Ozone and UV Light Disinfection Guidelines

Ozone and UV Light Disinfection

Ozone and UV Light Disinfection Guidelines

About Ozone and UV Light Disinfection

Ozone and UV light disinfection is a method of removing bacteria and other harmful materials from the air using ultraviolet (UV) light. More commonly known as germicidal irradiation, it is often used to remove pathogens from wastewater and other liquid or gas streams after treatment. The system uses UV “light tubes” attached to the surface of a water or gas stream that pass through an ozone-generating chamber, releasing ozone into the water stream. The ozone dissolves and kills most bacteria and viruses (including HIV), thereby reducing the amount of disinfectants (and their associated toxic byproducts) required, as well as removing odors.

Today’s systems use a single ultraviolet light tube to provide continuous UV irradiation for several weeks or months at a time. In other designs, multiple ultraviolet tubes are arranged in series or parallel to allow for UV wavelengths to be balanced and used more effectively. The ultraviolet light tubes are protected by a durable hard plastic or glass enclosure, while ozone gas is introduced into the water or gas stream through a venturi orifice, thus exposing the product to ozone for a sufficiently long time to allow for disinfection and oxidation reactions.

Modern disinfection systems have been shown to reduce harmful bacteria by 99.9999+% which is over 10 “reductions” of 10,000 (or over 10 log reductions). In addition, ozone is among the safest disinfectants. Ozone has a similar toxicity, if not lower than chlorinated disinfectants. This is because the industrial-strength ozone used in most systems is a mixture of ozone and oxygen; this mixture has a much higher efficacy than free elemental oxygen. The concentrations of free oxygen in the air are well below those levels found in modern ozonized water systems.

A major use of ozonated water is for drinking water purification. Ozone as a disinfectant has been studied as a possible replacement for chlorine in the creation and purification of drinking water. Water ozonation has the advantages of using less reagent, operating faster than alternative disinfection methods, and being able to kill most bacteria, viruses, and parasites by reacting with essential nutrients such as proteins, fats, carbohydrates and nucleic acids.

Ozone gas is produced from oxygen gas by ultraviolet light in an ozone generating machine. Ozone is an unstable gas that cannot be stored for long periods of time. This requires on-site ozone generators for food and drink service. UV tubes are used with the ozone gas to disinfect the water stream which passes through the UV tubes.

Ozone is a form of oxygen in which three of its valence electrons have been removed, giving it a partial negative charge. This increases its electronegativity compared to normal oxygen. In water, which has a high affinity for charges, this means that ozone binds strongly to positively charged minerals and weakly to other charged particles such as hydrogen ions. This then allows the ozone to oxidize organic materials including bacteria, viruses and cysts by a process called oxidation.

The UV lamps used in ozonation systems provide sufficient energy to break the O–O bond and create monatomic oxygen (O) which can further react with organic compounds. However, due to the short half-life of ozone (the molecule is stable for only about 3 minutes), ozonation as a disinfection technique is much more effective when combined with UV light.
Ozonation was first investigated as a disinfection method when used with ultraviolet light under the name ozone-light sterilization. Ozone-light sterilizers were widely used in the 1930s and 1940s but were abandoned after the 1950s due to higher reliability and lower cost of UV light sterilizers that were developed at that time.

Ozonating water treatment creates high concentrations of ozone gas which, after reacting with organic contaminants, breaks down into oxygen gas and monatomic oxygen atoms (ions). The process of breaking down organic pollutants releases free radicals such as hydroxyl (OH) and superoxide (O). It has been hypothesized that it is the breakdown of these free radicals, not the monatomic oxygen ions, which is responsible for eliminating contaminants. Dead parasite removal by ozonation in experimental fish ponds has been shown to be mediated by reactive nitrogen species such as peroxynitrite, rather than reactive oxygen species.

The ozone-light sterilizer used in the 1930s and 1940s was nearly identical to the modern UV-C light sterilizer. Ozone gas is generated from an ozone generator which consists of three ultraviolet lamps and a trivalent manganese dioxide catalyst. The most widely used ozone generators were based upon the high-voltage mercury arc lamps. The ozone is generated by photons bouncing off the surface of the manganese dioxide and is released into the atmosphere where it reacts with oxygen. The reaction occurs at room temperature and atmospheric pressure, which reduces its cost compared to alternatives such as chemical oxidation or high-pressure plasma treatment.

Ozonation is an effective method for inactivation of viruses and bacteria, but it is still heavily debated over whether ozonation can be considered a “proper” disinfection method. While there have been a few studies that show the efficiency of ozone inactivating bacteria and viruses, these have often been performed in ways that allow the pathogens to persist within the experiment.

Another concern is that ozone may damage or alter the metabolism of microorganisms. For example, some bacteria can be killed by ozone because of its ability to cause lipid peroxidation. So while ozonation may be able to kill fungi and viruses, it could also disrupt their vital metabolic functions.

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