THE BEST 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.
Ideally, kill time will be short (30 seconds or less) and sanitizer
concentration low. Chlorine and ozone meet these criteria.
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.
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.
Contact Prozone Water Products for more information
