Ozone: Looking to Nature for Drinking Water, Wastewater and Industrial Water Treatment Solutions

As the world is coming to grips with the reality that water is a highly valuable resource that is becoming ever more scarce, water treatment has entered a new era of criticality. Technology, economy, government regulation and public demand are all driving innovation to protect water from contamination and remediate already contaminated waters. Among the evolving strategies that are keeping up with the increasing demands of water treatment is ozone, which is driving more facilities to invest in this technology.

What is ozone?

A pale blue gas, ozone (O3) is composed of three oxygen atoms. Ozone is the most powerful oxidizing agent permitted for use in water treatment. In industrial settings, ozone water treatment can significantly reduce contaminants, toxins and many other pollutants from water in a vast range of industrial and municipal applications.

Ozone can be generated onsite and introduced into water and wastewater to oxidize a wide variety of inorganic, organic and microbiological problems including contaminants of emerging concern, 1,4-dioxane, micropollutants and cyanobacteria mycotoxins.

How does ozone form naturally?

In the stratosphere, ozone is produced from the interaction between solar ultraviolet radiation and oxygen molecules. At certain wavelengths, UV radiation will break apart oxygen molecules (O₂) into single atoms (O), which then bind to other oxygen molecules to form ozone (O3). Other natural processes such as volcanic eruptions and lightning also create ozone. Ozone in the upper levels of the atmosphere forms a protective layer between the earth and the sun’s ultraviolet rays.

Ground level (tropospheric) ozone is a main ingredient of smog and is created in the presence of sunlight by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC), which are pollutants emitted by cars, industrial plants and other sources. In this context, ozone poses a threat to human respiratory health.

How is ozone generated?

With an ozone generator, ozone can be produced by using an energy source to separate oxygen molecules (O₂) into oxygen atoms (O), which react with other oxygen molecules to form ozone (O3). A high voltage alternating current is applied across a dielectric discharge gap that contains an oxygen-bearing feed gas. This process is often referred to as corona discharge ozone generation.

How does ozone treat water and wastewater?

When ozone is dissolved in water, free radicals form that have excellent oxidizing capacity on pollutants and molecules. Ozone is an unstable compound, a reactive oxygen species, that works to degrade unwanted chemicals and toxins. Ozone can oxidize organic material in bacterial membranes, which weakens the cell wall and leads to cell rupture (cell lysis), causing the immediate death of the cell. It can also react with radical by-products of ozone decomposition or cause damage to the constituents of nucleic acids. Finally, it can break down carbon-nitrogen bonds and cause depolymerization.

The effectiveness of ozone water treatment relies on the susceptibility of the target organism, the concentration of ozone used and the length of exposure. The various applications of ozone require different doses, chemistry and reaction times for the best outcomes.

Ozone treatment is used for a wide variety of reasons in drinking water and water reuse applications, most commonly for taste and odor reduction, to remove color, surfactants, iron, manganese, phenols, hydrocarbons, organics or micropollutants, or to reduce overall toxicity in wastewater. Using ozone treatment to reduce the volume of excess biological sludge in wastewater treatment plants is one of the most common applications, which in turn lowers hauling and disposal costs.

When is ozone preferred over chlorine for iron and manganese oxidation?

Ozone oxidizes iron and manganese to form insoluble particulates that can easily be filtered from the water. Ozone water treatment is especially beneficial when conditions do not favor chlorine, such as when manganese is the primary contaminant and green sand filters are not employed or the pH is neutral to acidic, when iron is complexed with dissolved organic carbon, when sulfides are present or when THM is a concern.

How do ozone and ozone AOP differ?

While ozone is a powerful disinfectant and water purifying agent, there are situations in which ozone alone cannot effectively treat water. In these cases, ozone is employed as a critical component in an advanced oxidation process (AOP), which combines the power of ozone with one or more additional oxidants, such as hydrogen peroxide (H2O2) or ultraviolet (UV) light. With ozone AOP, the combination of ozone with these additional oxidants creates highly reactive hydroxyl radicals that are even more powerful oxidizing agents than ozone alone. Ozone AOP can remove persistent and refractory organic contaminants and other constituents of emerging concern.

Ozone advanced oxidation process (AOP) is generally preferred over other AOP, such as UV AOP, when the water has low UV transmittance and/or high TOC, when peroxide quenching is a concern, or if a plant requires the application of ozone for additional reasons such as the mitigation of pharmaceutical micropollutants.

How is ozone used in drinking water treatment?

As the most powerful oxidizing agent permitted for use in water treatment, ozone can be used as a primary disinfectant at water treatment plants. In micro-flocculation enhancement, ozone gas creates smaller, more numerous flocs for improved removal of particulate matter. Unlike chlorine, ozone treatment doesn’t generate disinfection by-products (DBPs) like THM, HAA, chlorate and NDMA, and it’s also more efficient than chlorine at reducing organics content in water. As a supplemental treatment in systems that use chlorine or hypochlorite for water disinfection, ozone can mitigate DPBs generated by the chlorine treatment process.

Ozone is the most effective technology available in the treatment of cyanobacteria, also known as blue algae, which is a major cause of bad taste and odor in drinking water. Ozone is more effective in treating cyanobacteria and mycotoxins (MIB2) than any other disinfection technology. It’s also highly effective in the mitigation of hydrogen sulfide, another common by-product of chlorine disinfection and contributor of bad odor, taste and color. Typical municipal drinking water applications for ozone treatment include mitigating pharmaceutical micropollutants, personal care products and other contaminants of emerging concern, such as 1,4-dioxane. It’s also used for TOC reduction and for bacterial and viral disinfection. Water treatment plants also use ozone for the oxidation of iron and manganese.

How is ozone used in wastewater treatment?

Wastewater treatment processes use ozone generation to mitigate cyanobacteria mycotoxins, pharmaceutical micropollutants, personal care products and other contaminants of emerging concern, such as 1,4-dioxane. It’s also used for biological sludge reduction and for disinfection, notably to destroy E. coli viruses. In the wastewater polishing stage, ozone works well for odor and color removal and for treating recalcitrant organic molecules (COD and TOC). It’s also highly effective at oxidizing specific molecules such as surfactants, hydrocarbons, phenols and cyanide.

For systems that treat water for direct or indirect potable reuse, ozone helps prepare the wastewater for further treatment. When reverse osmosis is used, a pre-treatment with ozone can reduce the organic load on membranes.

For most of these applications, ozone is applied as an advanced oxidation process, rather than a standalone technology.

How is ozone used in water reuse?

Water reuse is growing in favor as a sustainable water management practice and a cost-saving strategy in an age of rising water scarcity. Ozone is often a key component in a water reuse system, combining well with other treatment processes to achieve a desired water quality for a specific reuse. Ozone treatment can convert difficult to treat waters for indirect potable reuse, aquifer recovery and recharge, groundwater remediation, industrial water reuse, irrigation and secondary reuse and zero liquid discharge systems.

What are the safety concerns related to ozone generation?

The powerful oxidizing properties of ozone also make it potentially hazardous to human health. Ozone generators should be designed, installed, operated and maintained properly by an experienced vendor to avoid safety concerns. Potential effects on personnel include respiratory, eye and skin irritation, so facilities should provide personal protective equipment for anyone working with an ozone generator. At concentrated levels, ozone can present fire and explosion risk, so proper ventilation is essential to prevent the buildup of ozone. Regular maintenance, along with ozone detection and monitoring devices with alarms should be standard components in any operation using ozone generators.

Does ozone form any disinfection by-products?

The formation of disinfection by-products of ozone is minimal. Ozone rapidly decomposes to oxygen, leaving no traces of chlorite, chlorate or toxic halogenated compounds like THM and HAA. Bromate can be an issue if bromide is already present in the water. H2O2 or pre-formed chloramine injection can mitigate and/or prevent bromate formation.

Why work with De Nora?

De Nora has developed and delivered ozone generators for water treatment and advanced oxidation processes for industrial applications since the 1970s, supporting customers from design to commissioning and aftersales. We design single components to complete packaged systems that generate up to 6,000 pounds (113 kg/h) of ozone per day. With more than 1,500 Capital Controls Ozone Generators installed around the world, we support customers with on-site piloting and lab-scale testing in containerized plug-and-play pilot packages.