Ozone vs. UV

The two key technologies that form the mainstay of the discussion around secondary disinfection are UV and ozone. While UV has been relatively well understood by aquatics designers and operators, ozone, a rapidly-advancing technology, has been given less attention despite the many compelling reasons to choose ozone over UV.


What is Ozone?

Ozone is a gas that is dissolved in water to kill microorganisms, destroy organics, and break down chloramines by oxidation. This occurs immediately at the ozone gas injection point, and continues as the side-stream remixes with the main return. A small residual (~0.1 PPM) of dissolved ozone will enter the pool, providing further oxidation of contaminants.


What is UV?

UV light inactivates microorganisms and breaks down chloramines with light energy. This happens while the water is in the UV chamber only, and as long as the water has no turbidity. No further primary sanitation process occurs once the flow leaves the chamber. UV provides no oxidation except as trace amounts as a result of the formation of a limited number of hydroxyl free radicals in or near the UV chamber.


Comparing Ozone and UV

There is sometimes confusion as to the difference between ozone and UV systems. Actually, they are completely different technologies, however the confusion may stem from UV-generated ozone that was popular in residential pools and spas until the late 1990s when breakthrough compact CD ozone generators took over that market. UV generated ozone is never used on a public pool because the systems cannot make enough ozone to benefit the pool water. CD generated ozone, on the other hand, is extremely safe and effective for pool water sanitation.

Ozone is a gas that is dissolved in water to kill microorganisms, destroy organics, and break down chloramines by oxidation. In comparison, UV light inactivates microorganisms and breaks down chloramines with light energy. With UV, this chloramine breakdown only happens while the water is in the UV chamber, and as long as the water has no turbidity. With Ozone, oxidation occurs immediately at the ozone gas injection point and continues as the side-stream remixes with the main return.

While both Ozone and UV provide very effective Crypto reduction as documented by third-party testing and validation, there are distinct differences between the two technologies when it comes to other areas of concern for commercial aquatics designers and operators, with clear advantages to Ozone over UV.

Ozone is a Powerful Oxidizer
Ozone gas dissolves in water to kill microorganisms, destroy organics that create chloramines, and breaks down existing chloramines by oxidation. This oxidation happens immediately at the ozone gas injection point and continues as the side-stream remixes with the main return. A small residual (~0.1 PPM) of dissolved ozone then enters the pool, providing further oxidation of contaminants. There are no consumables in an ozone system.

Ozone and UV are Comparable in Cost
Ozone and UV technologies are comparably priced. Operational costs of each system vary with the local price of electricity. However, the minimal maintenance and reduced chemical requirements of an ozone system create significant benefits. Meanwhile, UV lamps must be replaced every 3 to 12 months and must be figured into the maintenance costs for these systems.
 
Combined CD Ozone + Germicidal UV is Better Yet
When ozone is combined with germicidal UV light to create an Advanced Oxidation Process (AOP), you have the best of both worlds. The AOP system produces even stronger oxidation than CD ozone alone. It is important to note that the germicidal UV light used in the DEL Ozone Solar Eclipse AOP is NOT the same wavelength as light used for generating ozone, and it makes all the difference. In the Solar Eclipse, the UV light at 254 nanometers wavelength is absorbed by ozone, starting the chemical reaction that characterizes Advanced Oxidation Processes. Read more about AOP on our Advanced Oxidation Process page.
 
UV (ultraviolet) Ozone Has Some Shortcomings
UV ozone bulbs wear out relatively quickly (they are less durable than the CD electrode technology used in DEL ozonators) and need to be replaced for continued sanitation. Please note that the bulbs may continue to generate illumination even after they stop producing the wavelengths that generate ozone.  Adhering to manufacturer bulb replacement guidelines will help to solve this issue. Also, UV systems may consume up to 80% more electricity than comparably sized CD ozone generators, and they create much more heat.
 
Other Options
Ozone vs. Salt
Ozone vs. Chlorine
Ozone vs. Biguanides
Ozone vs. Ionizers