State Sanitary and Epidemiological
rationing Russian Federation

4.1. CONTROL METHODS. CHEMICAL FACTORS

Determination of the concentration of residual free chlorine in drinking and fresh water natural water chemiluminescent method

MUK 4.1.965-99

Russian Ministry of Health

Moscow 2000

1. Guidelines developed federal center State Sanitary and Epidemiological Supervision Ministry of Health of the Russian Federation ( N. S. Lastenko, I. V. Bragina, V. B. Skachkov) and VAKhZ, ENTC "EkMOS" ( V. A. Ishutin, A. A. Stekhin, I. A. Pushkin, G. V. Yakovleva, A. A. Simonov)

2. Approved and put into effect by the Chief State Sanitary Doctor of the Russian Federation G. G. Onishchenko on March 22, 2000.

3. Introduced for the first time.

3.3. materials

Filter paper

3.4. Reagents

4. Safety requirements

4.1. When working with reagents, the safety requirements established for toxic, caustic and flammable substances in accordance with GOST 12.1.005-88 are observed.

4.2. When performing measurements using the LIK device, observe the electrical safety rules in accordance with GOST 12.1.019-79 and the instruction manual for the device.

5. Qualification requirements for operators

Persons qualified as a chemical technician with experience in working with the LIK device are allowed to perform measurements.

6. Measurement conditions

When performing measurements, the following conditions are met:

6.1. Preparation of solutions and preparation of samples for analysis are carried out under normal conditions at an air temperature of 20 + 15 ° C, atmospheric pressure of 630-800 mm Hg. Art., air humidity up to 90%.

6.2. Measurements on the LIK device are carried out under conditions recommended technical documentation to the LIK device.

7. Preparing to take measurements

7.1. Preparing to plot a graduated graph

7.1.1. open water faucet and 10 minutes after the expiration of water from it, rinse a 2-3 liter jar three times and pour 1.5-2.0 (2.5-3.0) dm 3 of water into it. The bank is closed paper napkin and let it stand for 24 hours at room temperature. Measured with a pH meter pH value and sulfuric (nitric) acid bring it to a value of (4.5 ± 0.2).

7.1.2. Preparation of chlorine water.

A flask with a ground stopper with a capacity of 500 cm 3 is rinsed three times with water prepared according to. and pour 400 cm 3 of this water into it. Then a weighed amount of calcium hypochloride or chlorinated water with a known concentration of active free chlorine is added to the flask in such an amount that 2.0-2.5 mg of residual chlorine is contained in 1000 cm 3 of the source water. After that, water prepared according to is introduced into the flask. to the mark, close it with a stopper and mix thoroughly by shaking for 5 minutes.

7.2. Determination of the initial concentration of active free chlorine in chlorine water

7.2.1. Preparation of a 0.005% solution of methyl orange. 50 mg of methyl orange are dissolved in distilled water, in a flask with a capacity of 1000 cm 3, 1 cm 3 of this solution is equivalent to 0.0217 mg of residual free chlorine.

7.2.2. Preparation of 5 N solution of hydrochloric acid.

60-70 cm 3 of distilled water are poured into a volumetric flask with a capacity of 1000 cm 3 and 40 cm 3 of concentrated hydrochloric acid are slowly added in portions, the volume of the flask is brought to the mark with distilled water.

7.2.3. Determination of the concentration of residual free chlorine. 100 cm 3 of analyzed chlorine water is poured into a porcelain cup, 3 drops of 5 N hydrochloric acid solution are added, mixed and quickly titrated with a solution of methyl orange until a persistent pink color appears. The concentration of residual free chlorine is calculated by the formula:

X \u003d (mg / dm 3), where

The amount of 0.005% methyl orange solution used for titration, cm 3;

0.0217 - titer of methyl orange solution;

0.04 - empirical coefficient;

V - the volume of the initial chlorine water of the sample, cm 3 .

7.4. Building a Graded Plot

7.4.1. Carrying out the analysis of chlorine water with the initial concentration of residual free chlorine on the LIK device.

Attention!When constructing a graph, in order to avoid contamination of the reagent, one nozzle of the pipette dispenser is used only for the selection of the reagent, and the second - for chlorine water.

The lid of the device is moved forward as far as it will go, the dosing lid is removed, a glass cuvette is removed from the reaction chamber and 0.1 cm 3 of the luminol-based reagent is poured into it with a pipette dispenser. The cuvette with the reagent is placed in the reaction chamber and closed with a dosing cap. Then, 0.2 cm 3 of chlorine water, prepared using a pipette dispenser, is introduced into the cavity of the dispenser cap, after changing its tip.

The cover of the device is moved all the way back, pressed on it by hand, and the readings of the device are taken. The determination is repeated 5 times, the average value of the signal is calculated, which will correspond to the initial concentration of residual free chlorine in the prepared chlorine water.

7.4.2. Preparation of dilutions from the original chlorine water.

5 clean test tubes with a ground-in stopper are rinsed three times with water prepared according to. Into each test tube, respectively:

1 - 0.5 cm 3; 2 - 1.0 cm 3; 3 - 1.5 cm 3; 4 - 2.0 cm 3; 5 - 2.5 cm 3 of the initial chlorine water, prepared according to., in the same test tubes, respectively, make:

1 - 4.5 cm 3; 2 - 4.0 cm 3; 3 - 3.5 cm 3; 4 - 3.0 cm 3; 5 - 2.5 cm 3 of water prepared according to. The tubes are stoppered and the contents are thoroughly mixed by shaking for 3 minutes. If the initial concentration of free active chlorine in water was 2.0 mg / dm 3, then: in test tube 1 - 0.2 mg / dm 3, in test tube 2 -0.4 mg / dm 3, in test tube 3 - 0.6 mg/dm 3 , in test tube 4 - 0.8 mg/dm 3 , in test tube 5-1.0 mg/dm 3 .

After preparing the dilutions of chlorine water, they are analyzed on the LIK device, as indicated in. and according to the data obtained, a calibration graph is built in the coordinates: the value of the measured signal (relative units) - the concentration of free active chlorine (mg / dm 3).

The constructed graph is refined and corrected only after the VCI device has been verified (once a year) by analyzing three dilutions of chlorine water with a known concentration.

8. Performing measurements of the concentration of residual free chlorine in tap water

8.1. Determination of residual free chlorine in water

Open the tap and 10 minutes after the outflow of water from it into a measuring glass with a volume of 100 cm 3, 70 - 80 cm 3 are taken and analyzed on the LIK device, as indicated in. Calculate the average value of the signal and the graduated graph determine the desired value of the concentration of residual free chlorine.

8.2. Determination of bound residual free chlorine

In a measuring glass with a volume of 100 cm 3 add 2 drops of 20% sulfuric acid. Open the tap and 10 minutes after the outflow of water from it, 50-60 cm 3 of water are taken into the glass, stirred for 1 minute and analyzed on the LIK device, as indicated in.

The average value of the signal is calculated, the desired concentration is determined from the calibration curve, and the value of the residual free chlorine concentration, obtained by , is subtracted from the obtained value. The difference determines the concentration of bound free chlorine in the form of chlorine, dichloramine.

8.3. Determination of chlorine capacity of water

Chlorine is added in portions to the source purified water, mixed, a sample of 100 cm 3 is taken, 30 minutes after the addition of chlorine, it is analyzed on the LIK device, as indicated in. The value of the signal on the device should correspond to the concentration of residual free chlorine 0.01-0.02 mg/dm 3 .

9. Registration of measurement results

The measurement results are documented in the protocol in the form:

Protocol No.

Protocol for the determination of residual chlorine

1. Date of analysis ______

2. Sampling location ____________

3. Name of laboratory __________

4. Legal address _____________

Results of chemical analysis

Responsible executor

Laboratory manager

10. Measurement error control

The control of the error in measuring the content of chlorine in water is carried out using prepared chlorine water with a concentration of chlorine in it of 2.0-2.5 mg/dm 3 . + Δ , then the reproducibility of the measurement is satisfactory. If not, then eliminate the causes.

When chlorine is dissolved in water, hydrochloric and hypochlorous acids are formed:

Cl 2 + H 2 O ↔ H + + Cl - + HClO.

Chlorine is called active, which stands out in free form when a substance reacts with hydrochloric acid. The mass fraction of active chlorine in the substance (in percent) is equal to the mass of molecular chlorine, which is released from 100 g of the substance when interacting with an excess of HCI. The term "active chlorine" includes, in addition to dissolved molecular chlorine, other chlorine compounds, such as chloramines (monochloramine - NH 2 Cl and dichloramine - NHCl 2, and also in the form of nitrogen trichloride NCl 3), organic chloramines, hypochlorites (hypochlorite -anion ClO -) and chlorites, i.e. substances determined by the iodometric method.

Cl 2 + 2I - \u003d I 2 + 2Cl -

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

HClO + H + + 2I - = I 2 + Cl - + H 2 O

NH 2 Cl + 2H + + 2I - \u003d I 2 + NH 4 + + Cl -.

Active chlorine contains many substances. The oldest is known as javel water (Javel is a suburb of Paris), which was prepared back in 1785 by C. Berthollet from chlorine and potassium liquor and proposed to replace chlorine water for bleaching fabrics with it. Since 1820, they began to use the sodium analogue of zhavel water - "Labarac liquid". These solutions usually contain 8 to 15% available chlorine. Wide application found bleach - a cheap technical product with a variable composition, which depends on the conditions of production. It bleaches fabrics and cellulose, disinfects wastewater, neutralizes toxic substances. Hypochlorite solutions are used to flush polymer coatings with metal meshes in the production of capacitors or for the treatment of polymer soles so that they better adhere to the upper of the shoe.

The iodometric method of determination is based on the fact that chlorine-containing strong oxidizing agents release iodine from an iodide solution. The released iodine is titrated with sodium thiosulfate solution using starch as an indicator. The results of the determination are expressed in mg Cl per 1 liter of water. The sensitivity of the method is 0.3 mgCl/L with a sample volume of 250 ml, however, when using solutions of thiosulfate with different concentrations, the sample volume can be, depending on the required sensitivity of the determination, from 500 to 50 ml of water or less.

The content of active chlorine is determined in a disinfected drinking water, in wastewater contaminated with chlorine or chlorine-releasing compounds. In natural water, the content of active chlorine is not allowed; in drinking water, its content is set in terms of chlorine at the level of 0.3-0.5 mg/l in free form and at the level of 0.8-1.2 mg/l in bound form. Active chlorine in the indicated concentrations is present in drinking water for a short time (no more than several tens of minutes) and is completely removed even with short-term boiling of water. When determining active chlorine, samples cannot be preserved; the determination should be carried out immediately after sampling. The limiting indicator of harmfulness for active chlorine is general sanitary.

Objective: measurement of active chlorine content in water and in samples disinfectants.

Research objects: samples tap water and samples of disinfectants containing chlorine-containing substances.

Reagents and equipment:

• buffered acetate solution (pH = 4.5),
• potassium iodide,
• universal indicator paper,
• 0.5% starch solution,
• 0.005 N sodium thiosulfate solution,
• burettes, 250 ml conical flasks, 100 ml graduated cylinder, glass rods, 5 ml pipettes,
• scales.

Working process:

1) Conduct a preliminary study of the samples for the content of active chlorine, for example, using a test system. If necessary, dilute the samples.

The sample volume required for analysis at a concentration of active chlorine from 0.5 to 5.0 mg/l is 50 ml, at a concentration of 0.3 to 0.5 mg/l - 250 ml.

2) Pour 0.5 g of CI into a conical flask and dissolve in 1-2 ml of distilled water.

3) Add 1 ml of buffer solution and then 50-250 ml of analyzed water (depending on the preliminary results of the analysis).

3) Close the flask with a stopper and place in a dark place. After 10 minutes, titrate the released iodine with 0.005 N sodium thiosulfate until a light yellow color appears, then add 1 ml of 0.5% starch solution and continue titrating until the blue color disappears.

4) Carry out calculations and draw conclusions.

X \u003d (a. K. 0.177. 1000) / V,

where: X – total residual chlorine, mg/l;

a – volume of 0.005 N sodium thiosulfate solution used for titration, ml;

K - correction factor;

V is the volume of the analyzed sample;

Additional Information. Chlorine content. Before deciding on cleaning waste water chlorination, it is specially investigated. In this case, it is necessary to determine at what rate the reactions between the substances contained in the water and chlorine proceed, whether they reach the end, what excess of added chlorine is required in order for the reaction to proceed to the desired degree in a given period of time t.

OA- shows the content of substances that are rapidly oxidized by chlorine.

AK- the process of oxidation and chlorination of substances that slowly react with chlorine, which do not have time to react during the experiment and remain in solution together with residual chlorine.

HF– absence of substances that react with chlorine.

Questions and tasks for independent work:

1. Why is water chlorinated? What are the advantages and disadvantages of using chlorinated drinking water?

2. Can you suggest other approaches to solving this problem? State the advantages and disadvantages of each of the proposed methods.

3. How much active chlorine contains one ton of substance with mass fraction its 52%?

4. Why is chloroform stored in dark flasks filled to the top?

5. Formally, active chlorine can contain compounds in which there is no chlorine at all - after all, this concept does not determine the true content of chlorine in the compound, but its oxidizing ability with respect to KI in an acidic environment. Suggest several compounds in the solutions of which "active chlorine" can be determined.

Preparation of solutions

1. To prepare a 0.01 N solution of sodium thiosulfate, 2.5 g of it is dissolved in freshly boiled and cooled distilled water, 0.2 g of Na 2 CO 3 is added and the volume is adjusted to 1 liter.

2. To prepare a 0.005 N solution of sodium thiosulfate, add 500 ml of a 0.01 N solution of sodium thiosulfate, 0.2 g of Na 2 CO 3 to a 1 liter volumetric flask and bring the volume to the mark. The solution is used when the content of active chlorine is less than 1 mg/l.

3. To prepare a 0.5% starch solution, mix 0.5 g of soluble starch with a small amount of distilled water, and then pour it into 100 ml of boiling distilled water and boil for several minutes. After cooling, the solution is preserved by adding chloroform or 0.1 g of salicylic acid.

4. To prepare acetate buffer (pH = 4.5), 102 ml of 1 M acetic acid (60 g of glacial acetic acid in 1 liter of distilled water), 98 ml of 1 M sodium acetate solution (136.1 g CH 3 COONa. 3H 2 O in 1 liter of distilled water) and bring the volume of the solution with distilled water to the mark.

1. Determination of free active chlorine (iodometric method)

When introduced into water, chlorine hydrolyzes, 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 they are discharged after treatment into a sewer or reservoir. When dumping NE into a reservoir after a full biological treatment the content of residual free active chlorine should not exceed 2.5 mg/dm 3 .

Method Essence. When the analyzed water is acidified and potassium iodide is added to it, all of the listed substances release iodine:

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

НClО + 2J - + H + = J 2 + Cl - + H 2 O

ClO - + 2H + + 2J - = J 2 + Cl - + H 2 O

NH 2 O + 2H + + 2J - = 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, such an expression of the results of the analysis is conditional, because one mole of these substances emits two iodine atoms and, therefore, corresponds to 2 moles of active chlorine, i.e. results are overstated.

Reagents

Sodium thiosulfate, 0.01 N solution;

Potassium iodide, acetic acid, 30% solution;

Starch, 0.5% solution.

Definition progress. 50 ... 100 ml of the 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 minutes, the released 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- volume of sodium thiosulfate solution used for titration, cm 3 ;

To- correction factor to bring the concentration of sodium thiosulfate solution to exactly 0.01 N;

V- the volume of the 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 "combined active chlorine"

Substances united by the concept of "active chlorine" are strong oxidizing agents Cl 2; HClO and ClO -, and "combined chlorine" are relatively weak oxidizing agents NH 2 Cl; NHCl 2 and NCl 3 formed during the chlorination of wastewater, containing ammonium ions, ammonia. The subsequent behavior of each of these substances when chlorinated wastewater is mixed with other wastewater as it passes through pipes varies considerably, so further separations are sometimes necessary.

With regard to "free active chlorine" is 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 determinations as follows.

Method Essence. In a neutral environment (pH=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 Mohr's salt solution. Then a very small amount of potassium iodide is introduced into the solution, the catalytic action of which leads to a rapid interaction of the monochloramine and the indicator with the formation of the same red color, which is titrated with Mohr's salt solution. Then potassium iodide is introduced in excess, and dichloramine enters the reaction, which is determined by the same titration. If the wastewater contains nitrogen trichloride NCl 3 , it will be partly identified as dichloramine NHCl 2 .

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

Reagents

N,N-diethyl-n-phenylenediamine, sulfate salt. Dissolve 0.15 g of the sulfate salt of diethyl-n-phenylenediamine 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 first added . The solution is diluted to 100 cm 3 and stored in an iron glass bottle;

Phosphate buffer solution, pH=6.9. Dissolve 48.4 g of Na 2 HPO 4 in distilled water. 2H 2 O and 30 g KH 2 PO 4 , add 100 cm 3 0.8% EDTA solution and dilute to 1 dm 3 ;

Mohr's salt standard solution Fe(NH 4) 2 (SO 4) 2 . 6H 2 O, 1 cm 3 of which corresponds to 0.1 mg of chlorine. In distilled water, 1 cm 3 of 25% (by volume) sulfuric acid is first introduced, 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, dissolve 10 g of KI in 100 cm 3 of distilled water.

Definition progress.

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

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

3. Determination of dichloramine. After determination of monochloramine, 10 cm 3 of a 10% potassium iodide solution are added, mixed, allowed to stand for 2 minutes and titrated with Mohr's salt solution until colorless.

It is assumed that total concentration active chlorine does not exceed 4 mg/dm 3 . Otherwise, a smaller sample volume is taken, and distilled water for dilution is introduced before the introduction of 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, cm3;

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

2. Determination of chlorine capacity

Wastewater treatment with chlorine or bleach solution is one of the most common and relatively cheap methods of disinfection and purification of wastewater from pollution by organic substances. But since WW usually contain substances that react with chlorine and substances that react with it very slowly or incompletely, and organic substances that are not oxidized by chlorine at all, determining the oxidizability of wastewater does not provide sufficient data to draw conclusions about how water will be chlorinated. Therefore, before deciding on the issue of WW purification by chlorination, it is specially studied. In this case, it is necessary to determine at what rate the reactions between the substances contained in the water and chlorine proceed (oxidation and substitution reactions by chlorine), whether they reach the end, what excess of added chlorine 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 wastewater using the so-called diagram method.

Chlorine is treated as filtered or settled water, and together with the suspensions contained in it.

Definition progress. A number of equal volume portions of the analyzed wastewater are taken and placed in vessels with ground stoppers, in which they are treated with various amounts of chlorine water (or bleach solution), the first portion - the smallest amount, the second - 2-3 times more, etc. d. It is recommended to carry out two series of such experiments, changing the duration of treatment. The first series of WW samples are treated with various amounts of chlorine for a very short time, for example 5 minutes. The results of these experiments show the presence in the SW of substances that rapidly react with chlorine. The second series of samples is processed for as long as the chlorination process will be carried out in the proposed treatment facilities (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 on the abscissa axes the amount of chlorine introduced into each solution in order, starting from the smallest, and on the ordinate axis the corresponding amount of remaining chlorine, and combine the obtained curve points (Fig. 1).

* On the territory of the Russian Federation, GOST R 51593-2000 applies.

** On the territory of the Russian Federation, GOST R 51232-98 applies.

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 sulphate (sodium thiosulfate) according to GOST 27068.

All reagents used in the assay must be of analytical grade (pure for analysis).

Porcelain evaporating cups according to GOST 9147.

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

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

Sodium phosphate disubstituted anhydrous according to GOST 11773.

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

Distilled water according to GOST 6709.

Diethyl paraphenylenediamine oxalate or sulfate.

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

4.3 . Training to analysis

4.3.1. Cooking standard solution Mora salts

1.106 g Mohr's salt Fe(NH 4 ) 2 (SO 4 ) 2 6H 2 O is dissolved in distilled water, acidified with 1 cm 3 of a 25% sulfuric acid solution H2SO4 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 number 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. It should be stored in dark place.

4.3.2. Preparation of phosphate buffer solution

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

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

0.1 g of diethyl paraphenylenediamine oxalate (or 0.15 g of 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 . Conducting an analysis

4.4.1. Determination of free chlorine content

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

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

4.4.2. Determination of the content of monochloramine

A crystal (2-3 mg) of potassium iodide is added to a flask with a titrated solution, the solution is stirred. In the presence of monochloramine, a pink color instantly appears, whichTitrate immediately with 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 content of monochloramine, about 1 g of potassium iodide is again 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 solution of Mohr's salt until the color disappears. Mohr salt consumption ( With, cm 3) corresponds to the content of dichloramine, mg/dm 3 .

4.5 . Results processing

X 3 = A+B+C,

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

AT- content of monochloramine, mg/dm 3 ;

With- the content of dichloramine, mg/DM 3 .

INFORMATION DATA

1. APPROVED AND INTRODUCED BY Decree State Committee standards of the Council of Ministers of the USSR dated 25.10.72 No. 1967

2. INTRODUCED FOR THE FIRST TIME

3. REFERENCE REGULATIONS AND TECHNICAL DOCUMENTS

All documents presented in the catalog are not their official publication and are intended for informational purposes only. Electronic copies of these documents can be distributed without any restrictions. You can post information from this site on any other site.

The instruction is intended for sanitary doctors who control the domestic and drinking water supply of populated areas. Guided by this instruction, the bodies of the sanitary and epidemiological service present sanitary requirements to the administration of water pipelines or to the owners of local water sources, who are responsible for providing the population with safe drinking water.

I. Chlorination of water in water pipes

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

2. Chlorination of water should be carried out in all cases of obtaining it from surface water bodies (after mandatory preliminary purification), as well as when receiving water from underground sources, the bacterial parameters of which do not comply with GOST "Drinking Water".

Note: Other methods permitted by the Main Sanitary and Epidemiological Directorate of the USSR Ministry of Health can also be used for water disinfection.

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

4. In order to establish indications for chlorination of water sources used for domestic and drinking water supply, as well as in order to develop the main provisions on the chlorination regime, a preliminary sanitary and laboratory examination of the water source is carried out in accordance with the program provided for current GOST"Sources of centralized domestic drinking water supply. Rules for the selection and assessment of quality" (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 amount of chlorine absorption of water, are experimentally determined.

The working dose of chlorine chosen for water disinfection should provide the proper bactericidal effect, i.e. the number of Escherichia coli in the treated water should be no more than 3 in 1 liter, total number 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 should be at least 0.3 and not more than 0.5 mg / l (GOST "Drinking Water").

6. When chlorinating water from some sources, mainly open ones, difficulties may arise due to 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 decontamination must be applied, which include the following:

a) Double chlorination, i.e. introduction of chlorine prior to treatment facilities into the suction conduits of the 1st lift (usually at doses of 3-5 mg/l) and finally after filters (usually at doses of 0.7-2 mg/l); is used when the source water is of high color, with a high content of organic matter and plankton.

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

c) Rechlorination, i.e. the introduction of knowingly high doses of chlorine (up to 10-20 mg / l) with subsequent binding of excess chlorine (dechlorination sour gas or activated charcoal) it 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 Escherichia coli is more than 10,000 in 1 liter (in water samples taken at the water intake point). In addition, it is used to avoid the appearance of a chlorine-phenol smell in the presence of phenols in the source water.

d) Chlorination with post-fracture doses, i.e. taking into account the break point on the residual chlorine curve; at the same time, water disinfection is carried out with free chlorine, which is much more effective than combined chlorine (chloramines); It is used mainly in cases of high bacterial contamination of the source water.

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

7. The choice of one or another method of chlorination, 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. Based on the data obtained in accordance with, the water supply administration establishes the main provisions for the method of treating water with chlorine, which include a scheme for the use of chlorine, dosage of reagents and chlorination schedules, depending on the flow of water. 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, the forces and means of the departmental laboratory in accordance with GOST "Drinking Water". The determination of residual chlorine before supplying to the network is carried out every hour, and on water pipes from open reservoirs - every 30 minutes; in the same place, a sample is taken for bacteriological analysis at least 1 time per day, simultaneously with the next determination of residual chlorine.

9. Sanitary and laboratory control over the effectiveness of chlorination of water supplied by a water supply system for domestic and drinking needs is carried out by a sanitary and epidemiological station by determining the number of Escherichia coli and the total number of bacteria at the most characteristic points of water intake (closest to pumping station, the most remote, the most elevated, dead ends, standpipes). Sampling points and frequency of analysis are determined by schedules approved by the local sanitary and epidemiological service.

10. The quantitative determination of residual active chlorine in water is performed by the iodometric or orthotolidine method, which are described in.

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

To determine residual chlorine in large water pipelines, it is advisable to use automatic analyzers, in particular, photoelectronic systems of the Academy of Public Utilities of the RSFSR, which provide continuous recording 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-fracture doses (free chlorine) and during chlorine ammonization (combined chlorine). Free chlorine has a relatively fast disinfecting effect, while combined chlorine is less effective (see above - d). For their separate quantitative determination, a method based on the use of paraaminodimethylaniline should be used (see). international standards drinking water, the orthotolidine-arsenite method is also recommended, which has not yet been used in the USSR.

11. When performing water chlorination work, the safety precautions specified in.

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 potent toxic substances(approved by the Ministry of Health of the USSR on June 24, 1965 N 534-65). In this case, ammonia should be stored separately from chlorine.

Storage of bleach stocks is allowed only in undamaged standard packaging, in closed warehouses, dry, dark and well ventilated, at an air temperature not exceeding 20°C. It is forbidden to store explosive and flammable substances, lubricating oils, foodstuffs, hardware and gas cylinders.

12. Bodies of the sanitary and epidemiological service in the process of scheduled inspections of water pipelines, as well as according to epidemic indications, (at least once a month) must check the correctness of laboratory and production control over water quality, including the correctness of the basic provisions on the method of treating water 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 condition of the main water supply facilities, on the treatment methodology and on improving the quality of water should be entered in a special journal of the established form, stored at the waterworks.

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

II. Chlorination of water at local water supply

14. With local water supply, i.e. when using water without a distributing network of pipes, directly from the source (wells, springs, open reservoirs), chlorination of water requiring disinfection is usually carried out 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 empirically;

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 determined qualitatively by the blueness of chlorinated water from the addition of several crystals of potassium iodide and a few drops of 1% starch solution to it, as well as by the presence of a slight smell of chlorine 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 the capacity of a teaspoon 2-2.5 g of bleach, a tablespoon 9-12 g, a glass - 120 g.

The measured amount of bleach is poured into a mug or bowl, a little water is added to it and rubbed 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 is made according to.

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

Perchlorination is carried out 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 water from open sources - at least 20 mg / l of active chlorine. After thoroughly mixing the solution of bleach poured into the water with a wooden shovel or oar, leave the water alone for 15 minutes in summer and 30 minutes in winter. After that, the smell of water is checked: at strong smell chlorine rechlorination is considered sufficient, in the absence of smell or a very slight smell of chlorine, it is necessary to repeat the introduction of bleach.

To remove excess chlorine (dechlorination), the water is filtered through activated or ordinary 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 the disinfection of mine wells and disinfection of water in them", approved by the Main Sanitary and Epidemiological Directorate of the USSR Ministry of Health on January 18, 1967 N 663-67.

III. Chlorine disinfection of waterworks during their construction and operation

18. Disinfection of water supply facilities (wells, reservoirs and pressure tanks, settling tanks, mixers, filters, water supply network) can be preventive (before commissioning new facilities, after periodic cleaning, after repair and emergency work), as well as according to epidemic indications ( in case of pollution of structures, as a result of which there is a threat of waterborne 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 upon 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 necessary contact in this case increases to 24 hours or more.

20. Before disinfection of waterworks, in all cases, their preliminary mechanical cleaning and washing. Water network, the cleaning of which is difficult, intensively washed for 4-5 hours at the maximum possible speed of water movement (at least 1 m / s.).

21. Disinfection of artesian wells before putting them into operation is carried out in those cases when, after washing them, the water quality does not comply with GOST "Drinking Water" in terms of bacteriological indicators.

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 should be preceded by appropriate repair work).

Disinfection is carried out in two stages: first, the surface part of the well, then the underwater part. To disinfect the above-water part in the well, a pneumatic plug is installed several meters below the static level, above which the well is filled with a solution of chlorine (or bleach) with an active chlorine concentration of 50-100 mg/l, depending on the degree of expected 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 performed until the noticeable smell of chlorine disappears in the water, after which a water sample is taken for a control bacteriological analysis.

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

22. Disinfection of tanks large capacity recommended for irrigation. 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 hydro-panel.

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

Pressure tanks of small capacity should be disinfected by 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 washed with clean tap water (to the content in wash water 0.3-0.5 mg/l residual chlorine). In a similar way, sedimentation tanks, displacers, as well as filters are disinfected after their repair and loading.

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

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

Note: The estimated volume of chlorine solution for network disinfection is determined by the internal volume of 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. Flushing and disinfection of water facilities and networks is carried out by the forces and means of a construction organization (before putting them into operation) or the administration of a water supply system (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 water analyzes. Based on these materials, local bodies of the sanitary and epidemiological service give a conclusion on the possibility of putting the facilities into operation.

25. With the publication of this instruction, "Instruction for the disinfection of domestic and drinking water with chlorine for 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 Academy of Medical Sciences of the USSR.

** The term "disinfection" refers to water treatment, and the term "disinfection" refers to the treatment of waterworks and networks with disinfectants.

Appendix No. 1

I. Determination of the content of active chlorine and bleach

Reagents:

1. 10% potassium iodide solution

2. Hydrochloric acid (1:5 by volume)

3. 0.01 N sodium hyposulfite solution

4. 0.5% starch solution

The course of the analysis: weigh out 3.55 g of bleach, grind in a porcelain mortar with a small amount of water and a homogeneous slurry and dilute a little more with water. Then the liquid is poured into a volumetric flask, the mortar is rinsed several times, and the volume of 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 studied lime. 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 the titration is continued until the blue color disappears. The amount of ml of 0.01 N hyposulfite solution used for titration directly indicates the % of active chlorine in the studied bleach.

II. Quantitative determination of residual active chlorine in tap water

Iodometric method

Reagents:

1. Potassium iodide chemically pure crystalline, not containing free iodine.

Examination. 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. There should be no blueing of the reagent.

2. Buffer mixture: pH = 4.6. Mix 102 ml of a molar solution of acetic acid (60 g of 100% acid in 1 l of water) and 98 ml of a molar solution of sodium acetate (136.1 g of crystalline salt in 1 l of water) and bring to 1 l 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. Setting the titer of 0.01 N hyposulfite solution is carried out as follows: pour 0.5 g of pure potassium iodide into the flask, dissolve in 2 ml of water, first add 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 sodium hyposulfite titer is calculated using the following formula: K = 10/a, where a is the number of milliliters of sodium hyposulfite used for titration.

Analysis progress:

a) add 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 potassium iodide dissolves;

d) add 10 ml of a 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 amount of milliliters of the buffer solution should be 1.5 times the alkalinity of the test water;

e) add 100 ml of the test water;

e) titrate with hyposulfite until the solution turns 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 used for titration,

To- correction factor to the titer of sodium hyposulfite.

Orthotolidine method

Reagents:

1. 0.1% solution of orthotolidine - 1 g of orthotolidine is transferred into a porcelain cup, 5 ml of 20% hydrochloric acid are added, triturated into a paste and 150-200 ml of distilled water are added. After dissolution of 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. The scale of constant standards, which imitates active chlorine standards in color. 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 liter.

The number of solutions "a" and "b" indicated in the table is added to the Nessler cylinders, adjusted to a volume of 100 ml with distilled water. Store standards sealed for no more than 6 months, protected from direct sunlight.

Note:

1) The water to be tested must be at room temperature (about 20°C).

2) If there is color in the test water, color compensation is applied, looking from the side.

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

In 3 jars, 1 liter of the test water to be chlorinated is poured. Then, 1% bleach solution is added to each jar in the amount approximately indicated in the table.

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 examination is performed.

To determine the residual chlorine, 5 ml of a 10% potassium iodide solution, 10 ml of a buffer solution (see the description of the iodometric method) are poured into a flask and 200 ml of chlorinated water from a can are pipetted. The liberated iodine is titrated with a 0.01 N hyposulfite solution until a pale yellow color is obtained, 1 ml of a 0.5% starch solution is added, and the titration is continued until the blue color disappears. Residual chlorine content in mg/l is 0.355´ 5H, where H is the amount of ml of hyposulfite used 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 added to the water remaining in the jars. After that, the number of Escherichia coli and the total number of bacteria in water are determined in accordance with the rules of bacteriological analysis (GOST 5215-50).

The optimal working dose of chlorine is the one at which the number of preserved Escherichia coli does not exceed 3 per 1 liter of water, and the total number of bacteria does not exceed 100 per 1 ml. The content of residual chlorine should not exceed 0.5 mg/l.

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

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

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

Reagents:

1. 1% alcohol solution of hydrochloric acid para-aminodimethylaniline (dimethide paraphenylenediamine): 1 g is dissolved in 100 ml of ethyl alcohol (rectified). Used as an indicator.

2. Phosphate buffer solution pH=7.0´ 3.54 g of monosubstituted potassium phosphate (KH 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% oxalic acid solution: 2.5 g in 100 ml of distilled water.

5. 0.01 N solution of ferrous sulfate (FeSO 4´ 7H 2 O) is prepared from the main 0.1 N solution by diluting it 10 times with distilled water. To prepare the stock solution, weigh 28 g of FeSO 4´ 7H 2 O and transferred to a volumetric flask (liter), dissolved in distilled water, acidifying a solution of 2 ml of sulfuric acid (1:3), and then adjusted with water to the mark.

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

Analysis progress:

a) Add 1 ml of a buffer solution and 2 ml of an 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). Stirring vigorously, the sample is titrated with a solution of ferrous sulfate until it becomes colorless (1st titration);

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

Titrate the sample with a solution of ferrous sulfate until it becomes colorless (2nd titration).

c) After that, 1 ml is added to the same sample oxalic acid. If dichloramine is present in the water, a pink color occurs again, in the presence of which the sample is titrated with a solution of ferrous sulfate until provided (3rd titration).

The calculation is made according to the formula:

X = 0,355 ´ To ´ H ´ 10, where

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

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

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

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

Example:The titer coefficient of the iron sulfate solution is 0.98, i.e. when the titer was set to 25 ml of iron sulfate, 24.5 ml of a 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 color). 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); no dichloramine.

Appendix No. 2

Basic safety precautions for water chlorination

1. When using liquid chlorine, 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 mechanical ventilation, providing 12-fold air exchange in 1 hour. Exhaust openings for ventilation are located no higher than 30 cm from the floor, and the exhaust pipe of the fan is located at a height of 2 m above the roof ridge. The fan motor must be switched on from the vestibule before entering the chlorination room.

Note: Installations for ammoniation (cylinders with ammonia, scales, flow meters) should be placed in separate room isolated from the chlorination room. The room is equipped exhaust ventilation with air extraction under the ceiling.

3. The chlorination room should have good lighting, natural and electric, with such an installation of light sources so that divisions on the meter scale are clearly visible: the calculated 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 an oxygen pillow.

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

6. When entering the chlorination room, you must turn on the fan and make sure that there is no characteristic smell of chlorine. If there is a smell of chlorine, a gas mask should be put on and steps should be taken to eliminate the gas leak. The location of the leak is determined by wetting the joints of the joints 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 2 m deep and 1.5 m in diameter is arranged in the yard, filled with a solution of lime and having a water supply. The tank must have watertight walls and bottom, it is located no closer than 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 forbidden to use blowtorches, primus, electric stoves.

10. Transportation of chlorine from the warehouse to the chlorination plant is carried out by road or on spring carts. Loading and unloading of cylinders (or barrels) with chlorine is done with extreme care, avoiding impacts, damage to valves, rolling cylinders with your foot on the ground. Cylinders are stacked on wooden linings with carved nests, well reinforced in the body, in sunny weather they are covered with a tarpaulin to protect them from heating.

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

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

13. After finishing work, showering should be provided.