How to use sodium hypochlorite?
Sodium hypochlorite is one of the few substances that, despite its simplicity, finds application in so many branches of industry, economy, and medicine. This is largely due to one of the main components of this agent, chlorine. Contrary to appearances, this element occurs in nature in greater quantities than, for example, carbon, making up 2.9% of the world's oceans and 0.045% of the Earth's crust. Chlorine compounds naturally occur in humans, in the blood, skin, and teeth; even white blood cells need chlorine to fight infections.
Currently, chlorine is used in countless processes that are part of the production of many products that accompany us in everyday life. Chlorine is used for water disinfection, in the paper industry, food industry, textile production, detergents, aluminum production, rubber recycling, pharmaceuticals, medical devices, and insulation materials. Additionally, chlorine is used in the production of useful organic chemicals and inorganic chemical substances such as paints, glass, ceramics, fuel cells, and cosmetics.
Table of Contents:
1. Sodium Hypochlorite - History, Properties, Storage
2. Sodium Hypochlorite in Orchard Management
3. Sodium Hypochlorite in the Storage of Perishable Vegetables
4. Disinfecting Vegetable Crates with Sodium Hypochlorite
5. Sodium Hypochlorite and Poultry Farm Disinfection
6. Water Treatment with Sodium Hypochlorite
7. Disinfecting Wells with Sodium Hypochlorite
8. Disinfecting Pool Water with Sodium Hypochlorite
9. Post-Flood Disinfection with Sodium Hypochlorite
10. Disinfection in Brewing and Sodium Hypochlorite
11. Applications of Sodium Hypochlorite in Endodontics
12. Other Uses of Sodium Hypochlorite
Sodium Hypochlorite - Historical Overview
It is not possible to definitively determine who discovered sodium hypochlorite (NaOCl), but it is known that the history of this substance dates back to the 18th century when the French chemist C.L. Berthollet produced potassium hypochlorite between 1785 and 1788 by mixing gaseous chlorine with a solution of potassium carbonate. Since then, he produced hypochlorite with Percy in the town of Javel, which was later absorbed by Paris.
In the meantime, the bleaching properties of hypochlorite led to its increasingly frequent use in the textile industry, and by the end of the 19th century, Pasteur discovered that sodium hypochlorite was effective in combating pathogenic microorganisms; unfortunately, this was before the discovery that diseases are caused by bacteria. Earlier, between 1820 and 1822, Labarraque and Semmelweis discovered that chlorine products were effective in protecting wounds from infections and preventing the spread of "childbed fever."
During World War I, a 5% NaOCl solution, known as Dakin's solution, was introduced in medicine and used to treat war wounds. At a time when antibiotics were unknown, treating purulent wounds and gas gangrene by washing injuries with this solution produced good results. Over the years, it has been proven that NaOCl has a disinfectant effect on all known microorganisms, fungi, and viruses.
What is Sodium Hypochlorite?
Sodium hypochlorite is chemically a sodium salt of hypochlorous acid with the chemical formula NaOCl. It can be produced in three ways:
- by adding chlorine to sodium hydroxide at the appropriate concentration
- from calcium chloride and a sodium solution as a by-product during the synthesis of sodium chloride
- during the electrolysis of table salt
When dissolved in water, it has a yellow-green, translucent color with a pH of 12 to 13 (i.e., it is highly alkaline) and a characteristic sharp chlorine odor. In itself, it is very unstable and is therefore mainly used in aqueous solution form.
How to Store Sodium Hypochlorite?
Sodium hypochlorite is an unstable substance, and its decomposition is accelerated by:
- temperature - the higher the temperature, the faster the decomposition
- sunlight - exposure to direct sunlight can cause a loss of 10 - 20 g of free chlorine within a few hours
- heavy metals such as copper, nickel, iron
Storage Requirements for Sodium Hypochlorite:
- ensure ventilation
- store at air temperatures below 25°C
- protect from sunlight
- use containers made of polyethylene, polyester, glass, or rubber-lined steel (sodium hypochlorite must not be stored in steel or metal containers)
Sodium Hypochlorite in Orchard Management
Sodium hypochlorite is used in viticulture and orchard management to prevent and combat canker, apple tree cancers, and various fungi attacking fruit trees. Trees should be sprayed in a leafless state, i.e., in spring or autumn. The recommended concentration of the spray solution is 3%, with an application rate of approximately 500 liters per hectare. Such treatments are commonly used in the Netherlands, France, and Germany, and have recently become popular in Poland as well.
Sodium Hypochlorite in the Storage of Perishable Vegetables
Storing perishable vegetables for the long term is a significant problem for growers. Vegetables such as cucumbers, sweet peppers, tomatoes, lettuce, spinach, kale, cauliflower, broccoli, zucchini, summer potatoes, and mushrooms spoil easily. Even if the vegetables are not completely spoiled, consumers still do not buy them due to unattractive appearance, usually manifested as dryness and discoloration. Unfortunately, such vegetables are susceptible to pathogens, causing them to rot and degrade quickly.
The storage period of perishable vegetables can be extended through appropriate post-harvest treatment, which includes selecting only healthy, undamaged, and non-wilted vegetables, followed by washing and cooling. However, these actions do not remove the fungal flora, which contributes to the growth of fungi and mold. Therefore, the best way to avoid crop degradation is to disinfect the vegetables during the washing stage using sodium hypochlorite. This is a popular method in the USA and Western Europe and has recently been adopted in Poland.
For effective disinfection, the water used to wash the vegetables should be 5°C warmer than the vegetables (this prevents pathogens from re-entering through the stomata), and its pH should be between 6.8 and 7.2. Sodium hypochlorite is added to the water to achieve an active chlorine concentration of 50 - 200 mg/l. For washing broccoli, cauliflower, cucumbers, lettuce, and mushrooms in a shower over a conveyor belt, a chlorine concentration of 100 - 150 mg/l is recommended, while for sugar peas, it should be 50 - 100 mg/l. For tomatoes and young potatoes, the vegetables should be bathed in a disinfecting solution with a concentration of 500 - 600 mg/l for potatoes and 200 - 350 mg/l for tomatoes.
Disinfecting Vegetable Crates with Sodium Hypochlorite
Crates and containers for storing vegetables should have certificates allowing them to come into contact with food. However, since vegetables can be stored in these containers for up to a year, it is essential to maintain them to prevent conditions favorable to plant diseases. Fungi and bacteria primarily develop during transportation and the initial storage phase, as environmental conditions in cold storage later significantly limit pathogen growth.
Unfortunately, disinfecting the vegetables alone does not solve the problem because bacteria can transfer to the vegetables from crates harboring pathogenic microorganisms. Therefore, it is also essential to disinfect the containers used for transporting and storing vegetables. Pathogen-free vegetable containers will protect against losses in the initial storage phase and prevent further mold and disease development in the final stage, which will be appreciated by our recipients and contractors.
Disinfection should be conducted before the storage cycle, but if leaks from the vegetables or other signs of pathogens are observed during use, it should be repeated. Disinfection should also be carried out if odors indicating vegetable diseases are detected and on containers sourced from outside the company.
Effective disinfection with sodium hypochlorite involves mechanically removing visible contaminants using high-pressure water or another method ensuring effectiveness, then exposing the containers to a 1.5% sodium hypochlorite solution for 15 minutes; finally, the crates should be rinsed thoroughly with clean water.
Sodium Hypochlorite and Poultry Farm Disinfection
Disinfection on a poultry farm should be carried out before purchasing new chicks. The disinfection process should start with removing dirt and washing the interior of the chicken coop with water and a cleaning agent so that the wash water does not remain on the farm. Then, a 3% sodium hypochlorite solution should be prepared, which will be our disinfectant. 100 liters of the prepared solution are sufficient for about 600 m². It is important to disinfect not only the floor but also the interior and exterior walls and the entire surroundings.
Water Treatment with Sodium Hypochlorite
Disinfection of water intended for communal supply in case of various natural disasters is carried out using different chlorination methods, but we will focus on sodium hypochlorite. This method guarantees high biocidal efficacy, ease of use and dosing, and provides long-term protection against secondary contamination during transport and storage. This is due to the so-called residual free chlorine concentration in the water, i.e., the concentration after 30 minutes of contact between the water and the preparation, when some free chlorine has already been used for water disinfection. Typically, this concentration should not exceed 0.3 mg/l, but in exceptional conditions, up to 2 mg/l is allowed.
Disinfecting Wells with Sodium Hypochlorite
During floods, wells are often flooded with dirty water, and for households not connected to the water supply, it is essential to quickly restore the well to a condition where clean drinking water can be drawn. The disinfection of wells begins with removing all water, cleaning out the sludge, and removing several centimeters of sand from the bottom, which should then be replaced with a similar amount of clean gravel. The well lining should be cleaned and any defects cemented, then clean water should be added to the normal level. The amount of sodium hypochlorite needed for disinfection is about 750 ml per meter height for a well with a diameter of 100 cm; for wider or narrower wells, the amount will vary accordingly. The measured amount of sodium hypochlorite is diluted in a bucket with a small amount of water and poured into the well, then the water should be thoroughly mixed with a stick or by transferring the water using a bucket. After 24 hours, all the water should be removed; this process should be repeated until the chlorine smell disappears.
Disinfecting Pool Water with Sodium Hypochlorite
Sodium hypochlorite is excellent for disinfecting water in small home pools and large water parks. For effective disinfection, 200 - 250 ml of 15% sodium hypochlorite solution is recommended for every 10,000 liters of water. Sodium hypochlorite works best in water with a pH between 7 and 7.4 and a temperature between 18 and 22°C, so to ensure effective disinfection, these water parameters should first be established.
Post-Flood Disinfection with Sodium Hypochlorite
Water that enters homes during floods is extremely dangerous epidemiologically. Having previously carried compost, toilets, chemicals, and other materials, it is full of pathogenic bacteria. It is not permissible to allow residues of such water to remain in our homes, and therefore, after every flood, everything of value should be disinfected, and items that cannot be saved should be discarded without exception.
All surfaces that may have been splashed or dampened by floodwater should be disinfected. Only clean water with a 1.5% sodium hypochlorite solution should be used for this purpose. The water from washing and disinfection must be disposed of in the sewage system and not poured out in the yard. A pressure washer is best for spraying surfaces with the prepared solution, while walls and ceilings inside the house should be covered with the solution using a brush or roller. Disinfection should be carried out wearing a mask, gloves, and protective goggles. The room should be ventilated continuously during disinfection. After disinfection is complete, the room should be ventilated for 24 hours, and the disinfected walls should be washed with warm water.
Disinfection in Brewing and Sodium Hypochlorite
When brewing beer at home, it is impossible to sterilize all fermenters, i.e., the entire brewing equipment. However, it is possible to disinfect the most critical equipment components that influence the proper development of yeast.
To ensure proper yeast growth, it is necessary to minimize the population of other bacteria. Everything that comes into contact with the wort or young beer, from turning off the burners and cooling the wort to consumption, should be disinfected. However, before starting disinfection, the fermenter must be cleaned of yeast residues. This can be done with warm water, a sponge, and dishwashing liquid, followed by thorough rinsing. Wild yeast, molds, or other bacteria may reside in the fermenter's nooks and crannies, so disinfection is also necessary.
The fermentation container can be disinfected with a 1.5% sodium hypochlorite solution, but it should be thoroughly washed afterward, and the room should be well-ventilated. Disinfection with sodium hypochlorite is effective against all bacteria, viruses, and fungi, so we highly recommend this agent. Disinfection should be performed wearing gloves and protective goggles.
Applications of Sodium Hypochlorite in Endodontics
Sodium hypochlorite is often used in root canal treatment as a tissue-dissolving agent in the root canal; importantly, sodium hypochlorite also dissolves the smear layer, the removal of which is essential for proper root canal closure. Solutions with concentrations of 2.5% to 5% are most commonly used. Sodium hypochlorite should be used very cautiously due to its irritating effect on live tissues. Additionally, care should be taken with orthodontic instruments, as sodium hypochlorite is corrosive.
Other Uses of Sodium Hypochlorite
In addition to the applications of sodium hypochlorite described above, this agent has many other functions in various areas, including:
- production of intermediates in the pharmaceutical industry
- bleaching of textiles
- production of household chemical products
- disinfection of sanitary fittings
- production of plant protection products
- manufacture of various compounds, e.g., hydrazine, anthranilic acid, chloropicrin
- degassing in the hydrometallurgical production of toxic liquid and gaseous waste
- as a reagent in photometric studies
- production of modified food starch
- bactericidal and fungicidal treatment of grain
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