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Ozone is a powerful and fast-acting disinfectant and can purify water 3000 times faster than chlorine. Ozone disinfection works by breaking through the cell membrane of the microorganisms and destroying the DNA, enzymes and proteins inside the bacterial cell. This kills the cell by a process known as lysis.
Unlike chlorine, there are no disinfection by-products (DBPs) associated with ozone disinfection as ozone breaks down into oxygen.
Ozone is unstable, and although it is produced naturally in the environment by reactions with UV light, industrially it must be made using an in-situ generator. If ozone is used as a disinfectant, it must be monitored regularly to ensure adequate disinfection and effective removal of harmful pathogens from the water.
Ozone is used as a disinfectant in a variety off applications. Read below to find out why it needs to be monitored and to find out some of the latest guidelines and regulations surrounding ozone in water.
Ozone is widely used in drinking water processing plants; it is an extremely effective disinfectant against bacteria and viruses. It requires little contact time, reducing treatment time, whilst leaving behind no chemical residues. Ozone must be monitored to ensure adequate disinfection of the water; if ozone levels are too low harmful pathogens may not be killed.
Ozone can be used alone, or with other disinfectants. It is often used as a pre-treatment prior to sand or active carbon filtration. Ozone disinfection remains in the distribution system for a shorter time and is therefore less able to suppress regrowth of harmful microorganisms. Therefore, ozone is sometimes used in combination with other disinfectants such as chloramines.
When ozone is used in the treatment of drinking water, a desired concentration of ozone is chosen. Then a dose is given for a set amount of time to leave the desired residual. The WHO state that a residual value of around 0.5 mg/L after a contact time of up to 20 minutes is typically used. The doses required for this are usually in the range 2–5 mg/L but will vary depending on the type of water.
In pools and spas ozone can be used as a primary disinfectant; it is used as an alternative to chlorine-based disinfectants. It is particularly effective at killing Cryptosporidium and Giardia, both of which are unaffected by chlorine disinfection. Ozone is often used with chlorine or bromine as a secondary disinfectant due to the difficulty in maintaining constant residual.
A benefit of using ozone as a pool or spa disinfectant is that it does not affect the pH of the water. However, it does have a large initial cost, but when using ozone, the free chlorine levels can be much lower (0.5 mg/L for a pool, and 2–3 mg/L in spas and hydrotherapy pools).
Ozone needs to be monitored in pools and spas because if levels are too low it could mean there is inadequate disinfection in the water. Ozone should be tested daily in pools and spas. For spas and hot tubs, industry guidelines recommend ozone levels should be in the range 1.2 – 1.5 mg/L O3. For more information on spa and hot tub testing take a look at our testing your hot tub and spa guide.
Ozone can be used in the wastewater industry for odour abatement (reduction of smell). It can also be used to remove heavy metals from water bodies. Ozone is often applied with UV light or ultrasound technology to increase the rate of reaction and decrease the required contact time. Ozone needs to be monitored in wastewater because if levels are too low it could mean there is inadequate disinfection in the water, and harmful pathogens may not be killed. Regulations for ozone levels in wastewater will be specific to local areas.
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