Five to 10 years ago, our industry knew very little about ultraviolet treatment systems for recreational swimming environments. Today UV is one of the top industry buzzwords. As a result, many new suppliers are attempting to enter what they consider a lucrative market, often promising fantastic
results at unbelievable savings. They quote studies or parts of
studies that benefit their sales pitches to the facility owners or
designers. Adding to the problem, virtually every study cited is
related to drinking water or waste-water treatment, not
I have heard so many presentations that tout “studies,”
and they all assume disinfection and the destruction of chloramines
in recreational water require the same equipment and the same
processes as those used in drinking water.
Nothing can be further from the truth.
Drinking water is treated 100 percent before use. At no time is it
mixed with the source water that is being treated. And the
temperature of the water is 55 to 65 degrees Fahrenheit (ground
temperature) the vast majority of the time.
What is the facility operator to do? Get educated. Do your
research. Trust a reputable supplier who is not only going to sell
you a system, but service it as well. Ask questions. Get
If ultraviolet disinfection systems had been in use for drinking
water in the United States for more than 20 years, why were they
not introduced into the recreational swimming pools market at that
time? Low-pressure (LP) UV manufacturers learned it was a different
application with different conditions. If it was used in
recreational swimming pools in Europe for 20 years, what did they
use? What did they discover?
They discovered low-pressure technology that was successful for
drinking water did not work as effectively in pools. That led
UV-lamp manufacturers to develop medium-pressure lamp (MP)
technology. The recreational pool market for UV systems then
Several significant factors in pool applications make LP lamp
technology unsuitable for disinfection and the destruction of
chloramines. They are as follows:
- The wavelength emitted by LP lamps is narrow — 254
nm. This radiation is capable of destroying monochloramine, which
would be effective if the water were being treated in its entirety
in one single pass.
That is not the case. Therefore, trichloramine and dichloramine,
which are far less healthy, are produced from the monochloramine
still in the untreated water. Once the tri and di appear, LP cannot
effectively destroy them because di and tri compounds absorb UV
light at 297nm and 345nm, according to research from Purdue
- The temperature of pool water is normally around 80 to
85 degrees; spas are in the 95 to 104 degree range. Low-pressure
lamps have a relatively low surface temperature; therefore, the
influence of water temperature is significant. The optimal water
temperature for LP lamps is 68 degrees Fahrenheit (20 degrees
Celsius). At temperatures above that, the UV output drops off
Medium-pressure lamps operate at a much higher temperature and can
operate effectively in a much greater temperature range with no
effect on the UV output,
according to Dr. James Bolton of Bolton Photosciences Inc. in Edmonton Canada
- Low-pressure lamps are vulnerable to photorepair when an
organism is exposed to sunlight for a short period of time,
approximately 30 to 180 minutes.
What does this mean? In swimming pools, the water passes through
the UV chamber after filtration and returns to the pool during the
turnover cycle. At this time, the DNA that was broken down by LP
lamps can repair itself. We are, in effect, showing that we are
“destroying” the parasite when it passes through the UV
chamber; it is, however, reappearing in the pool water only to be
reactivated again. This is a cycle that repeats itself.
However, studies have shown medium-pressure lamps break down the
DNA and do not allow photorepair, according to a study published in
the journal Applied and Environmental Microbiology by researchers
J.L. Zimmer and R.M. Slawson.
- Medium-pressure lamps break down organics, assisting in
water clarity. Low-pressure lamps will not, according the U.S.
Environmental Protection Agency.
- Low-pressure systems use multiple lamps to achieve enough
intensity to treat the water. This creates several issues.
Typically, several lamps are monitored by a single sensor to be
able to verify the proper dose and intensity is being applied. One
can only be sure that the flow nearest the closest lamp is
effectively being disinfected. Second, if one of several lamps has
failed, do you replace them all? How do you monitor the lamp hours?
Do you number each one and keep a record of each?
With medium-pressure systems, you have a specific monitor for a
single lamp, or a properly positioned monitor to accurately check
two lamps, to be able to verify the calibrated intensity is being
- Multiple lamps with LP technology mean more maintenance
issues. Most LP manufacturers do not provide automatic wiper
systems to keep the quartz clean; they are simply not practical
with multi-lamp LP systems. This then requires manual cleaning,
which is very time-consuming. Again, when one or more lamps fail,
do you replace them all?
Research is an important tool in developing new products and
testing existing products to meet the requirements of our industry.
But it is important to review the results objectively rather than
use those parts of the study to advance one’s
For example, several manufacturers have cited a recent study on the
“Impact of Chlorine and Monochloramine on Ultraviolet Light
Disinfection,” from Duke University/University of North
Carolina. They extract data from this study, trying to claim that
LP technology is more effective than MP technology.
The problem with the extrapolation is that they fail to cite the
conclusion arrived at or the conditions under which the study was
conducted. The study involves dosing from 300 mj/cm2 to 1500mj/cm2
to find out if UV will degrade chlorine and monochloramine. The UV
dose range for chloramine destruction and disinfection is from
40mj/cm2 to 60mj/cm2 in swimming pools.
The study concluded: “Chlorine and monochloramine in water
decay steadily when exposed to monochromatic (LP) and polychromatic
(MP) UV light. However, total decay of chlorine and monochloramine
are relatively small in the UV dose range that is generally applied
for disinfection (15-130mj/cm2).”
The assumption that MP lamps burn more chlorine than LP lamps and
thus are not as effective is simply misguided.
What does all this mean? How does one make a decision that will be
cost-effective while providing the risk management that the
- Ask for references.
- If a company makes a statement, ask for third-party documentation.
- When they size a model, ask how they determined the size.
- Are they an authorized distributor for start-up, training, parts and service?
- Ask for a typical service agreement so you know what it may cost to maintain the system.
- Does the manufacturer have UL and NSF approval for swimming pools?
- Is the control panel suitable for use in a wet-chemical plant room?
- Find out how many systems the installer has installed.
- Require a written warranty.
- If the unit must be validated per state code, require a validation certificate with the system.
Remember the old adage, “If something sounds too good to be true, it probably is.”