Water treatment operations, both large and small, are turning to ultraviolet radiation (UV) as an alternative to reduce or eliminate the use of chlorine for disinfection. Chlorine is a commonly used and effective disinfectant. Operators at waste water, drinking water, environmental remediation facilities, and even homeowners with backyard swimming pools use chlorine to protect against disease-causing organisms.
However, there are some microbial pathogens, such as Cryptosporidium and Giardia, that are resistant to chlorine disinfectant. Plus, adding chlorine and other chemicals to treat water is an expensive endeavor, and the process adds safety concerns. The EPA has also set limitations on the amount of residual chlorine and disinfection byproducts created by chlorine treatment in drinking water and wastewater effluent. All of these factors are leading system operators to consider UV treatment.
How UV disinfection works
We receive UV radiation from the sun, but the wavelength of UV light that destroys organisms is largely blocked by the Earth’s atmosphere. In a water treatment application, UV disinfection is applied in a pressurized closed vessel (usually a stainless-steel tube) by amalgam lamps. UV light doesn’t kill pathogens. It penetrates an organism’s cell wall, disrupts the cell’s DNA, and destroys its ability to reproduce. If the cell can’t reproduce, it’s no longer harmful to the human body.
Compliance with EPA’s LT2 Rule
Adding a UV disinfection system will enable water treatment facilities to comply with the EPA’s Long Term 2 Enhanced Surface Water Treatment Rule (LT2 rule), which requires additional inactivation of Cryptosporidium and takes effect in 2014.
Unfiltered water systems, did not have Cryptosporidium removal requirements prior to the LT2 rule. A UV disinfection system was implemented by the State of Texas to provide 3-log inactivation of Cryptosporidum along with ozone to provide primary Giardia and virus disinfection and chloramines to provide system residual treatment.
A versatile technology
UV treatment systems are a very effective and versatile system. The University of Connecticut’s Storrs Campus is leading the country in its research, operating a new water reclamation facility that receives treated waste water from the university’s water pollution control facility. The waste water is screened, then filtered by one of three micro-filtration trains, and finally disinfected by UV light. This reclaimed water is then available for non-potable use. The University then plans to use the reclaimed water primarily at their Central Utilities Plant in its cooling tower, chilled water system, and boilers.
The benefits are clear
The use of UV systems for disinfection is becoming much more common. UV provides chemical-free disinfection, and it is considerably more efficient at the inactivation of Cryptosporidium than ozone or chlorine.
Retrofitting an existing system depends on a number of factors—in particular, the available space for installation and future maintenance. UV systems may not be right for every operation, but it’s clear that UV treatment works.