What are the main reasons for increases in microbiological contamination?
Once the basic sources such as personal hygiene, contaminated raw materials and inadequate cleaning of process equipment have been eliminated the most common causes are inadequate terminal disinfection and weaknesses in plant operation and maintenance. Traditionally, terminal disinfection has been some kind of fogging but this is difficult and expensive to use so it is avoided whenever possible. Regulatory changes in the form of the Biocidal Products Directive have already caused a number of traditionally used fogging agents to be withdrawn, further reducing the frequency of use. This process of chemical withdrawal will accelerate as the costs associated with safety testing many of the chemicals become prohibitive.
What is the best way of eliminating microbial problems?
The increased use of chemicals is an option but this increases running costs and all the problems of using chemicals remain. Ozone has been found to be highly successful in eliminating bacteria, moulds and yeasts in food production areas and there are numerous successful installations now in operation. A substantial amount of independent research has been conducted to establish the correct amount of ozone to achieve the desired levels of disinfection and subsequent field trials have fully substantiated these findings. Ozone treatment can be fully automatic and requires no consumable material enabling it to be used daily to achieve maximum affect. After treatment all the residual ozone decays back to natural oxygen leaving the room fresh and sweet smelling when people re-enter the room.
Does ozone affect product?
In most cases it is not necessary to remove product from the space being ozonated. In traditional cheese storage for example ozone is used daily to control the growth of mould and to discourage cheese mites. In the cheese packaging and in the fresh fruit markets ozone is used during packaging to eliminate mould and bacteria.
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 that naturally occurring 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 splots 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. 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.
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 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, odour/VOC/bacteria content and the reactivity of any surfaces. Because these parameters it is necessary to use computer models to determine the correct amount of ozone to use in any particular installation.
What is the right level of ozone?
The amount of ozone required to achieve a specific result varies from site to site and computer models are used to simulate the conditions in each plant before any equipment is specified. The factors that affect the levels depend a lot on the time available for the treatment, the room temperature and the air changes that occur as well as the type of microbiological material that is being targeted.
As people are not normally present when disinfection processes are being carried out the question of any operator exposure should not arise unless the insufficient time has been allowed after the system has been shut down before people re-enter the room. Normally a time delay of a couple of hours is sufficient for the levels to decay to a level that does not conflict with health and safety guidelines.
The occupational exposure levels for ozone vary across the world. In the UK there is no time limit for exposure at levels 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 that for the EU is similar.
Ozone has been shown by extensive independent laboratory trials to be effective at reducing odour and bacteria even when used at very low concentrations. Ozone Industries has found that by accurately controlling the amount of ozone generated to ensure that it is always at a safe level it is even possible to achieve effective bacterial and mould control in a production plant that is working 24/7 when no normal opportunity exists for deep disinfection.
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 a disinfection process. The corona discharge electrodes are simple and inexpensive to clean or replace and they consume very little electrical energy. The output from the machines can be easily controlled to suit the size of room and the level of odour.
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, the temperature, the humidity 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 natural occurring levels but likely to be below the occupational exposure limit. Ozone at 0.05ppm and below has a fresh 'open air' smell.
Ozone Industries engineer and install systems to ensure that the correct levels are achieved and maintained for optimum safety. 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. When necessary Ozone Industries installation engineers conduct monitoring trials using specialist equipment to validate an installation.
Portable battery operated ozone monitoring equipment is available as are alarm detectors and also disposable paper test strips that change colour depending on the ozone level to aid the user in validating or monitoring a particular set up. Each of these can be very helpful especially in rooms with unusual shapes where poor air circulation can occur or when equipment has been moved.
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 serviced every 12 months primarily to remove any dust and dirt that has accumulated and to ensure that it is working correctly and to replace any worn parts. This operation is normally carried out by an Ozone Industries service engineer, by customer request.
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