Apr 17, 2003

Pool & Spa Disinfection

A Reduced Chemical Approach

The maintenance of a pool or spa can become tiresome for the
average consumer. Owning this type of recreational luxury can create a chore
most people despise. Sparkling clear pool water can be easy to obtain or it can
be a nightmare, especially if there is a lot of rain or many swimmers. Opening
a pool in the colder areas of the world often is a dreaded and avoided task,
and year-round pool ownership is never as simple as it looks. There are
alternatives on the market that work rather well for any size pool or
spa--public or private. Chlorine has been used and accepted for years because
it is inexpensive and easy to use. In addition, most health department
regulations are set for chlorine use, and a residual must be maintained.
Bromine is used for spas and hot tubs since the bromide ion can remain more
stable at higher temperatures. This article will address the use of ozone,
copper ionization and proper injection of chlorine for a reduced approach to
chemicals in providing a clean, clear, healthy pool and spa experience.

Bio-Slimes and Bacteria

Bio-slimes can form on the inside of pipes and filters and
on the walls of pools and spas that are improperly maintained. Organic matter
in the circulating water provides nutrition to the bacteria, and they form
strong bonds to the surfaces to which they are attached. Stagnant water
exacerbates the formation of biofilms. As the bacteria grow they form
polysaccharides that essentially are "bacterial cities," which are
groups of bacteria and can contain multiple species. The bacteria form these
biofilms, a common occurrence in nature, because there is strength in numbers.
However, in a pool or spa environment, they can cause disease and sickness. To
prevent the spread of a disease or waterborne illness, pools and spas must be
properly maintained and disinfected. Public and private pools, spas or water
parks must keep water bacteria free to prevent biofilms from forming. Chlorine
has been the choice for decades, but technologies such as ozone and
copper/silver ionization have been used to reduce the amount of chlorine needed
for disinfection while still retaining the residual that health organizations

Understanding Oxidation Reduction Potential (ORP)

Understanding what ORP means will help explain how to reduce
the use of chlorine. ORP levels need to be maintained in order to render
bacteria ineffective. ORP stands for oxidation-reduction potential, which in
practical terms is a measurement of the potential to oxidize contaminants. It
is the method that is used to electronically monitor a sanitizer's
effectiveness. "Redox potential" is another term that is used to
explain this phenomena. In the late 18th Century the word "oxidation"
meant to combine with oxygen and was a pretty radical concept. Examples of
oxidation can be seen daily and at different speeds. A piece of iron rusting or
slices of an apple turning brown are slow processes of oxidation. A fire, of
course, is an example of rapid oxidation and, as we now know, is the exchange
of two electrons. The atom that loses an electron is "oxidized" and
the atom that gains the electron is "reduced."

Chlorine, bromine and ozone are oxidizers because of this
electron reaction. In picking up an extra electron, they lose electrical
energy, making them hungry for more electrons, which makes them good water
sanitizers. It is their ability to oxidize or steal an electron from other
substances that makes them so good at sanitizing water. They alter the chemical
makeup of unwanted plants or animals and kill them. The remains are burned up
and produce byproducts that can be filtered.

In this process of oxidizing, the oxidizers are reduced, and
they lose the ability to further oxidize substances. They simply are used up.
To make sure that the chemical process continues, there must be a high enough
concentration of an oxidizer in the water to complete the process. This is
where the term "potential" comes into play. Potential energy is a
word that refers to ability, rather than action. It is energy that is stored
and ready to be put to work. In electrical terms, this potential is measured in
volts. In using the term to describe ORP, we are talking about the electrical
potential or voltage that is created when a metal is placed in water in the
presence of oxidizing or reducing agents. This voltage gives an indication of
the ability of oxidizers in the water to keep the water free from contaminants.

Without going into the actual explanation of how an ORP
meter works, let it be said that this meter measures the amount of oxidizers or
"good guys" in the water. The higher the voltage reading, the more
oxidizers there are available to combat the reducers or "bad guys,"
since it measures the electrical action created by the stealing of electrons.
If there were the same amount of oxidizers as reducers in the water, the
measurement would be zero and the water would be in pretty sad shape. Balanced
water has the ability to achieve a higher ORP level since there is a balance of
electrons. This is why alkalinity and pH are so important to proper pool and
spa maintenance.

In 1972, the World Health Organization set the standard for
drinking water disinfection at 650 millivolts (mV). This means that when a body
of water measures 650/1,000 (about 2/3) of a volt, the sanitizer in the water
is active enough to destroy harmful organisms almost instantaneously. Germany,
which has some of the strictest water quality standards in the world, has set
its standard at 750 mV for pools and spas. In 1988, the National Spa and Pool
Institute (NSPI) stated that ORP could be used as a supplemental measurement of
proper sanitizing activity when chlorine and bromine are used as the primary
disinfectant. The minimum reading would be 650 mV with no ideal or maximum
reading. The NSPI also stated that the use of ORP measurement does not
supersede or eliminate testing of sanitizer levels with standard kits.

Ozone as an Oxidizer

Now that there is a better
understanding of what ORP is and how the electrons produce measured activity to
gauge potential, it can be determined how ozone can be applied to oxidize
contaminants in water. The differences and sizing of the ozone generators will
not be discussed in this article because the two methods of ozone generation
(ultraviolet [UV] light and corona discharge) on this specific application
would need to be addressed in much more detail. Ozone is very good in spa and
pool sanitation, but since it leaves no residual, it needs to be applied in
conjunction with other treatment methods. Ozone helps flocculate particles in
the water to make them filterable. If well water that has high iron and
manganese is used to fill the pool or spa, these contaminants will be oxidized
first. Chlorine has the same effect, and these contaminants are part of the
biological oxygen demand (BOD) on the water that reduces the effectiveness of
sanitizing. Since ozone is good at providing oxidation of these contaminants,
then less chlorine will be needed to maintain the residual, reducing chemical
use. Another factor to consider is that when less chlorine is used, it is
easier to maintain a proper pH level since chlorine raises the pH and acid must
be used to reduce the pH. This is another chemical-savings advantage that ozone
has to offer. Ozone also is known to help flocculate body oils and suntan
lotions and makes these particles easier to filter, thus polishing the water.
Ozone does not affect the pH or alkalinity.

Copper and Silver Ionization for Disinfection

Copper and silver ionization are
very good disinfectant methods. They help kill many microorganisms and also
control algae. Ionization takes the brunt of the disinfection process, is not
affected by sunlight and does not alter the pH or alkalinity. The copper levels
don't have to be high (0.3 to 0.5 ppm usually is sufficient to help control
algae and render many bacteria lifeless). The electrical charge to the water
can help reduce scaling in the plumbing and on the sides of the pool. Picture
(A) shows a pool a few weeks after an ionization, ozone and chlorine injection
system was installed. The brownish/green color is from the iron being removed
from the inside of the pipes. There were massive amounts of iron and hardness
scale when the flow cell was installed, since the pool was filled with
iron-laden water from a well for many years. Picture (B) shows how the pool
cleared up after a few weeks and, over time, cleared even more as the
particulate was filtered and removed. The pipes now are free from any scale or
biofilms. Copper and silver are very safe if monitored and will not cause
staining if proper levels are maintained.

Chlorine as a Sanitizer

Maintaining the chlorine
residual is easier when using ozone and copper/silver ionization. The copper,
silver and ozone do most of the disinfection process. Therefore, not as much
chlorine is needed to maintain the proper ORP levels. UV light ozone generators
are used in most cases because they don't produce as high a level of ozone as
corona discharge systems. However, on larger pools and spas corona discharge is
the best method to produce enough ozone to satisfactorily maintain proper ozone
levels. The ORP can be monitored and chlorine automatically can be injected
with the proper residual, as required by health organizations being maintained.
ORP monitors do not distinguish between chlorine and ozone; they measure only
the potential by a means of electrical voltage as defined earlier. If the ozone
does not reach this level, then the injector injects chlorine until the set level
is achieved. A well-designed system will adjust the pH first, freeing up
hypochlorous ions that will increase the ORP level. Once the pH is adjusted,
the monitor will dose the correct amount of chlorine to reach the set point.
This method of control can reduce chlorine and acid usage substantially, since
it is dosed only when needed. Manual testing is recommended to ensure the
safety of the swimmers and monitor possible equipment failure.

Conclusions can be drawn on the
fact that copper/silver ionization, when monitored and controlled, kills many
bacteria and helps control algae and bio-slimes. Ozone oxidizes contaminants
and helps reduce chlorine and other chemical use.

There are many parameters to
take into consideration when employing the technology described in this
article. As with any other water treatment devices, ozone generators,
coppr/silver ionizers and chlorine injectors need to measure for and meet
specific criteria. Flow rates and the amount of gallons to be treated must be
analyzed carefully or system failure will be experienced. A thorough
understanding of ORP monitors, ozone, ionization and chemical feed pumps need
to  addressed in order to obtain
optimum results.

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