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Figure 1: Various
factor relationships
TITLE - Swimming in Chemicals?Engaging opening statement
To have the perfect swimming pool, two main factors
need to be taken into consideration and kept in
balance, sanitation and water balance. Sanitation
refers to the decomposition of organisms and
oxidation refers to the removal of organic debris such
as body waste from swimmers and plant matter from
the surroundings. There are a
number of ways to sanitise
swimming pools, the most
common of which is a
saltwater system using
chlorine to eliminate
contaminants in the water.
Water balance refers to the
level of chemicals in the
pool such as pH, alkalinity,
water hardness and
dissolved solids, which have
to be managed carefully to
fall within certain limits to optimise conditions,
preventing harm to the human body when swimming.
Chlorine is a popular option which both
sanitises and oxidises, and saltwater systems are
frequently chosen as the medium to deliver chlorine
into the pool, utilising a chlorine generator, an
electrolytic cell which after salt is
dissolved into the water, transforms the
chloride ions produced hypochloric acid
through the process below.
NaCl(s) Na+(aq) + Cl
-(aq)
The salt is added into the pool, which
dissolves and disassociates into its ions.
The negative chloride (Cl-) ions and
hydroxide (OH-) ions are attracted to
the positive anode, where the following
two reactions can happen:
2 Cl-Cl2+ 2 e
-E
oox= -1.36 V
2 H2O (l) O2+ 4 H++ 4 e-Eoox= -1.23 V
From the standard-state potentials, the water seems
preferential to be oxidised at the anode. However,
because the cell never reaches standard-state
conditions and the close potentials, as well as
overvoltage, it can be controlled so that the chloride
ion is preferentially oxidised to chlorine gas molecules.
The negative cathode attracts the Na+ ions in the water.
Na++ e
--> Na E
ored= -2.71 V
2 H2O (l) + 2 e--> H2+ 2 OH
-(aq) E
ored= -0.83 V
The water is much more easily reduced at the cathode
as it has a more positive standard-state potential value
than the half reaction of Na+ ions. The water is reduced
by electron gain, forming hydrogen molecules at the
negative electrode.
Cl2(g) + H2O HOCl + H(+)
+ Cl(-)
Hydrogen and chloride ions, along with Hypochlorous
acid, the active sanitising species are produced when
chlorine gas is filtered into the pool. Hypochlorous acid
in water exists in the following pH dependent
equilibrium with OCl-, hypochlorite ions.
HOCl H++ OCl
-
The concentration of HOCl and
OCl- ions are known as the
free available chlorine, being
the sanitising species. The
hypochlorite ion is relatively
ineffective as a disinfecting
component, compared to
HOCl. Therefore, it is
preferable to have a higher
amount of hypochlorous acid
to hypochlorite ions.
Le Chtelier's principle states that if a
dynamic equilibrium is disturbed by changing the
conditions, the position of equilibrium shifts to
counteract the change to reestablish an equilibrium.As
the pH decreases, becoming more acidic, the
concentration of H+ ions increase and according to Le
Chateliers Principle,
causes the equilibrium to
shift to the left, producing
more HOCl. With a more
alkaline solution, with pHs
of about 8, the opposite
occurs with more OCl- ions
produced. This relationship
can be seen in fig 1.
Therefore at higher pH
values the concentration of hypochlorous acid will
decrease and thus the sanitation capacity is reduced.
To reduce and control the fluctuations of
pH, a buffer is needed, among other additives that
may be used to help control it. Total alkalinity is a
measure of the waters buffering capacity, the ability
to neutralise acid and helps to control the pH level.
Alkalinity is usually present in bicarbonates and
carbonates, such as calcium or sodium bicarbonate,
otherwise known as baking soda, which are added to
the water to increase resistance against changes in
pH. This also causes the build-up of mineral or
calcium hardness. At low pH conditions, no calcium
carbonate precipitate is formed, and the water
becomes acidic, damaging the pool. In high pH
conditions, there is too much carbonate formed, and
a)
b)
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causes cloudiness of water and scale, from too much
content of calcium in the pool. In ideal conditions of
pH, the carbonate ions are in the bicarbonate form to
provide buffering.
When there are H+ ions present,
indicating low pH, the following reaction happens:
The pH is raised, as with the amount of H+ ions
reduced. To reduce the pH, HCl or muriatic acid is a
widely used solution to increase acidity in the
following reaction:
The H
+ ions will combine with ClO
-to formHClO and
decrease pH. To provide maximum comfort to the
swimmers, the pH should be maintained in between
a range of 7.2 to 7.6. Figure 3 below shows the ideal
zone of pH, and the conditions caused by various pHs.
Chlorine undergoes photolysis and decomposes
quickly in the presence of UV rays into hydrochloric
acid, and follows the reactions below.
2 OCl-+ UV 2 Cl
-+ O2(g)
2 HOCl-+ UV 2 HCl + O2
The prevention of free chlorine decay requires a
stabiliser such as cyanuric acid, which has the
characteristics and effects of both stabiliser and a
buffer. As a stabiliser, it greatly reduces the rate of
decomposition of chlorine by forming a weak bond
with available HOCl and OCl-, forming compoundswhich are not photosensitive, stabilising it from the
effect of UV light in a manner which does not use up
the chlorine.
According to Le Chateliers Principle, as
the concentration of OCl- decreases via photolysis,
the equilibrium balances by shifting from right to,
resulting in the decrease in the amount of
dichlorocyanuric acid and OH- and the production of
cyanuric acid and OCl-. Thus the net depletion rate of
OCl- is also slowed because as OCl- and HOCl
decomposes, it is replaced equally by a shift in the
equilibrium above. The free chlorine then is
maintained at a constant level, as long as there is
sufficient cyanuric acid and constant pH.
Testing has shown that onlyapproximately 15% of free chlorine residual is lost
over the day with the use of cyanuric acid, whereas
90% is lost without. However, the addition of
cyanuric acid also reduces the disinfectant power of
hypochlorous acid slightly because of the bonds
formed between them. This can be compensated for
by increasing the free chlorine concentration from
1mg/L to 3mg/L. The stabilising effect of cyanuric acid
becomes locked in at levels over 100 ppm and may
not be as effective in killing bacteria and algae.
During the oxidisation of organic compoundimpurities containing nitrogen such as perspiration,
saliva, body oils and urine by hypochlorous acid, if
there is an insufficient supply of HOCl to completely
oxidise the impurities, chloramines are formed, as
shown in the equations below.
Ammonia, as waste from swimmers react with HOCl
to form monochloramine, which then reacts with
more HOCl to form dichloramine, and repeats the
process to form trichloramine, which happens whenthere is an abundance of hypochlorous acid.
Chloramines are still sanitisers; however
they are 40 to sixty times less effective than the
hypochlorous acid. As well as the reduction in
effectiveness, chloramines also cause eye irritation
and a distinctive odour, whereas free chlorine has no
apparent smell.
A low level of chloramines is tolerable as they react
with each other in the following reaction:
The nitrogen gas is then lost and the HCl can
disassociate into H+ and Cl- ions. However, as it is in
equilibrium and a natural byproduct of the
disinfectant process, the overall content of
chloramines still accumulate.
The amount of chloramines can be
reduced with superchlorination, which involves an
extra-large dose of chlorine past the breakpoint to
completely oxidise contaminants. The process of
superchlorination and its effect on chloramine
concentration can be seen in fig 1b. If there is anoverabundance of HOCl in the pool, nitrogen
trichloride, which especially irritates the eyes and
Figure 3
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What is UV?
UV light inactivates microorganisms and breaks down chloramines with light energy. This happens while the water is in the
UV chamber only, and as long as the water has no turbidity. No further primary sanitation 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 free radicals in or near the UV chamber.
Comparing Ozone and UV:
There is sometimes confusion as to the difference between ozone and UV systems. Actually, they are completely different
technologies, however the confusion may stem from UV-generated ozone that was popular in 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. CD generated ozone, on
the other hand, is extremely safe and effective for pool water sanitation.
Ozone is a gas that is dissolved in water to kill microorganisms, destroy organics, and break down chloramines by oxidation.
In comparison, UV light inactivates microorganisms and breaks down chloramines with light energy. With UV, this
chloramine breakdown only happens while the water is in the UV chamber, and as long as the water has no turbidity. With
Ozone, oxidation occurs immediately at the ozone gas injection point and continues as the side-stream remixes with the
main return.
While both Ozone and UV provide very effective Crypto reduction as documented by third-party testing and validation, there
are distinct differences between the two technologies when it comes to other areas of concern for commercial aquatics
designers and operators, with clear advantages to Ozone over UV.
Ozone is a powerful oxidizer.
Ozone gas dissolves in water to kill microorganisms, destroy organics that create chloramines, and breaks down existing
chloramines by oxidation. This oxidation happens 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 then enters the pool, providing further
oxidation of contaminants. There are no consumables in an ozone system.
Meanwhile, UV light inactivates microorganisms and breaks down chloramines with light energy. This happens only while
the water is in the UV chamber, and as long as the water has no turbidity. Once the flow leaves the chamber no further
process occurs. UV provides no oxidation except as trace amounts as a result of the formation of a limited number of
hydroxyl free radicals.
Ozone and UV are comparable in cost.
Ozone and UV technologies are comparably priced. Operational costs of each system vary with the local price of electricity.
However, the minimal maintenance and reduced chemical requirements of an ozone system create significant benefits.
Meanwhile, UV lamps must be replaced every 3 to 12 months and must be figured into the maintenance costs for these
systems.
OZONE VS. UV
Ozone UV
Ozone kills cryptosporidium parvum UV inactivates cryptosporidium parvum
Ozone kills microorganisms UV inactivates microorganisms
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OZONE VS. UV
Ozone UV
Ozone is a powerful oxidizerUV is not an oxidizer
Ozone passes into the pool at low levels to
provide additional oxidation
UV affects the water only as it passes through the UV
chamber
Ozone functions well in cloudy water and is a
micro-flocculent, which aids water clarity
Only clear water can be effectively dosed with UV;
cloudiness in the water can absorb the UV light
Ozone oxidizes the organics and inorganics
that create chloramines, eliminating their
production
UV breaks down chloramines that have been previously
created
Ozone utilizes ORP (REDOX) to measure the
cleanliness of the water
UV systems utilize a UV intensity meter which measures
the UV dose regardless of water quality
Ozones reaction with free available chlorine
(FAC) is very slow and in a pool will not affect the
FAC levels; only chloramine destruction
UV can break down free available chlorine in the
water while it breaks down chloramines
Ozone cells require no replacement; require
annual periodic cleaning; no hazardous
components
Mercury vapor lamps are replaced at 3-12 months;disposal procedures must be considered as lamp gases
are considered hazardous waste
Ozone destroys biofilmUV does not affect biofilm
Ozone destroys Humic and Fulvic AcidUV does not affect Humic and Fulvic Acid
How is Ozone produced for Swimming Pools & Spas? Ultraviolet (UV) light and CoronaDischarge (CD) are the two methods. For UV, a special lamp gives off a specific wavelengthof ultraviolet light which converts oxygen (O2) molecules into ozone (O3) molecules bysplitting the oxygen molecules into individual oxygen atoms (O1) which then recombine withoxygen to form ozone. This all occurs instantly inside the ozone chamber in the ozonegenerator. With CD, ozone is produced by passing air through a high voltage discharge, orcorona. Air or concentrated oxygen dried to a minimum of -60C dew point passes through thecorona which causes the O2 bond to split, freeing two (O1) atoms which then collide withother (O2) molecules to create ozone. CD systems generally produce about 3-5 times moreconcentrate than UV units.
What does Ozone do? Ozone is the most powerful oxidizer and disinfectant that can be usedsafely to purify air and water. In fact, it is one of the most powerful alternatives to chemicalsanitation. Compared to chlorine, the most common water disinfection chemical, ozone is a
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more than 50% stronger oxidizer and acts over 3,000 times faster. Any pathogen orcontaminant that can be disinfected, altered or removed via an oxidation process will beaffected by ozone. Ozone has been scientifically proven as an affective broad-spectrumantimicrobial agent in deactivating bacteria, viruses, molds, spores, cysts, yeast, mildew andfungi. Ozone oxidizes iron, sulphur, manganese, hydrogen sulfate, and eliminates oils andother contaminants in the water.
This is why ozone is used by water bottling plants, is used to clean waste water and toxicwaste, is used to purify air in hotel rooms and why all Olympic Games Competition Poolshave been purified by ozone since 1984. Ozone is pH neural and will not adversely affectthepH.
Does a swimming pool or spa still need chemicals with ozone? The answer is yes. Ozone willhandle the bulk of sanitising requirements. However, due to the short life of ozone, a smallamount of sanitiser will be required to provide a residual in the water. Because residual levelsare so low there is no detectable taste or odour. Normal residual levels are around 0.5ppm to1ppm, thus reducing normal chemical usage by up to 90%. Ozone also works with mineralsystems and salt chlorinators and reduces their consumable consumption.
Other methods
There are a variety of other methods including ionisation, electrolysis and mineral systems,which operate either alone or in combination with chemical sanitisers. The trace-elementsystem Nature2, for example, claims to reduce the need for chlorine to just 0.5ppm. Anti Biotechnology uses low frequency sound waves and electromagnetic fi elds to assist in theremoval of impurities from water and to reduce the amount of chemicals required. TheAquabrite System is an environmentally friendly, simple, efficacious non-chlorine disinfection
system that has been tried and proven for more than 14 years. It uses the natural disinfectionqualities of copper and silver, through electrolysis, with a proprietary oxidising agent knownas Aquabrite. The synergistic effect of the copper and silver ions and the oxidising agentdisinfects the pool and spa water without creating irritants.
http://www.delozoneaquatics.com/about-ozone/ozone-vs-uv.php
http://autopilot.com/blog/post/211-A-Review-of-Swimming-Pool-Sanitization-Methods
http://www.ohanapool.com/TechInfo/howuvpoolsanitationworks.html
http://www.delozoneaquatics.com/about-ozone/ozone-vs-uv.php
http://www.ohanapool.com/TechInfo/advantagesofuvpoolsanitationoverchlorine.html
http://www.wescorhvac.com/Chloramine%20Basics.pdf
http://autopilot.com/blog/post/219-How-Does-Ozone-Work-to-Sanitize-My-Swimming-Pool-http://health.mo.gov/safety/recreationalwater/pdf/PoolSpaChem.pdf
https://www.facebook.com/l.php?u=http%3A%2F%2Fwww.houselogic.com%2Fhome-advice%2Fpools-
spas%2Fswimming-pools-alternatives-chlorine%2F&h=aAQHeb1N2
http://www.health.nsw.gov.au/environment/factsheets/Pages/chloramines.aspx
https://www.allchlor.com.au/newsview/sanitisation-is-a-crucial-and-constantly-changing--15
http://www.poolsolutions.com/gd/alternative-swimming-pool-sanitizers.html
http://www.autopilot.com/blog/post/211-A-Review-of-Swimming-Pool-Sanitization-Methods
Possible Solutions
Dr. John Marshall, of the Pure Water Association, an American consumer group campaigning for safer drinkingwater, states: "It shows we should be paying more attention to the chemicals we put in our drinking water and
we should be looking for other alternatives to chlorination. A number of safe, non-toxic options exist, such as
treating water with ozone gas or ultra violet light."
http://www.delozoneaquatics.com/about-ozone/ozone-vs-uv.phphttp://www.delozoneaquatics.com/about-ozone/ozone-vs-uv.phphttp://www.autopilot.com/blog/post/211-A-Review-of-Swimming-Pool-Sanitization-Methodshttp://www.autopilot.com/blog/post/211-A-Review-of-Swimming-Pool-Sanitization-Methodshttp://www.autopilot.com/blog/post/211-A-Review-of-Swimming-Pool-Sanitization-Methodshttp://www.delozoneaquatics.com/about-ozone/ozone-vs-uv.php8/10/2019 Chemistry Pool ERT
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While governments focus on tap water and reducing the levels of dangerous chlorine byproducts, it turns out
there are also options that are available for swimming pool managers.
Ozone
Is ozone viable for swimming pools? Recently a chemical-free public swimming pool was installed in Fairhope,
Alabama. It uses Ozone technology and avoids the use of chlorine altogether. This is a first for public pools in
North America. The United States Navy Dolphin program has switched to ozone technology over the lastseveral years. A spokesman there stated that these systems have delivered the best water quality they have
seen out of any systems they tried.
Numerous other private, public, commercial, waterpark and hotel and motel pools have switched to ozone
technologies as people become more concerned about chlorine and chlorinated byproducts. Other than the
issue of carcinogens and other health problems, what are the relative benefits of ozone versus chlorine?
One of the main problems with adopting ozone is that there is a higher initial capital cost to the swimming pool
compared to chlorine. However, over the life of the pool ozone and ultraviolet technologies reduce the on-going
operating and maintenance costs. These costs can be significant. Chlorine is famous for destroying pool
infrastructures, rusting ventilation systems and destroying pool liners. Ozone poses no such problems.
The ozone pool will be much cleaner, which means dirt, grease, oils, organics and other materials will wind up in
the filter system much faster than with chlorinated systems. If the filter and strainer maintenance is not stepped
up accordingly, the pool recirculating system will slow down and the pool will actually look dirtier than with
chlorine. However, proper maintenance of the filter system will solve this problem.
Part of the problem in adopting ozone is that engineers, architects, pool builders and designers are not familiar
with the technology. Some applications of ozone, particularly systems installed ten to fifteen years ago were
plagued with technical problems. Even though ozone systems have been in regular use in Europe and other
areas of the world since the 1950's, pools here have generally relied on chlorine. Since our engineering,
architectural and other technical training have all been geared to chlorine, it takes re-education to now apply
ozone. Many people in these industries are reluctant to shift gears.
What is the difference in technologies? Chlorine is a complex man-made chemical that found original use in the
infamous mustard gas of the First World War. Ozone has been in use for over 100 years, primarily in Europe
and was first put to use for water purification, odor control and in hospitals. Ozone is made from oxygen or O2,
which is converted through electricity to ozone or O3. Ozone is a much more powerful oxidant than chlorine.
However, the shelf life of ozone is limited. It must be manufactured and used on-site. This is done through
ozone generators which convert oxygen in the air into ozone.
Ozone is considered a short-term disinfectant and chlorine is considered a long-term disinfectant. Chlorine is
also an entrenched technology. It has been widely used in North America and was first adopted at the turn of
the century. It is still the reigning champion of disinfection and has many supporters in the chemical and
swimming pool industries.
Some of the IssuesThere are credible researchers telling us that chlorine has some very serious health consequences when used
as a sanitizer in swimming pools. The obvious question is why hasn't the swimming pool industry adopted
alternative technologies on a much more industry-wide basis? After all, ozone technology for swimming pools
has been in regular use for over 50 years in Germany, France and other European nations.
Let's examine some of these issues. For drinking water or swimming pools, the European strategy is to use
ozone to reduce the organic load in water. When chlorine is required for long-term disinfection such as
distributing water through a municipal water distribution system, they use a very small amount of chlorine, thus
reducing the risk for people drinking the water.
It is the organics that cause problems when combined with chlorine. By reducing the organic load, the
Europeans keep the chloramines at a very low level. In European swimming pool systems, the same thoughtprocess prevails. In Germany, for example, the strategy is to use a large surge pool that the public doesn't even
see to apply ozone or disinfection chemicals. The disinfection by products are then removed by various filtration
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processes prior to the water being returned to the pool with a slight dose of chlorine. Under these standards,
swimming pool water is essentially treated to drinking water standards.
The North American model developed under much different circumstances than the European. In North America,
chemicals were adopted wholeheartedly around the turn of the century as the answer to the larger, more
expensive European models of water treatment. Engineers here found they could build water treatment plants
and swimming pools at greatly reduced capital costs if they used what were then considered miraculous
chemicals to treat water. And, for the most part, the systems did what they were designed to do and that was tokill micro-organisms that could lead to sickness and death. What they didn't anticipate was that chemicals like
chlorine would have very serious side effects. In North America we are now stuck with swimming pools that in
Europe would be considered surge tanks. The problem is to evolve ozone or other technology that can retrofit
swimming pools in an economical manner. These systems are now starting to appear in the marketplace. It is
not easy to engineers that switching to ozone technology is the way to go. Some of the earlier North American
produced ozone systems were problematic and many engineers do not want to risk specifying equipment if they
are not comfortable with the process.
The technology is becoming very reliable. Without a doubt, ozone is starting to gain a foothold in water
treatment and for swimming pools in North America. Some of the largest ozonation plants in the world have
been built in the United States. Major North American cities such as Los Angeles, Dallas and Montreal, Canada
have installed large ozone plants for water treatment. Some of the major pool operators in North Americaincluding Disney's water parks use ozone technology. The United States Navy has switched to ozone systems
for their Dolphin programs.
Other encouraging signs include the City of Fairhope, AL which has distinguished itself with the implementation
of an Olympic-sized swimming pool that is operated as ozone based with only slight chemical assistance. Many
consumers are also requesting ozone systems for their backyard swimming pools. Regulations for these pools
do not require them to use chlorine or other chemicals and many owners are now opting for ozone systems.
Once pool owners switch, they realize that they no longer have to put up with red eye, rashes and the health
consequences of chlorinated pools.
As the technology becomes more prevalent, expect to see more expertise among local pool builders or pool
maintenance companies. However, many of these companies rely on repeat sales of chemicals. These
companies may be highly resistant to ozone systems as after-sales revenues will drop. However, for pool
maintenance companies ozone is a good thing. They should spend less time maintaining pools and the pools
will be cleaner and the water more appealing. In the future, expect ozone prices to drop. With better educated
consumers, demand for systems will definitely increase.
UV does not replace chlorine but allows you to run a lesser residual chlorine reading and allows the chlorine to
be used totally for disinfecting rather than go into combination with other elements. State departments of public
health have copies of state regulations and limitations for using UV in commercial pool applications. Codes vary.
Ultraviolet or UV
Ultraviolet light is part of the light spectrum, which is classified into three wavelength ranges:
- UV-C, from 100 nanometers (nm) to 280 nm
- UV-B, from 280 nm to 315 nm- UV-A, from 315 nm to 400 nm.
UV-C light is germicidal, that is it deactivates the DNA of bacteria, viruses and other pathogens and thus
destroys their ability to multiply and cause disease. It also breaks down chloramines that develop in indoor
swimming pool water. Specifically, UV-C light causes damage to the nucleic acid of microorganisms by forming
covalent bonds between certain adjacent bases in the DNA. The formation of such bonds prevents the DNA
from being unzipped for replication, and the organism is unable to reproduce. In fact, when the organism tries to
replicate, it dies.
Ultraviolet technology is a non-chemical approach to assist disinfection. In this method of disinfection, nothing is
added to the pool water except chlorine and pH control chemicals. This makes this process simple, inexpensive
and requires very low maintenance.Ultraviolet purifiers utilize germicidal lamps that are designed and calculated to produce a certain dosage of
ultraviolet (usually at least 16,000 microwatt seconds per square centimeter but many units actually have a
much higher dosage.)
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WATER APPLICATIONS
under sink installs & water vending machines
aircraft, boats & recreational vehicles
water wells & water cisterns
swimming pool & hot tubs
farms, ranches & trailer parksschools & hotels
aquarium, hatcheries and nurseries
Short wave low pressure mercury vapor tubes produce ultraviolet wavelengths that are lethal to micro-
organisms. Approximately 95% of the ultraviolet energy emitted is at the mercury resonance line of 254
nanometers. This wavelength is in the region of maximum germicidal effectiveness and is highly lethal to virus,
bacteria and mold spores. Therefore, the water or air that passes through the chamber is exposed to the
germicidal UV light and the genetic material of the micro-organism is deactivated, which prevents them from
reproducing.
Ultraviolet radiation (UV)
UV pool watersanitisation devices use UV rays to kill micro-organisms in the water of a pool or spa.
The system is installed in the filtration system and after the water is filtered it passes through the UV
chamber. As with ionisers this system takes care of the sanitising of the water but an oxidiser still
needs to be used.
Pros:much less chlorine or bromine needs to be used
Cons:may have a high initial cost to set up
Ozone
Ozoneis a gas that is formed by UV rays separating an oxygen molecule (O2) causing the
separated O molecules to attach to other O2 molecules resulting in O3being formed. The
O3 (ozone) is a powerful sanitiser and oxidiser before it is rapidly broken down into oxygen again
(O2). Ozone is actually a highly toxic gas that must be removed from the pool or spa before use.
Because there is no residual ozone remaining in the water additional small amounts of sanitisers
and oxidisers must be used.
Pros:powerful sanitising and oxidising agent, use much less chlorine/bromineCons:requires the use of some sanitising chlorine/bromine
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Comparison of Ozone VS UV in Water
ULTRA VIOLET (UV)
OZONE
The energy is not enough to destroy all
types of bacteria, virus, protozoa, and
fungus.
Mercilessly kills all bacteria and
virus.
Requires more contact time as the UV
rays is stationery & hence water has to
be exposed to it for a longer time.
The reaction is instantaneous as the
gas mixes with water. The reaction
rate is 3,200 times faster than any
known method.
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If the water is turbid & has high level
of suspended solids, the penetration of
the rays is not deep.
Reduces turbidity and the suspended
dissolved solids do not make any
difference.
Scale forms on the tube thereby
reducing the disinfections rate.
Disinfections rate is constant and
there is no scale formation.
Cannot eliminate algae & biofilms. Eliminates algae & biofilms.
Cannot kill SPORES of bacteria & virus. Eliminates even SPORES.
Does not act as flocculent. Act as flocculent.
Does not eliminate ODOR. Eliminates ODOR.
Does not eliminate COLOUR. Eliminates COLOUR.
Cannot treat waste water.
Treats any type of water.
UV light cannot increase or decrease
energy
Ozone can be increased or decrease
to to desired level for effective
treatment of water
The Intensity of the bulbs start
reducing
Intensity can not waver once fixed.
Has very narrow application (Bacteria
elimination only)
Has wide applications like
eliminating bacteria, odor, color,
treating waste water, effluent & so
on
UV intensity can not be measured Ozone presence can be felt.
Can not stop corrosion. Stops corrosion completely
Can not store as SPORES will breed and
bacteria will come alive.
Treatment is permanent.
Bulbs get fused often No bulbs involved
Needs maintenance No maintenance required
Has no effect on compounds Oxidizes the compounds.
http://www.ozoneworld.com/accessories.html
http://www.fluidquip.com.au/uv-technologies-/swimming-pools/
http://www.ozoneworld.com/accessories.htmlhttp://www.ozoneworld.com/accessories.htmlhttp://www.fluidquip.com.au/uv-technologies-/swimming-pools/http://www.fluidquip.com.au/uv-technologies-/swimming-pools/http://www.fluidquip.com.au/uv-technologies-/swimming-pools/http://www.ozoneworld.com/accessories.html8/10/2019 Chemistry Pool ERT
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How Does Ultraviolet Disinfection Work?Ultraviolet energy causes permanent inactivation of micro-organisms by disrupting its DNA so
that they are no longer able to maintain metabolism or reproduce. All bacteria, spores, viruses
and protozoa (including Cryptosporidium and Giardia oocysts are permanently inactivated by UV).
The maximum effectiveness occurs at between 240nm and 280nm. The Hanovia UV systems
produce these wavelengths in abundance.
The Mechanism of Ultraviolet DisinfectionStrong sunlight disinfects water by permanently de-activating bacteria, spores, moulds and
viruses. Over a century ago, scientists identified the part of the electromagnetic spectrum
responsible for this well-known effect; wavelengths between 200nm and 300nm, often called UV-
C. The most effective single wavelength is typically UV at 265nm, however recent research in the
USA has shown that 271nm light and 263nm light are the most effective UV wavelengths for the
deactivation of particular target organisms.
The mechanism of kill is well documented and unlike chemical disinfectants the organism is
unable to develop any immune mechanisms. The mechanism of kill involves the absorption of
photons of UV energy by the DNA, which fuses the DNA and prevents replication. DNA
(Deoxyribonucleic acid) consists of a linear chain of nitrogen bases known as purines (adenine
and guanine) and pyrimidines (thymine and cytosine). These compounds are linked along the
chain by sugar-phosphate components. The DNA of most forms of life is double stranded and
complimentary; the adenine in one strand is always opposite thymine in the other, and linked by
a hydrogen bond, and guanine is always paired with cytosine by a hydrogen bond. The purine and
pyrimidine combinations are called base pairs. When ultraviolet light of a germicidal wavelength is
absorbed by the pyrimidine bases (usually thymine) the hydrogen bond is ruptured. The dimer
that is formed links the two bases together, and this disruption in the DNA chain means that
when the cell undergoes mitosis (cell division) the DNA is not able to replicate. The most effective
wavelengths to achieve this effect are found between 263nm to 275nm, and the peak wavelength
distribution is dependent on the target organism.
The optimal operating temperature is 15oC, and the lamp output will fall off rapidly as the lamp
temperature migrates from this condition. These lamps should not be used if the water is hot or
cold, or if the water flow is intermittent as the temperature build up will cause the lamp output to
decrease. Frequent switching of these lamps will have a detrimental effect on lamp life, and the
most probable failure mode will be failure of the filaments, which become brittle. The article "The
dying of the light" describes the variable output of these mass produced lamps and offers somesuggestions as to how the performance might be optimised. Typically these lamps have an
efficiency of 25-30%, which is temperature dependent. The lamp life is typically 8000 hours, and
the lamps have the advantage of being mass produced and easily second sourced.
Amalgam lamps have been developed recently to overcome the problems associated with
traditional low-pressure technology. This type of lamp contains a mercury amalgam, and typically
up to 120mg of mercury is contained in each lamp. The Amalgam lamp is typically very long, and
not unusually can be more than 1.5 m (5 feet) in length. Once switched on, the Amalgam lamp
output is not effected by water temperature fluctuations, however the large size of the lamp does
mean that they can take up to 800 seconds to get to full power, and the warm up time is
temperature dependant, as the successive strikes below illustrate.
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Ultraviolet ApplicationsResearch is now being undertaken to verify the effect that shorter wavelength ultraviolet light
has on the other cell membrane of the organism. This shorter wavelength is more energetic and
is absorbed by the organisms outer membrane. A lethal insult is effected, which means that the
cell is unable to effectively regulate osmotic pressure. This effect coupled with the fusing of the
DNA means that UV is a simple, elegant disinfectant and one that will increasingly replace the
more traditional chemical techniques.
The Production of Ultraviolet LightUltraviolet light is most typically generated from a low pressure or a medium pressure lamp.
These lamp types are different in character and performance, and are described below:
Low Pressure ultraviolet lamps are the most common lamp type and are the oldest source of
ultraviolet light. The consist of a quartz envelope that separates two tungsten filaments. The lamp
is evacuated to
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contaminants that have entered the aquifer, such as NDMA or MTBE. In each case, the ability of a
monitoring system to measure the fluence being emitted by the lamp allows the operators to
have confidence in the integrity of the system. Hanovia systems are designed to be fail safe and
the control protocols that are used will not allow untreated water of effluent to be sent forward.
The dedicated ultraviolet monitor measures the output from each lamp. The monitors are sealed
and do not allow any operator adjustment. The Hanovia ultraviolet monitor measures intensity in
absolute units of mw/cm2. An online transmittance monitor measures the transmittance of the
fluid being treated, and not unusually surface water can have a very high fluctuation in
transmittance. Use is made of data logging facilities to demonstrate the adequacy of treatment,
and to provide a permanent record of disinfection. This transparency is often required by a
regulator or by those further up the supply chain to demonstrate that the water used to make
product or water used as a part of the manufacturing process in wholesome.
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