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Email: info@secondarydisinfectionsystems.com

Ultraviolet (UV) water systems utilize germicidal UV wavelengths to neutralize waterborne pathogens, harmful bacteria, viruses, and cysts, such as Cryptosporidium and Giardia. By delivering sufficient energy at the 254-nm wavelength, UV radiation disrupts the DNA of pathogenic microorganisms, preventing reproduction and stopping the spread of diseases through drinking water.

How UV Systems Disinfect Waterborne Pathogens

UV dosage, measured in mJ/cm², represents the energy delivered by a UV water purifier. Higher dosages provide more energy to treat contaminated water, and at a specific threshold, this energy effectively inactivates most microorganisms. UV systems primarily operate at two wavelengths: 185nm and 254nm. The 185nm wavelength generates ozone, which is an effective disinfectant but may pose challenges in certain systems.

  • Legionella Control at 254nm: A sufficient UV dose at 254nm inactivates Legionella, rendering it unable to reproduce. While not killed, this containment is adequate to prevent outbreaks, as non-reproducing bacteria typically cannot cause harm.
  • TOC Reduction at 185nm: Total Organic Carbon (TOC), resulting from decaying vegetation and bacterial growth, is critical in industries requiring ultrapure water, such as microelectronics and pharmaceuticals. The 185nm UV wavelength reduces TOC through:
    • Hydroxyl Creation: Highly reactive OH radicals combine with hydrocarbon molecules, producing water and carbon dioxide from TOC.
    • Molecular Destruction: UV photons directly break down the molecular structure of TOC.
    • Molecular Ionization: UV-charged molecules can be easily removed via downstream deionizing systems.
  • Chlorine Removal at 185nm: While chlorine is a valuable disinfectant, it can damage systems like reverse osmosis (RO) and nanofiltration (NF). UV light at 185nm effectively oxidizes and removes chlorine.
  • Ozone Destruction at 254nm: Ozone can be beneficial in some systems but harmful in others, affecting health, equipment, or final products. UV at 254nm rapidly eliminates ozone by splitting O3 into an oxygen molecule and an oxygen atom, which then forms additional oxygen molecules.

Benefits of UV Secondary Disinfection Systems

  • Efficiency: UV disinfection is a rapid process that does not require additional storage tanks.
  • Compatibility: UV systems can be seamlessly integrated into existing treatment setups without major construction or extra tanks.
  • Safety: Unlike chemical treatments like chlorine, UV avoids the use of hazardous substances.
  • Taste Preservation: UV does not alter water taste, unlike some chemical treatments.
  • Low Maintenance: UV systems require minimal upkeep, typically involving annual bulb replacement and quartz sleeve inspection, with no need for constant chemical additions.

Sizing a UV Secondary Disinfection System

Sizing a UV system depends on three key factors: maximum flow rate, disinfection level, and water transmittance.

  • Flow Rate: Determined by the gallons per minute (GPM) in the system, flow rates vary significantly between applications, such as a large industrial plant with 3” piping versus a residential system supplying a bathroom and kitchen.
  • Disinfection Level: Common levels include 16mJ/cm², 30mJ/cm², and 40mJ/cm², each providing increasing protection. The required level depends on the water source (e.g., pretreated municipal water versus lake or well water) and the presence of resilient viruses that demand higher energy.
  • Water Transmittance: This measures the water’s ability to transmit UV light. High turbidity or suspended solids (TSS) reduce transmittance, requiring pretreatment to ensure effectiveness.

UV units have defined maximum and sometimes minimum flow rate capacities. Excessive flow reduces UV exposure, while insufficient flow can cause overheating and damage the UV lamp. UV systems are typically used in constant-flow recirculating setups.

Pretreatment for UV Systems

The goal of a UV system is to maximize water exposure within the UV cylinder, which contains a transparent quartz sleeve. Quartz is used instead of glass because it allows ultraviolet wavelengths to pass through, unlike ordinary glass. For Class A point-of-use and point-of-entry disinfection, ANSI and NSF standards mandate a minimum UV dose of 38 mWs/cm² for clear water. Over time, untreated water can degrade the quartz sleeve’s performance, so a 5-micron pre-filter is recommended. Common issues include:

  • Calcium/Magnesium: These minerals cause scaling, similar to buildup on showerheads, which can coat the quartz sleeve and reduce UV exposure. Water softeners can mitigate scaling, extending sleeve life and improving overall system performance.
  • Iron: Iron causes dark orange staining that diminishes UV exposure. High iron levels can also affect the broader water system, making additional treatment advisable.
  • Turbidity: Particulates causing cloudiness reduce UV effectiveness. Pretreatment options, ranging from low-micron filters to reverse osmosis, can address turbidity based on its severity.

We can help you with all of your water treatment needs. Contact a Secondary Disinfection Systems expert today.

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