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Ozone Fundamentals for Water Treatment

Jun 8, 2020 3:06:56 PM / by De Nora

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Ozone is commonly used in the treatment of drinking water, but not everyone understands what it is, how it’s used, or the benefits and risks associated with it. We created this blog post to provide a brief introduction to Ozone.

How is Ozone Used for Water Treatment?

Ozone is among the most powerful oxidizing agents known to exist. For this reason, it is often used to compliment chlorine disinfection of drinking water. By using ozone, utilities can limit or avoid the use of chlorine if there’s a concern about dangerous byproduct formation. Once introduced to the treatment process, ozone can safely eliminate a wide range of organic compounds and microorganisms.

Stand-alone ozone effectively treats non-biodegradable contaminants, including micropollutants which are substantially untreated through the conventional activated sludge process. 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. Ozone can also be used to remove unwanted colors, smells, and flavors from the water.

What is Ozone? 

Ozone is an allotrope of oxygen (different structural modifications of the same element). There
are two main allotropes of oxygen: a diatomic molecule that is made up of two oxygen atoms,
oxygen or dioxygen (O2), and a triatomic molecule made up of three atoms of oxygen, ozone
(O3 ).

Triatomic oxygen (ozone, O3), is an inorganic molecule. As a gas it is pale blue in color with a distinctively pungent smell. This very reactive allotrope is destructive to materials like rubber and fabrics and is also damaging to lung tissue. Traces of it can be detected as a sharp, chlorine-like smell, coming from electric motors, laser printers and photocopiers. It is also the strange odor a person would smell after a thunderstorm.

Triatomic oxygen (ozone, O3), is an inorganic molecule. As a gas it is pale blue in color with a distinctively pungent smell. This very reactive allotrope is destructive to materials like rubber and fabrics and is also damaging to lung tissue. Traces of it can be detected as a sharp, chlorine-like smell, coming from electric motors, laser printers and photocopiers. It is also the strange odor a person would smell after a thunderstorm.

Having three molecules of oxygen, ozone (O3) is thermodynamically less stable than O2. In order to become stable, it gives up one molecule of oxygen to return to the diatomic state. The decomposition into oxygen also results in the liberation of heat.

How is Ozone Formed?

In nature, ozone is produced in the stratosphere when solar radiation strikes molecules of oxygen (O2). This impact causes photolysis or the splitting of the two oxygen atoms. If one of these atoms collides with another O2 molecule, they merge, forming ozone O3. The ozone layer acts as a filter for ultraviolet radiation that is harmful to the skin and for the eyes.

To create ozone, energy is applied to decompose the oxygen atom (O2) in order to add another oxygen atom to an oxygen molecule (O3). UV light, thermal plasma heat, arc discharge, radioactive decay and, the most popular, cold plasma electrical fields can be the source of this energy.

Ozone Generator Process with High Voltage

When ozone is generated starting from pure oxygen, normally the concentration is between six and 15 percent. If it is generated starting from dry air, the concentration produced is around 1.5 to 3.8 percent. Unfortunately, this is a rather inefficient process. Much of the energy that is applied is wasted as heat. Cooling water must be applied to remove this heat and create a stable gas stream.

Safety Aspects of Ozone

Although ozone is very useful in technology, it is also classified as a toxic gas and is extremely dangerous. When diluted in the atmosphere or into a room, you can smell it, in fact, "ozone" derives from a Greek word that means "emit odor".  

A person can only be exposed to ozone for a limited amount of time. When the concentration is low, nothing happens. A nose can detect ozone even when it is 10 times lower than the allowed concentration of 0.1 ppm. They just smell it and make their way to safety. If a person is exposed to a higher concentration, their nose becomes less sensitive to the odor. This is when safety equipment becomes critical.  

General regulations from OSHA state that a person can be exposed to 0.1 ppm for eight hours TWA maximum without any risk and 0.3 ppm for a maximum one hour. These thresholds are normally used to set the safety devices installed in a facility. At 0.1 ppm, normally, the system receives a warning alarm. At 0.3 ppm, there is generally an immediate shutdown interlock stopping the entire ozone generation plant. If the shutdown is overridden, the concentration can increase over the 0.3 ppm becoming harmful for operators and other employees. Sometimes oxygen can be even more dangerous because you can’t see it or smell it. Both high concentrations, or low concentrations of oxygen are also very dangerous.

Symptoms of Ozone Exposure

People exposed to elevated levels of ozone may experience a variety of symptoms. The most common symptom is a feeling of irritation in the eyes, nose and throat. Some people may also experience respiratory or cardiac symptoms such as shortness of breath, chest pain, wheezing and even death. If an equipment operator is experiencing one or more of these symptoms, it is advised to seek medical help immediately. 

Source: Ozone Fundamentals, Alex Bettinardi

Disinfecting Isn't Enough.

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Tags: water treatment, ozone, ozone safety

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