Water Conditioning & Purification Magazine

Ozone in Water Treatment

By Alex Bettinardi

How does ozonation work?
Ozone is a pale blue gas composed of three oxygen atoms (O3). Ozonation is a water treatment method where ozone is generated onsite and introduced into water to eliminate a wide range of organic compounds and microorganisms. The transformation of oxygen into ozone, a very powerful oxidant, occurs with the use of energy. Inside the ozone generator vessel, ozone is produced from oxygen present in the feed gas by means of a silent electric discharge (non-thermal plasma). Ozone is dissolved into the water. It produces a direct oxidation reaction on the pollutants/molecules.

Ozone generator installed in 2012 for drinking water disinfection at the Daquing Water Treatment Plant, China.

Where is ozone used to treat water?
Ozone was first used in water treatment in the late 1800s and is more widely used in Europe and Asia than the United States. The first drinking-water plant with ozone was built in Nice, France, in 1906. Ozone is used for industrial water treatment processes, in large swimming pools and aquariums and also in municipal wastewater applications for direct and indirect potable reuse processes.

How is ozone used at water treatment plants?
Ozone is used as a stand-alone technology in some cases. It can also be combined with hydrogen peroxide (H2O2), ultraviolet light or active chlorine to perform an advanced oxidation process (AOP). This AOP produces highly reactive hydroxyl radicals (•OH). These reactive species are the strongest oxidants that can be applied in water. They are used to address contaminants with high chemical oxygen demand (COD) or non-biodegradable molecules. They also improve the overall quality of the water. Ozonation can be used to complement chlorine disinfection of drinking water. By using ozone, utilities can reduce the use of chlorine if there’s a concern about dangerous byproduct formation. Ozone also treats groundwater that has been polluted by metals (like iron and manganese) and inorganics, such as hydrogen sulfide (H2S), that are easily oxidated by O3.

Containerized ozone generator installed in 2016 or water reuse in a refinery in Oman.

Why is ozonation a good solution for micropollutants in wastewater?
Ozone is among the most powerful known oxidizing agents and has one of the highest redox potentials. The formation of byproducts is very low and sometimes absent. Stand-alone ozone effectively treats non-biodegradable products, including micropollutants substantially untreated through the conventional activated sludge process.

Are there other ways that micropollutants are removed?
There are several technologies available to remove micropollutants, including reverse osmosis (RO) membranes. RO membrane filtration concentrates the micropollutants and effectively removes them, but doesn’t actually destroy them, so the concentrated brine reject must be disposed. Granular activated carbon (GAC) is the most convenient and simple technology for this application. GAC is typically used in combination with ozone because GAC alone is not always enough. The advantage of ozonation is related to the direct oxidation of micropollutants. Ozonation transforms micropollutants into more biodegradable compounds that are easily adsorbed and decomposed on the downstream filter, commonly called the biological activated filter.

How serious are micropollutants? Should treatment operations be concerned?
Endocrine disrupting compounds (EDCs) are chemicals that, at certain doses, can interfere with endocrine systems. These disruptions can cause cancerous tumors, birth defects and other developmental disorders. Drugs and pharmaceutical residuals are not effectively treated with the traditional wastewater treatment plants. Switzerland is the first country that has enacted a specific law, but many countries are conscious about this serious concern. Some countries, like Germany and France, are addressing the micropollutant issue even faster than Switzerland, despite a lack of regulation.

Would you say that ozonation is the best technology for combating micropollutants?
In most cases, GAC alone is not enough to protect the population from the risks posed by EDCs. Ozonation is surely one of most effective and convenient treatment options available when used in combination with other technologies. Technologies often paired with ozonation include GAC and biological filtration, which uses a different filter media.

What equipment is used in an ozone system?
A typical ozone system scheme includes:

  • the feed gas preparation system section, either liquid oxygen (LOX), oxygen concentrated from air using pressure-swing adsorption (O2 by PSA) or dry air
  • one or more ozone generators, according to required equipment redundancy
  • the side-stream ozone injection system, including booster pumps and Venturi injectors, may include the hydrogen peroxide injection in an AOP application
  • the reaction tank/pipe reactor to ensure the proper contact time, specific process by process
  • the thermal and catalytic residual ozone destruction units
  • safety and process control instrumentation, including O3 and O2 monitors
    The overall ozonation process is controlled by a main PLC that also allows remote monitoring of all the important operating parameters. When a dedicated building is not available, fully containerized solutions are an excellent option, especially for plants that are upgraded or retrofitted with an ozone system that wasn’t in the original building plan.

About the author
Alex Bettinardi has been the Technical and Sales Support Manager for North and South America ozone sales for De Nora since 2015. He manages the technical and commercial bidding process, strategy definition, municipal and industrial market development, technical and sales training, as well as knowledge transfer and support for reps and distributors selection. Before joining De Nora, Bettinardi was the Managing Director at Ozono Elettronica Internazionale. He can be reached via phone, +39 3346205360 or email, alex.bettinardi@denora.com.

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