What is ozonation, and how does it help purify water?

The chemical compound ozone is relatively familiar to most of us, particularly those of us who live in sunny environments and originally heard of ozone as the Earth’s protection against the sun’s energy. It may come as a surprise to some, however, ozone is also extensively used as a disinfecting agent for multiple applications, including water due to its unique set of properties. The question and inspiration behind this article are what exactly is the process of ozonation and how does it help purify water?

Ozonation is the process of oxidizing and then removing dissolved metals, organic material and microorganisms from water. Ozone is a strong oxidizing agent which has the ability to convert dissolved contaminants into insoluble compounds which are released as gas or easily removed through post-filtration.

What is Ozone?

In simplest terms, ozone is a gas composed of three oxygen molecules O₃. Ozone formation is a naturally occurring process that takes place in the Earth’s outer atmosphere and can also be emulated in a reactor. It is a two-step process, the process begins by exposing oxygen (O₂) to concentrated ultraviolet radiation which breaks the oxygen into two individual oxide ions (O-).

O₂ + UV → 2O

The second part of the process is that these two oxide ions then bond to two separate (O₂) molecules forming 2 ozone molecules (O₃). These ozone molecules are extremely unstable and eventually break down into stable oxygen molecules within 8 hours, however, until that point they are able to be utilized accordingly.

2O + 2O₂ → 2O₃

When it comes to utilizing ozone in the purification of water, due to its short lifespan, it is created in situ and immediately applied to the water being processed. This in-situ production is done in the form of small microreactors that emulate the same aforementioned process as the Earth’s outer atmosphere and then immediately pump the ozone into the water being processed.

What happens when ozone interacts with water?

When ozone comes into contact with water, it breaks down into ordinary oxygen and two hydroxyl radicals. These hydroxyl radicals are highly reactive and can oxidize organic compounds, metals and microorganisms in the water.

The reaction between ozone and water:

Ozone + Water = 2 Hydroxyl Radicals + 2O₂ + H₂O

Hydroxyl radicals are free radicals that have an unpaired electron in their outer shell and can easily react with other substances by stealing electrons from them.

How does ozone help to purify water?

Note that ozone is a powerful oxidant which breaks down contaminants and impurities in water. It does this by releasing oxygen atoms which then react with dissolved ions present in the water releasing impurities from the solution, enabling them to be released as gas or easily filtered out. Ozone is also used to remove microorganisms from water by oxidizing material in their membranes and subsequently killing their cells.

Metals are removed from water through ozonation when they are oxidized from a soluble to an insoluble state and then filtered out. Although this doesn’t necessarily work for all dissolved metals, an example of this is when dissolved manganese ions are exposed to ozone they form insoluble manganese dioxide (MnO₂) which precipitates as a solid. This solid is easily filtered out of the water, if ozone hadn’t been applied to the water, the dissolved manganese would have flowed straight through the filter so essentially, the ozone enables the metals to be filtered out.

Microorganisms like bacteria and viruses are susceptible to ozonation due to the oxidation of fragile cell membranes. The oxidation of cell membranes breaks down the membrane’s semi-permeable qualities leading to intracellular leakage and eventually death. This susceptibility of cell membranes to ozone oxidation is exploited on a mass scale when treating water, sufficient ozone is produced and applied to the water to remove bacteria and viruses from water sources that would have otherwise been unpotable.

Hydrocarbons are broken down into water, oxygen and carbon dioxide when oxidized by ozone. The way ozone breaks down dissolved hydrocarbons efficiently utilizes its powerful oxidation properties in a similar manner to the way it brings metals out of solution. The hydrocarbons which are generally made of a combination of Carbon, Hydrogen and Oxygen atoms are broken down through oxidation and removed from the solution in the form of carbon dioxide, water and oxygen. Ozone is efficient at breaking down all BTEX hydrocarbons (Benzene, Toluene, Ethylbenzene, Xylene) these are common hydrocarbons found in crude oil. An example of how Benze is broken down when oxidized by ozone is highlighted below:

C₆H₆ + 11 O₃ —- > 6Co₂ + 3 H₂O + 11 O₂

Ozonation provides a multifaceted water treatment solution when coupled with a post-processing filtration system. An ozone & filtration system has the ability to purify waters with diverse contaminants, with the only waters that are completely unsuitable being highly saline sources that require desalination prior.

Will ozonation have any health effects on the user?

As a general rule, ozonation is not harmful to humans, particularly when using well-maintained devices. In fact, it can be beneficial in many ways. For example, it’s often used to purify water in hospitals, since ozone is able to kill bacteria and viruses without using chemicals that might be harmful to patients.

Although ozone is technically considered an additive form of water treatment, it is distinctly different from other additive processes like chlorination in that the additive will not be present in the finished product, whereas chlorine remains in chlorinated water right up to consumption or use. This clear difference enables ozone water treatment to be considered one of the cleanest and healthiest methods of water treatment as the process removes contaminants without leaving anything behind.

Why is pool water treated with ozone?

You may be surprised to learn that the use of ozonation in swimming pools is quite common. Most people think that chlorine is the only way to keep their pool clean, but ozone has some distinct advantages over chlorine, which makes it a viable alternative for many projects.

Ozone has been used as a disinfectant since the early 1900s when scientists first experimented with it as a means of purifying water. It quickly became clear that ozone was more effective than traditional methods of killing bacteria and viruses. Ozone provides a superior service to other alternatives by safely neutralizing microorganisms without adding chemicals that can then affect the smell of the water and irritate people’s skin and eyes. Although having higher setup costs than a standard pool chlorination unit, ozone pool water treatment systems have no ongoing costs and produce superior-quality pool water.