معالجة مياه حمامات السباحة (انواع الكلور المستخدم /الجرعات اليومية /الجرعات الطارئة)

Swimming pool chemistry

A swimming pool system lacks the three purifiers that protect water quality in natural bodies of water:

1. Aeration, the addition of oxygen to the water from the continuous flow of water through lakes, streams and rivers.

2. Dilution of sediment from continuous water flow.

3. Prevention of contaminant build-up by water flow, movement and dilution, and biodegradation by aquatic organisms.

As a swimming pool lacks these purifiers, it is subject to rapid stagnation.

Also, it is usually contaminated with bacteria, algae, dust and dirt, and organic materials from swimmers wastes, sweat, urine and even faeces.

A swimming pool must be disinfected as part of a total system to remove bacteria, algae and organic contaminants leaving water with acceptable clarity and colour.

Volume of a swimming pool length × width × depth. If length 25 m, width 10 m, depth 1 m to 2 m (average 1.5 m),

then volume = 25 × 10 × 1.5 = 375 cubic metres (375 000 litres).

Chlorine and water

When chlorine is added to water, a mixture of hypochlorous acid, HOCl, the active sanitizing species, and hydrochloric acid, HCl, forms within seconds at room temperature.

Cl₂ (aq) + 2H₂O <=> HOCl + Cl^- + H₃O⁺

chlorine + water <=> hypochlorous acid + chloride ion + hydronium ion

In dilute solution and pH > 4, the equilibrium displaces to the right, and little Cl₂ exists in solution.

The chlorine added to swimming pool water does not produce a concentrated solution of a strength to yield such a low pH.

However, the oxidizing property of the added chlorine is in the HOCl formed and produces the main disinfecting action of added chlorine solutions.

Hypochlorous acid dissociates almost instantaneously into hydrogen and hypochlorite ions.

The reaction is reversible. The dissociation depends on the pH and temperature.

Hypochlorous acid exists in a pH dependent equilibrium with hypochlorite ion (OCl^-) in swimming pool water.

H₂O + HOCl <=> H₃O⁺ + OCl^- water + hypochlorous acid <=.> hydronium ion + hypochlorite ion

Chlorination of swimming pools

: Distribution of HOCl and OCR^-in water at pH levels

Most swimming pools are sanitized with chlorine-based compounds.

When chlorine compounds are dissolved in water, hypochlorous acid forms, which does the actual sanitizing.

In most cases, the non-chlorine part of the chlorine compound serves no other purpose than to hold the chlorine until the product dissolves.

The three categories of sanitizer contain chlorine in different forms.

All three sanitizers are compatible and effective with other chemicals in swimming pool water.

Each will do its function without causing objectionable tastes, odours or colours in the water, if properly applied.

Swimming swimming pool chlorine may be calcium hypochlorite or sodium hypochlorite.

Chlorine gas in swimming pools

Chlorine is a member of the halogen family of sanitizers.

Its use in swimming pools is in the form of a gas, as a liquid, in granular or tablet forms.

When added to swimming pool water it acts as an oxidizer, sanitizer, disinfectant and biocidal agent.

Chlorine gas is referred to as having 100% available chlorine, is relatively low cost and is used in public swimming pools and most bulk drinking and waste water treatment systems.

However, it is a gas that must be delivered in bulky metal cylinders and has to be applied to the water through sophisticated metering systems operated by trained personnel.

It is highly corrosive, toxic, and very acidic because of the H₃O⁺ and Cl^-.

Operators of regulated public swimming pools may be required to install separate feeding equipment to add soda ash to neutralize the acidity from the chlorine gas.

If chlorine gas were the only chemical available to disinfect water, there would be few home swimming pools.

Inorganic hypochlorites

Hypochlorites including calcium hypochlorite, sodium hypochlorite and lithium hypochlorite are used as a disinfectant, sanitizer, bactericide, algicide and oxidizer in swimming pool water.

Calcium hypochlorite is also used as a disinfectant in drinking water.

Calcium hypochlorite, Ca(OCl)₂

Calcium hypochlorite, Ca(OCl)₂, 65% available chlorine, white granular powder or compressed into pucks, pH 11.8, also contains 5 to 8% of insoluble material, which can cause cloudy water.

A by-product of this reaction is the calcium ion, (Ca²⁺), a major component of water hardness, and a contributor to scaling tendencies in the swimming pool.

Ca(OCl)₂ + H₂O Ca²⁺ + 2OCl^- + H₂O

calcium hypochlorite + water calcium ion + hypochlorite ion + water

Chlorinated isocyanurates, cyanuric acid, (CNOH)₃

Chlorinated isocyanurates, stabilized chlorine, are a group of chlorine swimming pool sanitizers that contain stabilizer (cyanuric acid or isocyanuric acid) as the granular form dichlor 56% available chlorine and the tablet or stick form trichlor 90% available chlorine, the latter usually used in a chlorine feeder.

Chemical feeder: a device that dispenses chemicals into the swimming pool water at a predetermined rate.

Some provide chlorine or bromine while others add cyanuric acid, (CNOH)₃, also called conditioner and stabilizer.

A granular chemical added to the swimming pool water, which provides a shield to chlorine for

protection from the UV radiation from the sun. It is also found in dichlor / trichlor products.

Dichlor

: Trichloroisocyanuric acid, TCCA, C₃Cl₃N₃O₃, white crystalline powder, disinfectant, bleaching agent

"Dichlor" is the common name for dichloroisocyanuric acid, C₃HCl₂N₃O₃, or the active ingredient in dichlor cleansing powder sodium dichloroisocyanurate C₃Cl₂N₃NaO₃.

Dichlor is a quick dissolving chlorine compound made up of chlorine and cyanuric acid (stabilizer) and has a pH of 6.9.

Shock treatment with dichlor is not recommended as it may result in over stabilization and chlorine lock.

If dichlor is used, a monthly check of the cyanuric acid level is recommended, to prevent over stabilization and chlorine lock.

18.7.2.5 Chlorinating concentrates

Both the granular and tablets forms are based on cyanuric acid, (CNOH)₃, the central structure of which is composed of alternating carbon and nitrogen atoms.

In the granular form two atoms of chlorine are added, giving an available chlorine of 56%.

Because this is a sodium salt, it has excellent solubility at 26.1% w / v and a nearly neutral pH of 6.7.

It may be added directly to the swimming pool by hand broadcasting or it can be pre-dissolved and added as a hypochlorite solution.

The tablet form contains three atoms of chlorine, giving it 90% available Cl₂.

It has a relatively low pH of 2-3.

Because of its high available chlorine content, much less needs to be added.

So it, too, has a minimal impact on pH.

Its low solubility of 1.2%. w / v makes it ideal for use in tablet form in continuous feeding systems.

This trichloro product should not be added directly to the swimming pool in either its tablet or granular form.

Its high available chlorine, slow solubility and acidic pH give it the potential to bleach, or pit any swimming pool surfaces that it contacts.

Both products are free of insoluble residues, produce a minimal impact on pH and do not contribute to water hardness or scaling.

After the chlorine has been consumed in performing the sanitizing functions, the cyanuric acid remains dissolved in the water to provide maximum stabilization for the free chlorine residual.

Secondary chemical treatment with substances that control pH and buffer the swimming pool, is also needed for optimum swimmer comfort.

Depending on swimming pool conditions, secondary treatment might include decolorizing, additional algicide, and chemicals to adjust mineral levels (hardness) or retard evaporation.

Chlorinating tablets, chlorinating concentrate

Pool chlorinating concentrates provide the effectiveness of HOCl, the ease and convenience of concentrated solids, and the benefits of stabilization, to provide outstanding water quality with minimum effort and expense.

Granular compounds react with water to produce the same active sanitizing species, hypochlorous acid. Therefore, it is an effective bactericide and algicide that will oxidize organic contaminants.

Tablets react similarly, but produce three units of hypochlorous acid.

Both the granular compounds and tablets have a by-product, cyanuric acid, which is supposed to stabilize free chlorine residual without interfering with its sanitizing effectiveness.

However, the binding action of cyanuric acid reduces the concentration of free available chlorine and demonstrably reduces sanitizer efficiency.

Pool owners who use cyanuric acid must have higher free residual chlorine to compensate for this fact so that sanitizer efficiency is maintained.

Some Australian States have banned the use of cyanuric acids in commercial installations. So to describe cyanuric acid products as a conditioner is misleading.

Hypochlorous acid, HOCl

Hypochlorous acid, HClO, is the active form of chlorine in swimming pool water.

Hypochlorous acid is a weak acid and dissociates poorly below pH 6, so it exists mainly as HOCl at low pH. Between pH 6.0 and 8.5, a very sharp change occurs from undissociated HOCl to almost complete dissociation.

At 20^oC and pH greater than 7.5, hypochlorite ions, OCl^-, predominate. HOCl is about 100 times more effective as a sanitizer than OCl^- because the negative charge on the OCl^- ion hinders it entering living cellular structures and oxidizing the contents.

Free chlorine in waters.

Free chlorine (free available chlorine, free residual chlorine, residual chlorine) is the amount of chlorine left in the swimming pool water after the chlorine demand has been satisfied.

It is the amount of free chlorine in the swimming pool water that is available to oxidize, sanitize or disinfect the water.

Free chlorine is active chlorine and is not combined with any other molecule, e.g. ammonia.

It is free to kill bacteria and algae in a swimming pool and is the chlorine available to do its job of sanitizing the water.

A portion of the free available chlorine is present as hypochlorous acid, which reacts to destroy organic material in the swimming pool water.

The standard method for determining free chlorine is to measure the amount of oxidant by its ability to liberate iodine from acidified iodide solution.

Titrate a water sample with a standard iodide solution and detect the iodine released by the blue colour formed with a fresh starch indicator.

Find the amount of iodine released by back titration with sodium thiosulfate, hypo.

The reagent is only oxidized to tetrathionate by the iodine. With chlorine it is oxidized to sulfate.

HOCl + 2I^- + H₃O⁺ --> Cl^- + I₂ + 2H₂O

hypochlorous acid + iodide ion + hydronium ion --> chloride ion + iodine + water

I₂ + 2S₂O₃^2- --> S₄O₆^{2 -}+ 2I^-

iodine + thiosulfate ion --> tetrathionate ion + iodide ion

Devices called rapid test meters can be used to test for chlorine and pH.

With a DPD test kit, DPD1 shows free available chlorine and DPD3 shows total chlorine. The difference, if any, is the level of combined chlorine.

Available chlorine

Available chlorine content is the term used to compare the amount of oxidizing power that products containing chlorine have compared to gas chlorine (Cl₂).

It permits easy comparison of relative values of chlorine compounds.

Available chlorine is the amount of free chlorine that is available to sanitize or disinfect the water.

It is also called Residual Chlorine and Free Available Chlorine.

When chlorine gas dissolves in water, it forms hydrochloric acid and hypochlorous acid.

Since only the hypochlorous acid sanitizes, only half the chlorine added to the water is usable.

Chlorine gas is defined as 100% available chlorine, so compounds for which all the chlorine in solution is active will have percentages twice the value based on composition. Ca(OCl)₂, which is 99.2% available chlorine for the pure material may be quoted as 100% available chlorine.

It produces two moles of active chlorine compared to only one mole from Cl₂.

However, it has more than twice the molecular mass, a ratio of 143: 71.

So, on a mass basis, both chlorine gas and calcium hypochlorite are equally effective.

Materials releasing other oxidizing agents when dissolved in water have available chlorine defined in the same manner.

Approximate percentage available chlorine of substances added to swimming pool water are as follows:

Cl₂ chlorine gas 100% (by definition)

Bleaching powder (chloride of lime) 35%

Ca(OCl)₂ calcium hypochlorite 99%, commercial products 70%

NaOCl, sodium hypochlorite 95% (solution 100%)

Commercial bleach (industrial product) 12%

Commercial bleach (household product) 3%

ClO₂, chlorine dioxide 263%

NH₂Cl, monochloramine 138%

NHCl₂, dichloramine 165%

CONClCONClCONCl, C₃Cl₃N₃O₃, trichloroisocyanuric acid 91%

CONClCONClCONH, dichloroisocyanuric acid 72%

CONClCONClCON^-Na^+, sodium dichloroisocyanurate 64%

Dissolve chlorine in swimming pool water by electrolysis

Add common salt to water at concentration of approximately 4000 ppm to generate hypochlorous acid continuously with an electrolysis cell.

The water will gradually become basic so you must add an acid to keep the pH between 7.2 and 7.8 for optimum swimmer comfort and to maintain sanitizer efficiency.

Cathode (-) reaction: 2e^- + 2H₂O 2OH^- + H₂ (g)

water hydroxyl ion + hydrogen

Anode (+) reaction: 2Cl^- Cl₂ (g) + 2e^-

chloride ion chlorine

Overall Reaction: 2Cl^- + 2H₂O Cl₂ (g) + H₂ (g) + 2OH^-

chloride ion + water chlorine + hydrogen + hydroxyl ion

Swimming pool water and pH

Lower the pH of the swimming pool below pH 7 to increase the oxidizing strength of the HOCl but more acidic solutions will corrode many components For tiled swimming pools, the recommended pH range is pH 7.4-8.0 and you must add about 200 mg / L calcium chloride to offset removal of calcium salts from the grouting between the tiles.

A test for chlorine in water may measure the free residual chlorine or the free residual chlorine plus the chloramines, which are termed combined chlorine.

The lower the pH, the more

readily chloramines form. Above pH 7 few chloramines form, so keep the pH above 7.

Superchlorination, shock treatment, breakpoint chlorination

: Chlorine dosage and residual chlorine for breakpoint chlorination

Superchlorination is adding 7 to 10 times the normal dose of chlorine to the swimming pool water to destroy ammonia, nitrogen, chloramines and other contaminants.

Shock treatmen is adding large amounts of an oxidizer such as chlorine, hydrogen peroxide or potassium peroxymonosulfate to the swimming pool water to destroy ammonia and nitrogen compounds, chloramines and other contaminants.

Superchlorination is used to get rid of chloramines.

When HOCl is added to pool water at first chloramines form by reaction with nitrogen compounds from humans.

With increased concentration of HOCl the chloramines are destroyed as in the the following equation with the products being off-gassed.,

But with excess HOCl, the chlorine concentration in the water rises as chlorine no longer combines with organic compounds.

2NH₃ + 3HOCl N₂ (g) + 3HCl + 3H₂O

ammonia + hypochlorous acid nitrogen + hydrochloric acid + water

When chlorine in its various forms is added to water, it is used up in oxidizing any material for which it is a sufficiently strong oxidizing agent, e.g. iron II, sulfide, nitrite.

Next, chloramines, called combined chlorine, form from reactions of chlorine with organic nitrogen compounds.

The breakpoint when further addition of chlorine is not used to oxidize nitrogenous compounds, but remains as free available chlorine.

When you superchlorinate or shock treat your swimming pool, the goal is to reach a high enough level of free chlorine to break apart all molecular bonds, specifically the combined chlorine molecules, ammonia or nitrogen compounds and to completely oxidize all organic matter. If you add enough chlorine to achieve this breakpoint chlorination, chlorine added after that point will be free available chlorine.

Superchlorination refers to further additions of chlorine that will remain in the water as residual chlorine to react with any material later added to the swimming pool water.

Maintain a free chlorine residual at all times to achieve sparkling clear, sanitary swimming pool water by periodic super chlorination of the swimming pool water.

When chloramines are removed, better efficiency of chlorine is achieved. More of the chlorine residual can then exist as the free or active form, rather than as the less effective combined form.

You can use potassium monopersulfate for strong oxidation reactions to oxidize any chloride ion back to chlorine.

Superchlorination is the remedial action that should be taken when the DPD test detects the presence of 0.2 ppm or greater of combined chlorine in the swimming pool.

Superchlorination simply involves the addition of 5 to 10 × normal daily dose of chlorine.

Super chlorination should be routinely performed on very hot days under heavy loads after heavy rains or if DPD test shows combined chlorine in excess of 0.2 ppm combined chlorine.

Superchlorination is a remedial action and is recommended to remove gross amounts of chloramines,

correct eye and nasal discomfort, or destroy a visible algae growth. It also eliminates waiting, vacuuming, scrubbing and back washing to remove algae that will have appeared while chloramines accumulated.

However, although it works well, eventually if you keep loading chemicals and contaminants in a swimming pool you will have problem

[ltr]          [/ltr]
[ltr]           MICROBIOLOGICAL PARAMETERS[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]   Parameter                         Standard[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]Fecal coliforms                  <1 CFU/100 ml[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]Escherichia coli                 <1 CFU/100 ml[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]Pseudomonas aeruginosa           <1 CFU/100 ml[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]Staphylococcus aureus            <30 CFU/100 ml[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]________________________________________________________[/ltr]

[ltr]           PHYSICOCHEMICAL PARAMETERS[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]   Parameter                         Standard[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]Alkalinity                         60 to 150 mg/l CaCO₃[/ltr]
[ltr]                                                     [/ltr]
[ltr]Chloramines        indoor pools    ≤0.5 mg/l [/ltr]
[ltr]                   outdoor pools   ≤1.0 mg/l[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]Residual disinfectant[/ltr]
[ltr]   Free chlorine: indoor pools    0.8 to 2.0 mg/l [/ltr]
[ltr]                   outdoor pools   0.8 to 3.0 mg/l [/ltr]
[ltr]   Total bromine                   2.0 to 5.0 mg/l [/ltr]
[ltr]   Ozone                           0.0 mg/l[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]Hardness                           150 to 400 mg/l CaCO₃[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]pH                                 7.2 to 7.8[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]Turbidity                          ≤1.0 NTU[/ltr]
[ltr]________________________________________________________            [/ltr]

[ltr]the following physicochemical parameters, at the corresponding minimum frequencies:[/ltr]
[ltr]________________________________________________________[/ltr]

[ltr]                           SAMPLINGS[/ltr]
[ltr]_________________________________________________________[/ltr]

[ltr]          Parameter                        Frequency[/ltr]
[ltr]_________________________________________________________[/ltr]

[ltr]Alkalinity                     Once a week[/ltr]
[ltr]_________________________________________________________[/ltr]

[ltr]Residual disinfectant          Before the opening of the pool, [/ltr]
[ltr](only the measurement of       after closing and every 3 [/ltr]
[ltr]disinfectants used is          hours during operation[/ltr]
[ltr]required)[/ltr]
[ltr]_________________________________________________________[/ltr]

[ltr]Chloramines (only when         Before the opening of the pool,[/ltr]
[ltr]chlorine is used)              after closing and halfway[/ltr]
[ltr]                               through operation[/ltr]
[ltr]_________________________________________________________[/ltr]

[ltr]pH                             Before the opening of the pool,[/ltr]
[ltr]                               after closing and halfway[/ltr]
[ltr]                               through operation[/ltr]
[ltr]_________________________________________________________[/ltr]

[ltr]Clarity                        Before the opening of the pool,[/ltr]
[ltr]                               after closing and halfway[/ltr]
[ltr]                               through operation[/ltr]
[ltr]_________________________________________________________[/ltr]

[ltr]Temperature                    Before the opening of the pool,[/ltr]
[ltr]                               after closing and halfway[/ltr]
[ltr]                               through operation[/ltr]
[ltr]_________________________________________________________ [/ltr]

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