What is the best way of eliminating the bad odours?
There are many methods of odour control available on the market but most are either very expensive to install, have high running costs or occupy large amounts of space. Ozone has been found to be highly successful in eliminating unwanted odour in factory exhaust stacks and provided the amount used is accurately controlled it is an ideal solution. The ozone is fed into the exhaust duct at the earliest point and the oxidation reactions take place within the confines of the duct. The equipment is compact, light weight and simple to install. It is normally completely automatic and has very low running costs so is an appropriate solution in many of those smaller applications that prove so difficult to resolve.

What is ozone?
Ozone is a naturally occurring substance that is sometimes called "activated oxygen". It contains three atoms of oxygen (O₃) instead of the usual two found in normal oxygen (O₂) that is essential for life. High in the atmosphere the ozone layer is created by the action of the solar radiation on the oxygen atoms. At ground level the unmistakeable fresh smell in the air following a thunderstorm is ozone created by the effect of the lightning discharge on the oxygen atoms. Ozone is also created naturally as a result of photochemical reactions due to the pollutants such as NOx and SOx that are found in the atmospheres of cities and industrial areas. Ozone can also be created artificially by generating a high voltage electrical corona across a dielectric to form what is known as a "silent discharge".

Ozone is the second most powerful oxidant known and the naturally occurring level not only protects all life from the harmful effects of solar ultraviolet radiation but also is very effective at destroying bacteria, viruses and odours. Artificially generated ozone is just as effective as naturally occurring ozone provided that the amount is carefully controlled. This requirement for control is a key consideration when selecting an ozone generator.

How does ozone work?
The ozone gas molecule O₃ is unstable allowing it to readily decay into O₂ thereby releasing a single oxygen atom that is highly reactive. When the ozone comes into contact with an odour or a Volatile Organic Compound (VOC) an oxygen atom splits off from the ozone molecule and reacts with the odour or VOC, oxidising it into harmless and non odorous substances that are predominantly CO₂ and H₂O. The ozone will also react with certain surfaces so the use of stainless steel or plastic is necessary.

Many odours are the result of bacterial action and when ozone comes into contact with a bacteria or a virus, the oxygen reacts with the cell membrane. Initially the ozone attacks the glycoproteins, glycolipids and certain amino acids such as tryptophan in the bacterial membrane. It also acts upon the sulfhydral groups and some enzymes resulting in the disruption of normal cellular activity. Bacterial death is rapid and is often attributed to changes in the cell permeability followed by cell lysis.

As each of these reactions occur the amount of ozone present continuously reduces until all the ozone has decayed back to the original normal bi-atomic oxygen, making it a safe and environmentally friendly with no harmful residues. As the ozone molecule is unstable even if none of these reactions occur the ozone (O₃) rapidly reverts back to oxygen (O₂). The level of ozone in the discharge will stabilise at a predetermined level that is a function of the feed concentration, air velocity, temperature, odour/VOC/bacteria content and the reactivity of any surfaces. Because these parameters are all highly variable the need each system need to be engineered specifically to achieve optimum performance.

What is the right level of ozone?
The amount of ozone required for each project is dependent on the process parameters and is defined by site trial.

What are the Occupational Exposure Levels of Ozone?
The occupational exposure levels for ozone vary across the world. In the UK there is no limit on exposure below 0.2 parts per million (ppm). In many European countries there is an eight hour time weighted average exposure limit of 0.1ppm, while in the U.S.A the comparable level is 0.08ppm. The World Health Organisation (WHO) has an average Air Quality Guideline of 0.05 - 0.06ppm measured over an eight hour period and the EU is similar.

How is ozone produced?
The silent corona discharge method that mimics the action of the lightning is the most usual method of ozone production for an odour control application. The corona discharge electrodes are simple to operate and they consume very little electrical energy. The output from the machines can be easily controlled to suit the process requirements and the level of odour.

Maintenance of the equipment?
Although the ozone generator is long lasting and trouble free it does require some attention from time to time to remove accumulated dust and dirt to ensure that it is operating at peak performance. The generator should be service annually primarily to remove any dust and dirt that has accumulated and to ensure that everything is still performing as required. This operation is normally carried out by an Ozone Industries service engineer at the request of the client.

Suitable Products
Odour Application Assessment Form

Nuisance Odour Control Q & As

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