1. Determination of free active chlorine (iodometric method)

When introduced into water, chlorine is hydrolyzed, forming hypochlorous and hydrochloric acids.

Cl 2 + H 2 O HOCl + HCl

The resulting hypochlorous acid dissociates into hypochlorite ion OCl - and hydrogen ion H +.

Chlorine is widely used for the disinfection of wastewater in circulating water consumption systems, as well as before being discharged after treatment into the sewer or water body. When dumping DM into a reservoir after complete biological treatment, the content of residual free active chlorine should not exceed 2.5 mg / dm 3.

The essence of the method... When the analyzed water is acidified and potassium iodide is added to it, all of the above substances release iodine:

Cl 2 + 2J - \u003d J 2 + 2Cl -

НClО + 2J - + H + \u003d J 2 + Cl - + H 2 O

ClO - + 2H + + 2J - \u003d J 2 + Cl - + H 2 O

NH 2 O + 2H + + 2J - \u003d J 2 + NH 4 + + Cl -

The released iodine is titrated with sodium thiosulfate in the presence of starch. The content of active chlorine is expressed in mg / dm 3 in terms of chlorine. With regard to hypochlorous acid, hypochlorite ions, monochloramine, this expression of the analysis results is arbitrary, since one mole of these substances releases two iodine atoms and, therefore, corresponds to 2 moles of active chlorine, i.e. the results are too high.

Reagents

Sodium thiosulfate, 0.01 N. solution;

Potassium iodide, acetic acid, 30% solution;

Starch, 0.5% solution.

Determination progress. 50 ... 100 ml of analyzed water is poured into a conical flask equipped with a ground glass stopper, 0.5 g of potassium iodide is added and 10 ml of acetic acid is added. After 5 min, the liberated iodine is titrated with 0.01 N. sodium thiosulfate solution (with an active chlorine content above 1 mg / dm 3) or 0.005 N. sodium thiosulfate solution (with an active chlorine content of 0.1 to 1 mg / dm 3). At the end of the titration, add 1-2 ml of starch solution.

where a - the volume of sodium thiosulfate solution used for titration, cm 3;

TO - correction factor for bringing the concentration of sodium thiosulfate solution to exactly 0.01 N;

V - the volume of analyzed water, cm 3;

0.355 - the amount of chlorine equivalent to 1 ml of 0.01 N. sodium thiosulfate solution, mg.

"Free active chlorine" and "bound active chlorine"

Substances, the combined concepts of "active chlorine" - are strong oxidizing agents Cl 2; HClO and ClO -, and "bound chlorine" are relatively weak oxidants NH 2 Cl; NHCl 2 and NCl 3 formed during the chlorination of waste water containing ammonium ions, ammonia. The subsequent behavior of each of these substances when mixing chlorinated wastewater with other wastewater, as it passes through pipes, is significantly different, so sometimes further separations are necessary.

With respect to "free active chlorine", they are usually satisfied with the determination of the total content: Cl 2 + HClO + ClO -, and to find the content of each of the chloramines, it is necessary to carry out the determinations as follows.

The essence of the method... In a neutral medium (pH \u003d 6.9) free active chlorine (Cl 2; HClO and ClO -) instantly react with the indicator N, N / - diethyl-n-phenylenediamine, forming red compounds.

Monochloramine and dichloramine do not react with the indicator under these conditions. Free active chlorine is titrated with a solution of Mohr's salt. Then a very small amount of potassium iodide is introduced into the solution, the catalytic action of which leads to a rapid interaction of monochloramine and an indicator with the formation of the same red color, which is titrated with a solution of Mohr's salt. Then, potassium iodide is introduced in excess, and dichloramine enters into the reaction, which is determined by the same titration. If the wastewater contains nitrogen trichloride NCl 3, it will be partially identified as dichloramine NHCl 2.

The first determination must be carried out very quickly at pH 6.9 (or slightly higher) so that monochloramine NH 2 Cl does not enter into the reaction. It takes 2 minutes for it to fully react; if the solution has an elevated temperature - 1 min.

Reagents

N, N-diethyl-n-phenylenediamine, sulfate salt. Dissolve 0.15 g of diethyl-n-phenylenediamine sulfate salt in distilled water that does not contain chlorine, into which 2 cm 3 of a 10% (by volume) solution of sulfuric acid and 2.5 cm 3 of a 0.8% solution of EDTA are added ... The solution is diluted to 100 cm 3 and stored in an iron glass bottle;

Phosphate buffered saline, pH \u003d 6.9. 48.4 g of Na 2 HPO 4 are dissolved in distilled water. 2H 2 O and 30 g KH 2 PO 4, add 100 cm 3 of a 0.8% EDTA solution and dilute to 1 dm 3;

Standard solution of Mohr's salt Fe (NH 4) 2 (SO 4) 2. 6H 2 O, 1 cm 3 of which corresponds to 0.1 mg of chlorine. Distilled water is preliminarily injected with 1 cm 3 of 25% (by volume) sulfuric acid, then 1.106 g of Mohr's salt is dissolved in it and diluted to 1 dm 3;

Potassium iodide. To prepare a 0.5% solution, dissolve 0.5 g of KI in 100 cm 3 of distilled water. To prepare a 10% solution, 10 g of KI is dissolved in 100 cm 3 of distilled water.

Determination progress.

1. Determination of free active chlorine. First, 5 cm 3 of a phosphate buffer solution (pH \u003d 6.9) and 5 cm 3 of a solution of diethyl-n-phenylenediamine sulfate salt are poured into a titration flask equipped with a ground stopper, mix, 100 cm 3 of the analyzed sample is introduced and immediately titrated with a solution Mohr's salts until completely discolored.

2. Determination of monochloramine. After determination of free active chlorine, 1 cm 3 of a 0.5% solution of potassium iodide is added to the solution, stirred and titrated with a solution of Mohr's salt until complete discoloration.

3. Determination of dichloramine. After determining monochloramine, add 10 cm 3 of a 10% solution of potassium iodide, mix, let stand for 2 minutes and titrate with a solution of Mohr's salt until discoloration.

It is assumed that the total concentration of active chlorine does not exceed 4 mg / dm 3. Otherwise, take a smaller sample volume, and inject distilled water for dilution before introducing the analyzed sample into the preparatory mixture.

, (2)

where V 1 is the volume of Mohr's salt solution consumed in the first, second or third titration, cm 3;

V is the volume of the sample taken for analysis, cm 3;

0.1 is the amount of active chlorine corresponding to 1 cm 3 of Mohr's salt solution, mg.

2. Determination of chlorine content

Treatment of wastewater with chlorine or a solution of bleach is one of the most common, relatively cheap ways of disinfecting and purifying wastewater from contamination with organic substances. But since usually DM contain substances reacting with chlorine and substances interacting with it very slowly or incompletely, and organic substances that are not oxidized by chlorine at all, the determination of the oxidizability of wastewater does not provide sufficient data to draw conclusions about how the water will be chlorinated. Therefore, before deciding on the purification of dry matter by chlorination, it is specially investigated. In this case, it is necessary to determine the speed at which the reactions between the substances contained in the water and chlorine (oxidation and substitution reactions with chlorine) take place, whether they reach the end, what excess chlorine added is required in order for the reaction to proceed to the desired degree in a given period of time. These questions can be answered by determining the chlorine capacity of waste water using the so-called diagrammatic method.

Chlorine treats both filtered or settled water, and together with the suspensions it contains.

Determination progress. A number of portions of the analyzed wastewater of the same volume are selected and placed in vessels with ground-in stoppers, in which they are treated with different amounts of chlorine water (or a solution of bleach), the first portion is the smallest amount, the second portion is 2-3 times larger, etc. etc. It is recommended to carry out two series of such experiments, varying the duration of treatment. The first series of CB samples are treated with varying amounts of chlorine for a very short time, for example 5 minutes. The results of these experiments show the presence of substances in the DM that quickly react with chlorine. The second series of samples is processed for as long as the chlorination process will take place in the proposed treatment plant (usually 1-2 hours). After the scheduled time has elapsed, the amount of unreacted chlorine in each solution is determined (by the iodometric method) and a diagram is plotted by plotting the amount of chlorine introduced into each solution in order on the abscissa axis, starting from the smallest, and on the ordinate - the corresponding amount of the remaining chlorine, and combine the obtained points of the curve (Fig. 1).

**.

* Within the territory of Russian Federation GOST R 51593-2000 is in force.

** On the territory of the Russian Federation, GOST R 51232-98 is in force.

Chloroform (trichloromethane).

Salicylic acid.

Glacial acetic acid according to GOST 61.

Potassium dichromate according to GOST 4220.

Soluble starch according to GOST 10163.

Sodium carbonate crystalline according to GOST 84.

Sodium sulfate (sodium thiosulfate) according to GOST 27068.

All reagents used in the analysis must be of the "analytical grade" qualification (analytical grade).

Porcelain evaporating cups in accordance with GOST 9147.

All reagents used for analysis must be of analytical grade (analytical grade).

Potassium phosphate monosubstituted according to GOST 4198, x. h.

Disubstituted sodium phosphate anhydrous according to GOST 11773.

Trilon B (complexone III, disodium salt of ethylenediaminetetraacetic acid) according to GOST 10652.

Distilled water in accordance with GOST 6709.

Diethyl paraphenylenediamine oxalate or sulfate.

All reagents used for analysis must be of the "analytical grade" qualification (analytical grade).

4.3 . Preparationto analysis

4.3.1. Preparation of standard Mohr's salt solution

1.106 g Mohr's salt Fe (NH 4) 2 (SO 4) 2 6H 2 O dissolved in distilled water, acidified with 1 cm 3 of 25% sulfuric acid solutionH 2 SO 4 and bring freshly boiled and cooled distilled water to 1 dm 3. 1 cm 3 of the solution corresponds to 0.1 mg of active chlorine. If the determination is carried out in 100 cm 3 of water, then the amount of milliliters of Mohr's salt used for titration corresponds to mg / dm 3 of chlorine, or monochloramine or dichloramine. The solution is stable for a month. Store it in a dark place.

4.3.2. Preparation of phosphate buffered saline

To 2.4 g of sodium phosphate disubstituted Na 2 HPO 4 and 4.6 g of monosubstituted potassium phosphate KH 2 PO 4, 10 cm 3 of a 0.8% solution of Trilon B are poured and brought to 100 cm 3 with distilled water.

4.3.3. Preparation of the indicator diethylparaphenylenediamine (oxalate or sulfate) 0.1% solution

0.1 g of diethyl paraphenylenediamine oxalate (or 0.15 g of the sulfate salt) is dissolved in 100 cm 3 of distilled water with the addition of 2 cm 3 of a 10% sulfuric acid solution. The indicator solution should be stored in a dark glass bottle.

4.4 . Analysis

4.4.1. Determination of free chlorine content

In a conical flask for titration, 5 cm 3 of a phosphate buffer solution, 5 cm 3 of an indicator solution of diethyl paraphenylenediamine oxalate or sulfate are placed and 100 cm 3 of analyzed water is added, the solution is stirred. In the presence of free chlorine, the solution turns pink; it is rapidly titrated from a microburette with a standard Mohr's salt solution until the color disappears, stirring vigorously. The consumption of Mohr's salt used for titration ( A,cm 3), corresponds to the content of free chlorine, mg / dm 3.

If the analyzed water contains significant amounts of free chlorine (more than 4 mg / dm 3), less than 100 cm 3 of water should be taken for analysis, since large amounts of active chlorine can completely destroy the indicator.

4.4.2. Determination of monochloramine content

A crystal (2 - 3 mg) of potassium iodide is added to the flask with the titrated solution, the solution is stirred. In the presence of monochloramine, a pink color appears instantly, whichtitrate immediately with standard Mohr's salt solution. The number of milliliters of Mohr's salt used for titration ( B, cm 3), corresponds to the content of monochloramine, mg / dm 3.

4.4.3. Determination of dichloramine content

After determining the monochloramine content, about 1 g of potassium iodide is added to the titrated solution, stirred until the salt dissolves, and the solution is left to stand for 2 minutes. The appearance of a pink color indicates the presence of dichloramine in the water. The solution is titrated with a standard Mohr's salt solution until the color disappears. Mohr's salt consumption ( FROM, cm 3) corresponds to the content of dichloramine, mg / dm 3.

4.5 . Processing results

X 3 \u003d A + B + C,

where A - content of free chlorine, mg / dm 3;

IN - the content of monochloramine, mg / dm 3;

FROM - content of dichloramine, mg / dm 3.

INFORMATION DATA

1. APPROVED AND PUT INTO EFFECT by the Decree of the State Committee of Standards of the Council of Ministers of the USSR dated 25.10.72 No. 1967

2. INTRODUCED FOR THE FIRST TIME

3. REFERENCE REGULATORY AND TECHNICAL DOCUMENTS

Designation of NTD to which the link is given

(

• A bit of history
• Water chlorination methods
• Dechlorination of water
• Electrochemical analyzers

A bit of history

The history of the use of substances containing active chlorine goes back more than two centuries. Soon after the discovery of chlorine by the Swedish chemist Scheele in 1774, it was discovered that under the influence of this gas, yellowish and ugly fabrics made of plant fibers (flax or cotton), previously moistened with water, acquire a remarkable whiteness. Following this discovery in 1785, the French chemist Claude Louis Berthollet used chlorine to bleach fabrics and paper on an industrial scale.
In the 19th century, it was discovered that "chlorine water" (as the result of the interaction of chlorine with water was called at that time) has not only whitening, but also disinfecting effect. In 1846, one of the hospitals in Vienna introduced the practice of rinsing hands with "chlorine water" for doctors. This was the first time chlorine was used as a disinfectant.
In 1888, at the International Hygiene Congress in Vienna, it was recognized that infectious diseases, including cholera, can be spread through drinking water. From that moment on, a systematic search began for the most effective way to disinfect water. And when a water supply system appeared in big cities, chlorine found a new use - to disinfect drinking water. It was first used for this purpose in New York in 1895. In Russia, chlorine was first used for disinfecting drinking water at the beginning of the 20th century in St. Petersburg.
Chlorination turned out to be the easiest and cheapest way to disinfect water, so it quickly spread throughout the world. Now we can say that the traditional method of disinfecting drinking water, adopted throughout the world (in 99 cases out of 100), is chlorination, and today hundreds of thousands of tons of chlorine are consumed annually to chlorinate water. For example, in the USA, more than 98% of water is chlorinated, and for this purpose, an average of 500 thousand tons of chlorine is used annually. In Russia - 99% and up to 100 thousand tons. In the current practice of disinfecting drinking water, chlorination is most often used as the most economical and effective method in comparison with any other known methods, since it is the only way that ensures the microbiological safety of water at any point in the distribution network at any time due to the chlorine aftereffect.

Chlorine water and hypochlorous acid

Now we know well that chlorine, reacting with water, does not form "chlorine water", but hypochlorous acid ( HClO ) - the first substance obtained by chemists that contained active chlorine.
From the reaction equation:

HClO + HCl ↔ Cl 2 + H 2 O

It follows that theoretically from 52.5 g of pure HClO you can get 71 g Cl 2 , that is, hypochlorous acid contains 135.2% active chlorine. But this acid is unstable: its maximum possible concentration in solution is no more than 30%.
The rate and direction of decomposition of hypochlorous acid depends on the conditions:
in an acidic environment at room temperature, there is a slow reaction:

4HClO → 2Cl 2 + O 2 + 2H 2 O ,

In the presence of hydrochloric acid in the solution, equilibrium is quickly established:

HClO + HCl ↔ Cl 2 + H 2 O strongly shifted to the right.

In weakly acidic and neutral solutions, hypochlorous acid decomposes:

2HClO → O 2 + 2HCl accelerated by visible light.

In slightly alkaline media, especially at elevated temperatures, a disproportionation reaction takes place with the formation of chlorate ions:

.

Therefore, in reality, aqueous solutions of chlorine contain only insignificant amounts of hypochlorous acid and there is little active chlorine in them.
In a highly alkaline environment (pH\u003e 10), when the hydrolysis of the hypochlorite ion is suppressed, decomposition occurs as follows:

2OCl - → 2Cl - + O 2

In a medium with a pH value from 5 to 10, when the concentration of hypochlorous acid in the solution is noticeably higher, the decomposition proceeds according to the following scheme:

2HClO + ClO - → ClO 3 - + 2H + + 2Cl -
HOCl + ClO - → O 2 + 2Cl - + H +

With a further decrease in pH, when there are no ClO - ions in the solution, the decomposition proceeds in the following way:

3HClO → ClO 3 - + 2Cl - + 3H +
2HClO → O 2 + 2Cl - + 2H +

Finally, when the pH of the solution is below 3, decomposition will be accompanied by the release of molecular chlorine:

4HClO → 2Cl 2 + O 2 + H 2 O

As a summary of the above, we can say that oxygen decomposition occurs at pH above 10, oxygen and chlorate decomposition at pH 5-10, chlorine and chlorate at pH 3-5, and chlorine decomposition of hypochlorous acid solutions at pH less than 3.

The bactericidal properties of chlorine and hypochlorous acid

Chlorine easily dissolves in water, killing all life in it. We found that after mixing gaseous chlorine with water in an aqueous solution, equilibrium is established:

Cl 2 + H 2 O ↔ HClO + HCl

HOCl ↔ H + + OCl -

The presence of hypochlorous acid in aqueous solutions of chlorine and the anions resulting from its dissociation OSl - have strong bactericidal properties. At the same time, it turned out that free hypochlorous acid is almost 300 times more active than hypochlorite ions ClO - ... This is explained by a unique ability HClO penetrate bacteria through their membranes. In addition, as we have already indicated, hypochlorous acid is susceptible to decomposition in light:

2HClO → 2 1 O 2 + 2HCl → O 2 + HCl

With the formation of hydrochloric acid and atomic ( singlet) oxygen (as an intermediate), which is the strongest oxidizing agent.

Reaction with proteins
Hypochlorous acid reacts with amino acids with a side amino group, replacing the hydrogen of the amino group with chlorine. Chlorinated amino acids decompose quickly if they are not contained in proteins; in proteins, chlorinated amino acids are much more durable. However, the decrease in the number of amino groups in the protein due to their chlorination increases the rate of the breakdown of the latter into amino acids.
In addition, it has been found that hypochlorous acid is an effective inhibitor of sulfhydryl groups, and in sufficient quantities it can completely inactivate proteins containing amino acids with these groups. By oxidizing sulfhydryl groups, hypochlorous acid prevents the formation of disulfide bridges, which are responsible for crosslinking proteins. It was found that hypochlorous acid can oxidize an amino acid with a sulfhydryl group 4 times: react 3 times with a -SH group giving R-SOH, R-SO 2 H and R-SO 3 H derivatives, and the 4th time with an amino group in alpha- position. Each of the first three intermediates can condense with another sulfhydryl group and cause proteins to clump together.

Reaction with nucleic acids
Hypochlorous acid reacts with both DNA and RNA and with individual nucleotides. The reaction with heterocyclic NH-groups is faster than the reaction with the amino group not in the heterocycle; therefore, the fastest reaction occurs with those nucleotides that have heterocyclic NH-groups - guanosine monophosphate and thymidine monophosphate. The reaction of uridine monophosphate, which, although it has a heterocyclic NH-group, is very slow. Adenosine monophosphate and cytisine monophosphate, which do not have a heterocyclic NH-group, react with side -NH 2 groups rather slowly.
This interaction of hypochlorous acid with nucleotides in nucleotides prevents the formation of hydrogen bonds between polynucleotide chains.
The reaction with the carbohydrate scaffold does not occur, and the outer support of the molecules remains intact.

Chemical properties of chlorine and hypochlorous acid

Since both chlorine and hypochlorous acid are oxidizing agents, they interact with reducing agents present in water:

• iron (Fe 2+) , which is usually present in the bicarbonate form, is converted to ferric chloride, which is rapidly hydrolyzed to iron III hydroxide:

2Fe (HCO 3) 2 + Cl 2 + Ca (HCO 3) 2 → 2Fe (OH) 3 ↓ + CaCl 2 + 6CO 2 (0.64 mg Cl 2 / mg Fe)

The reaction leads to a decrease in the pH value (water acidification) and proceeds at the optimum pH value \u003d 7. The reaction is almost instantaneous for inorganic iron, while for organo-salt complexes of iron, its rate is slower;

• manganese (Mn 2+) , which is usually present as divalent manganese and is oxidized to manganese (IV) dioxide:

Mn 2+ + Cl 2 + 4OH - → MnO 2 ↓ + 2Cl - + 2H 2 O (1.29 mg Cl 2 / mg Mn).

The reaction takes place in an alkaline medium at a pH value of 8 to 10. The optimum pH value is 10;

• sulfides (S 2 - ) , which are most often found in groundwater and can oxidize depending on the pH value of the water to sulfur or sulfuric acid:

H 2 S + Cl 2 → S ↓ + 2HCl (2.08 mg Cl 2 / mg H 2 S)or
H 2 S + 4Cl 2 + 4H 2 O → H 2 SO 4 + 8HCl (8.34 mg Cl 2 / mg H 2 S)at pH \u003d 6.4;

• nitrites (NO 2 - ) , which actively react with the hypochlorous acid formed when chlorine is dissolved:

NO 2 - + HClO → NO 3 - + HCl (1.54 mg Cl 2 / mg NO 2 - ) ;

• cyanides (CN - ) , which are also oxidized by chlorine (hypochlorous acid) at pH values \u200b\u200babove 8.5:

CN - + Cl 2 + 2OH - → CNO - + 2Cl - + H 2 O (2.73 mg Cl 2 / mg CN - ) ;

• bromides (Br - ) , oxidizing them to hypobromous acid:

Br - + HClO → HBrO + Cl - (0.89 mg Cl 2 / mg Br - ) .

2NH 4 + + 3Cl 2 → N 2 + 6Cl - + 8H + (7.6 mg Cl 2 / mg N-NH 4 +),

But the reaction has an extremely complex mechanism, the first stages of which lead to the formation of chloramines:

• monochloramine: NH 4 + + HOCl → NH 2 Cl + H 3 O +; (a)
• dichloramine: NH 2 Cl + HOCl → NHCl 2 + H 2 0; (b)
• trichloramine: NHCl 2 + HOCl → NCl 3 + H 2 O. (c)

The whole complex of organic and inorganic chloramines forms "Combined chlorine"so called as opposed to "Free chlorine"... The release of nitrogen occurs at an increased level of chlorination during subsequent reactions of mono- and dichloramine (hydrolysis, neutralization, oxidation). At neutral pH, monochloramine is the dominant form if the molar ratio is HOCl: NH 4 + less than one. This compound is oxidized by chlorine by the reaction:

2NH 2 Cl + HOCl → N 2 + 3HCl + H 2 O (g)

In this case, the summed reaction is the result of the addition of the equations a and r :

2NH 4 + + 3HOCl → N 2 + 3HCl + H 2 O + H 3 O + .

Chlorination process instrumentation

At the water treatment plant, chlorine is supplied in a liquefied state in specialized containers with a capacity of 800 liters, small and medium-sized cylinders in accordance with GOST 949. But chlorine in a gaseous state is used to disinfect water. Gaseous chlorine is obtained from liquid chlorine by evaporation in coil evaporators, which are vertical cylindrical apparatus with coils placed inside, through which liquid chlorine passes. Dosing of the obtained gaseous chlorine into water is carried out through special devices - vacuum chlorinators.
After the introduction of chlorine into the treated water, it must be well mixed with water and a sufficient duration of its contact with water (at least 30 minutes) before water is supplied to the consumer. It should be noted that the water before chlorination must already be prepared and, as a rule, chlorination is usually carried out before the clarified water enters the clean water tank, where the required contact time is ensured.
The main advantages of using chlorine gas for water disinfection
are:

• low cost of the water disinfection process;
• simplicity of the chlorination process;
• high disinfecting ability of gaseous chlorine;
• chlorine affects not only microorganisms, but also oxidizes organic and inorganic substances;
• chlorine eliminates water tastes and odors, its color, does not contribute to an increase in turbidity.

However, chlorine is a highly active poisonous substance that belongs to the second hazard class. The Cl 2 content in the air 6 mg / m 3 has an irritating effect on the respiratory tract, 12 mg / m 3 is hardly tolerated, the concentration above 100 mg / m 3 is life-threatening: breathing becomes frequent, convulsive, long pauses, respiratory arrest occurs after 5 - 25 minutes Inhalation of higher concentrations of chlorine can lead to instant death as a result of reflex inhibition of the respiratory center.
The maximum permissible concentration of chlorine in the air of the working area is 1.0 mg / m 3, in the atmosphere of settlements one-time 0.1 mg / m 3, the daily average 0.03 mg / m 3.
Chlorine gas is a strong oxidizing agent, supports the combustion of many organic matter, fire hazardous in contact with combustible substances. Turpentine, titanium and metal powders in a chlorine atmosphere are capable of spontaneous combustion at room temperature. Chlorine forms explosive mixtures with hydrogen.
In the design, construction and operation of chlorination plants, it is necessary to take into account the requirements aimed at protecting the maintenance personnel from the harmful effects of chlorine ("Rules for the production, transportation, storage and consumption of chlorine" (PB 09-594-03), "Rules for the construction and safe operation of vessels working under pressure "and" Rules for the storage and transportation of chlorine "(PBH-83)).
At times, the cost of ensuring safety in chlorination exceeds the cost of the actual chlorination of water.
In this regard, the use of sodium hypochlorite as a chlorine agent in the chlorination of water is a good alternative to gaseous chlorine. We are dedicated to sodium hypochlorite ( « Sodium hypochlorite. Properties, theory and practice of application » ), there is also given a comparison between the processes of water chlorination with gaseous chlorine and sodium hypochlorite.

Active, free, bound and residual chlorine

In order to understand how much chlorine should be dosed into water for its disinfection, it is necessary to separate the concepts active, free, combined and residual chlorine.
In general, it is generally accepted that active chlorine - this is chlorine in the composition of a chemical compound, capable of displacing iodine from the latter when its aqueous solution interacts with potassium iodide. The active content in chlorine-containing preparations characterizes their bactericidal properties.
However, as it was found out earlier, the amount of active chlorine required for water disinfection should be determined not only by the number of pathogenic bacteria, but also by the total amount of oxidizable organic substances, microorganisms, as well as inorganic substances found in chlorinated water. Therefore, the correct determination of the applied dose of active chlorine is extremely important: a lack of chlorine can lead to the fact that it does not have the necessary bactericidal effect, and its excess will lead to a deterioration in the organoleptic qualities of water. Therefore, the dose of active chlorine (chlorine consumption) should be set depending on the individual properties of the treated water on the basis of laboratory testing.
It is best if, when designing a chlorine-disinfection unit for water, the calculated dose of active chlorine will be taken based on the need to purify water during the period of its maximum pollution, for example, during floods.
Residual chlorine - chlorine remaining in the water after the administered dose and after the oxidation of the substances in the water. He can be free and bound, i.e. represented by various forms of chlorine. It is the residual chlorine that is the indicator of the sufficiency of the taken chlorine dose. According to the requirements of SanPiN 2.1.4.1074-01, the concentration of residual chlorine in water before it enters the network should be in the range of 0.3 - 0.5 mg / l.
Free chlorine - part of the residual chlorine present in water in the form of hypochlorous acid, hypochlorite anions or dissolved elemental chlorine.
Chlorine bound - part of the residual chlorine present in the water in the form of inorganic and organic chloramines.

Calculation of active chlorine dose (chlorine consumption)

Before telling you about the calculation of the dose of active chlorine, it should be reminded once again that “... the dose of active chlorine (chlorine consumption) should be set depending on the individual properties of the treated water on the basis of laboratory testing…».
When analyzing the chemical properties considered in the framework of this publication, it was not in vain that we indicated the stoichiometric coefficients of chlorine consumption for each of the reactions presented. We will need them to calculate the dose of active chlorine.
The approximate total dose of active chlorine required for the oxidation of organic substances, microorganisms, and inorganic substances will consist of:

• residual dose of chlorine (D x rest)

taken equal to 0.3-0.5 mg / l according to SanPiN 2.1.4.1074-01.

• chlorine doses for disinfection (D x des)

taken according to SNiP 2.04.02-84 after filtration:

• for surface waters - 2-3 mg / l
• for groundwater sources - 0.7-1 mg / l.
• chlorine doses for ferrous oxidation (D x Fe)

taken 0.7 mg Cl 2 for 1 mg of iron (II) (SNiP 2.04.02 - 84): D x Fe \u003d 0.7. With Fe , mg / l;

• chlorine doses for manganese oxidation (D x Mn)

taken 1.29 mg Cl 2 1 mg Mn (II): D x Mn \u003d 1.29. C Mn, mg / l;
With the combined content of iron and manganese in water, as a rule, their joint oxidation occurs.

• chlorine doses for the oxidation of sulfides (D x S) ; accepted:
• or 2.08 mg Сl 21 mg H 2 S: D x S \u003d 2.08. С S, mg / l
• or 8.34 mg Сl 21 mg H 2 S,if pH ≤ 6.4: D x S \u003d 8.34. C S, mg / l;
• chlorine dosage for nitrite oxidation (D x NO)

taken 1.54 mg Сl 21 mg NO 2 - : D x NO \u003d 1.54. C NO, mg / l;
Doses of oxidation of sulfides and nitrites at their increased value are best established on the basis of technological research data.

• chlorine doses for the oxidation of organic substances (D x Org)

When presence of ammonium ions in source water, concentration residual free chlorine falls due to the formation of chloramines, but the total concentration of residual chlorine remains unchanged.
As a rule, in the test (analysis) protocols of water, the concentration of ammonium ions ( NH 4 + ) are expressed in terms of nitrogen ( N ). In order to go from this value to the concentration of ammonium ions, it is necessary to multiply the result of the analysis for nitrogen by 1.28; those. C NH4 \u003d 1.28. C N .
As we have already indicated, in the presence of residual free chlorine, only dichloramine ( NHCl 2 ) and trichloramine ( NCl 3 ). In the absence of residual free chlorine, monochloramine ( NH 2 Cl ) and dichloramine.
The amount of active chlorine used to form dichloramine will be: C Cl \u003d 3.94. C NH4 .
It follows that the presence of ammonium ions in water with a concentration of more than 0.3 mg / l can completely transfer free chlorine to a bound state, and the total residual chlorine content in this case can be limiting (1.2 mg / l). In this situation, it is impossible to conduct the process of regulation and analytical control of free chlorine; therefore, it is necessary to take measures to reduce the concentration of ammonium ions in the source water.

Water chlorination methods

So, in the previous sections of this publication, we found out that today the chlorination of water is an activity that is constantly carried out at stations for the treatment of drinking water, treatment of household and some industrial wastewater and at municipal water supply systems. In addition, chlorination is carried out as a short-term or periodic measure necessary for disinfection of the water supply network sections, filters, clean water reservoirs, etc. being put into operation.
As for the chlorination technique, here it is necessary to take into account the purpose of the chlorination process, the presence of contaminants in the source water and their nature, as well as (which is important) possible seasonal fluctuations in the composition of the water. Particular attention should be paid to the specific features of the technological scheme of water purification and equipment included in the treatment facilities.
For the purposes of chlorination, the existing methods of water treatment with chlorine or other chlorine agents containing active chlorine can be combined into two main groups:

• Pre-chlorination (prechlorination, prechlorination).
• Final chlorination (postchlorination).

Pre-chlorination of water most often used as a means of improving some water treatment processes (for example, coagulation and deferrization), as well as an effective way to neutralize some toxic compounds in wastewater treatment. In this case, excess chlorine is spent on the oxidation of various water impurities, is sorbed by coagulant flakes, oxidizes microorganisms capable of immobilization and development on the surface of equipment and pipelines, as well as in the thickness of the filter loading, etc. As a rule, large doses of chlorine are used during prechlorination, and the stage there is no dechlorination of water, since the excess amount of chlorine is usually completely removed at other stages of the water purification process.
Final chlorination of water (post-chlorination) is the process of water disinfection, which is carried out after all other methods of its treatment and is, therefore, the final stage of water purification. If the water is not treated other than disinfection, then in such case it will be post-chlorination.
Postchlorination can be carried out with small doses of chlorine ( normal chlorination), and its increased doses ( overchlorination). If, when using chlorination, other disinfectants are used together, then it is called combined chlorination.
Normal chlorination It is used for disinfection of water taken from sources that are safe in sanitary terms and which have good physical and chemical characteristics. Chlorine doses should provide the necessary bactericidal effect without deteriorating the organoleptic indicators of water quality. The amount of residual chlorine after a 30-minute contact of water with chlorine is allowed not to exceed 0.5 mg / l.
Rechlorination It is used in cases where sharp fluctuations in bacterial contamination of water are observed and when normal chlorination does not give the proper bactericidal effect or leads to a deterioration in the organoleptic indicators of water quality (for example, if there are phenols in the water). Rechlorination removes many unpleasant tastes, odors and, in some cases, can be used to purify water from toxic substances. The dose of residual chlorine during transchlorination is usually set in the range of 1-10 mg / l. There are cases when overchlorination was carried out in very high doses: up to 100 mg / l ( superchlorination). Large doses of chlorine give a fast and reliable effect.
Combined chlorination methods , that is, the treatment of water with chlorine in conjunction with other bactericidal preparations can be used to enhance the effect of chlorine or fix it in water for a longer period. Combined chlorination methods are used not only for the treatment of large quantities of water in stationary water supply systems, but also as individual means of water disinfection. Combined methods include: chlorination with manganization, silver chloride and chloride chloride methods, as well as chlorination with ammonization.
Chlorination with manganation (adding КМnО 4 ) is used in the treatment of waters with unpleasant odors and tastes caused by the presence of organic matter, algae, actinomycetes, etc. In some cases, such a mixture is more effective than overchlorination. To introduce a solution of potassium permanganate into water, use proportional dosing units .
The introduction of potassium permanganate can be carried out both before and after chlorination, and the dose depends on the place of its introduction into the treated water during the technological process. In cases where water is treated in front of the sedimentation tanks, the dose КМnО 4 can reach up to 1 mg / l, since when interacting with chlorine, excess potassium permanganate not consumed for oxidation is reduced in water to manganese (IV) oxide МnО 2 who lingers on fil-fucking. If potassium permanganate is introduced into purified water, i.e. after filters, then in order to avoid precipitation МnО 2 its concentration should not exceed 0.08 mg / l.
Combined silver chloride and copper chloride methods carried out by the simultaneous introduction of chlorine and ions of silver and copper into the water. Strengthening the bactericidal effect of chlorination is within the total disinfecting effect of chlorine and silver or copper ions. The silver chloride method can be used not only for disinfecting drinking water, but also for preventing their repeated bacterial contamination, that is, for preserving water. Due to the fact that the bactericidal effect of silver increases with heating, the bactericidal effect of the silver chloride method increases in the warm season.
Obtaining the required concentration of silver ions is achieved by introducing silver nitrate or "silver water" into the water. In this case, the concentration of silver ions must be strictly controlled, since the MPC for silver in water is 50 μg / l (the same as for antimony and slightly more than for lead).
As we have already said, the main problem that arises during the chlorination of water is the instability of active chlorine during the storage and transportation of purified water. One of the most common ways to fix active chlorine in water is chlorination with ammonization... Ammonization is carried out by introducing ammonia or ammonium salts into the disinfected water. Depending on the intended purpose, ammonization should be carried out immediately before chlorination (preliminary ammonization) or after it (post-ammonization).
The duration of the bactericidal action during chlorination with ammonization depends on the mass ratio of chlorine and ammonia. The longest action is achieved when the ratio of chlorine and ammonia corresponds to the formation of monochloramine, the oxidation potential of which is lower than that of free chlorine. The consumption of active chlorine in the case of using a solution of chloramine is not less than when using solutions of free chlorine.
Therefore, a particularly great effect when combining chlorination with ammonization is observed when disinfecting waters rich in organic substances that are easily oxidized by chlorine. In this case, the loss of chlorine due to the decomposition of chloramine can no longer play a significant role, since they will be less than the amount of chlorine that, in the absence of ammonia, would go to the oxidation of organic impurities of water. In this regard, less monochloramine is consumed for oxidation processes of organic substances present in water, as well as for corrosion processes.
When disinfecting waters with low chlorine absorption, the opposite phenomenon can be observed: the concentration of active chlorine during chlorination with ammonization decreases more intensively than during conventional chlorination. This phenomenon is explained by the oxidation and decomposition of monochloro-amine, which occurs especially intensively with an excess of active chlorine. The maximum oxidation rate is observed at pH \u003d 7-9. Decomposition of monochloramine is especially intense at pH \u003d 5-7.
It should be borne in mind that the speed of the process of disinfection of water with chloramines is less than the speed of disinfection with chlorine, therefore, the contact between water and chlorine using preliminary ammonization should be longer (at least 2 hours).
In the practice of water purification, it is also used double chlorination (preliminary and final chlorination). In this case, different requirements are imposed on each of these processes: primary chlorination is carried out in order to prepare water for the subsequent stages of purification (chlorine is introduced into the supply water line); the final chlorination is required to ensure the required concentration of residual chlorine in the water, which guarantees its proper sanitary quality (chlorine is introduced after filters). Double chlorination is most often used for surface sources with a high color value of the source water and a high content of organic substances in it.

Dechlorination of water

Excess active chlorine in excess of the MPC is removed dechlorination... With a slight excess, chlorine can be removed by aeration (non-pressure aeration of water), and at high concentrations of residual chlorine, the method of dosing chemical reagents into the water should be used: sodium thiosulfate (hyposulfite), sodium sulfite, ammonia, sulfur dioxide (sulfur oxide (IV)) , which will bind active chlorine, or treat water on filters with active carbon.
When reagent treatment of chlorinated water, use should be made of proportional dosing systems for chemical solutions based on metering pumps with controllers and sensors for active chlorine.
The method of pressure filtration through activated carbon has advantages over dosing of chemical reagents, because in this case, no foreign substances are introduced into the water, at the same time, not only excess chlorine is absorbed by coal, but also many other impurities that impair the organoleptic properties of water. At the same time, the de-chlorination process proceeds automatically, and its control is not difficult.

Analytical control of the chlorination process

The main provisions concerning the analytical control of the content of residual, free and total chlorine in drinking water were set out a long time ago in « Instructions for the control over the disinfection of household drinking water and the disinfection of water supply facilities with chlorine for centralized and local water supply, approved by the Chief Sanitary Doctor of the USSR on November 25, 1967 under No. 723a-67. Since then, a number of regulations have been adopted that also regulate methods for laboratory analytical control of the content of free and total chlorine in water. They are listed in the Table.

ISO 7393-1:1985	“Water quality. Determination of free chlorine and total chlorine. Part 1. Titrimetric method using N, N-diethyl-1, 4-phenylenediamine "
The standard specifies a titrimetric method for the determination of free chlorine and total chlorine in water. The method is applicable for total chlorine concentrations in terms of chlorine ( Cl2) from 0.0004 to 0.07 mmol / L (0.03 - 5 mg / L), and at higher concentrations - by diluting the samples.
ISO 7393-2: 1985	“Water quality. Determination of free chlorine and total chlorine content. Part 2. Colorimetric method using N, N-diethyl-1, 4-phenylenediamine for routine control "
The standard specifies a method for the determination of free chlorine and total chlorine in water, suitable for use in the field. The method is used at a chlorine concentration between 0.03 and 5 mg / l.
ISO 7393-3: 2000	“Water quality. Determination of free chlorine and total chlorine content. Part 3. Method of iodometric titration for determination of total chlorine content "
The standard specifies a method for iodometric titration for the determination of total chlorine content. The method is used with a chlorine concentration between 0.71 and 15 mg / l.
MUK 4.1.965-99	"Determination of the concentration of residual free chlorine in drinking and fresh natural water by the chemiluminescent method"
Methodical guidelines establish a method of chemiluminescent quantitative chemical analysis of water from centralized household drinking water supply to determine the content of residual free chlorine in it in the concentration range from 0.01-2.0 mg / dm 3. The measurement of the concentration of active free chlorine is based on its ability to initiate chemiluminescence of luminol in an alkaline medium, the intensity of which is proportional to its concentration in the analyzed sample. Concentration of active free chlorine from water is not carried out. The lower limit of measurement is 0.0001 μg.
GOST 18190-72	"Drinking water. Methods for determining the content of residual active chlorine "
The standard applies to drinking water and establishes methods for determining the content of residual active chlorine : iodometric method, method for determination of free residual chlorine by titration with methyl orange, method for separate determination of free monochloramine and dichloramine by Palin's method

Currently, based on these methods, express analyzers of free and total chlorine in water have been developed. These include: indicator test strips, test boxes and modern photometers for individual substances.
The simplest express method for analyzing water quality in water treatment processes - indicator test strips ... The measuring principle (colorimetric) is based on changing the color of the strip and comparing it with a calibrated color panel. With their help, the increased content of various pollutants in the water is recorded, and the range of a number of quality ingredients of drinking water is determined (see Table 1). They are produced by many companies (Merckoquant, Bayer, etc.) and are intended mainly for monitoring the chlorine content in swimming pool and aquarium water. Insufficient sensitivity of test strips does not allow analyzing indicators of the physiological usefulness of drinking water, as well as determining a number of hygienically significant pollutants at the MPC level. Measurement error when using test strips ± 50 - 70%.
Colorimetric kits (manufacturers - Aquamerck, Microquant, Aquaquant, etc.), the so-called test boxes (see Table 1). The measuring principle is based on changing the color of the solution (colorimetric) and comparing it with a calibrated color panel. The analysis is performed in a transparent measuring cell, where the source water is poured and the ready-made reagent test is introduced. After passing through a chemical reaction, the water changes color, which is compared with the color scale. A calibrated color bar is usually applied directly to the measuring cell. With their help, they also register an increased content of various pollutants and harmful impurities in water, but unlike test strips, they have a greater sensitivity and lower measurement error (see Table 1). Although for test boxes, the measurement error is quite large and amounts to ± 30 - 50%.
These two types of rapid analysis are suitable only for routine rapid control of predetermined significant values \u200b\u200bof the content of impurities in water.

Table 1

Index	One. meas.	Measuring range
		Test strips	Test boxes	Photometers
Aluminum	mg / dm 3	10-250		0,01-1,00
Ammonium	mg / dm 3	10-400	0,2-1,5	0,1-50,0
Iron	mg / dm 3	3-500	0,1-50	0,01-5,00
General hardness	oJ		1-100	1-250/500/750
Hardness carbonate	oJ	4-24	1-100
Potassium	mg / dm 3	250-1500		0,01-50,0
Calcium	mg / dm 3	10-100	2-200	0,01-2,70
Cobalt	mg / dm 3	10-1000
Magnesium	mg / dm 3		100-1500	0,01-2,00
Manganese	mg / dm 3	2-100		0,1-20,0
Copper	mg / dm 3	10-300	0,1-10	0,01-5,00
Molybdenum	mg / dm 3	5-250	0,2-50	0,1-40,0
Arsenic	mg / dm 3	5-500
Nickel	mg / dm 3	10-500	0,02-0,5	0,01-7,00
Nitrate ion	mg / dm 3	10-500	10-150	0,1-30,0
Nitrite ion	mg / dm 3	2-80	0,1-2	0,5-150
Hydrogen peroxide	mg / dm 3	0,5-25	0,2-10,0
Lead	mg / dm 3	20-500	-
Silver	mg / dm 3	0,5-10		0,001-1,000
Sulfate ion	mg / dm 3	0,2-1,6		0,1-150
Sulfite ion	mg / dm 3	10-400
Formaldehyde	mg / dm 3	10-100	0,5-1,5
Phosphate ion	mg / dm 3	10-500	1-5	0,1-30,0
Chloride ion	mg / dm 3	0,5-3	25-2500	0,1-20,0
Chlorine total	mg / dm 3	0,5-20	0,1-2,5	0,01-10,00
Free chlorine	mg / dm 3	0,5-10	0,1-2,5	0,01-5,00
Chromium	mg / dm 3	3-100	0,005-0,1	0,001-1,000
Cyanide	mg / dm 3	1-30	0-0,2	0,001-0,200
Zinc	mg / dm 3	10-250	0,1-5	0,01-3,00

For a more accurate quantitative analysis of water ingredients, modern photometers , characterized by a high level of sensitivity and less measurement error.
There are two types of photometers - cuvette and reagent. IN cuvette photometers tests contain all the necessary reagents in a special test tube-cuvette and are used for both the reaction and measurement. The device automatically recognizes cuvette tests (in the wavelength range of 340-820 nm) by the barcode, which eliminates the possibility of error. IN reagent photometers tests contain ready-made reagents either in powder, in sealed packaging, or in vials with a convenient dosing system. Ready-made tests do not require special training. They are simply added to the measured water sample, then a chemical reaction takes place and the colored solution is transferred to the measuring cuvette. The cuvette is installed in the photometer, where the measurement is made. The measurement result of the analyzed ingredient is recorded on the display of the photometer. The measurement error with photometers ranges from 15 to 25%.
Quality certificates included with test kits eliminate the need to test every batch of reagents. Also, there is no need to prepare calibration solutions and time-consuming calculations during calibration. For example, analysis of free chlorine in drinking water (in the range of 0.03 - 6 mg / l) using a photometer takes only 3 - 5 minutes, while its determination by the classical method (according to GOST 18190-72) requires 20 - 30 minutes ...

Automatic chlorine analyzers

Although development modern methods preparation and conduct of analyzes and made it possible to greatly reduce the time for their implementation, yet laboratory control does not remove the issue of continuous production control of the chlorine content in water. This is due to the fact that when automating the chlorine dosing process from an analytical device, it is necessary to receive a signal about the chlorine content in water in the "on-line" mode. Therefore, to measure the mass concentrations of chlorine in water, a number of analyzers have been created that differ from each other in their principle of operation - the measurement method.
In automatic analyzers, mainly four measurement methods are used: optical (photometry and colorimetry), iodometry, chemiluminescence and electrochemical method in various versions (amperometry, conductometry, etc.).

In this publication, we will consider the characteristics of only individual representatives of automatic analyzers, divided into groups based on the measurement method underlying the work.

Colorimetry (ISO 7393-2).
Industrial automatic photometric analyzer of residual (free) and total chlorine in water brand CL-17 (company "HACH-Lange") is designed to ensure continuous cyclic control of the content of total or free (residual) chlorine with a time interval of ~ 2.5 minutes.
The principle of operation is based on a photocolorimetric method for measuring the concentration of chlorine when coloring a solution as a result of the interaction of total chlorine with N`N-diethyl-1,4-phenylenediamine (DPD) in a stream of water using ready-made reagents supplied by the manufacturer. Reagents (~ 400 ml of two types) supplied with the analyzer are sufficient for continuous operation for 1 month. Reagents can be purchased separately.

CL-17 Analyzer Specifications

The analyzer assemblies are mounted in a plastic case (IP62), which can be installed in a rack or panel.
The analyzer is calibrated using GSO solutions of potassium iodate or solutions of iodine of crystalline analytical grade.

Chemiluminescence (MUK 4.1.965-99).
Auto analyzer of active unbound chlorine "Fluorat AS-2" (TU 4215-252-20506233-2002) is intended for continuous automatic measurement of the mass concentration of active unbound chlorine in drinking water by recording the intensity of chemiluminescence arising from the reaction of interaction between luminol and unbound chlorine.
In general, the analyzer principle of operation is reduced to measuring the value of the chemiluminescence intensity in the analyzed sample passing through the flow cell, and is divided into the following stages:

• dosing of the reagent (luminol solution) into the flow of the investigated water and carrying out the chemical reaction directly in the measuring cuvette under controlled conditions;
• registration of the optical characteristics of the working medium in the measuring cuvette (radiation intensity as a result of the reaction of interaction between luminol and unbound chlorine);
• processing of measurement results and calculation of analysis results by a digital converter according to the calibration characteristic stored in the main memory;
• output of the received information to peripheral devices, storage of measurement results in the analyzer archive.

Technical characteristics of the analyzer "Fluorat AS-2":

Chlorine mass concentration measurement range, mg / dm 3	0,1 - 5,0
Limits of the permissible basic relative error,%, in the measuring range: from 0.1 to 0.5 mg / dm 3 from 0.5 to 5.0 mg / dm 3	± 50 ± 20
Time to establish the operating mode, min, no more	30
Duration of a single measurement, min, no more	5
Analyzer power consumption, W, no more	50
Analyzer overall dimensions, mm, no more
length	600
width	500
height	215
Analyzer weight, kg, no more	50

The analyzer is equipped with programmable alarms, analogue output to the recorder (default: 4 - 20 mA, optional: 0 - 10 mV, 0 - 100 mV, 0 - 1 V). Output to an external computer or printer via an optional RS 232 interface is possible.
The analyzer assemblies are mounted in a metal case, which is mounted on a panel.

Iodometry (GOST 18190-72, ISO 7393-3).

Analyzers of residual chlorine "VAKKh-2000S"
are intended for measuring the mass concentration of residual active chlorine by the iodometric measurement method.
The principle of operation of the VAKKh-2000S analyzer is based on the implementation of the iodometric method for determining the content of residual active chlorine in water with coulometric generation of iodine addition to the sample under study (precisely known amount) and potentiometric measurement of the potential difference arising at the same time on the electrodes of the electrochemical cell.
The analyzer is also produced in a semi-automatic version, intended for use in laboratory conditions. In this case, pre-selected water samples are analyzed.

Technical characteristics of the analyzer of residual chlorine "VAKKh-2000S"

The analyzer is equipped with programmable alarms, an analogue output to a recorder (default: 0 - 5 mA, optional: 4 - 20 mA), relay outputs for controlling external devices are installed on request. The threshold concentration value is set from the functional keyboard of the analyzer. It is possible to output to an external computer or printer via an additionally installed RS 232 interface (on request - RS-485).
The analyzer assemblies are mounted in a metal case, which is installed on a table.
The analyzer is calibrated using freshly prepared sodium hypochlorite solutions, the concentration of active chlorine in which is preliminarily set using a laboratory iodometric technique in accordance with GOST 18190-72 for GSO solutions of potassium iodate or for iodine solutions of crystalline purity grade.

Electrochemical analyzers

Variants of electrochemical methods used to determine different forms of chlorine content in water are very diverse, but they have a certain similarity.
Firstly, any electrochemical process takes place in an electrochemical measuring cell, into which the water under investigation enters. Secondly, there are three electrodes in the cell: the main (working), the auxiliary, and the reference electrode, which serves to maintain a constant potential of the electrode used for measurement. Thirdly, to maintain the required potential value, a source of a fixed external voltage is used, the so-called potentiostat.
When a measuring cell is connected to a suitable measuring transducer, a fixed external voltage is applied to the electrodes. Due to the difference in the area of \u200b\u200bthe working surface of the electrodes, polarization of the cathode occurs. The polarization current is displayed by the transducer as very high signal values, which gradually decrease and then stabilize. Thus, the movement of free electrons from the anode to the cathode creates an electric current, the magnitude of which, under constant conditions, will be proportional to the concentration of free chlorine in the working medium. The value of this current is processed by the transmitter and converted to the concentration of free chlorine in mg / l, which is then shown on the display. It should be noted that all chlorine analyzers based on any electrochemical method require periodic validation using the iodometric method as a traditional laboratory measurement technique.
As we can see, this method is more convenient for automation, since an electrical signal is immediately generated in the measuring cell. Devices that implement electrochemical methods are distinguished by their simplicity and low cost. During their work, they do not require any consumable chemical reagents.
However, these methods are very nonselective, therefore, they are most often used to measure the content of active chlorine in water with a constant chemical composition, since any change in the composition of the analyzed water will invariably cause a change in the electrochemical processes occurring in the measuring cell on the electrodes.
As we have already noted, there are a lot of models of chlorine analyzers operating on the basis of the electrochemical measurement principle, so we will limit ourselves to considering only two of them.

Chlorine analyzer brand Q45H.

Chlorine analyzer Q45H ("Analytical Technology, Inc", USA) is designed for continuous monitoring of the chlorine content in water.
The Q45H analyzer uses a membrane polarographica sensor that is housed in a flow-through electrochemical cell. There are two modifications of sensors for this analyzer: a free chlorine sensor and a combined chlorine sensor. The free chlorine sensor is used only with a flow-through type of installation in an electrochemical cell, while bound chlorine sensors can be installed both in a flow-through (in an electrochemical cell) and in a submerged (non-flowing) version (for example, in a vessel).
The electrochemical cell is designed to maintain continuous constant parameters of the analyzed water flow: its velocity and pressure in contact with the sensor surface, which will not depend on fluctuations in the water velocity and pressure in the source water pipeline. Depending on the expected concentration of chlorine in the water, two types of electrochemical cells are used: large and small volumes of the flow path. The first cell is designed for measurements of high chlorine concentrations, the second for chlorine concentrations less than 200 μg / l. The flow rate of the analyzed water in the cell of the first type should be at least 30 l / h, the second - in the range from 15 to 20 l / h.
For proper operation of the combined chlorine sensor with its immersed (non-flowing) installation, the flow rate of the analyzed water must be at least 0.12 m / s.
Since the membrane sensor is sensitive to significant fluctuations in pH, then if the pH value of the original analyzed water can change regularly, there is a possibility of significant inaccuracies in the analysis of the concentration of free chlorine. To avoid this, an additional pH electrode can be installed in the electrochemical cell, which will
automatically correct these changes, ensuring the required measurement accuracy, even if the pH value varies significantly and approaches 9.

Chlorine Analyzer Specifications Q45 H

The analyzer is equipped with programmable alarms, two analog outputs: 4 - 20 mA, relay outputs for controlling external devices are installed on request: 6A / 250V AC or 5A / 24V DC. The threshold concentration value is set from the functional keyboard of the analyzer.
The analyzer is mounted in a polycarbonate case (IP-66) that can be mounted on a wall, panel or pipe.

Analyzer of chlorine content in water ASKhV / M1032S.

Analyzer of chlorine content in water ASHV / M1032Sdesigned for measuring and controlling residual or total chlorine in the process of preparing drinking, waste and recycled industrial waters, as well as water in swimming pools.
The principle of operation is based on measuring the potential of the working electrode relative to the reference electrode while passing current between the working and auxiliary electrodes in an open cell operating in a potentiostatic mode. АСХВ / М1032 Structurally consists of a measuring cell module, consisting of two electrodes (working and auxiliary electrodes are combined into a single system) and a temperature sensor located in a separate chamber with mechanical cleaning and a remote control unit (BDU-RH), built on the basis of a microprocessor, with graphic display and control keys. The BDU-RH is used to amplify the signal at the output of the measuring cell module. The use of temperature and pH compensation ensures high measurement accuracy. The measured value is displayed on the BDU-RH display.

Specifications analyzer of chlorine content in water АСХВ / М1032С

For communication with other devices, two analogue current outputs (4 - 20 mA) are provided. These outputs can be used to relay the following signals: chlorine content in water, water temperature or regulator performance.
The analyzer is mounted in a plastic case and, together with the measuring cell, is fixed to a panel that can be mounted on a wall or pipe.
The analyzer is validated using freshly prepared sodium hypochlorite solutions, the concentration of active chlorine in which is preliminarily set using a laboratory iodometric technique in accordance with GOST 18190-72 for GSO solutions of potassium iodate or for iodine solutions of crystalline purity grade.

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The instruction is intended for sanitary doctors who control the drinking water supply of populated areas. Guided by this instruction, the authorities of the sanitary and epidemiological service impose sanitary requirements on the administration of water pipelines or on the owners of local water sources, who are responsible for providing the population with good-quality drinking water.

I. Chlorination of water in water pipelines

The quality of water in a centralized water supply depends on the quality of water from sources, water intake conditions, the correct organization of sanitary protection zones and the implementation of the appropriate regime in them, a regime for purifying and disinfecting water, as well as on the sanitary-technical condition of water intake devices and water supply networks. In order to provide the population with good-quality drinking water, it is necessary to strictly observe sanitary requirements in the construction and operation of all water supply facilities, including installations for water chlorination.

2. Chlorination of water must be carried out in all cases of obtaining it from surface water bodies (after mandatory preliminary treatment), as well as when receiving water from underground sources, the bacterial indicators of which do not correspond to GOST "Drinking water".

Note: Other methods approved by the Main Sanitary and Epidemiological Directorate of the USSR Ministry of Health can also be used to disinfect water.

3. Chlorination of water in pipelines should be carried out, as a rule, with the use of liquid chlorine. For stations with a capacity of up to 3000 m 3 / day, it is allowed to use bleach or calcium hypochlorite in the form of a two-third base salt (DTSGK). The reagents used for the chlorination of water must be subjected to control analysis at the waterworks to check the content of active chlorine and other components in them, in accordance with the established standards ("Liquid chlorine" - GOST 6718-53, "Chlorine lime" - GOST 1692-58 , "Temporary instruction on the use of DTSGK for disinfection purposes", approved by the Ministry of Health of the USSR on November 6, 1960, N 311-60).

4. In order to establish indications for the chlorination of water from sources used for domestic drinking water supply, as well as in order to develop the main provisions for the chlorination regime, a preliminary sanitary and laboratory examination of the water source is carried out, carried out in accordance with the program provided for by the current GOST "Sources of centralized economic - drinking water supply. Rules for selection and quality assessment "(2761-57).

5. In order to establish the working dose of chlorine for chlorination, the effect of water disinfection and the amount of residual active chlorine, which depends on the chlorine absorption of water, are determined empirically.

The working dose of chlorine chosen for water disinfection must provide an appropriate bactericidal effect, i.e. the number of E. coli in the treated water should be no more than 3 in 1 liter, the total number of bacteria - no more than 100 in 1 ml after the contact period of water with chlorine (at least 30 minutes). The content of residual chlorine in this case must be at least 0.3 and not more than 0.5 mg / l (GOST "Drinking water").

6. When chlorination of water from some sources, mainly open ones, difficulties may arise associated with the need to obtain the proper disinfection effect and at the same time ensure that the water meets hygienic requirements in terms of organoleptic properties (smell and taste). In such cases, one or another of the special methods of disinfection should be applied, which include the following:

a) Double chlorination, i.e. the introduction of chlorine before the treatment plant into the suction conduits of the 1st rise (usually in doses of 3-5 mg / l) and finally after the filters (usually in doses of 0.7-2 mg / l); it is used when the color of the source water is high, with an increased content of organic matter and plankton.

b) Chlorination with preammonization, i.e. introduction of ammonia or its salts into water immediately before the introduction of chlorine (usually at the ratio of doses of ammonia and chlorine 1: 4, 1:10). In this case, disinfection is provided due to the combined chlorine (chloramines). This method is used to prevent specific odors arising after chlorine treatment of water. During preammonization, the contact of water with chlorine should be at least 1 hour.

c) Rechlorination, i.e. the introduction of obviously high doses of chlorine (up to 10-20 mg / l), followed by binding of excess chlorine (dechlorination with sulfur dioxide or activated carbon); is used in cases of forced use of water sources, the bacterial contamination of which exceeds the limit established by GOST 2761-57, i.e. the average number of E. coli is more than 10,000 in 1 liter (in water samples taken at the point of water intake). In addition, it is used to avoid the appearance of chlorine-phenolic odor in the presence of phenols in the source water.

d) Chlorination with post-breakdown doses, i.e. taking into account the breakpoint on the residual chlorine curve; in this case, water is disinfected with free chlorine, which is much more effective than combined chlorine (chloramines); used mainly in cases of high bacterial contamination of source water.

e) The use of chlorine dioxide can also be recommended to improve the efficiency of disinfection and prevent specific odors in the water.

7. The choice of this or that chlorination method, which guarantees full compliance of drinking water with the requirements of GOST "Drinking Water", is carried out by the administration of the waterworks on the basis of sanitary-chemical, sanitary-bacteriological and technological analyzes of raw and treated water, taking into account production experience in its purification and disinfection ...

8. On the basis of the data obtained in accordance with, the administration of the water supply system establishes the main provisions for the method of water treatment with chlorine, which include the chlorine use scheme, the dosage of reagents and chlorination schedules, depending on the water consumption. These basic provisions must be agreed with the local authorities of the sanitary and epidemiological service.

Laboratory and production control over the quality of water at the waterworks and in the distribution network is provided by the administration of the water supply system, by the forces and means of the departmental laboratory in accordance with GOST "Drinking water". Determination of residual chlorine before feeding into the network is carried out every hour, and on water pipelines from open reservoirs - every 30 minutes; in the same place a sample is taken for bacteriological analysis at least once a day, at the same time as the next determination of residual chlorine.

9. Sanitary and laboratory control over the effectiveness of chlorination of water supplied by the water supply for household and drinking needs is carried out by the sanitary and epidemiological station by determining the number of E. coli and the total number of bacteria at the most characteristic points of the water intake (the nearest to the pumping station, the most remote, the most elevated, dead ends, water columns). Sampling points and frequency of analyzes are determined by schedules approved by the local authorities of the sanitary and epidemiological service.

10. The quantitative determination of the residual active chlorine in water is carried out by the iodometric or orthotolidine method, the description of which is given in.

The iodometric method is preferable with active chlorine concentrations of at least 0.5 mg / l, orthotolidine - at lower concentrations.

To determine residual chlorine on large water pipelines, it is advisable to use automatic analyzers, in particular, photoelectronic systems of the Academy of Public Utilities of the RSFSR, which ensure continuous registration of residual chlorine in water.

In the practice of chlorination, it may be necessary to separately determine the main forms of active chlorine, in particular, during chlorination with post-breakdown doses (free chlorine) and during chlorammonization (combined chlorine). Free chlorine has a relatively fast disinfecting effect, while bound chlorine is less effective (see above -d). For their separate quantitative determination, you should use a method based on the use of para-aminodimethylaniline (see). International drinking water standards also recommend the orthotolidine-arsenitic method, which has not yet found application in the USSR.

11. When performing work on the chlorination of water, the safety measures specified in Art.

The storage conditions for chlorine and ammonia stocks must meet the requirements of the current Sanitary Rules for the Design, Equipment and Maintenance of Warehouses for the Storage of Strong Poisonous Substances (approved by the USSR Ministry of Health on 24.VI.1965, N 534-65). In this case, ammonia must be stored isolated from chlorine.

Storage of bleach stocks is allowed only in undamaged standard packaging, in closed warehouses, dry, darkened and well ventilated, at an air temperature not exceeding 20 ° C. It is forbidden to store explosive and flammable substances, lubricating oils, food products, metal products and gas cylinders in the same room with bleach.

12. Bodies of the sanitary and epidemiological service in the process of routine inspections of water pipes, as well as for epidemic indications (at least once a month) must check the correctness of laboratory and production control over water quality, including the correctness of the main provisions on the method of water treatment with chlorine, established by the administration of the water supply system (see clause 8 of this instruction).

All comments and suggestions on improving the sanitary state of the head facilities of the water supply system, on the method of treatment and on improving the quality of water should be entered in a special log of the established form, stored at the waterworks.

13. In the absence of a departmental laboratory (on low-power water pipelines) for production control over the work of the station, a regular position of a laboratory assistant should be provided who monitors the correct chlorination and performs the simplest analyzes (the content of active chlorine in bleach, in prepared chlorine solutions, determination residual chlorine in water, etc.).

II. Chlorination of water in local water supply

14. With local water supply, i.e. when using water without a distribution network of pipes, directly from a source (wells, springs, open reservoirs), chlorination of water requiring disinfection is usually performed with bleach in clean containers - tanks, barrels, tanks or other special containers. In this case, the following conditions must be observed:

a) bleach is introduced into the water at a dose established by experience;

b) for reliable disinfection of water, its contact with chlorine should be at least 30 minutes in summer, and at least 1 hour in winter;

c) properly chlorinated water should contain residual chlorine in the amount of 0.3-0.5 mg per liter.

Note: In exceptional cases, in the absence of other possibilities, residual chlorine can be qualitatively determined by the blueness of chlorinated water from the addition of several crystals of potassium iodide and a few drops of a 1% starch solution to it, as well as by the presence of a weak chlorine smell in the water.

15. A solution of bleach is prepared with a strength of 1-5%, i.e. to prepare the solution, 10-50 g of bleach is taken per 1 liter of water. In the absence of scales, you can use spoons, glasses and other objects of known capacity to measure lime, taking a teaspoon capacity of 2-2.5 g of bleach, a tablespoon of 9-12 g, and a glass of 120 g.

A measured amount of bleach is poured into a mug or bowl, a little water is added to it and pounded into a creamy mass without lumps. Then this mass is diluted with the required amount of water and mixed thoroughly. The prepared bleach solution is used for chlorination after settling. The content of active chlorine in bleach and the selection of the working dose of chlorine are made in accordance with.

16. In some cases, depending on the quality of the water, in order to increase the reliability of its disinfection, it is recommended to use overchlorination, ie. the introduction of deliberately excessive doses of active chlorine, followed by the removal or chemical binding of the excess chlorine.

Rechlorination is performed as follows. A solution of bleach is added to the water at the rate of at least 10 mg / l of active chlorine, and when disinfecting contaminated waters from open sources - at least 20 mg / l of active chlorine. After thoroughly mixing the bleach solution poured into the water with a wooden shovel or oar, leave the water alone in summer for 15 minutes, in winter - for 30 minutes. After that, the smell of water is checked: with a strong smell of chlorine, overchlorination is considered sufficient, in the absence of smell or a very weak smell of chlorine, it is necessary to repeat the introduction of bleach.

To remove excess chlorine (dechlorination), water is filtered through activated or regular charcoal, and in the absence of coal, sodium hyposulfite is added to the water (at the rate of 3.5 mg of hyposulfite per 1 mg of active residual chlorine).

17. Disinfection of mine wells and disinfection of water in them is carried out in accordance with the "Temporary instructions for disinfection of mine wells and disinfection of water in them", approved by the Main Sanitary and Epidemiological Directorate of the Ministry of Health of the USSR on January 18, 1967 N 663-67.

III. Chlorine disinfection of water supply facilities during their construction and operation

18. Disinfection of water supply facilities (wells, reservoirs and pressure tanks, sedimentation tanks, mixers, filters, water supply systems) can be preventive (before commissioning new facilities, after periodic cleaning, after repair and emergency work), as well as for epidemic indications ( in case of pollution of structures, as a result of which there is a threat of occurrence of water outbreaks of intestinal infections).

19. To increase the reliability of disinfection and reduce its duration, it is recommended to use solutions with an active chlorine concentration of 75-100 mg / l with contact for 5-6 hours. It is possible to use solutions with a lower concentration of active chlorine - 40-50 mg / l, but the duration of the required contact in this case increases to 24 hours or more.

20. Before disinfection of water supply facilities, in all cases, their preliminary mechanical cleaning and rinsing is mandatory. The water supply network, which is difficult to clean, is intensively washed for 4-5 hours at the maximum possible speed of water movement (at least 1 m / sec.).

21. Disinfection of artesian wells before putting them into operation is carried out in cases where, after washing, the water quality by bacteriological indicators does not correspond to GOST "Drinking water".

During the operation of wells, the need for disinfection arises when water pollution is detected directly in the well due to its defects (in such cases, disinfection must be preceded by appropriate repair work).

Disinfection is carried out in two stages: first, the surface of the well, then the underwater part. To disinfect the topside, a pneumatic plug is installed in the well a few meters below the static level, above which the well is filled with a chlorine solution (or bleach) with an active chlorine concentration of 50-100 mg / l, depending on the degree of the alleged pollution. After 3-6 hours of contact, the plug is removed and, using a special mixer, a chlorine solution is introduced into the underwater part of the well so that the concentration of active chlorine after mixing with water is not less than 50 mg / l. After 3-6 hours of contact, pumping is carried out until the noticeable smell of chlorine disappears in the water, after which a water sample is taken for control bacteriological analysis.

Note: The calculated volume of the chlorine solution is taken to be greater than the volume of the wells (in height and diameter): when disinfecting the above-water part - 1.2-1.5 times, the underwater part - 2-3 times.

22. Disinfection of large-capacity tanks is recommended using the irrigation method. A solution of bleach (or chlorine) with a concentration of 200-250 mg / l of active chlorine is prepared at the rate of 0.3-0.5 l per 1 m 2 of the inner surface of the tank. The walls and bottom of the tank are covered with this solution by irrigation from a hose or a hydraulic control unit.

After 1-2 hours, the disinfected surfaces are washed with clean tap water, removing the spent solution through a mud outlet. Work should be carried out in overalls, rubber boots and gas masks; before entering the tank, a tank with a bleach solution is installed to wash the boots.

Low-capacity pressure tanks should be disinfected by the volumetric method, filling them with a solution with a concentration of 75-100 mg / l of active chlorine. After contact for 5-6 hours, the chlorine solution is removed through a mud pipe and the tank is rinsed with clean tap water (to a content of 0.3-0.5 mg / l of residual chlorine in the wash water). A similar method is used to disinfect sedimentation tanks, displacers, as well as filters after their repair and loading.

The control bacteriological analysis after the disinfection of the structures is done at least 2 times with an interval corresponding to the time of complete water exchange between sampling. With favorable results of analyzes, the structures can be put into operation.

23. Disinfection of the water supply network is carried out by filling the pipes with a solution of chlorine (or bleach) with a concentration of 75 - 100 mg / l of active chlorine (depending on the degree of pollution of the network, its deterioration and sanitary-epidemic situation). The introduction of the chlorine solution into the network continues until the points farthest from the place of its supply contain at least 50% of the specified dose of active chlorine. From this moment on, the further supply of the chlorine solution is stopped and the network filled with the chlorine solution is left for at least 6 hours. At the end of the contact, chlorine water is drained and the network is washed with clean tap water. The conditions for discharging water from the network are determined on site in agreement with the authorities of the sanitary and epidemiological service. At the end of the flush (with a content of 0.3-0.5 mg / l of residual chlorine in the water), samples are taken from the network for control bacteriological analysis. Disinfection is considered complete if the results of two analyzes taken successively from one point are favorable.

Note: The estimated volume of chlorine solution for disinfecting the network is determined by the internal volume of the pipes with the addition of 3-5% (for a probable outflow). The volume of 100 m pipes with a diameter of 50 mm is 0.2 m 3, 75 mm - 0.5 m 3, 100 mm - 0.8 m 3, 150 mm - 1.8 m 3, 200 mm - 3.2 m 3 , 250 mm - 5 m 3.

24. Washing and disinfection of water supply structures and networks is carried out by the forces and means of the construction organization (before putting them into operation) or the water supply administration (after repair and emergency work) in the presence of representatives of the sanitary and epidemiological service. The results of the work are documented in an act, which indicates the dosage of active chlorine, the duration of chlorination (contact) and final flushing, data from control analyzes of water. On the basis of these materials, the local authorities of the sanitary and epidemiological service give an opinion on the possibility of putting the facilities into operation.

25. With the publication of this instruction "Instructions for the disinfection of household drinking water with chlorine at centralized and local water supply" N 203-56 dated January 26, 1956 is canceled.

______________________________

* Prepared by the Institute of General and Communal Hygiene named after A.N. Sysina of the USSR Academy of Medical Sciences.

** The term "disinfection" means the treatment of water, and the term "disinfection" means the treatment of water supply facilities and networks with disinfectants.

Appendix N 1

I. Determination of the content of active chlorine and bleach

Reagents:

1.10% solution of potassium iodide

2. Hydrochloric acid (1: 5 by volume)

3.0.01 N sodium hyposulfite solution

4.1.5% starch solution

Analysis progress: 3.55 g of bleach are weighed out, ground in a porcelain mortar with a little water and a homogeneous slurry and diluted with a little more water. Then the liquid is poured into a volumetric flask, the mortar is rinsed several times, and the volume of the liquid is brought to 1 liter.

5 ml of potassium iodide solution, 5 ml of hydrochloric acid, 10 ml of settled bleach solution and 50 ml of distilled water are poured into a flask with a ground stopper. In this case, free iodine is released, in an amount equivalent to the active chlorine contained in the lime under study. After 5 min. the released iodine is titrated with 0.01 hyposulfite solution to a pale yellow color, then 1 ml of starch solution is added and titrated until the blue color disappears. The amount of ml of 0.01 N hyposulfite solution consumed for titration directly indicates the% of active chlorine in the bleach under study.

II. Quantification of residual active chlorine in tap water

Iodometric method

Reagents:

1. Potassium iodide, chemically pure crystalline, does not contain free iodine.

Checking. Take 0.5 g of potassium iodide, dissolve in 10 ml of distilled water, add 6 ml of buffer mixture and 1 ml of 0.5% starch solution. The reagent should not turn blue.

2. Buffer mixture: pH \u003d 4.6. Mix 102 ml of a molar solution of acetic acid (60 g of 100% acid in 1 liter of water) and 98 ml of a molar solution of sodium acetate (136.1 g of crystalline salt in 1 liter of water) and bring to 1 liter with distilled water, previously boiled.

3. 0.01 N sodium hyposulfite solution.

4. 0.5% starch solution.

5. 0.01 N solution of potassium dichromate. The titer of 0.01 N hyposulfite solution is set as follows: 0.5 g of pure potassium iodide is poured into the flask, dissolved in 2 ml of water, first 5 ml of hydrochloric acid (1: 5), then 10 ml of 0.01 N solution of dichromate potassium and 50 ml of distilled water. The released iodine is titrated with sodium hyposulfite in the presence of 1 ml of starch solution added at the end of the titration. The correction factor for the titer of sodium hyposulfite is calculated using the following formula: K \u003d 10 / a, where a is the number of milliliters of sodium hyposulfite used for titration.

Analysis progress:

a) introduce 0.5 g of potassium iodide into a conical flask;

b) add 2 ml of distilled water;

c) stir the contents of the flask until the potassium iodide dissolves;

d) add 10 ml of buffer solution, if the alkalinity of the test water is not higher than 7 mg / eq. If the alkalinity of the test water is higher than 7 mg / eq, then the number of milliliters of the buffer solution should be 1.5 times the alkalinity of the test water;

e) add 100 ml of test water;

f) titrate with hyposulfite until the solution is pale yellow;

g) add 1 ml of starch;

h) titrate with hyposulfite until the blue color disappears.

Calculation: The content of active chlorine in mg / l in the test water is calculated by the formula:

X = 3,55 ´ H ´ TO

where H - the number of ml of hyposulfite consumed for titration,

TO - correction factor for sodium hyposulfite titer.

Orthotolidine method

Reagents:

1. 0.1% solution of orthotolidine - 1 g of orthotolidine is transferred into a porcelain cup, add 5 ml of 20% hydrochloric acid, grind into a paste and add 150-200 ml of distilled water. After dissolving orthotolidine, the solution is transferred to a liter cylinder, brought to 505 ml with distilled water and then brought to 1 liter with 2% hydrochloric acid.

2. A scale of constant standards, imitating the color of active chlorine standards. Prepare 2 solutions:

a) 15 g of copper sulfate (CuSO 4´ 5H 2 O) and 10 ml of strong sulfuric acid are dissolved in distilled water and brought to 1 liter.

b) 0.25 g of potassium dichromate (K 2 Cr 2 O 7) and 1 ml of strong sulfuric acid are dissolved in distilled water and brought to 1 l.

The number of solutions "a" and "b" indicated in the table is introduced into Nessler's cylinders, and the volume is brought to a volume of 100 ml with distilled water. The standards are stored sealed for no more than 6 months, protected from direct sunlight.

Active chlorine mg / l	Solution "a" ml	Solution "b" ml	Analysis progress
		10,0	1 ml of orthotolidine and 100 ml of test water are added to the Nessler cylinder, mixed and left in a dark place. After 5-10 minutes. compare the color to the standard scale by looking from above. A standard with a matching color indicates the content of active chlorine in water mg / l.
		20,0
		30,0
		38,0
		45,0
		51,0
		58,0
		63,0
		67,0
		72,0

Note:

1) The test water should be at room temperature (about 20 ° C).

2) If color is present in the test water, apply color compensation by looking from the side.

III. Method of choosing a working dose of chlorine for water disinfection

3 cans are filled with 1 liter of the test water to be chlorinated. Then, a 1% bleach solution is added to each jar in an amount roughly indicated in the table.

Source nature and water quality	For disinfection		The required amount of 1% bleach solution in l per 1 cubic meter. or in ml per 1 l
	g per 1 cubic meter or mg per liter
	active chlorine	25% bleach
Artesian waters, waters of clean mountain rivers, clarified, filtered water of large rivers and lakes	1-1,5		0,4-0,6
Clear well water and filtered water from small rivers	1,5-2		0,6-0,8
Water of large rivers and lakes		8-12	0,8-1,2
Contaminated water from open sources	5-10	20-40

After adding bleach, the contents of each jar are thoroughly mixed and left alone for 30 minutes. Then, in all banks, the content of residual chlorine in the water is determined and a bacteriological study is performed.

To determine the residual chlorine, 5 ml of a 10% solution of potassium iodide, 10 ml of a buffer solution (see the description of the iodometric method) are poured into the flask and 200 ml of chlorinated water is introduced with a pipette from a jar. The liberated iodine is titrated with 0.01 N hyposulfite solution to a pale yellow color, 1 ml of 0.5% starch solution is added and titrated until the blue color disappears. Residual chlorine content in mg / l is 0.355´ 5H, where H is the number of ml of hyposulfite consumed for titration. After 30 minutes of contact with chlorine, 1 ml of 1% sodium hyposulfite solution, previously sterilized by boiling (to bind excess chlorine), is introduced into the water remaining in the jars. After that, the number of E. coli and the total number of bacteria in the water are determined in accordance with the rules of bacteriological analysis (GOST 5215-50).

The optimal working dose of chlorine is considered to be that at which the number of preserved Escherichia coli does not exceed 3 in 1 liter of water, and the total number of bacteria is not more than 100 in 1 ml. The content of residual chlorine must not exceed 0.5 mg / l.

If in all samples of the investigated water a sufficient disinfection effect is not obtained or the content of residual chlorine exceeds 0.5 mg / l, then the experiment is repeated with higher or lower doses of chlorine.

Note: In the conditions of local water supply, in the absence of the possibility of conducting bacteriological analysis, the dose of chlorine is established on the basis of determining the concentration of residual chlorine in the water and determining the intensity of the smell of chlorinated water. As a working dose for chlorination, take the dose at which the water acquired a faint smell of chlorine, and the residual chlorine content in it is at the level of 0.3-0.5 mg / l.

IV. Method for the separate determination of free and bound (chloramine) active chlorine

Reagents:

1.1% alcohol solution of hydrochloric acid paraaminodimethylaniline (dimetidparaphenylenediamine): 1 g is dissolved in 100 ml of ethyl alcohol (rectified). It is used as an indicator.

2. Phosphate buffer solution pH \u003d 7.0´ 3.54 g of monosubstituted potassium phosphate (KN 2 PO 4) and 8.6 g of disubstituted sodium phosphate (Na 2 HPO 4´ 12H 2 O) is dissolved in 100 ml of distilled water.

3.1% potassium iodide solution: 1 g in 100 ml of distilled water (store in a dark glass bottle).

4. 2.5% solution of oxalic acid: 2.5 g in 100 ml of distilled water.

5.01 N solution of ferrous sulfate (FeSO 4´ 7H 2 O) is prepared from a basic 0.1 N solution by diluting it 10 times with distilled water. To prepare the stock solution, 28 g of FeSO 4 are weighed´ 7Н 2 О and transferred into a volumetric flask (liter), dissolved in distilled water, acidifying a solution of 2 ml of sulfuric acid (1: 3), and then brought to the mark with water.

The titer of 0.01 N solution is adjusted to 0.01 N solution of potassium permanganate: 25 ml of FeSO 4 solution is added to the flask and 2 ml of sulfuric acid (1: 3) is added and titrated in the cold with KMnO 4 solution until pink color does not disappear within 30 sec.

Analysis progress:

a) Add 1 ml of buffer solution and 2 ml of indicator to a flask with 100 ml of test water. In the presence of free chlorine, the water turns pink (due to the formation of semiquinone). Vigorously stirring the sample, titrate with a solution of ferrous sulfate until discoloration (1st titration);

b) Add 1 ml of potassium iodide to the same sample. In the presence of monochloramine in the water, an equivalent amount of iodine is released, under the influence of which a pink color is formed again.

Titrate the sample with iron sulfate solution until discoloration (2nd titration).

c) Then add 1 ml of oxalic acid to the same sample. If dichloramine is present in the water, a pink color reappears, in the presence of which the sample is titrated with a solution of ferrous sulfate until it is ensured (3rd titration).

The calculation is made according to the formula:

X = 0,355 ´ TO ´ H ´ 10 where

X - concentration of free, monochloramine or dichloramine chlorine in water in mg / l.

H - the number of ml of the consumed solution of ferrous sulfate, respectively: during the first titration - to calculate free chlorine, the second - monochloramine, the third - dichloramine;

TO - the titer coefficient of the solution of ferrous sulfate. 0.355 - titer for active chlorine 0.01 N growth of iron sulfate at TO=1,0;

10 - coefficient for recalculating the concentration of chlorine per 1 liter of water (when titrating 100 ml)

Example: The titer coefficient of the ferrous sulfate solution is 0.98, i.e. when setting the titer to 25 ml of ferrous sulfate, 24.5 ml of 0.01 N solution of potassium permanganate went. For 100 ml of the test water, a solution of iron sulfate was consumed during titration: the first - 0.1 ml, the second - 0.05 ml, the third - 0 (after adding oxalic acid, there was no pink coloration). The test water contains: free chlorine - 0.35 mg / l

X = 0,355 ´ 0,98 ´ 0,1 ´ 10 and monochloramine - 0.17 mg / l

X = 0,355 ´ 0,98 ´ 0,05 ´ ten); dichloramine is absent.

Appendix N 2

Basic safety measures for water chlorination

1. When liquid chlorine is used, the chlorination room is located in an isolated room, which, in addition to the entrance from the pumping station, must have an emergency exit with a door opening from the chlorination room to the outside.

2. The chlorination room is equipped with mechanical ventilation, which provides 12-fold air exchange per hour. Exhaust openings for ventilation are located no higher than 30 cm from the floor, and the fan outlet pipe is 2 m above the roof ridge. The fan motor must be turned on from the vestibule before entering the chlorination room.

Note: Installations for ammonization (ammonia cylinders, scales, flow meters) should be located in a separate room, isolated from the chlorination room. The room is equipped with exhaust ventilation with air suction from the ceiling.

3. The chlorination room must have good lighting, natural and electric, with such an installation of light sources that the divisions on the meter scale are clearly visible: the estimated air temperature in the room must be at least + 18 °.

4. In the vestibule in front of the entrance to the chlorination room, there are cabinets for storing overalls and gas masks (one for each attendant), a first-aid kit for emergency assistance, and a pillow with oxygen.

5. Cylinders with chlorine are installed on portable vertical stands in order to be able to easily remove them from the premises; it is forbidden to fix cylinders against the walls. Cylinders connected to chlorinators are installed on the existing scales in order to control the chlorine consumption. An intermediate cylinder (receiver) must be placed between the pressure reducing valve of the working cylinders and the inlet valve of the chlorinator to purify chlorine before releasing it into the chlorinator (gas meter).

6. When entering the chlorination room, turn on the fan and make sure that there is no characteristic smell of chlorine. If you smell chlorine, wear a gas mask and take steps to stop the gas leak. The place of the leak is determined by wetting the joints of the compounds with ammonia, upon interaction with which chlorine forms a white cloud.

7. Defective chlorine cylinders are immediately removed from the chlorination room. To neutralize them, a container with a depth of 2 m and a diameter of 1.5 m is arranged in the yard, filled with a solution of lime and having a water supply. The tank must have waterproof walls and a bottom; it is located at least 10 m from the exit from the chlorination room.

8. Smoking is prohibited in the chlorination room.

9. Heating of cylinders and chlorine-conducting tubes (when they freeze) is carried out by applying rags soaked in hot water; it is prohibited to use blowtorches, primus, electric stoves.

10. Transportation of chlorine from the warehouse to the chlorination room is carried out by road transport or on spring carts. Loading and unloading cylinders (or barrels) with chlorine is done with extreme caution, avoiding impacts, damaging the valves, rolling the cylinders with your foot on the ground. The cylinders are stacked on wooden lining with cut-out seats, well-fixed in the body, and covered with a tarpaulin in sunny weather to prevent heating.

11. When using bleach, working solutions should be prepared in a room equipped with ventilation, ensuring at least 5-fold air exchange per hour.

12. When preparing bleach solutions, work is carried out in gas masks and in overalls (dressing gowns, overalls, rubber boots, gloves).

13. After finishing work, shower should be provided.

11.02.10

What is the danger of chlorination of tap water?

Chlorination of water is the most common way of disinfecting drinking water using gaseous chlorine or chlorine-containing compounds that react with water or dissolved salts in it. As a result of the interaction of chlorine with proteins and amino compounds contained in the membrane of bacteria and their intracellular substance, oxidative processes, chemical changes in the intracellular substance, decay of the cell structure and the death of bacteria and microorganisms occur.

Disinfection (disinfection) of drinking water is carried out by dosing chlorine, chlorine dioxide, chloramine and bleach (not to be confused with the term purification of drinking water from lime). The required dose of the dosed substance is established by a trial chlorination of water: it is determined by the chlorine absorption of water (the amount of chlorine required to bind organic compounds contained in water).

In order to destroy microbes, chlorine is introduced in excess on the basis that 30 minutes after water chlorination, the residual chlorine content is at least 0.3 mg / l. In some cases, double chlorination of water is carried out - before filtration and after water purification. Also, in case of epidemiological disasters, superchlorination is carried out, followed by dechlorination of water.

For the chlorination of water at water treatment plants, liquid chlorine and bleach are used (for small-capacity plants).
Chlorination of water with liquid chlorine. When chlorine is introduced into water, hypochlorous and hydrochloric acids are formed

NOS1 h * H + + OC1-.

The hypochlorous ions OC1 ~ resulting from the dissociation of hypochlorous acid possess, along with the undissociated molecules of hypochlorous acid, bactericidal properties.

The sum of C12 + HOC1 + OC1- is called free active chlorine.

In the presence of ammonium compounds in the water or with the special introduction of ammonia into the water (ammonization of water - see § 114), monochloramines NH2CI and dichloramines NHCb are formed, which also have a bactericidal effect, somewhat less than free chlorine, but longer. Chlorine in the form of chloramines, in contrast to free chlorine, is called with bound active chlorine.

The amount of active chlorine required for water disinfection should be determined not by the number of pathogenic bacteria, but by the total amount of organic substances and microorganisms (as well as inorganic substances capable of oxidation) that may be in the chlorinated water.

Proper chlorine dosing is essential. An insufficient dose of chlorine can lead to the fact that it does not have the necessary bactericidal effect; an excessive dose of chlorine impairs the taste of water. Therefore, the chlorine dose should be set depending on the individual properties of the water being purified on the basis of experiments with this water.

The calculated dose of chlorine in the design of a disinfecting installation should be taken on the basis of the need to purify water during the period of its maximum pollution (for example, during floods).

The indicator of the sufficiency of the accepted dose of chlorine is the presence in the water of the so-called residual chlorine (remaining in the water from the administered dose after the oxidation of the substances in the water). According to the requirements of GOST 2874-73, the concentration of residual chlorine in water before it enters the network must be in the range of 0.3-0.5 mg / l.
The content of free residual chlorine in drinking water is regulated by SanPiN 2.1.4.1074-01 "Drinking water. Hygienic requirements for water quality in centralized drinking water supply systems. Quality control" (the content of free residual chlorine in water is 0.3 - 0.5 mg / l) and SanPin 2.1.4.1116 - 02 “Drinking water. Hygienic requirements for the quality of water packaged in containers. Quality control "(content of free residual chlorine in water is not more than 0.05 mg / l). The limiting sign of the harmfulness of the substance, according to which the standard is established, is organoleptic (although this is far from the case ...)

Chlorine is our modern day's worst enemysince it has been used as a drinking water disinfectant since 1904. By preventing some diseases, it is the cause of the appearance of other, more terrible diseases: heart problems, cancer, and also premature old age. Ironically, even chlorine, widely used as a water disinfectant, turns out to be a dangerous carcinogen.

On the one hand, chlorination of water has saved humanity from the risk of infectious diseases and epidemics. On the other hand, scientists in the 70s and 80s found that chlorinated water promotes the accumulation of carcinogenic substances in water. Among the population consuming chlorinated drinking water, cases of cancer of the esophagus, rectum, breast, larynx, and liver disease have been identified. Because when chlorine interacts with organic substances in water, chemicals are formed. These substances - trichlomethanes- are carcinogenic, which has been proven by scientists empirically. After all, as you know, chloroform causes cancer even in rats.

This effect from the harmful effects of chlorine can be caused in two ways: when chlorine enters the body through the respiratory tract, and when chlorine enters through the skin. Scientists all over the world are researching this problem. They associate many dangerous diseases with the ingestion of chlorine or harmful by-products of water chlorination into the human body. These diseases include: bladder cancer, stomach cancer, liver cancer, rectal and colon cancer. But not only the digestive organs are affected.

What is the problem?

The most important problem of this method is the high activity of chlorine, it enters into chemical reactions with all organic and inorganic substances in the water. Water from surface sources (which are mainly sources of water intake) contains a huge amount of complex organic substances of natural origin, and in most large industrial cities, dyes, surfactants, oil products, phenols, etc., enter the water with industrial effluents.

Chlorination of water containing the above substances produces chlorine-containing toxins, mutagenic and carcinogenic substances and poisons, including dioxides, namely:

Chloroform with carcinogenic activity

Dichlorobromomethane, chloride bromomethane, tribromomethane - mutagenic

2,4,6-trichlorophenol, 2-chlorophenol, dichloroacetonitrile, chlorgyeredine, polychlorinated biphenyls - which are immunotoxic and carcinogenic substances

Trihalomethanes - carcinogenic chlorine compounds

These substances have a delayed killing effect on the human body. Purification of drinking water from chlorine does not solve the problem, since many of the hazardous compounds formed in the water during its chlorination process enter the human body through the skin, during washing, taking baths or visiting the pool. According to some reports, one hour of taking a bath containing an excessive amount of chlorinated water corresponds to ten liters of drunk chlorinated water.

The first attempts to link the oncological incidence of the population with the quality of drinking water were made back in 1947. But until 1974, chlorination of water was in no way associated with oncology. It was believed that chlorinated water does not adversely affect human health.

Unfortunately, data on the relationship between the consumption of chlorinated drinking water from surface water sources and the incidence of malignant neoplasms in the population began to accumulate only since the 70s. Therefore, there are still different points of view on this matter. According to some researchers, from 30 to 50% of cases of malignant tumors can be associated with the use of contaminated water. Others cite calculations according to which the consumption of river water (compared to water from underground sources) can lead to an increase in cancer incidence by 15%.

What is dangerous chlorine entering the human body

The side effect of the harmful effects of chlorine can be caused in two ways: when chlorine enters the body through the respiratory tract, and when chlorine enters through the skin. Scientists all over the world are researching this problem. They associate many dangerous diseases with the ingestion of chlorine or harmful by-products of water chlorination into the human body. These diseases include: bladder cancer, stomach cancer, liver cancer, rectal and colon cancer.

But not only the digestive organs are affected... Chlorine can also cause heart disease, atherosclerosis, anemia, high blood pressure. In addition, chlorine dries the skin (remember the feeling of tightness after the pool), destroys the hair structure (they begin to fall out more, become brittle, dull, lifeless), irritate the mucous membrane of the eyes.

US epidemiologists conducted a study: they compared a map of water chlorination with a map of the distribution of diseases of the bladder and digestive organs. A direct relationship was found: the higher the chlorine content in the water, the more often the disease occurs.

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British scientists from the University of Birmingham said that the consumption of chlorinated water during pregnancy can lead to the birth of children with severe birth defects - in particular, with heart and brain defects.

Experts led by Yuni Jaakkola studied data on 400,000 babies to find out how eleven of the most common birth defects are associated with high, medium or low chemical substancesemerging during chlorination in drinking water.

As you know, chlorination is a fairly common method of disinfection, which leads to a significant reduction in infections transmitted with drinking water. But one of the disadvantages of this method is the formation of by-products, most of which are so-called trihalomethanes, in particular chloroform, dichlorobromomethane, dibromochloromethane and bromoform.

As a result of the study, it turned out that a high level of chlorination by-products from 50 to 100% increased the risk of three congenital defects - a defect of the interventricular septum of the heart (a hole in the septum between the ventricles of the heart, which leads to mixing of arterial and venous blood and chronic lack of oxygen), so called the cleft palate (cleft in the palate), as well as anencephaly (complete or partial absence of the bones of the cranial vault and brain).

“The biological mechanisms that lead to birth defects with high levels of chlorination byproducts are still unknown. But our study not only provides additional evidence that chlorination can lead to birth defects, but also shows that the presence of its byproducts may be associated with some specific vices, "says Jaakkola.

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Chlorine is harmful to health a person should not be underestimated, doctors say. Despite the fact that water treatment plants use relatively low concentrations, even they are harmful to animal and human health. Inhalation of high concentrations of chlorine can be fatal to humans and cause a variety of illnesses, from headaches to neurotoxic reactions, possibly even the development of cancerous tumors.

Moreover, as experts note, water toxins enter the body not only through the respiratory system. Chlorine strips the skin of its natural fatty membrane, dries out, causes itching and premature aging. Even hair becomes dry and brittle when exposed to chlorinated water.

Chlorination of water is the most popular way to disinfect it, but not the safest one. The main risks of consuming tap water are associated with the by-products of chlorine when combined with other substances. There is evidence that this may contribute to the onset of cancer. Moreover, poor-quality water is the cause of 90% of diseases, and consuming good quality water can prolong life by 5-8 years.

Based on materials: www.bibliotekar.ru, www.ekomarket.ru, RBK.ru, RIA Novosti