Chemistry Pool ERT

8/10/2019 Chemistry Pool ERT

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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.php


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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.html


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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.


14/15

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


15/15

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.

http://www.usaswimming.org/ViewMiscArticle.aspx?TabId=1755&mid=7713&ItemId=3552

http://elecro.co.uk/shopcontent.asp?type=Guide_To_Swimming_Pool_Water_Chemistry
http://www.usaswimming.org/ViewMiscArticle.aspx?TabId=1755&mid=7713&ItemId=3552http://www.usaswimming.org/ViewMiscArticle.aspx?TabId=1755&mid=7713&ItemId=3552http://elecro.co.uk/shopcontent.asp?type=Guide_To_Swimming_Pool_Water_Chemistryhttp://elecro.co.uk/shopcontent.asp?type=Guide_To_Swimming_Pool_Water_Chemistryhttp://elecro.co.uk/shopcontent.asp?type=Guide_To_Swimming_Pool_Water_Chemistryhttp://www.usaswimming.org/ViewMiscArticle.aspx?TabId=1755&mid=7713&ItemId=3552

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