Ultraviolet (UV) System for Legionella and Waterborne Pathogen Control

uv chemical-disinfection for legionella controlAn Ultraviolet (UV) water system exposes living organisms, such as Legionella, other harmful bacteria, viruses and cysts (like Cryptosporidium and Giardia) to a germicidal ultraviolet wavelength. With enough energy, UV radiation at the 254-nm wavelength disrupts the DNA in pathogenic microorganisms so they cannot reproduce. The ultraviolet light prevents Legionella from spreading disease through drinking water and is effective for UV Legionella pathogen control.

How Do Ultraviolet (UV) Systems Work to Disinfect Legionella and Other Pathogens?

UV dosage is the measurement of energy in (mJ/cm²) delivered by a UV water purifier. The higher the dosage, the more energy delivered to treat contaminated water. At a certain threshold, this energy becomes sufficient enough to inactivate most of the microorganisms like Legionella present in water. There are two main UV wavelengths,185nm and 254nm. A 185nm light creates ozone, which is a good disinfectant but creates its own issues in some systems.

  • Legionella Control at 254nm: Legionella is inactivated with a high enough dose of UV light. It is not killed but contained, which is all that is necessary to prevent an outbreak. If the bacteria cannot reproduce, it cannot usually cause harm.
  • TOC reduction at 185nm: TOC is the total organic carbon in your water system. This is produced by decaying vegetation and bacterial growth. TOC reduction is important in industries that need ultrapure water such as the microelectronics and pharmaceutical industries. 185nm UV Has three ways to remove TOC from water:
    1. Creation of hydroxyls: These are free OH radicals that are highly reactive. These hydroxyls can combine with hydrocarbon molecules creating both water and carbon dioxide molecules from the TOC.
    2. The destruction of the molecules. Ultraviolet photons work directly on the make-up of the molecule and destroy it.
    3. Ionization of the molecule. If the molecule is charged by the UV energy it can easily be removed down the line through a deionizing system.
  • Chlorine removal (185nm)- Chlorine though good for disinfecting water can also cause some major issues in systems. Chlorine for instance can do real damage to RO (reverse osmosis) and NF (nanofiltration) systems. UV light has always been a good oxidizer of chlorine.
  • Ozone Destruction (254nm)- In some water systems ozone is a positive while in other processes it can be harmful both to an individual’s health as well as equipment and final products. UV is a very quick and effective way to remove ozone. In this process the 03 molecule is split into an oxygen molecule and an oxygen atom. The atom will then combine with other atoms to create more Oxygen molecules.

Pros of a UV Legionella Control System:

  1. UV is efficient- UV is a quick reaction process and there is no need for extra storage tanks.
  2. Easy addition to other systems- With UV it can usually be installed in line after other treatments. No large-scale construction or additional tanks are needed.
  3. UV is safe- Using chemicals like chlorine is not as effective of a treatment method but it does use hazardous chemicals.
  4. No changes in taste- Chemicals at times can cause changes in the taste of the water. There is no change with UV systems.
  5. Easy maintenance- Once a UV system is installed there is very limited maintenance. Maintenance includes annually changing the bulb and inspection of the quartz sleeve. However there is no need for constant maintenance or addition of chemicals.

How Do You Size an Ultraviolet (UV) Legionella Control System?

There are three variables that go into sizing a UV Legionella pathogen control system: maximum flow rate, disinfection level, and the transmittance of the water.

  • Flowrate – Flowrate is determined by many variables. The primary question is what is the GPM in the line when pushing water throughout the system. The flow rate in a plant with 3” piping through a plant will be much different than that of a home feeding a bathroom and kitchen.
  • Disinfection level – There are three basic levels of disinfection 16mJ/cm2, 30mJ/cm2, and 40mj/cm2. Each offers an extended amount of protection. It is also good to take into consideration your water source. If you water is already treated by the city you may need a lower level than if your water is coming from a lake or well. There are also some viruses that are harder to kill than most bacteria and need a higher energy point.
  • Transmittance of the water – Transmittance is the waters ability to transmit the UV light. If the water has high turbidity (cloudiness) or suspended solids (TSS), the UV will not transmit as well as it would through crystal clear water. Pretreatment it discussed later which can go a long way to improving this.

All UV units have a maximum flowrate capacity, and some have a minimum flowrate as well. If the flow is too high, water will pass through without enough UV exposure. If the flow is too low, heat may build up which can damage the UV lamp. UV units are most often used in constant flow recirculating systems.

Pretreatment for UV Systems

When using a UV system the main goal is maximum exposure of the water through the UV cylinder. This cylinder will have a clear quartz sleeve for the water to pass through. A common question is why use quartz and not just glass. Ordinary glass is not transparent to the ultraviolet wave lengths. Quartz on the other hand is. For class A point of use and point of entry disinfection, the ANSI and NSF require that clear water receive a dose of 38 mWs/cm2 (38 milliwatt seconds per square centimeter) of UV light. Over time untreated water can cause issues with the quartz sleeve. At least a 5 micron pre-filter should be used prior to the UV Legionella pathogen control system. Here are some of the things that can cause issues over time.

  • Calcium/magnesium – Calcium and Magnesium can cause scaling. Similar to the scaling that you see in your shower heads. This scaling can appear on the quartz sleeve which over time will effect the UV exposure rates. If you have a scaling problem this has or will cause more issues throughout your entire water system and using a softener of appropriate size will help reduce the chance of major issues in your water system over time as well as extending the life of the Quartz sleeve.
  • Iron – Iron staining is dark orange of color and can also affect exposure on the quartz sleeve. Iron can also cause major issues with your water systems on a whole. Additional water treatment would be a good idea if you have high levels of iron in your system.
  • Turbidity – turbidity is the measure of particulates that cause cloudiness in water. This cloudiness can also affect the UV exposure. Pending on how high your turbidity is there are many ways to get it out of your water. These processes include low micron filters all the way up to reverse-osmosis.

Industrial Ultraviolet (UV) Legionella Control System Water System Service, Design & Sales

Contact us right now at info@legionellacontrolsystems.com or 888-416-8626 for sizing, sales, leasing and service of UV systems in Indiana, the Midwest and throughout the U.S. for your industrial water systems. Our experienced engineers are ready to help.

Contact Legionella Control Systems for CDC Legionella risk assessment and Legionella testing.