong oxidizing power and residual-free characteristics. Compared to traditional chlorine disinfection, ozone demonstrates superior performance in killing microorganisms, removing organic matter, and improving overall water quality.
1. Disinfection and Sterilization
Ozone is one of the most powerful oxidizing agents known for its disinfection capabilities. It can rapidly kill bacteria, viruses, and protozoa (such as Cryptosporidium) in water. Unlike chlorine disinfection, ozone does not produce harmful disinfection byproducts (DBPs) such as trihalomethanes (THMs), which are often a concern in chlorinated water systems.
2. Removal of Organic Matter and Odors
Ozone effectively oxidizes natural organic matter (NOM) in water — such as humic acids — as well as pesticide residues, industrial pollutants, and odor-causing compounds like hydrogen sulfide (H₂S) and ammonia (NH₃). This significantly improves the organoleptic qualities (taste, odor, and appearance) of the water.
3. Removal of Inorganic Pollutants
Ozone can also oxidize low-valence inorganic ions such as iron (Fe²⁺) and manganese (Mn²⁺) into their high-valence forms (e.g., Fe³⁺ and Mn⁴⁺), which are insoluble and can be easily filtered out. Additionally, ozone is effective in removing reducing substances such as hydrogen sulfide, improving both water clarity and safety.
4. Advanced Oxidation Processes (AOPs)
When ozone is combined with ultraviolet light (UV) or hydrogen peroxide (H₂O₂), it produces hydroxyl radicals (·OH) — highly reactive and non-selective oxidants with exceptional oxidation potential. These hydroxyl radicals can break down trace organic pollutants that are difficult to remove using conventional treatment methods, including pharmaceuticals, personal care products (PPCPs), and endocrine-disrupting chemicals (EDCs).
Solubility and Behavioral Characteristics of O3 Water
“O3 in water” is not simply a matter of bubbling ozone gas into water — it involves complex physical dissolution and chemical behavior.
1. Solubility Characteristics
Ozone is much more soluble in water than oxygen (O₂), but its solubility is significantly influenced by temperature, pressure, and pH:
• Lower temperatures result in higher ozone solubility;
• Higher pressures increase the amount of ozone that can dissolve;
• Ozone is more stable at lower pH values (i.e., in more acidic conditions).
Under typical conditions, the saturation concentration of ozone in water is approximately 10 mg/L at 20°C and 1 atm (atmospheric pressure). However, the actual dissolved ozone concentration is often lower than this saturation level due to operational and environmental factors.
2. Half-Life and Stability
Ozone exhibits poor stability in water and gradually decomposes into oxygen (O₂). Its half-life in water can range from a few minutes to several hours, depending on factors such as:
• Water quality (e.g., organic content, turbidity)
• Temperature
Because of its relatively short half-life, ozone typically needs to be rapidly mixed and reacted with water in a contact reactor to maximize its utilization efficiency before it breaks down.
The Action Mechanism of Ozone in Water Treatment
The core role of ozone in water is to destroy the molecular structure of pollutants through direct oxidation and indirect generation of free radicals.
• Direct oxidation:
Ozone molecules directly react with pollutants, suitable for certain functional groups that are easily attacked by ozone (such as double bonds, amino groups, etc.).
• Indirect oxidation:
Ozone decomposes to produce hydroxyl radicals (·OH), which are species with stronger oxidizing ability than ozone itself and can react with almost any organic or some inorganic substances in water.
This dual mechanism enables ozone to achieve rapid and thorough pollutant degradation in water treatment.
Practical Application Fields of Ozone Water Technology
1. Drinking Water Treatment
Ozone is commonly used as a pre-oxidant or final disinfectant in municipal water supply systems and bottled water production. It effectively controls microbial risks, improves taste and odor, and helps remove contaminants, ensuring safer and better-quality drinking water.
2. Wastewater and Sewage Treatment
In the advanced treatment of industrial wastewater (such as from pharmaceutical, chemical, and textile dyeing industries) and municipal sewage, ozone is employed to decolorize, deodorize, and degrade biologically hard-to-treat organic compounds. This enhances the effluent water quality and can even enable water reuse or recycling, supporting sustainable water management practices.
3. Industrial Pure Water and Specialized Water ProductionIn industries with extremely high water quality requirements — such as electronics manufacturing, pharmaceutical production, and food & beverage processing — the “o3 in water” technology is utilized to produce ultrapure water and sterile water. These specialized water types are essential for meeting stringent production standards and ensuring product safety and process reliability.
4. Ozone Laundry
Ozone is used in commercial laundry to replace hot water and chemicals. Dissolved in wash water, it removes stains, kills germs, and deodorizes at low temperatures. Benefits include energy savings, reduced chemical use, fabric protection, and improved hygiene—ideal for hotels, hospitals, and laundries.
How to Add Ozone into Water? — Technology and Equipment
Dissolving ozone effectively into water is a key link in the implementation of the “o3 in water” technology.
1. Methods of Ozone GenerationCommon methods include:
• Corona discharge method (air or oxygen source)
• Ultraviolet method (less used for large scale)
• Water electrolysis method (cutting-edge research direction)
2. Dissolution Equipment and Technology:
• Aeration systems: such as microporous aeration discs, jet injectors
• Contact reactors: tower type, pipe mixers, Venturi jet mixing
• Key parameters: gas-liquid ratio, contact time, pressure control, mixing efficiency
Health, Safety, and Environmental Impact
Although ozone has many advantages in water, residual ozone poses certain health risks to humans, such as irritating the respiratory tract and damaging lung tissue. Therefore, most countries have set strict limits on the concentration of residual ozone in water (for example, the U.S. EPA recommends that it should not exceed 0.1 mg/L).To ensure safety, degassing devices (such as activated carbon, degassing membranes, gas-liquid separators) are usually installed in the subsequent process to remove residual ozone.In addition, the operation of ozone generation sites must also comply with safety management regulations such as explosion-proofing and ventilation.
Challenges and Future Trends
Currently, the “o3 in water” technology still faces some challenges:
• Equipment investment and operating costs are relatively high
• Issues with ozone generation efficiency and energy consumption
• The level of system control and automation needs to be improved
Future development trends include:
• Advanced Oxidation Processes (AOPs) that combine ozone with UV, H₂O₂, and others
• Intelligent control and online monitoring
• More efficient ozone catalysts and reactor designs
Conclusion
“O3 in water” is far more than just a chemical phenomenon — it is an essential component of modern water treatment technology.With its powerful oxidizing capabilities, ozone plays a critical role in ensuring water safety, enhancing treatment efficiency, and driving industry advancement.From drinking water disinfection to industrial wastewater purification, and from fundamental research to engineering practice, a solid understanding of the interaction mechanisms between ozone and water, as well as mastery of its technical essentials and safety protocols, is a crucial subject for every water treatment professional, researcher, and even the general public who values safe and clean water.