Shedding Some Light on UV

Editor's Note: We didn't have enough space to print Mr. George's entire letter in the print edition of Recreation Management. Here, we offer up his breakdown of some of the science around UV technology, and how different types of systems have their place, depending on the context of each individual swimming pool.

I read Rich Young's article, "The Latest (Surprising) News on UV Technology" in the September 2016 issue of Recreation Management and was quite intrigued with his analysis of several scientifically proven facts that he seems to disagree with.

Some of the facts in the article are wrong and can be substantiated by work done by Dr. Chip Blatchley at Purdue University.

1. UV, especially MP (medium pressure) validated systems that are properly sized for the pool they are installed on, can reduce the consumption of chlorine if the operator reduces the level of chlorine he is injecting into the pool. A well-balanced pool with a MP UV system does not require operators to operate close to breakpoint chlorination to maintain a residual in the water. It is correct that UV looks at chloramines and chlorine as it passes through the UV chamber and breaks them down. Therefore the lower the level of chlorine used, the lower the level of chloramines produced … and the lower the consumption.
    
2. The comment on LP system Amalgam high-intensity lamps putting out all the UV spectrums and intensity to destroy pathogens is totally false. LP lamps, all types, are monochromatic. All manufacturers of them and scientists will confirm this. What that means is LP lamps only provide one spectral output, 254 nanometers (nm). MP lamps are polychromatic, they provide intensity at a range of spectral outputs from 200 to 300 nanometers. The disinfection process uses wave lengths from 240 to 280 nanometers. Thus, beyond the wavelength produced by low pressure amalgam lamps.
    
3. Scientific studies, most recently one published by Dr. Ernest Blatchley of Purdue University, have proven that the myth that mono-chloramines produce di-chloramines and tri-chloramines is just that: a myth. There is no chain of one makes two and one plus two make three. In fact, a three-year study proved that LP lamps do not effectively destroy di-chloramines or tri-chloramines in a pool environment while MP lamps do. The spectral output required is above 254 nanometers (nm).
   
   Our industry in fact is at a crossroads, in a sense. The MAHC did not recommend guidelines for chloramines because we do not have an effective means at poolside to measure all three types. What we are presently measuring is the difference between total and free chlorine, and therefore we are in compliance with code. What a three-year study helped to prove was that we may be measuring the combined total of mono-chloramines, di-chloramines and tri-chloramines and thus we get a reading of "X" amount that puts us under the threshold of that particular state code. However, the study showed that the concentrations of di-chloramines and tri-chloramines in the water were not significantly destroyed by LP systems as they were by MP systems. They are the chloramines we worry about for health and safety reasons. As a result the U.S. EPA has presently reached out to the industry, providing a grant for someone to study how to make a poolside device that can individually measure all three to really tell us if our patrons are safe.
    
4. The myth that LP lamps last twice as long as MP lamps is just that. LP Amalgam lamps, not knockoffs, typically last between 14,000 and 16,000 hours. MP lamps, not knockoffs, last between 10,000 and 12,000 hours. I have actually many cases of them lasting more than 16,000 hours. Replacement by the operator is based on the actual effective dose that the MP lamp is providing to still disinfect and destroy chloramines. LP lamps simply measure so many hours of output, 70 percent, and recommend that the lamps be replaced. There is normally no effective measurement during their supposed life that they are effectively disinfecting.

Both types of systems have a place in recreational water, LP systems are effective in residential environments or low-flow venues with low bather loads. MP systems, because of their significant amount of power, are effective in the commercial environment, especially were high bather loads are common.