Recent research has shown that medium-pressure
ultraviolet lights may be superior at eradicating
recreational water illnesses.
The studies two published in Applied
& Environmental Microbiology and one in
Water Science and Technology: Water Supply
showed that E. coli damaged by
low-pressure UV can repair itself when exposed to light, a
process known as photoreactivation. E. coli DNA
exposed to medium-pressure UV under laboratory conditions
showed little to no repair.
In addition, the deactivated bacteria may cause growth
of new bacteria. According to a study by the Civil
Engineering Department of the National University of
Singapore, ?disinfection byproducts produced by UV
disinfection ? may serve as a carbon source in
finished water, resulting in regrowth of the
UV disinfection has become popular in indoor facilities
to reduce chloramines and kill viruses and bacteria such as
cryptosporidium, which takes nearly a week to kill
with chlorine. However, the debate between low vs.
medium-pressure UV has become heated as the issue of
recreational water illnesses moves to the forefront of
aquatic health. Many experts believe medium pressure, a
more costly option, is better because of the possibility of
photoreactivation. Others say that in aquatic environments,
there?s no real difference between the two.
?Medium is better due to the possibility of
photoreactivation,? said Tom Schaefer, national
sales manager at Engineered Treatment Systems in Beaver
Dam, Wis. ?But the reality is that for the pool,
it?s a ridiculous argument to make. If you have
bacteria and viruses in your water, and any residual
chlorine, it?s going to disinfect that within
Schaefer also argued that because photoreactivation
requires light and UV systems are more prevalent in indoor
pools where sunlight isn?t an issue, using low or
medium pressure does not make a difference.