ALTERNATIVE
SANITIZER?
While many consumers frequently refer to
ozonation as an "alternative
sanitizer," is both a sanitizer and
oxidizer. It also is the only treatment other
than chlorine compounds that is approved by the
U.S. Environmental Protection Agency (EPA). Remember, oxidation and
sanitation are critical to proper pool and spa
water treatment. Failure to consider both of
these can result in the growth of pathogens that
induce problems such as itchy skin and
life-threatening illnesses.
Pool and spa
water can have excellent clarity, no odor or
taste, and still be contaminated with bacteria,
viruses and fungi. True water sanitation can only
be judged by various chemical and biological
tests.
The public
health department usually sets levels for
bacteria that it considers safe. Typically, a
sanitizer is defined as an agent that can kill
99.9 percent of all growing bacteria.
Billions of
bacteria are introduced to pool r spa water each
time a bather enters. Outdoor pools and spas also
may be contaminated with various pathogens,
pyrogens and nuisance organisms.
WHAT
MAKES A GOOD SANITIZER?
"There is no single agent that will act as
an ideal sanitizer"
Several
factors influence a sanitizers effectiveness,
including concentration, intensity and nature of
the sanitizer; kill time; type and number of
organisms to be removed; pH; and organic loading.
It should come as no surprise that there is not
one consummate sanitizer (or product) for each
factor listed.
Ideally, kill
time will be short (30 seconds or less) and
sanitizer concentration low. Chlorine and ozone
meet these criteria.
WHAT
IS OXIDATION?
"Oxidation is frequently overlooked in the
treatment of pool and spa water"
As a general
rule, 90 percent of chlorine or bromine in a pool
or spa is used to oxidize organic loading (which
forms chloramines) and inorganic loading (which
can form carcinogenic or pyrogenic compounds).
Technically,
oxidation is the process of electron transfer.
Atoms or molecules that lose electrons are
oxidized.
Think of it in
simpler terms: Just as fire reduces wood to
ashes, oxidizing agents in water reduce organic
loading to carbon dioxide and water. The oxidizer
is like the oxygen that feeds the fire and allows
it to burn.
The oxidation
of organic and inorganic compounds is important
for a variety of reasons.
First,
sanitizers are neutralized by organic matter in
the water. For example, the oxidation of ammonia
by chlorine results in chloramines. This depletes
the chlorine reserve and causes many undesirable
effects, such as odor.
Second,
organic matter can provide protection to the very
pathogens you want to kill. Their cell coatings
can act as barriers to sanitizers that try to
disrupt cellular metabolism.
Finally,
organic matter provides nutrients that pathogens
and nuisance organisms need to reproduce and
grow.
Inorganic
compounds, pyrogens and metals can cause staining
and corrosion as well as reactions that are
harmful to bathers. Oxidizing inorganic
compounds, pyrogens and metals reduces them to
inert compounds that either precipitate or
coagulate. Then, the filter can remove them.
Some studies
show ozone may be the most powerful oxidizer and
sanitizer readily available. Despite this, ozone
still is not a stand-alone solution in pool and
spa water treatment.
Ozone is very
unstable, but this instability also gives ozone
its potency and quick reaction time (on the order
of 1/10 second with organic contaminants and
pathogens).
This high
reactivity also causes ozone’s only real
drawback - it’s impossible to establish an
ozone residual without considerable expense. The
typical European corona discharge-type
installations don’t comply to the DIN
standard or achieve an ozone residual in the
pool.
Instead, try
using chlorine or bromine as a residual sanitizer
and inject ozone via a bypass venturi (commonly
called sidestream injection).
OZONE AND SANITATION
"Bacteria and other microorganisms cannot develop a resistance to ozone"
There are three primary reasons why ozone is a powerful sanitizer. It is non-selective, it kills by rupturing the cell membrane (also called cellular lysis), and it has a short reaction time.
The term "non-selective" means that ozone will react with any pathogen it contacts. This is not the case with all products termed "alternative sanitizers."
Pathogens cannot develop a resistance to the method by which ozone kills (lysis). In the case of organisms such as algae, ozone only destroys the creatures’ ability to reproduce, and they cannot develop resistance.
Most alternative sanitizers kill by entering the cell and interfering with metabolic processes - essentially poisoning them. Like bacteria that have developed a resistance to antibiotics, most organisms can develop a resistance to those alternative sanitizers.
Before examining the final factor, take a look at how microorganisms die in the presence of a sanitizer.
When exposed to a lethal dose of any sanitizer, microorganisms are killed in equal percentages per unit of time. Therefore, the effectiveness of a sanitizer can be correlated directly to sanitizer concentration (known as a "CT value" in the drinking water industry) and varies from organism to organism.
Ozone is pH neutral. Changes in pH will not degrade its performance and, conversely, it will not affect the pH of the pool or spa.
Considering these factors, ozone is a potent oxidizer. We have found that the time required to kill most pathogens in the pool or spa, in conjunction with chlorine or bromine, will be approximately a few seconds at ozone concentrations of 0.1 - 0.3 mg/L.
Although ozone is a powerful sanitizer, it primarily acts as an oxidizer in the pool and spa environment.
Bather or organic loading exerts an ozone demand that can only be overcome in the bypass loop, which is one of the reasons why ozone should be used with chlorine or bromine.
Ozone reactions result in several outcomes. Simple molecules will be broken down into carbon dioxide and water.
More complex molecules may be broken down into a variety of configurations that precipitate and are removed by filtration.
Byproducts of these reactions may be other oxidants (i.e., hydroxyl radicals, etc.) that can cause further reactions. In short, an initial reaction of ozone with organic molecules may cause dozens of sub-reactions that also are beneficial.
Finally, we find that when used with chlorine or bromine, ozone reacts with the combined forms (i.e., chloramines and bromamines) to produce the free forms of these halogens (hypochlorous or hypobromous acid0 that act as the residual sanitizer.
There are several results from these reactions. First, the oxidation of organic loading deprives pathogens of a primary source of nutrients. Second, it eliminates a potential source of protection (organics can coat a cell and inhibit some sanitizers).
Third, it increases the oxidation reduction potential of the pool or spa water, commonly called ORP.
ORP is measure in millivolts and is a measure of the sanitation/oxidation capability of the water. A reading of 650 mV is commonly considered a nominal minimum for the inactivation of pathogens. This can be achieved by combining ozone and a halogen.
POINTS TO REMEMBER
"Ozone is an oxidizer and sanitizer, not an alternative sanitizer"
In summary, ozone acts primarily as an oxidizer in the pool and spa environment. It acts as the primary oxidizer when used with chlorine or bromine, thus allowing those chemicals to operate more effectively as sanitizers.
While ozone contributes to sanitation in this role, it is not its main function. So the next time you are discussing ozone, think in terms of oxidation and sanitation, and leave the term "alternative sanitizer" on the shelf.
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