Editor's Note: This is the first of two columns on
supplemental sanitization systems. Next month we'll look at UV
Since 1961, when the U.S. Public Health Service published a model ordinance governing the sanitation of public pools with chlorine, that has been the standard water treatment chemical. While chlorine is effective in reaching certain water quality standards, scientists are learning more about its limitations and hazards. These findings, in part, have inspired the Centers for Disease Control
and Prevention to form a Model Aquatic Health Code.
The soon-to-be-published MAHC will include a section on the
importance of supplemental disinfections systems (SDSs). In the
present draft, two recommended SDS technologies are listed in the
MAHC: ozone and ultraviolet light (UV).
UV achieved earlier adoption among pool designers for its
simplicity. Ozone, on the other hand, has been used to sanitize
municipal water for the past 100 years, is widely used as life
support for aquatic mammals and fish in commercial aquariums, and
is the primary supplemental sanitation technology for the hot tub
industry. But it still has yet to earn its place in supplemental
disinfection for commercial pools.
A big reason for that are the complexities and confusion within
the aquatics industry as to what ozone is, how it works and how it
compares with UV. To clear those up, it’s necessary to first
look more closely at the role of chloramines and RWIs as the
impetus for supplemental disinfection.
In the 1930s, chemists discovered that chlorine could react with
organic material in water and create chloramines. In pools, these
are documented to be unhealthy for people and can cause damage to
indoor facilities. Ever since the discovery of chloramines, the
challenge has been to balance antimicrobial efficacy (keep the
water sanitized) and swimmer safety (eliminate chloramines).
In the past two decades we have added to this an increasing
concern and awareness of recreational water illnesses, or RWIs.
“RWI” is a term coined by the CDC to describe illnesses
caused by microorganisms, as well as those from chloramines. Some
microorganisms, including Pseudomonas aeruginosa, E. coli,
Staphylococcus aureus, Giardia and cryptosporidium parvum (crypto),
can cause serious illness in swimmers.
In a perfect world, chlorine would handle all of these except
crypto, which is resistant to chlorine. However, the repeated
outbreaks of the chlorine-sensitive microorganisms have shown that
conventional chlorine treatments are not adequate and some type of
supplemental system should be considered.
Fortunately, new and improved technologies provide affordable
solutions that are readily available for the reduction of
chloramine compounds as well as increased protection from
microorganisms in the pool: the aforementioned supplemental
disinfection systems. By supplementing chlorine, SDSs provide
increased kill of microorganisms as well as reduction of
chloramines. This leads to significantly reduced chlorine
off-gassing and its harmful effects to swimmers and
Ozone, an SDS option, has been widely used for municipal water
and commercial pools in countries outside the United States for
more than 100 years. In recent years, the expensive, cumbersome
ozone systems of the past have given way to smaller, affordable,
modern systems that provide public pools with a viable water
quality solution at a low cost. The complexity rumors about ozone
systems are widely overstated and outdated. Today’s
commercial ozone systems are simple, compact and efficient. Many
are skid-mounted with flange-to-flange hook-ups, which enable easy
installation as a partial wall-mount or floor-mount.
An ozone system consists of two basic components that ensure
optimum performance at the lowest operating cost: an ozone
generation system and an ozone management system.
The ozone generation system manufactures ozone gas. The ozone
management system efficiently dissolves the gas into the water,
simultaneously ensuring no undissolved ozone is available to
off-gas in the pool equipment room or at the pool water
The ozone management system utilizes an oxidation reduction
potential (ORP) controller/monitor to maintain proper ozone levels
in the water. These components operate in unison and are easily
installed to an existing public pool as a side-stream to the
pool’s main filtration system. The ozone is introduced after
the filtration (and heater), and before the chlorine feeder. The
side-stream flow is normally 15- to 25 percent of the main flow,
depending on the size and type of pool. The ozone system output is
increased as the water quantity or organic loading increases.
Ozone is a safe and efficacious antimicrobial oxidizer. In
public recreational water, it is used in conjunction with chlorine.
Pool water clarity and quality is improved because of ozone’s
potent and rapid oxidation of organic and inorganic compounds.
Ozone is cost-effective, uses little energy, is safe for pool
patrons and will not cause structural degradation to the facility
or HVAC system.
An ozone system’s broad spectrum oxidation, when properly
sized and applied to any aquatic venue, will:
• Control the chloramine levels in the water to 0.2 ppm or
• Offer significantly more oxidation than free available
chlorine (FAC) alone
• Produce a minimum 3 log (99.9 percent) kill of
cryptosporidium parvum and other RWI pathogens in a side-stream
• Provide microflocculation to aid filtration and water
• Reduce the amount of chlorine usage to maintain an FAC
It is not recommended that ozone be used in conjunction with
bromine. When used with bromine, ozone oxidizes “spent”
bromine (bromide) back to useful bromine. This depletes the ozone
before it can oxidize the organic contaminants in the water.
Though ozone and UV systems are completely different
technologies, some people are confused about the distinction
between the two. Perhaps part of the confusion stems from
UV-generated ozone that was readily utilized for residential pools
and spas until the late 1990s, when breakthrough compact CD ozone
generators took over that market. UV-generated ozone is never used
on a public pool because the systems cannot make enough ozone to
benefit the pool water.
Ozone is a gas that is dissolved in water to kill
microorganisms, destroy organics and break down chloramines by
oxidation. This occurs immediately at the ozone gas injection
point, and continues as the side-stream remixes with the main
return. A small residual (~0.1 ppm) of dissolved ozone will enter
the pool, providing further oxidation of contaminants. There are no
consumables in an ozone system.
In comparison, UV light inactivates microorganisms and breaks
down chloramines with light energy. This only happens while the
water is in the UV chamber, and as long as the water has no
turbidity. No further process occurs once the flow leaves the
chamber. UV provides no oxidation except as trace amounts as a
result of the formation of a limited number of hydroxyl radicals.
UV lamps are replaced every three to 12 months, so replacement
costs must be considered when determining ownership expenses.
As a rule, ozone and UV technologies are comparatively priced.
Each costs approximately $30,000 for a 100,000-gallon pool, with
the ozone system having the larger footprint. Operational cost will
vary with the local price of electricity for either technology.
However, ozone does not entail the same maintenance costs as UV.
With savings from labor and reduced chlorine usage, a system can
pay for itself in three to six years on a 100,000-gallon pool,
depending on bather load.
Ozone and UV can be used together to create a synergistic
approach to water sanitation. This process has been in use for
drinking water, food processing and waste water for many years. It
is one of several advanced oxidation processes that are in
commercial use today in selected industrial processing. The
technology has rarely been used in public pools to date, but with
the advent of improved technology and cost reduction, perhaps it
will be the wave of the future for RWIs and chloramine
As aquatics facility operators and officials look to increase the
safety and health of our public recreational waters, it is clear
that supplemental disinfection systems will offer strong
protection. Several states have already mandated the use of SDSs
for their high-risk swimming venues such as interactive sprayparks,
and it is likely more states will rapidly adopt the MAHC for these
as well as all public aquatics facilities. With this in mind,
operators and officials are wise to learn about the power of ozone