Instructions for use of sodium hypochlorite. Sodium hypochlorite. properties, theory and practice of application. I. General provisions

Sodium hypochlorite - NaClO , is obtained by chlorinating an aqueous solution of sodium hydroxide ( NaOH ) molecular chlorine ( Cl2 ) or electrolysis of a solution of table salt ( NaCl ). You can read more about the methods for producing sodium hypochlorite (SHC) in the article posted on our website: “Sodium hypochlorite. Process of obtaining."
In the Russian Federation, the composition and properties of GPCN produced by industry, or obtained directly from the consumer in electrochemical installations, must meet the requirements of GOST or TU. The main characteristics of HPCN solutions regulated by these documents are given in Table 1.

2. DESCRIPTION AND MAIN CHARACTERISTICS

Anhydrous sodium hypochlorite (ASHH) is an unstable, colorless crystalline substance.
Elemental composition: Na (sodium) (30.9%), Cl (chlorine) (47.6%), O (oxygen) (21.5%).
Molecular mass NaClO (according to international atomic masses 1971) -74.44.
Highly soluble in water: 53.4 g of sodium hypochlorite dissolves in 100 grams of water at 20°C (or 130 g in 100 g of water at 50°C). Solubility NaClO presented in table 2.1.

Density aqueous solutions sodium hypochlorite

Freezing point of aqueous solutions of sodium hypochlorite

Thermodynamic characteristics of sodium hypochlorite in an infinitely dilute aqueous solution:

• standard enthalpy of formation, ΔH o 298: − 350.4 kJ/mol;
• standard Gibbs energy, ΔG o 298: − 298.7 kJ/mol.

Aqueous solutions of HPCN are very unstable and decompose over time even at ordinary temperatures (at a rate of 0.08 to 0.1% per day). The rate of decomposition of HPCN is affected by exposure to solar radiation and the presence of cations heavy metals and alkali metal chlorides. At the same time, the presence of magnesium or calcium sulfate, boric acid, silicates, etc. in an aqueous solution slows down the process of decomposition of HPCN. It should be noted that the most stable solutions are those with a highly alkaline environment (pH value > 10).
Sodium hypochlorite has three known crystalline hydrates:

• monohydrate NaOCl H 2 O - extremely unstable, decomposes above 60°C, at higher temperatures with explosion.
• crystal hydrate NaOCl 2.5 H 2 O - more stable than monohydrate, melts at 57.5°C.
• pentahydrate NaOCl 5 H 2 O - the most stable form, is white or pale green rhombic crystals. Non-hygroscopic, highly soluble in water. It diffuses in the air, turning into a liquid state due to rapid decomposition. Melting point: 18 - 24.4°C. When heated to a temperature of 30 - 50 °C, it decomposes.

2.1 Chemical properties of HPCN

Dissociation, hydrolysis and decomposition of HPCN in aqueous solutions

Sodium hypochlorite (SHC) is an unstable compound that easily decomposes with the release of oxygen. Spontaneous decomposition occurs slowly even with room temperature: for example, after 40 days the most stable form is HPCN pentahydrate ( NaOCl 5H 2 O ) loses about 30% of active chlorine:

2 NaOCl → 2 NaCl + O 2

When HPCN is heated, a disproportionation reaction occurs in parallel with its decomposition:

3 NaOCl → NaClО 3 + 2NaCl

Sodium hypochlorite forms hypochlorous acid and hypochlorite ion in water in ratios determined by the pH of the solution, namely the ratio between hypochlorite ion and hypochlorous acid is determined by the occurrence of sodium hypochlorite hydrolysis and dissociation reactions hypochlorous acid (see Fig. Change in the forms of active chlorine in a sodium hypochlorite solution depending on the pH of the solution).
Dissolving in water, HPCN dissociates into sodium cations and hypochlorous acid anions:

NaOCl → Na + + OCl −

Since hypochlorous acid ( HOCl ) is very weak, the hypochlorite ion in an aqueous environment undergoes hydrolysis:

OCl − + H 2 O ↔ HOCl + OH −

We have already mentioned that aqueous solutions of HPCN are unstable and decompose over time even at ordinary temperatures, and that the most stable solutions are those with a highly alkaline environment (pH > 11).
So how does HPCN decompose?
In a highly alkaline environment (pH > 10), when hydrolysis of the hypochlorite ion is suppressed, decomposition occurs as follows:

2 OCl − → 2 Cl − + O 2

At temperatures above 35°C, decomposition is accompanied by a disproportionation reaction:

OCl − → ClO 3 − + 2 Cl −

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

HOCl + 2 ClO − → ClO 3 − + 2 Cl − + H +
HOCl + ClO − → O 2 + 2 Cl − + H +

With a further decrease in pH, when the solution no longer contains ClO− ions, decomposition proceeds in the following way:

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

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

4 HClO → 2 Cl 2 + O 2 + H 2 O

As a summary of the above, we can say that at pH above 10 oxygen decomposition occurs, at pH 5-10 - oxygen and chlorate, at pH 3-5 - chlorine and chlorate, at pH less than 3 - chlorine decomposition of sodium hypochlorite solutions.
Thus, by acidifying a solution of sodium hypochlorite with hydrochloric acid, chlorine can be obtained:

NaOCl + 2HCl → NaCl + Cl 2 + H 2 O .

Oxidative properties of HPCN
An aqueous solution of sodium hypochlorite, which is a strong oxidizing agent, enters into numerous reactions with various reducing agents, regardless of the acid-base nature of the medium.
We have already considered the main options for the development of the redox process in the aquatic environment:
V acidic environment:

NaOCl + H + → Na + + HOCl
2 HOCl + 2 H + + 2e − → Cl 2 + 2 H 2 O
HOCl + H + + 2e − → Cl − + H 2 O

in a neutral and alkaline environment:

NaOCl → Na + + OCl −
2 OCl − + 2H 2 O + 2e − → Cl 2 + 4OH −
OCl − + H 2 O + 2e − → Cl − + 2 OH −

Below are the main redox reactions involving sodium hypochlorite.
Thus, in a slightly acidic environment, alkali metal iodides are oxidized to iodine:

NaClO + 2 NaI + H 2 O → NaCl + I 2 + 2 NaOH , (1)

in a neutral environment to iodate:

3 NaClO + NaI → 3 NaCl + NaIO 3 ,

in an alkaline environment until periodate:

4 NaClO + NaI → 4 NaCl + NaIO 4

It should be mentioned that the reaction ( 1 ) based on the principle of colorimetric determination of chlorine in water.
Under the influence of sodium hypochlorite, sulfites are oxidized to sulfates:

NaClO + K 2 SO 3 → NaCl + K 2 SO 4

nitrites to nitrates:

2 NaClO + Ca(NO 2) 2 → 2 NaCl + Ca(NO 3) 2

oxalates and formates to carbonates:

NaClO + NaOH + CHOONa → NaCl + Na 2 CO 3 + H 2 O

etc.
Phosphorus and arsenic dissolve in an alkaline solution of sodium hypochlorite, forming salts of phosphoric and arsenic acids.
Ammonia, under the influence of sodium hypochlorite, through the stage of chloramine formation, is converted into hydrazine (urea reacts similarly). We have already discussed this process in our article “Chlorination of drinking water”, so here we present only the total chemical reactions of this interaction:

NaClO + NH 3 → NaOH + NH 2 Cl
NH 2 Cl + NaOH + NH 3 → N 2 H 4 + NaCl + H 2 O

The above redox reactions are very important because affect the consumption of active chlorine and its transition to a bound state during chlorination of water. The calculation of the dose of active chlorine when used as a chlorine agent is similar to what we presented in the article “Chlorination of drinking water”.

2.2. Bactericidal properties of GPCN

2.3. Corrosive activity of GPCN

Sodium hypochlorite has a fairly strong corrosive effect on various materials. This is due to its high oxidizing properties, which we discussed earlier. Therefore, when selecting construction materials For the manufacture of water purification plants, this must be taken into account. The table below presents data on the corrosion rate of some materials when exposed to sodium hypochlorite solutions of various concentrations and at different temperatures. More detailed information on the corrosion resistance of various materials in relation to HPCN solutions can be found in the Chemical Compatibility Table ( in rar archive format), posted on our website.
It is equally important to take into account the fact that filter media that are used for fast bulk filters can change their filtering properties when exposed to HPCN, or more precisely active chlorine, for example, when selecting a filter medium for the process of catalytic deferrization - deferrization catalysts.
We should not forget that active chlorine has a negative effect on membrane processes, in particular it causes destruction of reverse osmosis membranes (we talked about this in our article “Reverse osmosis. Theory and practice of application.”), and at high levels (more than 1 mg /l) negatively affects ion exchange processes.
As for the materials from which the GPCN dosing system itself should be made, here it is necessary to focus on the concentrations of active chlorine in the GPCN working solutions, which, naturally, are significantly higher than the concentrations in the treated water. We'll talk about this a little later.

Corrosion rate of some materials when exposed to HPCN solutions

Material	NaClO concentration, wt.%	Temperature, °C	Corrosion rate mm/year
Aluminum	10 at pH > 7	25	> 10
Copper	2	20	< 0,08
	20	20	> 10
Steel St.3	0.1 at pH > 10	20	< 0,1
	> 0,1	25	> 10,0
Steel 12Х17, 12Х18Н10Т	5	20	> 10,0
Steel 10Х17Н13М2Т	< 34	40	< 0,001
		Boil.	1.0 ÷ 3.0
Steel 06ХН28МДТ	< 34	20 ÷ Tb.	< 0,1
Titanium	10 ÷ 20	25 ÷ 105	< 0,05
	40	25	< 0,05
Zirconium	10	30 ÷ 110	< 0,05
	20	30	< 0,05
Gray cast iron	< 0,1 при pH > 7	25	< 0,05
	> 0,1	25	> 10,0
Cast iron SCh15, SCh17	< 34	25 ÷ 105	< 1,3
Polyamides	< 34	20 ÷ 60	racks
Polyvinyl chloride	< 34	20	racks
		65	relates racks
Polyethylene	< 34	20 ÷ 60	racks
Polypropylene	< 34	20 ÷ 60	racks
Butyl rubber	10	20 ÷ 65	racks
	sat. solution	65	racks
Glass	< 34	20 ÷ 60	racks
Fluoroplastic	any	20 ÷ 100	racks

3. APPLICATION OF SODIUM HYPOCHLORITE

The industry of the Russian Federation produces GPNH in the form of aqueous solutions of various concentrations.
Sodium hypochlorite of various brands is used:

• grade A solution according to GOST 11086 - in the chemical industry, for disinfection drinking water and swimming pool waters, for disinfection and bleaching;
• solution grade B according to GOST 11086 - in the vitamin industry, as an oxidizing agent for bleaching fabrics;
• solution grade A according to specifications - for disinfection of natural and waste water in domestic and drinking water supplies, disinfection of water in fishery reservoirs, disinfection in Food Industry, obtaining bleaching products;
• solution grade B according to specifications - for disinfection of areas contaminated with fecal discharges, food and household waste; wastewater disinfection;
• solution grade B, G according to specifications - for disinfection of water in fishery reservoirs;
• solutions of grade E according to TU - for disinfection similar to grade A according to TU, as well as disinfection in health care institutions and enterprises Catering, civil defense facilities, etc., as well as disinfection of drinking water, wastewater and bleaching.

Sodium hypochlorite, used instead of liquid chlorine for the disinfection of drinking water, is subject to certain requirements regarding the concentration of alkali and heavy metals, such as iron, stability, and color. You can familiarize yourself with the main characteristics of GPCN solutions, regulated by regulatory documents.
Let's first discuss the treatment of water with sodium hypochlorite in various industries, and then return to the process of water disinfection using HPCN in domestic water supply systems.

3.1. Disinfection of swimming pool water by chlorination

In the Russian Federation, hygienic requirements for the design and operation of swimming pools, as well as the quality of water in them, are standardized by SanPiN 2.1.2.1188-03, but suppliers and manufacturers of imported equipment for purification and disinfection of water in swimming pools very often focus on the requirements of DIN 19643 standards.
Water purification and disinfection systems in swimming pools must provide:

Thus, installations for purification and disinfection of pool water in recirculation mode must ensure the removal of both contaminants (mechanical, colloidal and dissolved) and microorganisms entering the pool from the air and brought in by swimmers. At the same time, the concentrations of harmful substances that can be formed as a result of chemical reactions of water contaminants with reagents used for disinfection and adjustment of water composition should not exceed the maximum permissible concentration. Fulfilling these requirements is a rather complex engineering and economic task.
The main measures to ensure quality water in the pool, which must be carried out during its operation, are outlined by us on the “Operation of swimming pools” page of our website. In this publication we will focus only on the disinfection of pool water by chlorination.
We already know that chlorination is the most common reagent method of water disinfection, and also the most accessible and inexpensive. Chlorine is a powerful oxidizing agent and has a very broad spectrum of antimicrobial action - i.e. capable of destroying and destroying the vast majority of known pathogenic microorganisms. An important advantage of chlorine is its prolonged action, i.e. ability to persist for a long time active form in the pool water. Moreover, when combined with any other method of disinfection, it is chlorination that allows you to achieve the maximum effect of disinfecting water in the pool.
Let us briefly consider the physicochemical meaning of the processes occurring in pool water during and after chlorination. After dissolving the chlorine agent in the pool water at the optimal pH level (7.0 - 7.4), hypochlorite ion and hypochlorous acid are formed and is called the free chlorine level, which, according to current sanitary standards, must be maintained at 0.3 - 0.5 mg/ l.
Let us note that the indicated pH level of the water in the pool for the chlorination process was not chosen by chance - only in this pH range does the reaction of the chlorinating agent with water occur with the maximum “efficiency factor”, i.e. with maximum “yield” of free chlorine.
Free chlorine enters into oxidation reactions with pathogenic microorganisms and pollutants present in water. Main feature The process of chlorination of pool water is that in addition to microorganisms, which are the main objects of disinfection, there is a large amount of organic impurities of a protein nature (fat, sweat, creams, etc., brought in by bathers). As a result of interaction with active chlorine, they form inorganic and organic chloramines, forming combined chlorine. Moreover, the latter are very stable and have a strong irritant effect, which has a very negative effect on the overall quality of water in the pool.
The total content of free and combined chlorine in pool water is called total chlorine. The level of combined chlorine, which is determined by the difference between total and free chlorine, should not exceed 1.2 mg/l in pool water.
The following are most often used as chlorine agents for disinfecting pool water:

• chlorine gas;
• sodium, calcium or lithium hypochlorites;
• chlorinated derivatives of isocyanuric acid: chlorinated isocyanurates (sodium salt of dichloroisocyanuric acid, trichloroisocyanuric acid).

In the context of the direction of this publication, we will consider in comparison only two chlorine agents: chlorine gas and sodium hypochlorite (SPH).

Until a certain time, chlorine gas was the only chlorine agent used to disinfect pool water. But its use was associated with enormous costs to ensure the safety of the chlorination process ( This will be discussed in more detail when considering the process of disinfection of drinking water.). Therefore, it was pool equipment specialists who turned to the possibility of replacing chlorine with sodium hypochlorite. Having determined the optimal conditions for water disinfection during its recirculation (mainly pH range), requirements for technological equipment and for organizing control of chlorine content in water were developed technological schemes for skimmer and overflow pools and the hardware design of the process of cleaning and disinfection of water in the pool in the form in which we see it today.
To treat pool water, chemists have developed stabilized GPCHN formulations, the production of which is now mastered by many companies. Here are some of them:

The motto of the pool water purification process is: filtration and disinfection. The pages of our website dedicated to the operation of swimming pools detail the methods and sequence of operations that allow us to achieve high-quality, clear water in the pool. The only thing that is not indicated there is how to work with GPHN.
Features of the process of disinfecting pool water using preparations containing HPCN (in recirculation mode) are (listed in order of importance):

• reduced pH value (its value may be below 6.9);
• limited contact time of water with a disinfectant (chlorine agent) - as a rule, it is calculated in only a few minutes;
• increased water temperature (it reaches 29 o C);
• increased content of organic substances.

And in these “hellish” conditions for GPKhN, it is necessary to achieve maximum impact from it.
How is this done in practice? In general, everything starts at the pool design stage. When placing the pool circulation loop equipment, they try to ensure that there is maximum temporary contact between them from the point where the disinfectant is added to the water until the water enters the pool. Therefore, the point of introduction of the disinfectant is usually the pressure pipe of the circulation pump, i.e. the farthest point from the return nozzles. A pH measurement sensor is also installed there, and the corrective composition is introduced at the suction pipe of the circulation pump, which in this case serves as a kind of mixing unit. The water heater in the pool is placed as close as possible to the return nozzles in order, firstly, to reduce heat loss, and secondly, to avoid premature destruction of the HPCN.

Well, now let's describe algorithm for performing operations during operation pool:

• At the beginning values ​​are determined pH and Red-Ox potential. The first indicator is necessary to adjust the pH value to the optimal value: 7.2 - 7.4. The second serves as a kind of index of contamination of the water coming from the pool, and is intended for preliminary determination of the dose of disinfectant that will be added to the treated water. Such control can be performed either manually using appropriate devices, or automatically using sensors and secondary devices - controllers built into the circulation circuit.
• The second stage is actually pH adjustment , i.e. depending on the measured value, reagents are added to the water that reduce or increase the pH value (the latter, as a rule, are used more often, since during the operation of the pool the water “acidifies”). The pH value is monitored in the same way as in the previous case. But the addition of reagents can be done either manually (for pools with a small volume of water) or automatically (which is most often used for public pools). In the latter case, dosing of pH correcting reagents is carried out using dosing pumps that have a built-in pH controller.
• And finally, they produce injection of GPCN working solution into the treated water, which is carried out using the method of proportional dosing using dosing pumps . In this case, proportional dosing (control of the metering pump) is carried out according to a signal from a chlorine sensor installed either directly in the pipeline (preferably directly in front of the heater). There is another method for monitoring the quality of water disinfection in the pool and controlling the metering pump - monitoring the Red-Ox potential, i.e. indirect measurement of active chlorine in water. After the GPCN input unit, a dynamic mixer is usually installed or several sharp turns are made in the pressure pipeline of the circulation pump to thoroughly mix the treated water with the GPCN working solution. Both of these introduce additional resistance on the water return line to the pool. This must be taken into account when selecting a circulation pump.

As we have seen, the process of disinfecting pool water is quite complex and includes several stages. Therefore, to fully automate this process and eliminate the “human” factor from it, dosing systems were developed, consisting of one, two or even three dosing pumps, controllers, sensors, electrochemical cells etc. Their description can be found on this page.
Dosing of grade “E” hypochlorite is not much different from the dosing of stabilized preparations based on grade “A” sodium hypochlorite. Unless there is a need to monitor the total salt content of the water in the pool, since grade “E” hypochlorite contains table salt (see description of the production process). Therefore, when dosing it, this salt enters the treated water and increases the total salt content (taking into account the fact that the recirculation system is closed, and the total influx of fresh water is only 10% of the volume).

3.2. Treatment of domestic and industrial wastewater

Cleaning of drains consists of their neutralization and disinfection.
Disinfection of wastewater can be carried out by several methods: chlorination, ozonation and UV radiation.
Disinfection (with chlorine, sodium hypochlorite, or direct electrolysis) of household wastewater and its mixtures with industrial wastewater is carried out after their purification. For separate mechanical cleaning of household and industrial waters, but their joint biological treatment is allowed (SNiP 2.04.03-85) to provide for disinfection only domestic water after their mechanical cleaning with dechlorination before submitting them for biological treatment. The issue of wastewater disposal after disinfection must be resolved on a case-by-case basis in agreement with the territorial offices of the State Sanitary and Epidemiological Service in accordance with the requirements of SanPiN 2.1.2.12-33-2005 “Hygienic requirements for protection surface waters».
Before disinfection, wastewater is clarified, freeing it from suspended particles (mechanical treatment), and then the clarified water is oxidized biologically (biological treatment). Biological treatment is carried out by two methods: 1) intensive (artificial treatment) and 2) extensive (natural treatment).
Intensive method makes it possible to purify waste liquid at special treatment facilities located in a small area, but requires electricity, the construction of treatment facilities, qualified personnel to manage them and chlorination. Intensive treatment facilities include aeration tanks and bio-oxidizers (biological filters, percolators).
Extensive method requires a larger area, but is less expensive to construct and operate and produces a drainage free of helminth eggs and pathogenic bacteria. Chlorination is not required in this case. Extensive treatment facilities include biological ponds, irrigation fields and filtration fields.

Chlorination of wastewater.
Chlorination is used to treat domestic and industrial waters, to destroy animal and plant microorganisms, eliminate odors (especially those formed from sulfur-containing substances), and neutralize industrial wastewater, for example, from cyanide compounds.
Wastewater is characterized high degree organic load. Empirically established values ​​of disinfecting concentrations of active chlorine in wastewater can reach 15 mg/l. Therefore, the required doses of active chlorine and the duration of its contact with wastewater are determined by test chlorination. For preliminary calculations of wastewater disinfection, the following doses of active chlorine are taken: after mechanical treatment - 10 mg/l; after complete artificial biological treatment - 3 mg/l, after incomplete - 5 mg/l.
The performance of the chlorination installation is calculated based on the dose of active chlorine taken with a coefficient of 1.5. The duration of contact of chlorine with disinfected water depends on the form of chlorine compounds. For free active chlorine, the contact duration is 0.5 hours, for combined active chlorine - 1 hour. Residual chlorine after contact with waste water should include: free active chlorine - 1 mg/l, combined active chlorine - 1.5 mg/l.
The dose of active chlorine must exceed the specific value of chlorine absorption of water in such a way that the resulting concentration of active chlorine in the water provides the required technological effect (level of disinfection, degree of clarification, etc.). When calculating the dose of active chlorine for treating contaminated water, the value of its chlorine absorption, determined in accordance with the requirements of the ASTM D 1291-89 standard, must be taken into account.
If it is necessary to combat enteroviruses, double chlorination is provided: primary chlorination after complete biological treatment and secondary chlorination after additional filtration or settling of water. Doses of active chlorine for primary chlorination in the fight against enteroviruses are 3 - 4 mg/l with a contact duration of 30 minutes, secondary chlorination 1.5 - 2 mg/l with a contact duration of 1.5 - 2 hours.
Chlorination can be used to treat water containing ammonium. The process is carried out at temperatures above 70 o C in an alkaline environment with the addition of CaCl2 or CaCO 3 for the decomposition of ammonia compounds.
During the treatment of water containing humic substances, the latter are converted into chloroforms, dichloroacetic acid, trichloroacetic acid, chloraldehydes and some other substances, the concentration of which in water is much lower.
To remove phenols (content 0.42-14.94 mg/l), use a 9% sodium hypochlorite solution in an amount of 0.2-8.6 mg/l. The degree of purification reaches 99.99%. When water containing phenols is chlorinated, phenoloxyphenols are formed.
There is known data on the use of sodium hypochlorite to remove mercury from wastewater.
Chlorination of wastewater with liquid chlorine using chlorinators has a wider application compared to the process where HPCN is used. Liquid chlorine is introduced into wastewater either directly ( direct chlorination), or using chlorinator. We will tell you more about these processes when considering the process of disinfection (chlorination) of drinking water.
When sodium hypochlorite is used as a chlorine agent, the HPCN working solution is introduced into the treated water using the method of proportional dosing using dosing pumps .
Hygienic requirements for the organization and control of wastewater disinfection are established in the guidelines MU 2.1.5.800-99.

3.3. Use of sodium hypochlorite in the food industry

A high risk to consumer health is always caused by spoiled food products, which should in no way be underestimated. Most often, food spoilage is caused by microorganisms that, during the technological process of manufacturing a food product, enter it from poorly cleaned and poorly disinfected surfaces of technological equipment, from poorly prepared water, air, from low-quality raw materials, from incorrectly disposed wash water, and, finally, from production staff.
But the main source of microorganisms in the food industry is dust. In all areas of food production, contamination with microorganisms occurs in hard-to-reach places: complex equipment, tank lids, containers, sagging pipelines, seams, joints, curves, etc. Therefore, strict adherence to the technological production regime, high sanitary condition of the enterprise and carrying out cleaning and disinfection measures of both equipment and production premises with systematic microbiological control.
Back in the early eighties of the twentieth century, the Institute of Biology and its Application to Nutrition Problems (Dijon, France) conducted a study of disinfectants used in the food industry. At the same time, GPCN was rated among these products in the first class as the most suitable for these purposes and the most economical. It has shown high effectiveness against almost all plant cells, spores and bacteria. For this reason, sodium hypochlorite is widely used in the food industry for disinfection to destroy crustaceans and mollusks; for various washings; for the fight against bacteriophages in the cheese industry; for disinfection of tanks, cattle pens.
But in the food industry, disinfectants are selected each time specifically in accordance with the requirements. Thus, the requirements for a disinfectant during milk processing may differ or be completely different than, for example, in brewing or production soft drinks, or in meat processing production. In general, the purpose of using a certain type of disinfectant for a certain sub-sector of the food industry is to destroy or reduce not all microorganisms, but those that are exclusively harmful to manufactured products (which, as a rule, affect the quality and shelf life of products), as well as pathogenic microorganisms.
Therefore, sanitary standards and rules have been developed in the Russian Federation regarding ensuring microbiological safety for each of the sub-sectors of food production. Here are some of them:

1. SP 3244-85 "Sanitary rules for enterprises of the brewing and non-alcoholic industries."
2. IK 10-04-06-140-87 “Instructions for sanitary and microbiological control of brewing and non-alcoholic production.”
3. SanPiN 2.3.4.551-96 “Production of milk and dairy products. Sanitary rules and regulations".
4. "Instructions for sanitization equipment at dairy industry enterprises."
5. “Instructions for sanitary processing of equipment for the production of liquid, dry and paste-like dairy products for baby food.”
6. SP 3238-85 “Sanitary rules for meat industry enterprises.”
7. SP 2.3.4.002-97 “Food industry enterprises. Sanitary rules for small-capacity meat processing enterprises.”
8. “Instructions for sanitary processing of technological equipment and production premises at meat industry enterprises” (approved in 2003).
9. SanPiN 2.3.4.050-96 “Enterprises of the food and processing industry (technological processes, raw materials). Production and sale of fish products. Sanitary rules and regulations".
10. “Instructions for sanitary and microbiological control of production food products from fish and marine invertebrates." (No. 5319-91. L., Giprorybflot, 1991).
11. “Instructions for sanitary processing of technological equipment at fish processing enterprises and ships.” (No. 2981-84. M., Transport, 1985).

In addition to their specific criteria and the appropriate efficiency and selectivity of the disinfectant for the application, chemical disinfectants in the food industry are selected based on whether they will be used in an “open” or “closed” manner.
At disinfection in a closed system(CIP method) as a result of the use of automatic proportional dosing, which is widespread today, as well as automatic control of the washing and disinfection process, as a rule, there is no direct contact between operating personnel and the chemical product (except for the moment of preparation of the working solution). Therefore, in this case, there is no direct potential danger to operating personnel in relation to hazardous and aggressive environments, such as disinfectants and their solutions.
At open method disinfection, where a manual processing method is necessary, the opposite situation is observed. Here, the operating personnel, on the one hand, must ensure that they avoid direct contact with the chemical product by using personal protective equipment, and on the other hand, if possible, use the maximum disinfecting capabilities of the product.
In the food industry, as a rule, not pure active disinfectants are used, but their diluted solutions, which, in addition to active substances, contain a certain amount of auxiliary agents. These substances can be: surfactants to improve wetting of surfaces to be disinfected; complexing agents to reduce water hardness; emulsifiers and dispersants for uniform distribution of the reagent over the surface to be treated, etc.
In addition, since any disinfectant “works actively” in a certain pH range, depending on the main substance (disinfectant), ready-to-use disinfectant solutions or their concentrates must have an acidic, neutral or alkaline environment. A few examples: as we have seen, sodium hypochlorite and chlorine-containing compounds exhibit the greatest activity only in an alkaline environment, and peracetic acid is more effective in an acidic environment. Quaternary ammonium compounds in an acidic pH environment sharply lose their disinfectant properties, and aldehydes can be used in both acidic and neutral environments, etc.
Disinfection using chlorine agents is quite common in the food industry. In this publication, we will focus only on chlorine-containing disinfectants that contain sodium hypochlorite.
At the very beginning, it should be noted that, as a rule, all GPCN-based disinfectants used in the food industry, in addition to their main purpose - the destruction of bacteria and viruses, fungi and mold, remove oils, fats, proteins, blood residues, tea stains, coffee, fruits, etc., because they have whitening properties. All GPCN-based disinfectants are supplied in concentrated form, and the working solution is prepared on site by diluting the concentrate. As a rule, all products are alkaline (the pH value of the working solution ranges from 11 to 13). This is due to the chemical properties of HPCN, which we discussed earlier. The content of active chlorine in the working solution ranges from 60 to 240 mg/l. The table shows some of the most popular GPCN-based disinfectants and detergents.

Trademark	Compound										Manufacturer
	GPKhN (Sr.r.)	Alkali (pH)	WITH	P	ABOUT	F	A	AND	SJ	TO
SR 3000 D	+ 2%	+ pH=12	+		+						HWR-Chemie GmbH, Germany
DM CID	+ 2%	+ pH=12						+	+	+	Cid Lines NV/SA, Belgium
DM CID S	+ 2%	+ pH=12		+				+	+	+
Catryl-chlorine	+ 2%	+ pH=12						+	+		CJSC "Ekokhimmash", Russia
Katryl-chlor foam	+ 2%	+ pH=12		+				+	+
Neomoscan® RD-B	+ 1%	+ pH=12				+					Chemische Fabrik DR. WEIGERT GmbH & Co. KG, Germany
Divosan Hypochlolite	+ 1%	+ pH=11						+	+	+	JohnsonDiversey Great Britain
Calgonite CF 312	+ 1%	+ pH=12		+							Calvatis GmbH, Germany
Calgonite CF 353	+ 2,4%	+ pH=12	+	+		+
Calgonite CF 315	+ 1%	+ pH=12		+				+
Calgonite 6010	+ 4%	+ pH>12							+
SIP-BLUE 5	+ 3%	+ pH=11		+					+		NPO SpetsSintez, Russia
ACTIVE - LUX D	+ 2%	+ pH=11.5		+

Designations used in the table: C - silicates; P - surfactants, O - fragrances; F - phosphates; A - aldehydes; I - corrosion inhibitors; SZh - stiffness stabilizers; K - complexing agents.

We are well aware that the decisive factor when purchasing any food product is its taste characteristics. Therefore, food industry technologists are reluctant to use disinfectants with chlorine-containing agents, since active chlorine has a very “active effect” on the taste and smell of products. An exception is the external disinfection of process equipment, due to the fact that chlorine has a remarkable prolonged effect. Sodium hypochlorite is one of these products. Typically, a HPCN solution containing 30-40 mg/l of active chlorine is used to disinfect process equipment. The bactericidal effect of sodium hypochlorite manifests itself after applying the solution at 20-25°C and exposing it for 3-5 minutes. True, in this case it is necessary to take into account the corrosive activity of GPCN solutions, therefore, to reduce the corrosive effect, a mixture of sodium hypochlorite, caustic soda and sodium metasilicate (the “Hypochlor” preparation) is used. The corrosive activity of this drug is 10-15 times less than that of ordinary sodium hypochlorite.
As for the treatment of internal cavities of food processing equipment, HPCN is being actively replaced by preparations that do not contain chlorine.

3.4. Use of hypochlorite in fish farming

Fish ponds, fishing gear, live fish containers, fish farming equipment, as well as overalls and footwear of persons involved in fish farming and veterinary and sanitary activities are subject to periodic cleaning and disinfection (disinfestation). Most often, bleach is used for this. However, in Lately For this purpose, sodium hypochlorite was used in the form of diluted solutions.
GPHN is quite actively used in the disinfection of fishing nets, nets and plastic tanks for storing fish.
When using GPCN solutions in fish farming, the concentration of active chlorine obtained when using bleach solutions and GPCN solutions should be recalculated. In this case, they are guided by: “Veterinary and sanitary rules for fish farms” and “Instructions for veterinary supervision over the transportation of live fish, fertilized eggs, crayfish and other aquatic organisms.”

3.5. Use of hypochlorite in healthcare

Already during the First World War, sodium hypochlorite was successfully used as an antiseptic for dressings in the treatment of wounds and burns. However, at that time, the purely technical difficulties of mass production, and the not very good quality of the drug, contributed to the signing of an almost guilty verdict against him. In addition, new, as it seemed then, more effective drugs arrived, and soon they forgot about hypochlorite... and remembered it in the 60s of the twentieth century during the Vietnam War. There, in a situation where it was necessary to use the most effective means of fighting infection, they preferred sodium hypochlorite rather than the latest antibiotics. This sympathy was explained not only by the high effectiveness of HPCN, but also by the versatility of the drug. Indeed, in front-line conditions, instead of a dozen packages, it is better to have one bottle of solution on hand, which can be used to wash the wound, disinfect the skin before surgery, and treat instruments.
We are somehow accustomed to the fact that behind every name of a medicine there is a decoding of its complex chemical formula. Buying a variety of drugs, we are not interested in these intricacies, as long as it helps. But sodium hypochlorite deserves such attention. It turns out that in moderate concentrations hypochlorite is completely safe for humans. Hypochlorite, oddly enough, fits surprisingly well into the functioning of the body systems responsible for protecting against infection and restoring damaged tissues. They perceive it as something native and familiar. And he really is “one of us”: HPCN is constantly produced in small quantities by leukocytes, whose vocation is precisely to fight infection. It's no secret: the same pathogenic microbes have different effects on different people: someone will not even notice their attack, someone will feel a slight malaise, and for others the disease will take a severe, sometimes fatal course. Increased susceptibility to infection is known to be associated with a weakening of the body's defenses. Hypochlorite in the human body not only destroys microbes, but also “tunes” the immune system to recognize them (and this is one of its most important properties).
In case of severe illnesses, extensive wounds, burns, after prolonged compression of tissues and serious operations, self-poisoning of the body with tissue decay products usually develops. Toxic substances that accumulate in the body damage the organs responsible for neutralizing and removing them. The functions of the kidneys, liver, lungs, and brain may be significantly impaired. This can only be helped from the outside. In this case, hemosorption is usually carried out - the patient’s blood is passed through special sorbent filters. However, not all toxins are absorbed by these filters or are not completely absorbed.
An alternative to hemosorption was the method of electrochemical detoxification - intravenous administration of sodium hypochlorite, which can be called domestic “know-how” (we have already mentioned it when considering the bactericidal properties of sodium hypochlorite. Today it is difficult to remember exactly what prompted our scientists to study it. Searches unconventional means, or maybe just curiosity... But hypochlorite was lucky - employees of the Research Institute of Physico-Chemical Medicine (it was at this institute that they conducted research and actively introduced hemosorption, plasmapheresis, ultraviolet irradiation of blood into medical practice...) “took it into circulation” . Their interest in sodium hypochlorite was distinguished by one significant feature: the water from which hypochlorite is formed is an integral basis for all biological processes. The drug, unlike others used in similar cases, does not remove poisons from the body - it simply breaks them down into neutral molecules that do not cause any harm. Toxins quickly burn in the active oxygen of hypochlorite, and the patient’s condition improves before our eyes: blood pressure, heart rate, kidney function normalize, breathing improves, and the person regains consciousness... It is possible to get rid of toxins that cannot be removed from the body in any other way. According to resuscitators, the method makes it possible to operate on patients previously considered hopeless with a high chance of success.
Hypochlorite practically does not cause allergic reactions, which are so common in our time, which is precisely what many antibiotics do. But unlike antibiotics, which selectively kill certain types of bacteria, sodium hypochlorite destroys almost any pathogenic microorganisms, including viruses, and those microbes that “accidentally survived” upon contact with it sharply lose their harmful activity and become easy prey for other elements of the immune system. systems. Interestingly, bacteria that are slightly “damaged” by hypochlorite also lose resistance to antibiotics.
According to various authors sodium hypochlorite solution successfully used in surgical purulent pathology, both as a bactericidal drug for treating wounds and as an infusion detoxifying solution for intravenous administration central veins. Sodium hypochlorite can be injected into the body by everyone possible ways, while it performs not only the detoxification-oxidative function of the liver, but also stimulates the biological and molecular mechanisms of phagocytosis. The fact that sodium hypochlorite is directly formed in macrophages during phagocytosis suggests that it is natural and physiological and classifies the use of hypochlorite solutions as environmentally friendly non-drug methods treatment.
Moreover, the use of sodium hypochlorite solution turned out to be effective not only in purulent surgery, urology and gynecology, but also in pulmonology, phthisiology, gastroenterology, dentistry, dermatovenerology and toxicology. Recently, not only the bactericidal property of sodium hypochlorite, but also its high detoxifying activity has been successfully used.
Analysis of the use of various biological detoxifying systems (hemosorption, hemodialysis, forced diuresis, etc.) only indicated the prospects of using the electrochemical oxidation system as the most effective, physiological and technically uncomplicated method of detoxifying the body.
The pronounced therapeutic effect of sodium hypochlorite in a number of diseases and conditions of the body is associated not only with its detoxification properties, but also with its ability to improve blood counts, increase immune status, and have anti-inflammatory and antihypoxic effects.
The leading reaction that detoxifies toxins and metabolic products in the body is their oxidation by a special detoxifying enzyme - cytochrome P-450. The physiological effect is due to the fact that oxidized substances in the body become soluble in water (hydrophobic toxins turn into hydrophilic) and thanks to this they are actively involved in the processes of other metabolic transformations and are eliminated. IN general view this process in liver cells appears as oxidation enhanced by molecular oxygen and catalyzed by cytochrome P-450. This important detoxifying function of the liver cannot be fully compensated by any other body system. In severe forms of intoxication, the liver does not fully cope with its detoxification functions, which leads to poisoning of the body and aggravation of pathological processes.
By imitating the monooxidase system of the body, sodium hypochlorite provides significant assistance in the natural detoxifying functions of the body both in case of endotoxicosis and exotoxicosis, and in the case of toxalbumin, it simply cannot be replaced.
Solutions of sodium and calcium hypochlorite are used instead of bleach during routine, final and preventive disinfection for the disinfection of various objects and secretions in areas of infectious diseases, as well as for the disinfection of special objects. Disinfection is carried out by irrigation, wiping, washing, soaking objects that do not deteriorate with this method of treatment.
Crowding of people in a limited area, insufficient heating, high humidity, poor nutrition, the difficulty of strictly observing an adequate sanitary and anti-epidemic regime - a familiar situation in a tent camp in a disaster zone. Under these conditions, the effectiveness of using a medicinal solution of sodium hypochlorite in surgery, otorhinolaryngology, and therapy for the prevention of morbidity has been proven, both for refugees and medical personnel. The ease of preparation of the working solution and good results in the fight against numerous infectious agents, sometimes resistant to almost all antibiotics, have made it possible to recommend GPCN solutions for widespread use in medical care.
Treatment with sodium hypochlorite solutions allows not only to equally compensate for the acute shortage of a number of expensive medicines, but also to move to a qualitatively new level of medical care. The cheapness, accessibility and versatility of this medicinal solution makes it possible in our difficult times to at least partially restore social justice and provide quality care to the population both in a remote rural hospital and anywhere in Russia where there is a doctor.
These same advantages make it an important component for maintaining high hygiene standards throughout the world. This is especially evident in developing countries, where the use of HPCN became a decisive factor in stopping epidemics of cholera, dysentery, typhoid fever and other aquatic biotic diseases. So, during an outbreak of cholera in countries Latin America and the Caribbean at the end of the 20th century, sodium hypochlorite was able to minimize morbidity and mortality, as reported at a symposium on tropical diseases held under the auspices of the Pasteur Institute.

3.6. Using GPCN for bleaching laundry in laundry factories

It is believed that bleaching laundry during industrial washing is the most potentially dangerous operation of all operations used in washing clothes, and bleach, accordingly, is the most dangerous substance for fabric. Most bleaches used in industrial washing are strong oxidizing agents, under the influence of which most colored substances, after oxidation, become either colorless or soluble in water. And like any oxidizing agent, bleach simultaneously “attacks” both stains and fabric fibers. Therefore, when bleaching, destruction of the fabric fiber will always be a side process. There are three types of bleaches used in industrial washing: peroxide (peroxide or oxygen-containing), chlorine and sulfur-containing. In this publication, we will focus only on one of the chlorine-containing fabric bleaches - sodium hypochlorite.
Fabric bleaching using HPCN has a history of more than two centuries. The historical name for the sodium hypochlorite solution used for bleaching is labarrack water or javelle water. Strange as it may seem, over two centuries, practically nothing has changed in the technology of bleaching fabrics using HPCN solutions. Sodium hypochlorite is widely used as a bleach and stain remover in textile manufacturing and industrial laundries and dry cleaners. It can be safely used on many types of fabrics, including cotton, polyester, nylon, acetate, linen, rayon and others. It is very effective at removing soil marks and a wide range of stains including blood, coffee, grass, mustard, red wine, etc.
The bleaching properties of sodium hypochlorite are based on the formation of a number of active particles (radicals) and, in particular, singlet oxygen, which has a high biocidal and oxidative effect (for more details, see the article “ Chlorination of drinking water"), formed during the decomposition of hypochlorite:

NaOCl → NaCl + [O] .

Therefore, you cannot do without sodium hypochlorite when bleaching hospital linen or linen affected by mold.
The bleaching (oxidizing) properties of sodium hypochlorite solutions depend on its concentration, pH of the solution, temperature and exposure time. And although we have already considered them in section 2 of this publication, we will repeat ourselves a little in relation to the bleaching process.
In general, the higher the concentration of HPCN in the solution (the greater the activity of HPCN) and the longer the exposure time, the greater the bleaching effect. But the dependence of exposure activity on temperature is more complex. It “works” perfectly even with low temperatures(~40°C). With increasing temperature (up to 60°C), the activity of the bleach based on HPNC increases linearly, and at higher temperatures an exponential dependence of the growth in the activity of the bleach is observed.
The dependence of the bleaching properties of HPCN on the pH value is directly related to the chemical properties of HPCN. At a high pH value of the environment (pH>10), the activity of the bleach based on HPCN is relatively low, because Active oxygen is mainly involved in the bleaching process - it acts rather slowly. If the pH value of the medium begins to decrease, then the activity of the bleach first increases, reaching a maximum at the optimal pH value = 7 for hypochlorite, and then with an increase in acidity, the activity decreases again, but more slowly than is observed with an increase in pH in the alkaline direction.
In industrial washing, the bleaching operation is usually combined with the washing and rinsing operations, rather than being carried out separately. It's more convenient and faster. At the same time, the duration of the operations themselves is increased so that the bleach has time to process all the items in the bookmark evenly. At the same time, make sure that the GPCN-based bleach is not too active, since if it reacts too actively, it will be consumed before it can penetrate the center of the bookmark, which will affect the process of removing stains in the center of the bookmark, and the fibers of the fabrics located on the surface bookmarks will receive additional damage.
British Washing and Cleaning Association ( BritishLaunderersResearchAssociation, BLRA) recommendations have been developed for the use of sodium hypochlorite in removing stains and bleaching fabrics during industrial washing. Here are some of them:

• A working solution of bleach based on HPCN should be used with a washing liquid that has an alkaline pH, or in a mixture with soap or a synthetic detergent, so that the bleach “works” more slowly and more or less evenly saturates the entire volume of the load.
• It is necessary to add such a quantity of liquid commercial sodium hypochlorite solution that the concentration of free chlorine is approximately equal to 160 mg/l for the solution in the machine or 950 mg/kg for the dry weight of the load.
• The temperature of the liquid into which the bleach is added should not exceed 60°C.

According to BLRA experts, if these recommendations are followed, the bleaching process using HPCN will remove most common stains and cause minimal damage to the fabric.

3.7. Disinfection of drinking water

The dose of chlorine is established by technological analysis on the basis that in 1 liter of water supplied to the consumer there remains 0.3...0.5 mg of chlorine that has not reacted (residual chlorine), which is an indicator of the sufficiency of the dose of chlorine taken. The calculated dose of chlorine should be taken as providing the specified amount of residual chlorine. The calculated dose is prescribed as a result of trial chlorination. For clarified river water, the dose of chlorine usually ranges from 1.5 to 3 mg/l; during chlorination groundwater the dose of chlorine most often does not exceed 1-1.5 mg/l; in some cases, it may be necessary to increase the dose of chlorine due to the presence of ferrous iron in the water. With an increased content of humic substances in water, the required dose of chlorine increases.
After introducing the chlorine agent into the water being treated, good mixing with water and a sufficient duration (at least 30 minutes) of its contact with water before supplying it to the consumer must be ensured. Contact may occur in the filtered water tank or in the water supply pipeline to the consumer, if the latter is of sufficient length without water intake. When turning off one of the filtered water tanks for flushing or repair, when the time of contact of water with chlorine is not ensured, the dose of chlorine should be doubled.
Chlorination of already clarified water is usually carried out before it enters the clean water reservoir, where the time necessary for their contact is ensured.
Instead of chlorinating water after settling tanks and filters, in water treatment practice, it is sometimes used to chlorinate it before entering the settling tanks (pre-chlorination) - before the mixer, and sometimes before feeding it to the filter.
Pre-chlorination promotes coagulation, oxidizing organic substances that inhibit this process, and, therefore, allows you to reduce the dose of coagulant, and also ensures a good sanitary condition of the treatment facilities themselves. Pre-chlorination requires increasing doses of chlorine, since a significant part of it is used to oxidize organic substances contained in still unclarified water.
By introducing chlorine before and after treatment facilities, it is possible to reduce the total consumption of chlorine compared to its consumption during pre-chlorination, while maintaining the benefits provided by the latter. This method is called double chlorination.

Disinfection with chlorine.
We have already briefly considered the issue of instrumental design of the process of water chlorination using liquid chlorine as a chlorine agent. In this publication we will focus on those aspects that were not reflected by us.
Water disinfection with liquid chlorine is still more widely used compared to the process where HPCN is used. Liquid chlorine is introduced into the treated water either directly ( direct chlorination), or using chlorinator- a device that serves for preparing a solution of chlorine (chlorine water) in tap water and dosing it.
Continuous chlorinators are most often used to disinfect water; the best of them are vacuum ones, in which the dosed gas is under vacuum. This prevents gas from penetrating into the room, which is possible with pressure chlorinators. Vacuum chlorinators are available in two types: with a liquid chlorine flow meter and a gas chlorine flow meter.
In case of use direct chlorination rapid distribution of chlorine in the treated water must be ensured. For this purpose, a diffuser is a device through which chlorine is introduced into water. The layer of water above the diffuser should be about 1.5 m, but not less than 1.2 m.
To mix chlorine with the treated water, mixers of any type can be used, installed in front of the contact tanks. The simplest is brush mixer. It is a tray with five vertical partitions placed perpendicularly or at an angle of 45° against the flow of water. The partitions narrow the cross-section and cause a vortex-like movement, in which the chlorine water mixes well with the treated water. The speed of water movement through the narrowed section of the mixer must be at least 0.8 m/sec. The bottom of the mixer tray is arranged with a slope equal to the hydraulic slope.
Next, the mixture of treated water and chlorine water is sent to contact containers.

So, there are the main advantages of using chlorine for water chlorination:

1. The concentration of active chlorine is 100% pure substance.
2. The quality of the product is high, stable, and does not change during storage.
3. Simplicity of reaction and predictability of dose.
4. Availability of mass supplies - can be transported by special tank trucks, barrels and cylinders.
5. Storage - easy to store in temporary storage warehouses.

That is why, for many decades, liquefied chlorine has been the most reliable and universal means of water disinfection in centralized water supply systems in populated areas. It would seem - why not continue to use chlorine to disinfect water? Let's figure it out together...
GOST 6718-93 states that: “ Liquid chlorine is an amber-colored liquid that has an irritating and asphyxiating effect. Chlorine is a highly hazardous substance. Penetrating deeply into the respiratory tract, chlorine affects the lung tissue and causes pulmonary edema. Chlorine causes acute dermatitis with sweating, redness and swelling. Complications such as pneumonia and disorders of the cardiovascular system pose a great danger to those affected by chlorine. The maximum permissible concentration of chlorine in the air of the working area of ​​industrial premises is 1 mg/m 3 .»
In the textbook by Professor Slipchenko V.A. “Improving the technology of purification and disinfection of water with chlorine and its compounds” (Kyiv, 1997, p. 10) the following information is provided on the concentration of chlorine in the air:

• Perceptible odor - 3.5 mg/m3;
• Throat irritation - 15 mg/m3;
• Cough - 30 mg/m3;
• The maximum permissible concentration for short-term exposure is 40 mg/m 3 ;
• Dangerous concentration, even with short-term exposure - 40-60 mg/m3;
• Quick death - 1000 mg/m3;

There is no doubt that the equipment necessary to dispense such a deadly reagent (statistics almost regularly testify to this) must have a number of degrees of safety.
Therefore, PBC (“Safety Rules for the Production, Storage, Transportation and Use of Chlorine”) require the following mandatory peripheral equipment:

• scales for cylinders and containers with chlorine;
• shut-off valve for liquid chlorine;
• pressure chlorine pipeline;
• receiver for chlorine gas;
• chlorine gas filter;
• scrubber installation (chlorine neutralizer);
• analyzer for detecting chlorine gas in air,

and when consuming chlorine gas from cylinders more than 2 kg/hour or more than 7 kg/hour when consuming chlorine from a container - chlorine evaporators, which have special requirements. They must be equipped with automatic systems that prevent:

• unauthorized consumption of chlorine gas in volumes exceeding the maximum capacity of the evaporator;
• penetration of the liquid phase of chlorine through the evaporator;
• a sharp drop in the temperature of the chlorine in the evaporator radiator.

The evaporator must be equipped with a special shut-off solenoid valve at the inlet, a pressure gauge and a thermometer.
The entire process of water treatment with chlorine is carried out in special rooms - chlorination, which also have special requirements. A chlorination room usually consists of blocks of premises: a chlorine supply warehouse, a chlorination room, a ventilation chamber, auxiliary and utility rooms.
Chlorination rooms must be located in separate permanent buildings of the second degree of fire resistance. Around the chlorine warehouse and the chlorination room with the chlorine warehouse there must be a continuous solid fence, at least two meters high, with solid, tightly closing gates to limit the spread of the gas wave and prevent unauthorized persons from accessing the warehouse territory. The capacity of the chlorine supply warehouse should be minimal and not exceed 15-day consumption by the water supply plant.
The radius of the danger zone, within which it is not allowed to locate residential, cultural and community facilities, is 150 m for chlorine warehouses in cylinders, and 500 m for containers.
Chlorination plants should be located in low areas of the water supply facilities site and mainly on the leeward side of the prevailing wind directions relative to the nearest settlements(blocks).
The chlorine supply warehouse should be separated from other rooms by a blank wall without openings; the warehouse should have two exits on opposite sides of the room. One of the exits is equipped with a gate for transporting cylinders or containers. Entry of vehicles into the warehouse premises is not permitted; provision must be made for lifting equipment for transporting vessels from the car body to the warehouse. Empty containers should be stored in the warehouse. Doors and gates in all rooms of the chlorination room must be opened during evacuation. Stationary water curtains are provided at the exits from the warehouse. Vessels with chlorine must be placed on stands or frames and have free access for slinging and gripping during transportation. Equipment for neutralizing emergency chlorine emissions is located in the chlorine storage room. It must be possible to heat the cylinders in the warehouse before delivering them to the chlorination room. It should be noted that when chlorine cylinders are used over a long period of time, they will accumulate highly explosive nitrogen trichloride, and therefore, from time to time, chlorine cylinders must undergo routine flushing and purification of nitrogen chloride.
It is not allowed to place chloridation rooms in recessed rooms; they must be separated from other rooms by a blank wall without openings and provided with two exits to the outside, one of them through the vestibule. Auxiliary rooms of chlorination rooms must be isolated from rooms associated with the use of chlorine and have an independent exit.
Chlorination rooms are equipped with supply and exhaust ventilation. The exhaust of air by permanent ventilation from the chloridation room should be carried out through a pipe 2 m high above the roof ridge of the tallest building located within a radius of 15 m, and by permanent and emergency ventilation from the chlorine supply warehouse - through a pipe 15 m high from ground level.

That is the degree of danger of chlorine is minimized by the presence of a whole range of measures to organize its storage and use , including through the organization of sanitary protection zones (SPZ) of reagent warehouses, the radius of which reaches 1000 m for the largest structures.
However, as cities grew, residential development came close to the boundaries of the sanitary protection zone, and in some cases was located within these boundaries. In addition, the danger of transporting the reagent from the place of production to the place of consumption has increased. According to statistics, it is during transportation that up to 70% of various accidents of chemically hazardous substances occur. A full-scale accident of a railway tank with chlorine can cause varying degrees of damage not only to the population, but also to the natural environment. At the same time, the toxicity of chlorine, enhanced by the high concentration of the reagent, reduces industrial safety and the anti-terrorism resistance of water supply systems in general.
In recent years, the regulatory framework in the field of industrial safety when handling chlorine has been tightened, which meets the requirements of the day. In this regard, operating services have a desire to switch to a safer method of water disinfection, i.e. to a method that is not supervised by the Federal Service for Environmental, Technological and Nuclear Supervision, but ensures compliance with SanPiN requirements for the epidemiological safety of drinking water. For this purpose, the chlorine-containing reagent most often used in chlorination (second place after liquid chlorine) is sodium hypochlorite (SHC).

Disinfection with sodium hypochlorite
In water supply practice, concentrated sodium hypochlorite grade A with an active part content of 190 g/l and low-concentrated sodium hypochlorite grade E with an active part content of about 6 g/l are used to disinfect drinking water.
Typically, commercial sodium hypochlorite is introduced into the water treatment system after preliminary dilution. After diluting sodium hypochlorite 100 times, containing 12.5% ​​active chlorine and having a pH = 12-13, the pH decreases to 10-11 and the concentration of active chlorine to 0.125 (in reality, the pH value has a lower value). Most often, a sodium hypochlorite solution is used to treat drinking water, characterized by the indicators listed in the Table:

Thus, unlike chlorine, HPCN solutions are alkaline in nature and can be used to increase the pH level of the treated water.
As the pH value of the treated water changes, the relationship between hypochlorous acid and hypochlorite ions changes. Research in Japan has shown that when using sodium hypochlorite to disinfect water, the alkali concentration in the hypochlorite must be taken into account and maintained below a certain level. As pH increases, hypochlorous acid breaks down into ions H+ And C lO - . So, for example, at pH = 6 the proportion HClO is 97%, and the proportion of hypochlorite ions is 3%. At pH = 7 fraction HClO is 78%, and hypochlorite - 22%, at pH = 8 share HClO - 24%, hypochlorite - 76%. Thus, at high pH values ​​in water HClO turns into hypochlorite ion.
This means that the pH value of a solution of commercial sodium hypochlorite is increased due to the fact that the alkaline solution of sodium hypochlorite is more stable. On the other hand, by “alkalinizing” the treated water, we reduce the activity of the chlorine agent. In addition, at the interface between the treated water and the HPCN working solution, a precipitate of magnesium hydroxide and silicon dioxide is formed, clogging the water channels. Therefore, the concentration of alkali in sodium hypochlorite must be such as not to cause the formation of this precipitate. It has been experimentally established that the optimal pH range of water when treated with sodium hypochlorite is in the range from 7.2 to 7.4.
In addition to the pH value, the disinfecting properties of HPNC are influenced by temperature and the content of free active chlorine in the working solution. Data on the excess active chlorine required for complete sterilization of drinking water at various temperatures, exposure times and pH values ​​are given in the Table.

Water temperature, o C	Exposure time, min	Required excess chlorine, mg/l
		pH 6	pH 7	pH 8
10	5	0,50	0,70	1,20
	10	0,30	0,40	0,70
	30	0,10	0,12	0.20
	45	0,07	0,07	0.14
	60	0,05	0,05	0,10
20	5	0,30	0,40	0,70
	10	0,20	0.20	0,40
	15	0,10	0,15	0,25
	30	005	0,06	0,12
	45	0,04	0,04	0,08
	60	0,03	0,03	0,06

The loss of activity of HPCN solutions over time is clearly illustrated by the following table:

The introduction of the HPCN working solution into the treated water is carried out by the method of proportional dosing using dosing pumps. In this case, proportional dosing ( dosing pump control ) can be done either using pulse water meters or using a signal from a chlorine sensor installed either directly in the pipeline or after the contact tank. After the GPCN input unit or at the entrance to the contact tank, a dynamic mixer is usually installed to thoroughly mix the treated water with the GPCN working solution.
Sodium hypochlorite electrolysis grade “E”, obtained in non-diaphragm electrolysers, is supplied to the stream of processed water either through direct input (in the case of using flow-type electrolysers), or through a storage tank (in the case of using non-flow-type electrolysers), equipped with an automatic or manually controlled system dosing The dosing system can be controlled using either pulse water meters or a signal from a chlorine sensor installed either directly in the pipeline or after the contact tank.

Thus, it would seem that the advantages of using sodium hypochlorite over chlorine when chlorinating water are quite obvious: it is much safer - it is not flammable or explosive; no need for additional equipment, ensuring the safety of the chlorination process, in addition to the presence of: 6-fold ventilation, a reservoir for collecting leaked sodium hypochlorite and a container with a neutralizing solution (sodium thiosulfate). The equipment used when using GPHN to ensure the disinfection process at water treatment stations is not classified as industrially hazardous and is not supervised by the Federal Service for Environmental, Technological and Nuclear Supervision. This makes life easier for operators.
But is it? Let's return to the properties of HPCN.

We have repeatedly said that HPCN solutions are unstable and susceptible to decomposition. So according to the data Mosvodokanal found out that Sodium hypochlorite grade “A” loses up to 30% of the initial content of the active part as a result of storage after 10 days. Added to this is the fact that he freezes in winter at a temperature of -25°C, and in the summer it is observed sedimentation, which leads to the need to use railway tanks with thermal insulation for transporting the reagent.
In addition, it happened increase in the volume of use of the reagent by 7-8 times compared to chlorine due to low content active part and, as a consequence, an increase in the volume of transportation of railway tanks (daily one tank with a volume of 50 tons per station), what necessitated the presence of large warehouses for storing reagent stocks in accordance with the requirements of regulatory documents (30 days supply).
And as it turned out, Currently, the existing production capacity of concentrated sodium hypochlorite in the European part of Russia does not meet the future needs of Mosvodokanal in the amount of about 50 thousand cubic meters per year.
As for sodium hypochlorite grade “E”, Mosvodokanal draws attention to the fact that significant consumption of raw materials: about 20 tons/day of table salt at each station (for 1 kg of active chlorine there is from 3 to 3.9 kg of table salt). At the same time, the quality table salt (domestic raw materials) does not match requirements imposed by electrolyzer manufacturers. And the most important thing, electrolysis plants for producing low-concentrated sodium hypochlorite solutions have limited use and insufficient operating experience (the cities of Ivanovo and Sharya, Kostroma region).
And if experience in operating electrolysis plants can be accumulated, then you can’t argue with the properties of GPHN. Moreover, there are more unseemly examples: when hypochlorite was between two closed shut-off devices, constant gas emissions during the natural decomposition of HPCN led to explosions ball valves, filters, and other devices with chlorine release .
Operators have experienced problems with the selection of equipment and its operation in the environment of HPCN solutions, which have very high corrosive activity. Additional measures were also required to prevent calcification of the fittings, especially the entry points of injectors and diffusers.
You can’t discount the human factor either: the largest chlorine leak at a water treatment plant (above 5 tons) was caused by the use of GPCN. This happened at one of the largest US water treatment plants in the east of the country, when the driver of a tank truck with ferric chloride (pH=4) mistakenly drained the product into a tank with a HPCN solution. This resulted in an immediate release of chlorine.
These are the “horror stories”...
But let’s not forget that this is the opinion of Mosvodokanal specialists, whose stations process thousands of tons of water every hour and where industrial safety is initially ensured. Well, if we are talking about small towns, villages, etc. Here the organization of “chlorinator” “will cost a pretty penny.” Plus, insufficient ramifications of roads, and sometimes their complete absence, will call into question the safety of transporting such a dangerous substance as chlorine. Therefore, be that as it may, we must be guided by the fact that sodium hypochlorite, and in its form the chlorination of water, will find application there, especially since it can be obtained locally.

Conclusion:
While chlorination remains the main method of water disinfection, what chlorine agent should be used: chlorine or sodium hypochlorite, must be determined by the amount of water being treated, its composition and the possibilities of organizing a safe production process in each specific case. This is a task for designers.

3.8. Disinfection of gas purification equipment for water purification

1. Preliminary cleaning of the internal surface drinking water tanks (mechanical or hydraulic) to remove plaque and loose deposits from it. Such cleaning should be carried out, if possible, immediately after draining the water from the tanks. To reduce cleaning time and make work easier, today there is a wide range of chemicals (so-called technical detergents), which contribute to the detachment of even strongly adhered contaminants from the surface of containers. True, when choosing such substances, one must focus on their chemical and corrosive activity, i.e. chemical compatibility of the container's construction materials with technical detergents. These substances are applied to the surface of the container with subsequent exposure or added to water during hydraulic cleaning.
2. Thorough rinsing of drinking water tanks after pre-cleaning (most often with a directed stream of water (from a fire hose)). If chemical reagents were used when washing tanks, then cleaning from them must be carried out in strict accordance with the instructions for use of the reagent used.
3. Selecting a method disinfection depends on the volume of the tank, its design and the disinfectant used. Treating all surfaces of the tank after pre-cleaning with GPCN-based disinfectants is the cheapest and most reliable method. For example, a sodium hypochlorite solution with an active chlorine concentration of no more than 10 mg/l can be poured into an empty, pre-cleaned container. After a 24-hour exposure (minimum), the solution is drained and the tank is filled with water again. The main disadvantage of this method is that the lid and upper part of the walls of the tank remain untreated, since the working volume of any tank is 70 - 80% of the total volume. In addition, the large volume of the tank will require a correspondingly large amount of disinfecting reagent, which after use must be disposed of without the threat of harm to the environment.

Sodium hypochlorite (SHC) is considered a chemical compound used for disinfection and disinfection of various materials, surfaces, liquids, etc. In its pure form, it is a crystalline substance that does not have a characteristic color, and it is very unstable. Chemical formula sodium hypochlorite NaClO.

If we consider percentage the main chemical elements in this substance, then in sodium hypochlorite there is approximately 47% chlorine, sodium - 30%, and oxygen - 22%. This substance is able to quickly dissolve in an aqueous environment; the boiling point of anhydrous HPCN is approximately the same as that of water +101°C. Molar mass is 74.44 g/mol.

The main state document that regulates the quality of this chemical is GOST 11086 “Sodium hypochlorite. Technical conditions".

Method of preparation and types of HPCN

To obtain sodium hypochlorite, it is necessary to carry out the process of chlorination of sodium hydroxide using molecular chlorine. This substance can also be obtained by electrolysis of a solution of table salt. The production of sodium hypochlorite is complex chemical process, which is based on the production of different HPCN solutions. Each solution is different in concentration, so there are several brands of sodium hypochlorite.

According to the interstate GOST, sodium hypochlorite can be produced in only two grades: A and B. But it is worth noting that specifications have also been developed for this substance, which regulate the quality characteristics for other grades. According to these documents, sodium hypochlorite can be produced in 5 grades: A, B, C, D, E.

Each of these brands has its own specialization:

• . grade A is created for the disinfection of drinking water, as well as water for swimming pools,
• . brand B is designed for bleaching and cleaning fabrics,
• . grade V and G according to specifications specializes in water purification in fish farms,
• . grades A and E of sodium hypochlorite according to specifications are used for disinfection of drinking water resources, equipment in hospitals and sanatoriums, disinfection of wastewater, and fishery waters. These two brands are considered among the most versatile.

The worldwide use of sodium hypochlorite is due to its chemical ability to neutralize a number of harmful microorganisms. Its bactericidal properties are aimed at destroying a number of dangerous fungi and bacteria. The most prominent representatives of this class of organisms, which sodium hypochlorite actively fights, are:

• . fungus Candida albicans,
• . pathogenic enterococci,
• . some types of anaerobic bacteria.

A sodium hypochlorite solution is capable of killing all of the above microorganisms within 15-30 seconds. In addition, the higher the concentration of HPCN, the faster the disinfection process occurs. But the concentration level must be strictly controlled, since often the treated water reaches the consumer directly through treatment systems water supply

The principle of action of sodium hypochlorite is quite simple, since this substance has high biocidal properties. When sodium hypochlorite gets into water, it begins to actively decompose, forming active particles in the form of radicals and oxygen.

HPCN radicals can be considered the main “weapon” against harmful microorganisms. Active particles of HPCN begin to destroy outer shell or biofilm of a microorganism, thus leading to the final death of various pathogenic fungi, viruses and bacteria.

Due to such a powerful disinfecting effect, this substance must undergo strict quality control. Especially when it is used to purify drinking water. After treatment with sodium hypochlorite, the water will be checked for:

• . presence of heavy metals,
• . chromaticity,
• . stability level,
• . alkali concentration,
• . chlorine concentration.

Areas of application

The chemical composition of sodium hypochlorite is aimed at disinfecting and disinfecting water. Therefore, this substance occupies an important place in many areas. human life. World studies show that HPCN is used for disinfection in 91% of cases, the remaining 9% include potassium or lithium hypochlorite. But in order for this substance to give results and benefits in everyday life, it is necessary to carefully monitor the concentration of the solution. To do this, you need to carefully read the instructions for sodium hypochlorite.

The main three areas of use of this chemical are:

• . medicine,
• . light and heavy industry.
• . household use.

The instructions for using sodium hypochlorite in everyday life indicate that this substance can be used for disinfection and disinfection over ties, fabrics, plumbing blockages, etc.

In the industrial sector, sodium hypochlorite grades A and E have found their application in the field of bleaching fabric and wood materials. These two grades of GPHN contribute to the treatment of municipal and waste water.

Medicines and disinfectants with sodium hypochlorite play an important role. This substance is used to disinfect and clean wounds from burns, postoperative sutures, etc. This substance helped get rid of the scourge of cholera and typhoid fever in Latin American countries. It is also administered intravenously. In medicine, GPCN is used in:

• . dentistry,
• . gynecology,
• . surgery,
• . dermatology.

The price of sodium hypochlorite in the Russian Federation for 1 liter averages 60-70 rubles. It is packaged in polyethylene cans and barrels.

Chlorine has been an effective disinfectant for many years. It was used (and is now used) for disinfection:

"Calcium Hypochlorite Solid (65 or 68%)"

• various surfaces;
• cleaning wells;
• disinfection of cesspools and septic tanks.

But the positive effect, then and now, largely depends on the professionalism of those who use calcium hypochlorite for disinfection and on whether they use the instructions for using calcium hypochlorite for disinfection.

Powder white, with a faint smell of bleach - this is calcium hypochlor it neutral

When defining this product, the abbreviation KGN is used.

A special solution is prepared from this powder. It is cloudy, slightly whitish in color. Can be stored for no more than three days. A precipitate of insoluble calcium salts remains at the bottom of the solution.

General Application

The product is used for disinfection :

• cattle burial grounds (especially if there is a suspicion of a source of infection);
• cesspools and septic tanks;
• soil and asphalt;
• premises in which patients with cholera or tuberculosis were kept for a long time (acts as a bactericidal agent);
• public premises (hospitals, schools, kindergartens, camps, recreation centers and boarding houses);
• public restrooms;
• residential individual premises;
• household items (except for metal items that may corrode);
• dishes (after processing, the dishes must be thoroughly washed several times).

A product such as calcium hypochlorite 45 is used to disinfect drinking water and water in swimming pools.

This solution is not used to disinfect clothes; they almost immediately become unusable.

If the solution gets into your eyes or onto unprotected skin, it may cause redness and a burning sensation. Rinse eyes and skin with plenty of clean water

If the solution enters the stomach, it may cause inflammation of the gastrointestinal tract. This is a moderately dangerous drug. If the substance enters the human body, treatment should be prescribed by a doctor.

The use of calcium hypochlorite should be strictly supervised by specialists.

How to prepare the solution correctly

To disinfect KGN use:

• in the form of an unclarified solution;
• in the form of a light solution;
• activated solution;
• in powder form.

An unclarified solution is made from 200 grams of KGN powder and one liter of water.

A light solution is prepared from an unclarified solution.

1. The unclarified solution is allowed to settle.
2. The liquid that has formed above the sediment is drained (one liter of solution with a pure chlorine concentration of 10% is obtained).
3. The liquid is diluted to obtain a light solution (if one liter of solution with 0.5% chlorine is needed, then 50 ml of the activated solution is diluted in one liter of water (10% divided by 0.5%, 1000 ml divided by 20); if a different concentration is needed simple mathematical calculation methods are used).

To obtain an activated solution, ammonium salts are added to the light solution in proportions of one to two. This type of solution is prepared immediately before use.

In any case, only specialists have the right to manufacture drugs and test them.

Application of different types of solutions and powder

The question of where calcium hypochlorite solution is used is important. Here the accents are placed very precisely.

Unclarified solution is used for processing:

• production premises (600 ml. per square meter);
• outbuildings (600 ml. per square meter);
• garbage pits (600 ml per square meter);
• equipment used to remove waste.

The clarified solution is used for disinfection:

• residential premises (210 ml per square meter; after treatment, the room must be cleaned and ventilated);
• furniture (you can spray the product at the rate of 210 ml per square meter; you can use a solution for wet wiping of surfaces at the rate of 180 ml per square meter);
• dishes (one set of dishes for two liters of product);
• children's toys (small ones can be soaked in the solution, and large ones can be irrigated; after soaking, the toys must be cleaned with large quantity water).

The activated solution is used for outbreaks of viral and infectious diseases (600 ml per square meter).

The powder is used to treat patient discharge, food debris, and drinking water. The powder is used in large quantities or in one to one proportions.

Rules for working with the tool

Safety precautions during work must be observed.

• children under 18 years of age;
• pregnant women;
• persons with general contraindications.

Besides:

• the preparation of the solution must be carried out in rooms with a good ventilation system or in special fume hoods;
• specialists must be dressed in overalls and have protective masks on their faces. If you act strictly according to the instructions, then the person must be protected by a RU-60 respirator with a brand A cartridge; safety glasses, rubber gloves; protective aprons;
• The powder and solution can only be stored in containers with tight lids, in areas inaccessible to children, well ventilated and not damp;
• all treated household items and children's toys must be thoroughly washed until the smell of chlorine completely disappears;
• It is forbidden to simply throw the remaining powder in the trash; it is diluted with water and poured into the sewer;
• After finishing working with the product, you must wash your hands thoroughly (but it is better to take a shower).

Rules for providing assistance in case of KGN poisoning

In some cases, CCHF poisoning occurs (if safety precautions are not followed or an industrial accident occurs). Symptoms of poisoning:

• pain and pain in the eyes;
• sore throat;
• sore nose;
• cough;
• redness or burns.

When the first symptoms appear, you must:

• remove the injured person to the air;
• make him wash his hands and face well;
• force you to drink an alkaline drink (the best option is milk with baking soda dissolved in it);
• stop coughing;
• check the heartbeat rhythm and measure blood pressure;
• if redness or burns appear, it must be thoroughly washed and then treated with a soda solution;
• If KGN gets into your eyes, you need to rinse them with running water, drop them with albucit or novocaine (solution), and then consult a doctor.

If the substance gets into the stomach, you need to induce vomiting, and then drink milk or water with ammonia(a few drops per glass).

When using KGN, you must follow the instructions that were specially published for the manufacturers of the product and for those who use it for disinfection.

Our specialist clarifies the information, selects the optimal solution to your problem and agrees with you on a time convenient for you for the technician to leave.

A complete inspection of the premises, detection of areas inhabited by fungus, rodents or insects and destruction of infestations. Upon completion of treatment, you receive a free consultation to avoid recurrence of infection.

We monitor the sanitary and technical condition of the facility during the entire warranty period.

In aqueous solutions, hypochlorites can decompose quite quickly - however, it will depend on the temperature of the water and its pH. Strongly acidic solutions completely hydrolyze hypochlorites, decomposing them at room temperature to oxygen and chlorine. A neutral environment converts hypochlorites into chlorates and chlorides - the reaction slows down at room temperature and accelerates when it rises. Temperatures above 70°C significantly accelerate the decomposition process and are used industrially to produce chlorates.

Hypochlorites are strong oxidizing agents, but their oxidizing abilities in an aqueous solution strongly depend on its pH environment.

Hypochlorites placed in an alkaline solution react with hydrogen peroxide to form chloride and oxygen. The main feature of this reaction is the release of oxygen, which is in an excited singlet state, and not in the main triplet state. This is precisely the prerequisite for its high activity and phosphorescence in the near-infrared range.

Application of hypochlorites

In organic synthesis, alkyl hypochlorites are subjected to thermal or photochemical isomerization to produce δ-chlorohydrins. During the Hoffmann reaction, acid amides react with hypochlorites and are grouped inside the molecules into isocyanates, which are subsequently hydrolyzed to primary amines or form urethanes (if present).

The first hypochlorite to be used in industry was potassium hypochlorite, which was used in the bleaching of cellulose fabric.

Calcium and sodium hypochlorites are large-scale products that are obtained by passing chlorine through a suspension or solution of the corresponding hydroxide. Most hypochlorites produced by this method are used in a mixture with a specific chloride - for example, hypochlorite mixed with calcium chloride ends up as bleach.

Low cost and strength make it possible to use hypochlorites as a bleaching agent in the paper, textile and pulp industries. In addition, they are used for degassing organophosphorus and sulfur-containing toxic substances, as well as for chemical disinfection of waste and drinking water.

Sodium hypochlorite - NaClO, is obtained by chlorinating an aqueous solution of dry sodium (NaOH) or an electrode solution of dry sodium (NaCl). The molecular weight of NaClO (according to international atomic masses 1971) is 74.44. It is produced industrially in the form of aqueous solutions of various concentrations.

Aqueous solutions of sodium hypochlorite (SHC) have been used for disinfection since the early days of the chlorine industry. Due to its high antibacterial activity and wide spectrum of action on various microorganisms, this disinfectant is used in many areas of human activity, including water treatment.

The disinfecting effect of HCN is based on the fact that when dissolved in water, just like chlorine when dissolved in water, it forms hypochlorous acid, which has a direct oxidizing and disinfecting effect.

NaClO+H2O-NaOH+HClO

The reaction is equilibrium, and the formation of hypochlorous acid depends on the pH and temperature of the water.

In the Russian Federation, the composition and properties of hydrochloric acid produced by industry or obtained directly from the consumer in electrochemical installations must meet the requirements specified in (3.4). The main characteristics of HCN solutions regulated by these documents are given in Table 1.

Table 1. Main physicochemical parameters of sodium hypochlorite solutions produced in the Russian Federation (3, 4)

Indicator name	Standard for brands
	By (3)		By (4)
	Grade A	Brand B	Grade A	Brand B	Brand B	Brand G	Brand E
1.Appearance			Greenish-yellow liquid				Colorless liquid
2. Light transmission coefficient, %, not less	20	20	Not regulated				Not regulated
3. Mass concentration of active chlorine, g/dm3, not less	190	170	120	120	190	120	7
4.Mass concentration of alkali in terms of NaOH, g/dm3	10-20	40-60	40	90	10-20	20-40	1
5.Mass concentration of iron, g/dm3, no more	0,02	0,06	Not regulated				Not regulated

Notes:

For solutions according to (3), a loss of active chlorine after 10 days from the date of shipment of no more than 30% of the initial content and a change in color to a reddish-brown color are allowed.

For solutions according to (4), the loss of active chlorine after 10 days from the date of shipment for grades A and B is allowed no more than 30% of the initial content, for grades C and D - no more than 20%, for grade E - no more than 15%.

In accordance with (3-5), solutions of sodium hypochlorite of various brands are used:

solution grade A according to (3)- in the chemical industry, for the disinfection of drinking water and swimming pool water, for disinfection and bleaching;

solution grade B according to (3)- in the vitamin industry, as an oxidizing agent for fabric bleaching;

solution grade A according to (4)- for the disinfection of natural and waste water in domestic and drinking water supplies, disinfection of water in fisheries reservoirs, disinfection in the food industry, and the production of bleaching agents;

solution grade B according to (4)- for disinfection of areas contaminated with fecal discharges, food and household waste; wastewater disinfection;

solution grade B, G according to (4)- for disinfection of water in fishery reservoirs;

solution grade E according to (4)- for disinfection, similar to grade A according to (4), as well as disinfection in health care institutions, catering establishments, civil defense facilities, etc., as well as disinfection of drinking water, wastewater and bleaching.

It should be noted that for the production of sodium hypochlorite solutions of grade AB according to (3) and solutions of grade A according to (4), the use of exhaust chlorine from chlorine-consuming organic and inorganic industries, as well as caustic soda obtained by mercury methods, is not allowed.

Solutions of grade B according to (4) are obtained from exhaust chlorine at the stage of reducing the production of chlorine from organic and inorganic industries and diaphragm or mercury sodium hydroxide.

Solutions of grades B and G according to (4) are obtained from exhaust chlorine at the stage of reducing the production of chlorine and diaphragm caustic soda with the addition of a stabilizing additive - citral of the "Perfumery" grade according to (6).

Solutions of grade E according to (4) are obtained by electrolysis of a solution of table salt.

Safety and environmental requirements when working with sodium hypochlorite solutions

Solutions of sodium hypochlorite according to (3) and grades A, B, C, and T according to (4) are strong oxidizing agents; if they come into contact with the skin, they can cause burns, and if they get into the eyes, they can cause blindness. Sodium hypochlorite solution grade E according to (4) has a moderate irritant effect on skin and mucous membranes. Cumulative. does not have skin-resorptive properties and sensitizing effects; In terms of toxicity level, this solution belongs to low-hazardous substances of the 4th hazard class according to (7).

When heated above 35°C, sodium hypochlorite decomposes to form chlorates and release chlorine and oxygen. MPC of chlorine in the air of the working area is 1 mg/m3; in the air of populated areas 0.1 mg/m3 maximum one-time and 0.03 mg/m3 average daily (7).

Sodium hypochlorite is non-flammable and non-explosive. However, sodium hypochlorite according to (3) and grades A, B, C, and D according to (4) in contact with organic combustible substances (sawdust, rags, etc.) during the drying process can cause their spontaneous combustion. When contacted with painted objects, all grades of sodium hypochlorite can cause discoloration.

The premises for the production and use of sodium hypochlorite according to (3) and grades A, B, C and D according to (4) must be equipped with forced supply and exhaust ventilation. The equipment must be sealed.

Personal protection of personnel must be carried out using special clothing in accordance with (8) and individual funds protection: gas masks grade B or BKF according to (9), rubber gloves and goggles according to (10).

If sodium hypochlorite solution gets on your skin, you should wash it with plenty of water for 10-12 minutes; if the product splashes into your eyes, you should immediately rinse them with plenty of water and refer the victim to a doctor.

Spilled product according to (3) and grades A, B, C, and D according to (4) must be washed off with plenty of water. When spilling sodium hypochlorite grade E (4), it is necessary to collect it with a rag or rinse with water and wipe. Rinse the fabric with water.

Wastewater containing sodium hypochlorite must be sent to a neutralization station.

Sodium hypochlorite in polyethylene and glass containers should be stored in unheated ventilated warehouses. Sodium hypochlorite should not be stored with organic products, flammable materials or acids.

Use of sodium hypochlorite solutions in water treatment

Long-term practice of using sodium hypochlorite solutions for water treatment, both in our country and abroad, shows that these reagents can be used in a wide range:

For the treatment of natural and waste water in the domestic and drinking water supply system, for the disinfection of water in swimming pools and reservoirs for various purposes, for the treatment of domestic and industrial waste water, etc. Due to the fact that many volumes of publications are devoted to this problem, information is discussed below given in review materials (1, 11, 12).

Use of HCN solutions for drinking water treatment

The use of sodium hypochlorite solutions is preferable at the pre-oxidation stage and for sterilizing water before supplying it to the distribution network. Usually, HCN solutions are introduced into the water treatment system after dilution by approximately 100 times. At the same time, in addition to reducing the concentration of active chlorine, the pH value also decreases (from 12-13 to 10-11), which helps to increase the disinfecting ability of the solution. In addition to the pH value, the disinfecting properties of the solution are influenced by temperature and the content of free active chlorine. In table Table 2 shows data on the excess of free active chlorine required for complete sterilization at various temperatures, exposure times and pH values ​​of drinking water.

When treating drinking water, the residual content of active chlorine is allowed within 0.3-0.5 mg/dm 3 . In this case, the dose of active chlorine added to water can be significantly higher and depends on the chlorine absorption of the water (Table 3).

Table 2. Data on excess active chlorine required for complete sterilization of drinking water at various temperatures, exposure times and pH values ​​(1)

Water temperature, оС	Exposure time, min.	Required excess chlorine, mg/dm 3
		PH 6	pH 7	pH 8
10	5	0,50	0,70	0,120
	10	0,30	0,40	0,70
	30	0,10	0,12	0,20
	45	0,07	0,07	0,14
	60	0,05	0,05	0,10
20	5	0,30	0,40	0,70
	10	0,20	0,20	0,40
	15	0,10	0,15	0,25
	30	0,05	0,06	0,12
	45	0,04	0,04	0,08
	60	0,03	0,03	0,06

Table 3. Some data on the use of sodium hypochlorite in water treatment (11)

Technological process	The amount of active chlorine added to water, mg/dm 3	Recorded residual content of active chlorine, mg/dm 3
1	2	3
1.Disinfection of drinking water and purification of industrial wastewater
1.1.Chlorination of drinking water	3-10	0,3-0,5
1.2.Disinfection of pipelines, clean water tanks, water tower tanks	75-100	0,3-0,5
1.3. Neutralization of domestic waste and mine waters.	5-10	1.5 (not less)
1.4.Disinfection of cyanide-containing wastewater.	50*10 3-100*10 3
2.Fighting fish diseases
3.Railway and sea transport.
3.1.Decontamination of water on railways.	5
3.2. Neutralization of wastewater on railways.	10
3.3.Chlorination of water in cargo tanks of ships.	15
4.Public service system for the population.
4.1.Disinfection of drinking water containers.	750-1000
4.2.Disinfection of water in swimming pools	3-10	0,3-0,5

The use of hydrochloric acid solutions for the treatment of swimming pool water

The use of HCN solutions to disinfect water in swimming pools and ponds allows you to obtain clean, transparent water, free of algae and bacteria. When treating swimming pools with HCN solutions, it is necessary to carefully monitor the content of active chlorine in the water. It is also important to maintain pH at a certain level, usually 7.4-8.0, and even better 7.6-7.8. pH regulation is carried out by introducing special additives, for example, hydrochloric acid.

As in the case of drinking water treatment, the residual chlorine content in swimming pool water should be at the level of 0.3-0.5 mg/dm 3 . Reliable disinfection within 30 minutes. Provide solutions containing 0.1-0.2% sodium hypochlorite. At the same time, the content of active chlorine in the breathing zone should not exceed 0.1 mg/m 3 in public swimming pools and 0.031 mg/m 3 in sports pools. It should be noted that replacing chlorine gas with sodium hypochlorite leads to a decrease in the release of chlorine into the air and, in addition, makes it easier to maintain the residual amount of chlorine in the water.

Use of hydrochloric acid solutions for wastewater treatment

Sodium hypochlorite is widely used in the treatment of domestic and industrial wastewater to destroy animal and plant microorganisms; eliminating odors (especially those formed from sulfur-containing substances); neutralization of industrial wastewater, including those containing cyanide compounds. It can also be used to treat water containing ammonium, phenols and humic substances. In the latter case, chloroform, dichloro- and trichloroacetic acids, chloralgurates and some other substances can be formed, the concentration of which in water is much lower.

Sodium hypochlorite is also used to neutralize industrial wastewater from cyanide compounds; for the removal of mercury wastewater, as well as for the treatment of cooling condenser water at power plants (in the latter case, low-concentrated sodium hypochlorite grade E is used according to (1).

Some data on the required content of active chlorine in water when sodium hypochlorite solutions are used for its treatment are given in table. 3. The specific dose of the HCN solution when treating water is determined based on the data in this table and the properties of the solution used (see Table 1).

Sodium hypochlorite solution is also used in many other sectors of the national economy, but these applications are not considered in this review.

DETERMINATION OF THE BASIC CHARACTERISTICS OF SODIUM HYPOCHLORITE SOLUTIONS

Three samples of sodium hypochlorite solutions were studied.

Sample No. 1- imported HCN solution presented for testing by the company "DieEl Prospecten". Manufacturer - company "Bayer" (Germany). Estimated production time: June-July 2001.

Sample No. 2- grade A solution according to (3) from a batch manufactured by Sintez OJSC using the technology of the DiEl Prospecten company on September 5, 2001.

Sample No. 3- a solution obtained by chlorination of an industrial solution of caustic soda, the content of active chlorine exceeding grade A according to (4). Manufactured between 5 and 8 September 2001.

2.1. Determination of the initial composition of sodium hypochlorite solutions.

In accordance with (3), the following main characteristics of the compared solutions were determined:

• appearance;
• light transmittance coefficient, %;
• mass concentration of active chlorine, g/dm 3 ;
• mass concentration of alkali in terms of NaOH, g/dm 3 ;
• mass concentration of iron, g/dm 3 ;

For a more complete characterization of the studied HCN solutions, the following were additionally determined:

mass concentration of sodium chlorides, g/dm 3 ;

indicator of hydrogen ion concentration (pH);

mass concentration of sodium chlorate "NaClO3", g/dm 3;

The results of determining the main quality indicators of the studied solutions are given in Table 4.

2.2. Determination of the rate of decomposition of HCN solutions

Determination of the rate of decomposition of hypochlorite solutions was determined in two ways:

1. At room temperature (for samples No. 1 and 2). In this case, one sample of each GCN sample was stored under natural conditions (in the light during the day), and the second sample was stored constantly in the dark.
2. At a temperature of 55 o C (test speed). In this case, the test duration is 7 hours. Corresponds to a storage duration in the dark of 1 year.

The results of determining the rate of decomposition of HCN solutions at room temperature are given in Table 5. Data on the rate of decomposition of HCN solutions of all three samples at a temperature of 55 °C are given in Table 6. Unfortunately, testing of sample No. 3 was stopped prematurely (power outage due to an accident at the electrical distribution substation). However, the data obtained made it possible to calculate the percentage of the solution of hydrochloric acid no. 3 for a test period of 3 hours, that is, about 4 months of storage at room temperature (data are given in Table 4 in parentheses).

Table 5. Experimental data on the rate of decomposition of sodium hypochlorite at room temperature Table 5. Experimental data on the rate of decomposition of sodium hypochlorite at room temperature

Test date	Sample No. 1						Sample No. 2
	Storing in the light			Storing in the dark			Storing in the light			Storing in the dark
	AC content, g/dm3	Decomposition percentage, %		AC content, g/dm3	Decomposition percentage, %		AC content, g/dm3	Decomposition percentage, %		AC content, g/dm3	Decomposition percentage, %
		From the original	From previous		From the original	From previous		From the original	From previous		From the original	From previous
09/07/01	120,0			120,0			186,0			186,0
11.09.	117,1	2,42	2,42	117,1	2,42	2,42	172,9	7,04	7,04	176,0	5,38	5,38
14.09.	112,1	6,58	4,27	115,1	4,08	1,71	169,0	9,14	2,25	169,0	9,14	3,98
19.09.	110,0	8,33	1,87	112,0	6,66	2,69	159,7	14,14	5,50	163,0	12,36	3,55
22.09.	107,3	10,58	2,45	112,0	6,66	0	157,0	15,59	1,69	160,0	13,98	1,84

Table 6. Data on the rate of decomposition of sodium hypochlorite at a temperature of 55 o C

Note: The value of decomposition is indicated in parentheses in terms of a test duration of 3 hours.

Assessment of the initial quality of imported HCN solution

The initial content of active chlorine (AC) and sodium chloride in the imported HCN solution was assessed based on the following considerations:

1. According to the customer, the batch of sodium hypochlorite arrived from abroad at the end of July this year. Considering that for some, perhaps a short time, the product was in the manufacturer’s warehouse and transported, then as of the time of measurements 09/05/01) total time its storage and transportation was approximately 60 days.
2. Based on the results of two-week stability tests given in the table, it was assumed that the loss of active chlorine during these 60 days averaged 120-109,65 = 0.69 g/dm3 per day.

   (average value for cases of storage in light and in darkness).

3. From these considerations, the initial content of active chlorine in the imported product was calculated to be equal to
   120+0.69*60=161.4 g/dm 3

Assuming that the decomposition of sodium hypochlorite occurs mainly by the reaction

2NaClO -2NaCl+O2

You can estimate the initial content of sodium chloride in the initial HCN solution from the following considerations. For 1 g-mol of NaClO (74.5), its decomposition produces 1 g-mol of sodium chloride (58.5). Thus the conversion factor is 0.785. Hence, the initial content of sodium chloride in the product is 179-0.785*0.69*74.5/51.5*60=179-47=132 g/dm3

The obtained values ​​are close to the values ​​of active chlorine and sodium chloride in a solution of sodium hypochlorite produced at JSC Skoropuskovsky Experimental Plant (see Table 4).

DISCUSSION OF THE RESULTS OBTAINED

Comparison of the quality of the studied HCN solutions

First of all, attention is drawn to the sharp difference between solution samples No. 1 and No. 2 in appearance. The light yellow imported product, accordingly, has a high light transmittance coefficient (98%), and the product produced by Sintez OJSC, which is a slightly transparent dark red liquid, has a light transmittance coefficient of 31%. As follows from the data given in Table 4, this is directly related to the iron content in solutions. According to data (2), the maximum permissible iron content in HCN solutions should not exceed 0.005 mg/dm3. Therefore, the solution produced by Sintez OJSC, although it meets the requirements of the current regulatory document in this indicator (see Table 1), further lags behind requirements for sodium hypochlorite as a chemical product with high performance properties.

The sodium hypochlorite solution produced by OJSC SOZ (sample No. 3) is close to the imported one in terms of this indicator: the color is light yellow, the light transmittance is 88%. The iron content in this solution is 0.0047 mg/dm 3, which meets the requirements given in (d). The presence of iron in the HCN solution reduces its stability. This is evidenced, in particular, by the data on the decomposition rates of the studied HCN solutions given in Table. 5 and 6. Their values ​​for samples No. 1 and 3 are significantly lower than for sample No. 2, but very close to each other. From this we can draw an unambiguous conclusion that the requirements for HCN solutions according to (3) are significantly inferior to the requirements for the service properties of solutions required by industry and are based on the capabilities of technologies adopted at manufacturing enterprises of the former USSR and which, as is known, were at a low level .

The initial content of active chlorine in samples of HCN solutions No. 1 and 3 is less than in sample No. 2. Moreover, the content of sodium chloride in them corresponds to stoichiometric. At the same time, in sample No. 2, in which the active chlorine content is approximately 1.16 times higher than in samples No. 1 and 3, the sodium chloride content is 1.21 times higher than the stoichiometric ratio (177 g/dm 3 instead of 146 g / dm 3), which additionally indicates a low level of production culture, in particular, the lack of control over the temperature level of the technological process.

Thus, we can conclude that sodium hypochlorite, manufactured using POPs using the technology of the company "DiEl Prospecten" (sample No. 3), is practically similar to the imported product - sodium hypochlorite from "Bayer" (Germany). Moreover, despite the absence of special preservative additives, sodium hypochlorite (sample No. 3) is more stable than the German one and its guaranteed shelf life exceeds the German one by two to three months.

Research group

GOSNII "Chlorproekt"