What is ozone?
An inorganic molecule, Ozone (O3) is an allotropic form of oxygen; each molecule contains three atoms of oxygen instead of the standard two. It is a pale blue gas, formed naturally in the atmosphere and has a pungent odour. It is the ozone formed by lightning discharges during a thunderstorm which gives the air its characteristic fresh and clean smell afterwards.
How is ozone made?
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 formed by 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.
Why is ozone used for water treatment?
Ozone is a powerful oxidising agent which, when dissolved in water, produces a broad spectrum biocide that destroys all bacteria, viruses and cysts. Ozone water treatment has been used commercially for the treatment of potable water since 1904.
How does ozone work?
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 owes its biocidal effectiveness to its ability to oxidise organic material in bacterial membranes, which weakens the cell wall and leads to cell rupture causing immediate death of the cell.
In contrast, chlorine, and all other oxidising and non-oxidising biocides, must be transported across the cell membrane in order to interfere with either the nuclear reproductive mechanism or various enzymatic life giving reactions in the cell, in either event resulting in substantially less biocidal efficiency.
For this reason, ozone is capable of destroying all bacteria, algae and biofilms with no risk of resistance build up or immunity. Even resistant and problematic aqueous micro-organisms, such as Giardia, Cryptosporidium, streptococcus fecalis and E.coli causing grave human health concerns in potable water, are readily and rapidly inactivated by ozone. Ozone remains effective over a wide pH range.
Although viruses are more resistant to ozone destruction than bacteria, viral inactivation occurs more readily with ozonation than with halogenation.
Is the use of ozone technology safe?
Yes, oxidation is a natural process and eliminates the need for chemicals. Ozone water treatment has been used around the world for many years, with major beverage companies relying heavily on the technology.
Does ozone comply with ACoP L8?
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.
Is ozone treated cooling water classed as effluent by local water authorities?
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 bleed from an ozone treated non-ferrous 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.
Does ozone affect water balance?
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 no dissolved solids; therefore it will not affect water 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.
Is ozone corrosive?
Ozone, when correctly applied, has been proven to maintain minimal corrosion rates, similar to, and frequently better than, systems treated with traditional chemicals.
What are the environmental benefits of using Ozone as a disinfectant?
As the ozone gas is produced in situ and without the use of chemicals, there are immediate environmental benefits including:
- No pollutants are created
- Any waste water produced is safe to enter waterways and surface drains – there is no need for a foul sewer
- Waste water can be used in other grey water applications – saving water top up from other sources
- No chemical manufacture is required therefore reducing transport and eliminating the need for chemical drums
- Immediate elimination of risk of running out of chemical stock and delivery complications etc
How can Ozone be used in the food and drink industries?
Ozone has been used for over 100 years as a preservative for foods and food ingredients, as well as purification in the brewing industry, odour control and medical therapy.
Ozone is capable of destroying all bacteria algae and biofilms with no risk of resistance, build up, immunity or toxic residues, making Ozone an ideal choice for direct food and drink applications.
Ozone is a strong sanitisation and fumigation agent, which can be used to sanitise foods in the storage room and during shipping to prevent bacteria, mould and yeast on the food surface and to control insects. It can eliminate undesirable flavour produced by bacteria and chemically remove ethylene gas to slow down the ripening process, allowing extended distribution.
General practice for cleansing fresh fruits and vegetables consists of washing in ozonated water, and the wash water is recaptured and treated by filtration and ozonation. The treated wash water is free of bacteria, colour and suspended solids and can be recycled to reduce water usage. Unlike conventional halogen-based washing systems, wastewater discharged by the ozonation process is free of chemical residuals, a growing concern related to the environment and groundwater pollution.
Ozone is also commonly used in the disinfection of bottled drinking water. Ozone is particularly soluble in water; it is effective in killing microorganisms through oxidisation of their cell membranes. Ozone has a unique property of auto-decomposition and will leave no toxic residues. This feature gives bottling plants the opportunity to disinfect the drinking water and extend shelf life without chemically adding to the process water.
Is Ozone covered under the Biocidal Products Regulations?
Yes - The Biocidal Products Regulations (EU) 528/2012 (BPR) came into force on 1 September 2013 repealing the Biocidal Product Directive (Directive 98/8/EC) from this date. From 1 September 2013, Ozone is regulated as an “active substance” under the BPR.
Under the BPR, anyone who wishes to market an ozone generator for a Biocidal application within the EU must have their product authorised in accordance with the BPR. This process currently first requires an “active substance” dossier in respect of ozone to be submitted by September 2016 and thereafter a specific application for each product to be marketed within the EU to be submitted by September 2017.
SOCOTEC, formerly ESG, is a founding member of the European Ozone Trade Association (EUOTA) which has submitted its dossier to the Biocide Products Regulations body.