Sodium hypochlorite is widely used in water supply, drainage engineering and other fields. It can be used for disinfection, bleaching, coagulation, inhibition of filamentous bacteria, film washing, etc. As a popular science + professional article, this article discusses the nature and Talking about the mechanism of action, discuss all aspects of sodium.

　　1. The nature of sodium hypochlorite

　　Sodium hypochlorite is an inorganic substance with the molecular formula NaClO. It was widely used in bleaching and disinfection before it was not used as a wide range of water disinfectants. In recent years, as the disadvantages of chlorine and chlorine dioxide have gradually emerged, hyposodium disinfection has been adopted. It has replaced the trend of chlorine and chlorine dioxide disinfection and has become the mainstream disinfection process for water treatment and disinfection.

　　Sodium hypochlorite disinfectant is generally a slightly yellow liquid, and the color is similar to that of chlorine dioxide solution. As the concentration of sub-sodium increases, the yellow becomes darker. Generally, the content reaches the limit at 13%, and a lot of crystals will precipitate even higher. Sodium belongs to strong alkali and weak acid salt. It is easy to decompose when exposed to light and heat to generate sodium chloride and oxygen. In addition, subsodium is a dangerous chemical product (a solution above 5%), but its grade is not high. In the 2015 edition)": the dangerous goods number of sodium hypochlorite solution [containing available chlorine>5%] is: 83501; alias: bleach; UN number: 1791; CAS number: 7681-52-9.

　　Second, the role of sodium hypochlorite

　　1. Disinfection

　　Disinfection is one of the most important functions of hyposodium. As a chlorine disinfectant, its disinfection mechanism is basically the same as that of chlorine. The mainstream believes that there are the following two:

　　One is that sodium hypochlorite is hydrolyzed into hypochlorous acid in water:

　　NaC1O+H2O=NaOH+HC1O

　　HClO =HCl+{O}

　　Then hypochlorous acid is decomposed to generate new ecological oxygen, and the extremely strong oxidizing nature of ecological oxygen denatures the proteins of bacteria and viruses, thereby causing the death of pathogenic microorganisms;

　　The second is that hypochlorous acid can not only interact with the cell wall, but because the molecule is small and has no charge, it can invade the cell and oxidize the protein, destroy its phosphate dehydrogenase, and cause its glucose metabolism disorder to die:

　　R-NH-R+HC1O=RNC+H2O

　　In my opinion, both reactions should have an effect.

　　When used as a water supply disinfectant, the general post-chlorination dosage can be about 2mg/l of available chlorine, while the pre-chlorination depends on the characteristics of the raw water. It is best to conduct a small test experiment before and after the chlorine addition. In the case of ammonia nitrogen, the breaking point chlorination effect will occur, and a small test experiment should be carried out for dosing.

　　There can be multiple dosing points for sub-sodium, which are generally set in places where sub-sodium is mixed, such as water distribution wells, water drop wells, and disinfection special mixing wells. The contact time should not be less than 30 minutes. However, some factories set the sub-sodium dosing point at the filter At the water inlet end of the pond, I think quantitative dosing can be beneficial to the backwashing of the filter sand. I personally do not recommend it, because the addition of sub-sodium will destroy the biological function of the filter sand, weaken the filtering effect of the filter sand, and affect the subsequent dosing. Add measurement calculations.

　　When used as a disinfectant for sewage, the dosage is generally 3 to 7 times that of tap water disinfection. The actual dosage should also be guided by small-scale experiments; the dosage point is generally set at the total water outlet point, such as the water outlet of the deep bed filter. The outlet of the biological filter can also be set at the outlet of the secondary sedimentation tank, and a special clean tank can be set up to hold the disinfected water body. At this stage, sub-sodium disinfection is mostly used in water plants with advanced treatment instead of advanced treatment. Due to the implementation of lower emission standards, the water plants are seldom used.