Why do hydroponic grow rooms produce bad odours?
Warmth, humidity, the presence of vegetation and lack of air circulation.

What is the best way of eliminating the bad odours?
Because of the need to maintain temperature it is not practical to flush out the bad odours by using higher numbers of air changes. Artifical chemical fragrances can be used to mask the smell but these generally only makes matters worse. Ozone has been found to be highly successful in eliminating unwanted odour in rooms and providing the amount used is accurately controlled it is the ideal solution. Not only will it eliminate odour but it will also help reduce moulds and bacteria that may damage the plants. It has even been found to discourage insect infestations.

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 harmful ultraviolet radiation from the sun 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 that 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 it 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. If the ozone comes into contact with a Volatile Organic Compound (VOC) or an odour an oxygen atom splits off the ozone molecule and reacts with the VOC oxidising it into a harmless or non odorous substances that are predominantly CO₂ and H₂O. The ozone will also react with certain surfaces.

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). As a result of this natural decay back to oxygen the use of an ozone generator in a room does not lead to a continuous build up of ozone. The level of ozone will stabilise at a predetermined level that is a function of the room size, air changes, temperature, bacteria/VOC/odour content and the reactivity of any surfaces. Because these parameters are all highly variable the need for the ability to control any generator used is essential.

What is the right level 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 has an average Air Quality Guideline of 0.05 - 0.06ppm measured over an eight hour period.

Ozone has been shown by extensive laboratory trials to be effective at reducing bacteria and odour when used at levels no higher than 0.05ppm. These levels are considered safe to breathe 24 hours per day. Tests have also shown that at these levels there is no harmful effect on plants. By accurately controlling the amount of ozone generated it can be used safely and effectively to destroy unpleasant odours and control bacteria.

How is ozone produced?
There are principally two methods of ozone generation: Ultra-violet radiation and silent corona discharge. The ultra-violet light mimics the radiation method that occurs naturally from the sun in the upper atmosphere producing the ozone layer. The silent corona discharge method mimics the action of the lightning method of ozone production.

Which method of generation is best?
Both methods produce ozone reliably. Ultra-violet lamps must emit a very precise wave length of electromagnetic radiation to be effective and they must be kept scrupulously clean. These lamps contain mercury, have a limited effective life and can be expensive to replace and dispose of safely.

A Silent corona discharge machine on the other hand will produce up to 50% more ozone than comparable UV devices providing much greater flexibility and a wider range of application. The corona discharge electrodes are simple and inexpensive to clean or replace and generally use less electrical energy. They do generate minute traces of NO₂ but the amount is insignificant compared with the naturally occurring atmospheric levels.

When choosing new equipment apart from the usual factors of appearance and cost, the user should look for machines that have a high level of controllability to ensure maximum performance and safety, can be simply serviced and have low running costs.

How can you tell the level of ozone?
The level of ozone is dependent upon the size of the room, the output of the generator, the number of reaction surfaces, the number of air changes and the contaminant load. At high concentrations, ozone has a sharp smell similar to bleach that tingles the nose. This tells you immediately that the level is too high and above the occupational exposure limit. At lower levels, it has a slightly metallic odour. At this level you are above the naturally occurring levels but likely to be below the occupational exposure limit. Ozone at 0.05ppm and below has a fresh open air smell.

Most quality ozone companies supply a sizing chart with each ozone generator to enable the user to install and set up the machine correctly for optimum safety. The sizing chart provides easily understood instructions relating to different room sizes as an initial set up. Once the generator is put into service, small adjustments can be made to the output setting in order to achieve the optimum performance as the actual requirements for each room are slightly different.

Further control can be achieved by using a programmable timer built into the unit in combination with the output level setting control. This enables the generator to be automatically turned down or turned off at the most appropriate times of the day or week to suit the use of the room. The incorporation of such controls substantially increases the flexibility of the generator making its range of application almost limitless.

Disposable paper test strips are available that change colour depending on the ozone level to aid the user in validating or monitoring a particular set up. These can be very helpful especially in rooms with unusual shapes where poor air circulation can occur.

Maintenance of the equipment?
Some products are sold claiming that they are maintenance free. Such claims are generally found to be erroneous however as at the very least such equipment does require cleaning regularly to remove the build up of airborne dirt that tends to accumulate. Not only does this regular attention prolong the effective life of the equipment but it also ensures that it is operating at peak performance.

The generator should be cleaned every 3-4 months, depending on the environment and level of usage, primarily to remove any dust and dirt that has accumulated. This operation is normally very simple and should take no more than 5 minutes.

The ceramic plate or UV lamp should be replaced annually.

Hydroponics Q & As

© Ozone Industries Limited 2008