Ozonated water is water that has been infused with ozone gas, a highly reactive form of oxygen. This solution functions primarily as a powerful disinfectant and oxidizing agent. The ozone molecule (\(\text{O}_{3}\)) is significantly less stable than the common oxygen molecule (\(\text{O}_{2}\)) we breathe. Its instability makes it effective, as it readily releases an oxygen atom to react with contaminants, allowing it to break down organic and inorganic substances.
The Chemistry and Mechanism of Action
The power of ozonated water stems from the high oxidative potential of the ozone molecule. Ozone has an oxidation potential of +2.07 V, making it one of the strongest oxidants available for water treatment, surpassing chlorine and hydrogen peroxide. When ozone is dissolved in water, it reacts directly with contaminants or decomposes to form secondary oxidants, most notably the highly reactive hydroxyl radical (\(\cdot\text{OH}\)).
This strong oxidative property allows ozone to act as a broad-spectrum disinfectant by physically destroying microorganisms. It rapidly attacks the cell walls of bacteria, viruses, and protozoa, causing them to rupture and leak their cellular contents. Unlike disinfectants such as chlorine, which interfere with metabolic processes, ozone’s physical disruption ensures quick and irreversible inactivation of the pathogen, preventing resistance.
The oxidation process also targets non-microbial contaminants, such as iron, manganese, sulfides, and organic compounds, which affect water quality. Ozone oxidizes these substances into insoluble forms that can then be easily filtered out. This dual action of disinfection and oxidation contributes to improved taste, odor, and clarity of the treated water.
Practical Applications in Water Treatment and Health
Ozonated water is widely applied in municipal water treatment, often as a primary disinfectant before chlorine is added to maintain a residual effect in the distribution system. Its ability to inactivate chlorine-resistant pathogens, such as Cryptosporidium, makes it a highly effective initial treatment step. Using ozone also helps reduce the formation of undesirable chlorinated byproducts in the final drinking water.
The food and beverage industry uses ozonated water for sanitizing equipment and products. The U.S. Food and Drug Administration (FDA) classified ozone as “Generally Recognized as Safe” (GRAS) for use as an antimicrobial agent in the treatment, storage, and processing of foods. Aqueous ozone is sprayed directly onto produce, meat, and poultry to reduce microbial load, leaving no chemical residue as it decomposes back into oxygen.
In health-related fields, ozonated water is utilized in medical and dental settings for its antimicrobial properties. It is employed for surface sterilization, wound cleaning, and as a rinse in oral hygiene procedures. Its rapid action and non-toxic decomposition products make it a favored choice for effective, residue-free disinfection.
Generation Methods and Stability
Ozone gas must be generated on-site due to its inherent instability before being dissolved into water. The two primary commercial methods for generating the gas involve specialized equipment called ozone generators. The most common technique is the Corona Discharge method, which passes air or pure oxygen through a high-voltage electrical field, causing oxygen molecules (\(\text{O}_{2}\)) to split and reform as ozone (\(\text{O}_{3}\)).
A secondary method utilizes Ultraviolet (UV) light, where a specific wavelength of UV radiation splits oxygen molecules to create ozone, though this method typically produces lower concentrations. Once generated, the gas is efficiently mixed and dissolved into the water using devices like diffusers or venturi injectors. The amount of ozone that dissolves, known as its solubility, is affected by water temperature and pressure.
The short lifespan of dissolved ozone is a defining characteristic of ozonated water applications. In distilled water at room temperature, the half-life is approximately 20 to 25 minutes. The half-life is significantly reduced by higher temperatures, increased pH, and the presence of organic material. This rapid decomposition necessitates that ozonated water be produced continuously and used immediately at the point of application.
Safety and Regulatory Considerations
A safety advantage of ozonated water is that ozone rapidly breaks down into stable oxygen, leaving no long-lasting disinfectant residues on surfaces or in the water. However, the primary safety concern with ozonation of drinking water is the potential formation of disinfection byproducts, specifically bromate. Bromate is classified as a possible human carcinogen and forms when ozone reacts with naturally occurring bromide ions present in the source water.
To protect public health, regulatory bodies like the U.S. Environmental Protection Agency (EPA) have set a maximum contaminant level (MCL) for bromate in drinking water at 10 micrograms per liter (\(\mu\text{g}/\text{L}\)). Water treatment facilities must carefully control factors such as the ozone dose, pH, and contact time to minimize bromate formation while achieving sufficient disinfection. Techniques like adding hydrogen peroxide or adjusting the water’s alkalinity can suppress the chemical reactions that lead to bromate formation.
Regulation aims to balance the powerful disinfection benefits of ozone against the risk of creating harmful byproducts. Long-term exposure risk is managed by adherence to strict governmental standards for water quality. The short-lived nature of ozone ensures that the risk is contained to byproduct formation during the treatment process.