كيماويات تطهير وتعقيم حمامات السباحة مميزاتها وعيوبها واوقات استخدامها

DISINFECTION OF POOL WATER

مجموعة تكنولاب البهاء جروب

عميد دكتور

بهاء بدر الدين محمود

استشارى معالجة مياه 01117156569

A proper balance of the previously described water chemistry factors will provide water that will not damage pool components and is non-irritating to swimmers.

It is then necessary to provide for disinfection of the water to prevent the spread of disease organisms from person to person and prevent unwanted growth of bacteria and algae in the pool.

Chlorine

The most commonly used disinfectant for swimming pools is chlorine.

In its elemental form chlorine is a heavy greenish yellow gas which is so toxic that is has been used as a weapon in chemical warfare.

Because of the extremely high potential for injury or death from improper use of chlorine gas, a number of chlorine compounds have been formulated to provide chlorine in forms that can be handled and used safely by swimming pool operators.

The following forms of chlorine are commonly used in swimming pools:

Gas Chlorine: 100% available chlorine
Advantages:

Cheapest form of chlorine

No residue from carriers

Disadvantages:

Extremely dangerous

Special room needed for chlorine

Feed equipment is expensive

Special training and safety equipment needed

Lowers pH, must constantly add pH increaser

Because of the special hazards associated with the use of gaseous chlorine, its use has been
prohibited at public swimming pools .

Calcium Hypochlorite:

granular or pelletized 65% available chlorine

Advantages:

Relatively cheap

Can be mixed into solution for feed pumps

Can be used in some specially designed erosion feeders

Disadvantages:

Not stabilized - may lose strength if not tightly covered.

Does not dissolve completely - leaves residue

Does not dissolve completely - leaves residue

High pH (11.7) raises pH of pool

Highly reactive - may cause fires

WARNING - do not use in closed tablet feeders designed to use other forms of chlorine

Sodium Hypochlorite:

Liquid bleach 12.5% available chlorine

Advantages:

Next to gas is the cheapest chlorine available

No dissolving required - no residue

Can be used with chemical feed pumps

Disadvantages:

Bulky and heavy

Not stabilized-loses strength rapidly

High pH (10-13) raises pH of pool

Trichloroisocyanuric Acid:

sticks or tablets 90% available chlorine

Advantages:

Stabilized - chlorine doesn't dissipate

Easy to handle

Low cost, low maintenance erosion feeders

Highly concentrated - 90% available chlorine

Dissolves completely - very little residue

Disadvantages:

Cost slightly higher

Lowers pH - pH 2.8

Lowers total alkalinity

May elevate cyanuric acid levels

Not suitable for supeprchlorination

Other forms of chlorine less commonly used are

lithium hypochlorite,

potassium dichloroisocyanuric acid,

and sodium dichloroisocyanuric acid.

Free Chlorine Residual is the amount of chlorine in the pool which has not reacted with substances other than water.

It is the chlorine which is available to disinfect pool water and oxidize organic substances.

Free chlorine residual should be maintained between 1 and 3 ppm.

Combined Chlorine is chlorine in the pool which has reacted with substance other than water and is no longer available in its free state.

Some combined chlorines are bactericides but they contribute little to the disinfection process.

Chlorine combined with ammonia produces chloramines which cause eye irritation and an objectionable chlorine odor.

For this reason combined chlorine residual should be kept to a minimum preferably below 0.2 ppm.

Total Chlorine residual is the concentration of free chlorine plus combined chlorine.

To determine combined chlorine residual test for free chlorine and total chlorine.

Total chlorine - free chlorine = combined chlorine

Breakpoint Chlorination is the process by which combined chlorine and some organics are "burned out" of the pool by addition of large amounts of chlorine.

The reaction of chlorine with ammonia to form chloramines occurs in several stages with free chlorine consumed at each stage.

If enough chlorine is added to the water the total chlorine residual will rise to a point that forces the reaction of chlorine with ammonia to go rapidly to completion.

Compounds of nitrogen and chlorine are released from the water and the apparent residual chlorine decreases.

The point at which the chlorine residual suddenly drops is called the breakpoint.

When enough chlorine is added to pass the breakpoint, combined chlorine compounds disappear, eye irritation potential and chlorine odors disappear, and the chlorine remaining in the water is all in the free state.

Superchlorination:

In order to prevent buildup of chloramines in the pool it is necessary to periodically add large amounts of new chlorine in an effort to pass the breakpoint.

Public swimming pools should be supechlorinated about once a week.

The amount of chlorine needed to reach the breakpoint will vary depending on the amount of organic material introduced by bathers and on the level of free chlorine maintained in the pool.

If the amount of combined chlorine is known then the amount of new chlorine needed is ten times the amount of combined chlorine.

When combined chlorine residual is not known, superchlorination is accomplished by adding 10 ppm of new chlorine to the pool.

Ordinarily calcium hypochlorite at a dose of at least 1 lb. per 10,000 gallons is used for superchlorination.

The chart below shows the amounts of various chlorine compounds which can be used to introduce 10 ppm of chlorine to the pool.

Non-chlorine Shock Treatments Several products have been developed which oxidize organics without the use of chlorine.

Pools which use those products can accomplish the reduction of organics without closing the pool for any longer than it takes to dissolve and distribute the chemicals.

Those products are more expensive than chlorine but may be preferred where it is necessary to keep a pool open.

How pH affects free chlorine residual Chlorine reacts with water to form Hypochlorous acid (HOC1).

The reaction is different for each form of chlorine but hypochlorous acid is produced by each of those reactions and is the form in which chlorine serves best as a disinfectant.

Hypochlorous acid is a weak acid and easily dissociates to an ionized hypochlorite state as shown below.

HOC1 increasing pH-> H+ OC1-
Hypochlorous <-decreasing pH Hydrogen + Hypochlorite
Acid Ion Ion

This is important because both hypochlorous acid and the hypochlorite ion are counted as free chlorine residual on your test kit but only the hypochlorous acid portion is an effective disinfectant.

The balance between hypochlorous acid and the hypochlorite ion is affected by pH.

The higher the pH, the less hypochlorous acid present and the less effective free chlorine becomes.

At a pH of 7.2 about 66% of free chlorine is hypochlorous acid. At a pH of 7.8 only about 33% of free chlorine is hypochlorous acid.

Thus pH control is essential for maintaining the effectiveness of chlorine as a disinfectant.

Stabilizer - Cyanuric Acid

Hypochlorous acid is a highly unstable molecule which dissipates rapidly in the presence of sunlight.

This results in considerable loss of free chlorine form pools exposed to sunlight.

Proper stabilization of chlorine with cyanuric acid slows the rate of chlorine dissipation without appreciably sacrificing oxidation and disinfection activity.

Reaction of free chlorine with cyanuric acid produces a form of combined chlorine (chlorimide) which is active enough to aid disinfection and show up as free chlorine residual on your test kit.

Proper stabilization requires 30 to 50 ppm cyanuric acid. Outdoor pools should be initially treated with 40 ppm cyanuric acid.

The chart below can be used to determine the amount of cyanuric acid needed.

Cyanuric acid dissolves very slowly and is best predissolved in warm water before introducing into the pool.

If it is not predissolved it may take several days to dissolve completely.

Once added to the pool, cyanuric acid does not dissipate. It is removed from the pool only by splash out and backwash waste.

Stabilized chlorine products such as trichloroisocyanuric acid will add stabilizer to the pool and may cause a gradual rise in cyanuric acid concentration.

Excessive amounts of cyanuric acid can interfere with the disinfection process and at concentrations above 100 ppm may cause "chlorine lock" and clouding of the pool.

Cyanuric acid level is lowered by draining part of the water out of the pool and diluting the remaining water with fresh water.

Generally cyanuric acid level should be kept below 60 ppm. Stabilized forms of chlorine should not be used for superchlorination because cyanuric acid level may be increased.

Bromine

Bromine is chemically very similar to chlorine.

Bromine compounds tend to react more slowly than chlorine compounds so bromine is generally more stable and less subject dissipation in sunlight.

The dissociation of hypobromous acid into the bromine ion is less affected by pH than the corresponding reaction of chlorine.

This makes bromine active over a larger range of pH than chlorine.

Bromine will combine with ammonia to form bromamines similar to chlorine but unlike chloramines, bromamines are effective bactericides and do not produce the degree of odor and eye irritation associated with chloramines.

Bromine is less affected by high temperature and nitrogen wastes than chlorine so it is particularly attractive for use in hot water spas.

Bromine is more expensive than chlorine and has not yet received widespread acceptance by swimming pool operators.

The form of bromine most commonly used in pools and spas is the organic chemical bromo-chloro-dimethylhydantoin which contains both bromine and chlorine. It is marketed under various trade names and is generally in tablet form for use in erosion feeders..

Bromine residual should be maintained between 2 and 4 ppm.

Bromine residual is measured using the DPD #1 test used to measure free chlorine. If your test kit does not include a bromine scale then bromine residual is approximately 2.25 times the reading on the chlorine scale.

Biganide disinfectants

The only disinfectant other than chlorine and bromine which has been accepted as a primary disinfectant in public swimming pools is polyhexamethylene biguanide.

Biguanide is used at a concentration of 30 to 50 parts per million and a pH of 7.2 to 7.8 to kill germs and control algae growth.

A special test kit is needed to test the biguanide residual.

The main advantage of biguanide is the disinfectant concentration remains fairly stable so it requires less frequent adjustment than chlorine.

No automatic chemical feeder is needed.

Biguanide is not an oxidizer and will not destroy organic wastes the way chlorine and bromine do.

It must be used in conjunction with a peroxide shock treatment to prevent organic wastes from accumulating in pool water.

Biguanide is incompatible with chlorine and most algicides.

Chlorine in make-up water can cause clouding of biguanide pools.

Biguanide increases the staining potential of dissolved metals in a pool so copper based algicides, copper ion generators, and pool heaters should not be used.

Only chemicals recommended by the disinfectant manufacturers should be used.

Supplemental disinfection equipment

A variety of supplemental disinfection process equipment is being marketed for use on swimming pools.

The most common are copper/silver ion generators, ozone generators, and ultraviolet light generators.

While each process provides some disinfection activity, they are not accepted as primary disinfectants in public swimming pools because they are either too slow or do not provide a disinfectant residual.

Supplemental disinfection equipment, if used, must be used in conjunction with a free chlorine or bromine residual.

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