Environmentally Friendly & Safe
Comparison of Disinfection using UV vs Ozone
Ultra Violet Radiation (UV)(UV 254 nm) has been used for water purification systems for many years. By the 1960’s UV had become more widely used in commercial applications and was entering into the residential marketplace. Several firms have been in the marketplace building, selling and installing UV systems over the past few decades.
Ozone has been recognized by many experts in water and wastewater as the future of water purification and has recently seen significant use in Sewage Treatment Plants to complete the disinfection and purification of wastewater before releasing back to the environment. In 2015 Montreal, QC in Canada announced the installation of an Ozone plant at its Jean-R. Marcotte wastewater treatment plant in Rivière-des-Prairies. This project will be the world’s largest waste water treatment plant to use ozone to clean water. The city already uses ozone to treat its drinking water.
There have been many developments over the past several years in the advancement of systems that use ozone, based mainly on the extreme advantage that ozone has over virtually any other disinfection or purification approach. As note below, ozone is 45 times more effective than UV at only 99.9% (3-log) disinfection. When treating wastewater for safe use by humans, there is a need for 99.9999% (6-log) disinfection or more.
There are some key and important differences in how each system works and is managed.
Ultra Violet Radiation (UV) for Disinfection of Water :
Water entering into a UV system must be clear with little to no turbidity. The flow of water must be designed to match the UV intensity and the tubes through which the water flows must be maintained and cleaned on a regular basis. Since there is no residual in the water, it is possible for “stunned” bacteria to come back to life and reproduce.
The key focus of a UV system is deactivate the common bacteria that can affect humans. Other water treatment must be used to process the biological and nutrient matter in the water.
According to Viqua, “The ultraviolet (UV) treatment process is an extremely quick physical process. Ultraviolet light mutates and/or degrades DNA. DNA (or deoxyribonucleic acid) is the part of the cell that gives an organism its instructions on how to function and reproduce.
When the DNA is damaged, the organism becomes unable to function because its “instructions” are garbled or missing. An organism that has no instructions cannot function and reproduce, and cannot cause infection. It is rendered harmless and eventually dies.”
Edstrom tells us that, “Although 100% destruction of microorganisms cannot be guaranteed, it is possible to achieve 99.9% reduction in certain applications and with proper maintenance.” “Certain contaminants in water can reduce the transmission of UV light through the water, which reduces the UV dose that reaches the bacteria. These UV absorbing contaminants include turbidity, iron, and humic and fulvic acid, common to surface water supplies. Suspended particles are a problem because microorganisms buried within particles are shielded from the UV light and pass through the unit unaffected. UV disinfection is most effective for treating high-clarity purified reverse osmosis or distilled water.”
“Point” Disinfection UV units only kill bacteria at one point in a watering system and do not provide any residual germicidal effect downstream. If just one bacterium passes through unharmed (100% destruction of bacteria cannot be guaranteed), there is nothing to prevent it from attaching to downstream piping surfaces and proliferating.
Ozone for Disinfection and Purification of Water:
Ozone is a fairly recent strategy for disinfection and purification of water in North America. As reported by the US EPA in 1999, there was little use in the US, but there was widespread use in Europe. The US EPA also reports that ozone has the ability to achieve higher levels of disinfection than either chlorine or UV. For water to be safe for human use or consumption there is usually a need for several logs of disinfection. The US EPA reports that UV is not capable of achieving a 99.99% (4-log) disinfection. For a 99.9% (3-log) disinfection ozone is 45 times more effective that UV.
Primary Advantages for Ozone1
1. Ozone is effective over a wide pH range and reacts with bacteria, viruses, and protozoans and has stronger germicidal properties then chlorination. Has a very strong oxidizing power with a short reaction time.
2. The treatment process does not add chemicals to the water.
3. Ozone can eliminate a wide variety of inorganic, organic and microbiological problems and clarity, taste, and odor problems. The microbiological agents include bacteria, viruses, and protozoans (such as Giardia and Cryptosporidium).
Great Lake Clean Water – Limited Partnership has been designing and refining the WATERCLEANTM system for over 15 years. During this time we have been able to achieve performance results well beyond any other designs that use ozone. The key factors of success with ozone of contact time, time under pressure, and concentration of ozone have been mastered in the WATERCLEANTM design and extensively tested at CAWT2. In addition to being able to achieve up to a 99.999999% (8-log) disinfection of microbial problems, it can eliminate a wide variety of inorganic and organic problems and taste and odor problems. WATERCLEANTM has also proven its ability to mineralize and transform pharmaceuticals and other compounds of emerging concern and to reduce nutrients like nitrogen and phosphorus.
References:
Viqua – a Trojan Technologies Business – published on www.viqua.com
How UV Disinfection Works
The History of UV
CBC News
Montreal Upgrades Wastewater Treatment with Ozone
US EPA
US EPA - Ozone Fact Sheet
US EPA - UV Fact Sheet
Water-Research.net
1. Water-Research Ozone
Edstom Industries – published on www.water-research.net
How does UV Work?
2. Centre for Alternative Wastewater Treatment (CAWT) (Flemming College, Ontario Canada)