Sodium Hypochlorite Disinfection Development History and Finished Sodium Hypochlorite

The evolution of sodium hypochlorite disinfection has gone through several stages, from the initial discovery to the application of modern technology. The development process is as follows:

Technical Development and Application Expansion:

Due to the presence of bacteria and pathogens in tap water at the end of the 19th century, in 1897, British scientist Sir James Frazer proposed the use of chlorine gas for disinfection and proved its bactericidal effect. In the 20th century, the technology of chlorine gas disinfection was improved and perfected, and this stage was all about chlorine gas disinfection. Later, it was found that chlorine gas disinfection had by-products such as trihalomethanes. In 1811, Sir Humphry Davy, a British scientist, discovered chlorine dioxide, which was not widely used until the 1940s when its strong bactericidal, disinfecting, and bleaching effects were recognized. Later, due to safety issues with liquid chlorine and chlorine dioxide, in 1787, French chemist Claude Louis Berthollet discovered sodium hypochlorite, and in the early 20th century, American scientists began to replace liquid chlorine with sodium hypochlorite. In 1993, the first International Water Disinfection Safety Conference brought widespread attention to sodium hypochlorite as a water disinfectant. By 2008, the application of hypochlorous acid in clinical sterilization and disinfection was further expanded and verified, discovering that hypochlorous acid not only kills bacteria but also fungi and viruses.

Industrialization and Technological Progress

The production and research of sodium hypochlorite generators have a history of over a hundred years and have been proven to be a safe, reliable, low-cost operation, accurate disinfectant dosing, and excellent disinfection effect equipment.

Sodium hypochlorite generator systems can be divided into saltwater systems and seawater systems from the perspective of raw materials. A standard sodium hypochlorite generator system mainly consists of a salt dissolution tank, electrolysis cell, rectifier, storage tank, and water softener.

Finished Sodium Hypochlorite Dosing Technology Overview

Finished sodium hypochlorite solution is generally a by-product of chlor-alkali plants, prepared by the chlorination of sodium hydroxide solution;

Chlorine gas is passed into a sodium hydroxide solution to produce sodium hypochlorite solution, with a concentration generally around 10%.

Cl₂+2NaOH=NaCl+NaClO+H₂O 

The finished sodium hypochlorite solution dosing system mainly includes a water softening system, unloading system, storage system, and dosing system.

It is recommended that finished sodium hypochlorite be diluted to 5% for storage; storage temperature should not exceed 30°C, avoid light exposure, and the solution should be used within 7 to 10 days to ensure that the decay of the active ingredients does not significantly affect production.

Differences Between Food-Grade and Industrial-Grade Sodium Hypochlorite and Existing Problems

1. Whether chemical plants have the production qualifications for food-grade sodium hypochlorite needs to be a key focus.
2. Adding industrial-grade sodium hypochlorite to tap water may pose health risks.
3. There is a significant cost difference between food-grade and industrial-grade, and using industrial-grade sodium hypochlorite to reduce costs can have severe consequences.
4. Bromate exceeding standards were found in the finished sodium hypochlorite at a factory in Jiangsu.

Reason Analysis and Solutions:

1. Sodium hypochlorite is manufactured by external factories, and the quality cannot be directly controlled, which is prone to problems.
2. Strengthen the quality control of suppliers.
3. Increase the frequency of sampling and testing of incoming sodium hypochlorite.
4. Consider preparing sodium hypochlorite solution in the water plant itself to take the initiative.