Ozone is an allotropic form of oxygen; each molecule contains three atoms of oxygen instead of the standard two. Ozone is a powerful disinfectant and has been used commercially for the treatment of potable water since 1904.
Ozone is formed naturally in the atmosphere, as a colourless gas giving a very pungent odour It is the ozone formed by lightening discharges during a thunderstorm which gives the air its characteristic fresh and clean smell afterwards. An ozone smell can also be detected around office copy machines and laser printers. In fact, ozone in air can be readily detected by smell at concentrations as low as 0.01 ppm.
In the same way that ozone is formed naturally by the discharge of electricity during a thunderstorm, large quantities of ozone are produced in the modern electrical ozone generator This method of ozone generation is called corona discharge. A high voltage is passed across a gas stream containing oxygen. The energy of the high voltage splits an oxygen molecule (02); into two oxygen atoms (0) - which recombine with ordinary molecules of oxygen (02) to form ozone (03).
To improve the performance of the ozone generator, pure oxygen can replace the ambient air thus providing a greater percentage of oxygen in the airstream.
Ozone can also be formed in the proximity of certain types of ultra violet lamps, however this will only produce ozone at low concentrations. Since ozone is highly reactive and has a short half-life, it is very difficult to store and transport. Ozone must therefore always be generated on site for immediate use.
Ozone is the most powerful oxidising agent permitted for use at this time (only fluorine is stronger - its use is banned in most countries).
As an oxidising agent it is 51% stronger than chlorine and has a kill rate of 3.125 times faster Ozone readily oxidises organic material in bacterial membranes which weakens the cell wall and leads to cell rupture causing immediate death of the cell.
Ozone oxidises most organics and reduced many inorganic materials to a lower state that is more biodegradable. Some organic materials can be completely oxidised to carbon dioxide and water.
Ozone kills all bacteria, viruses, spores, mould, mildew, fungi, amoebae and cysts. The amount of ozone, the concentration of ozone, the composition of the host environment and the contact time of ozone with the organism all play a role in calculating the level of ozone required to destroy each type of organic growth.
The maximum permissible continuous exposure limit to ozone in air is 0.1 ppm averaged over an eight-hour work shift. It is possible to detect ozone by smell at levels as low as 0.01 ppm. With sufficient concentrations of ozone, irritation of the eyes, dryness of the throat and cough may be experienced. Ozone is a potentially toxic material and the exposure limit guidelines must always be adhered to.
A properly installed ozone system will dissolve a high proportion of the ozone dosed into the water with the intention of building a residual level. As ozone can be detected at levels ten times smaller than the current Health & Safety Guidelines, any escaping ozone in an enclosed area can easily be detected and the necessary action taken to remedy the situation.
All Waterwise Ozone Systems operated under vacuum, eliminating the risk of leakage of high concentrations of ozone.
The temperature and humidity of the air and the chamber where ozone is made is very important in maximising ozone output. The cooler and dryer in the air, then the greater the ozone output. Most Waterwise Ozone Systems are therefore fitted with air dryers and filters to pre-treat and condition the air feed.
Ozone has a neutral pH (about 7.0) so it does not affect the pH of the system's water Ozone has no calcium or alkalinity, and has no dissolved solids; therefore it will not affect the water's balance.
Ozone does remove trace amounts of dissolved metals such as iron manganese and copper by oxidising them to their highest oxidation state. They will then precipitate out of the water and should be removed by filtration.
Ozone is highly reactive and because of this has a very short half life once dissolved into water The natural reaction for ozone (03) is to return to its oxygen form (02). This reaction time is typically 10-20 minutes at 20ºC. This means that any blowdown from an ozone treated cooling system will not contain any chemical biocides or corrosion inhibitors or toxic residues and thus will not be classed as effluent and may be disposed to surface drainage.
When ozone is injected to a properly designed ozone water treatment system there is very little ozone which is not dissolved. The ozone layer is located in the lower stratosphere between altitudes of 9 and 19 miles. What does escape would be like a drop in the ocean and would never reach this region.
The simplest form of ozone detection is smell. At levels as low as O.O1 ppm ozone can be detected by the human sense of smell. For a more accurate form of detection, several manufacturers promote devices that can detect ozone by means of light detraction or drop test chromatography.
There are methods for continuous ozone detection by means of Redox and direct ozone determination (Amperometric cell).
Ozone detection methods are very similar in design to other oxidising biocide monitors such as chlorine or bromine.
Ozone has been scientifically proven to be most effective under almost all conditions at controlling bacterial, biofilms and other amoebae in cooling systems without the need for secondary biocide or biodispersant, as proven by the Department of the Environment and others. Documented test data is available.
No. Ozone, when correctly applied, has been proven to maintain uniformly low corrosion rates, similar to and frequently better than systems treated with traditional chemicals. Documented test data available.
Typically mild steel corrosion rates will be less than 3 mpy and yellow metal corrosion rates from 0.01 to 0.5 mpy. These figures have bee confirmed by independent testing in the UK and the USA.
Ozone is listed as an oxidising biocide in L8 and has been formally tested by the DoE who confirmed the effectiveness as a biocide without the need for secondary biocide or dispersant.
It is possible for ozone to replace all chemical biocide treatment in the vast majority of cooling water systems. In some cases it will also replace corrosion and scale inhibitors. Restrictions can apply where water is stored in large open tanks and open water collection troughs in an enclosed factory area as this could lead to an accumulation of ozone near close contact with factory personnel.
Ozone has been used directly for controlling bacteria levels in cooling towers for around 14 years in the UK and by Waterwise Technology for 10 years. The technology originated in the USA and Germany and has been applied successfully for over20 years.
It has been successfully proven that ozone forces the separation of suspended matter and removes biofilm and surface deposits. This has been shown to give rise to an excess of sludge or sediment build up which, if not removed, can lead to a rise in annual corrosion rates. It is important that this excess is removed. Waterwise Ozone Systems incorporate effective solids removal separators down to 40 microns.
Whilst ozone, at high concentrations in air, will break down certain materials which contain carbon-carbon double bonds, such as nylon acetyl resins etc. (PVC, ABS plastic, viton rubber, PTFE and most engineering plastics are unaffected). When dissolved in water at the levels of ozone employed by Waterwise in cooling water treatment, it will have no adverse affect on the materials used in cooling towers, as confirmed by cooling tower manufacturers.
The Health & Safety Executive provide a Guidance Note EH38 that details applications, exposure limits and effects of ozone. Ozone is listed as an oxidising biocide in Health & Safety Approved Code of Practice L8.
With ozone introduced to a cooling system significantly reduced blowdown requirement will be very evident. In some instances blowdown has been eliminated altogether However, this extreme course of action is fraught with many problems and needs very careful consideration. It is not a practical approach.
There is no automatic "across the board" figure for ozone dosage. The dosage requirement for a cooling system depends on a number of factors, predominantly:
Applications may look similar, however each will have its own solution and dosage rates.
In many cases ozone can provide a complete replacement to chemical dosing of cooling systems. However, should a cooling system require additional chemicals in the form of scale or corrosion inhibitors, then they must be compatible with ozone.
Phosphonates, phosphates and other organic chemicals traditionally used are readily broken down by ozone. Their use can therefore give rise to problems such as using up available dissolved ozone and producing bi-products, which affect the water quality. Waterwise can provide a full range of compatible inhibitors and scale prevention system where necessary.