Where does the residual chlorine in drinking water come from?
A: The residual chlorine in tap water is the remaining amount after the water plant adds chlorine disinfectant to the water before it emerges. The water plant must not only ensure that the water from the water plant has a certain amount of residual chlorine, but also ensure that the tap water also has a certain amount of residual chlorine when it reaches the end of the pipe network in contact with the user. The purpose of adding disinfectants to water is to kill microorganisms in tap water and water pipe networks, including algae and pathogens in water, to prevent the spread and spread of water-borne infectious diseases.
How to correctly understand the residual chlorine in tap water?
A: If we smell the chlorine in the tap water, it means that the local tap water is disinfected. It also means that pathogenic microorganisms in the water have been effectively killed, so such water is actually more reassuring than drinking without residual chlorine. But what we usually worry about is the disinfection by-products formed by the reaction of the disinfectant with organic matter or algae in the water. There are 600-700 disinfection by-products reported in the literature, including trihalomethanes, haloacetic acids, bromates, chlorites, cyanogen halides, and the like. These disinfectants are invisible to us and require professional means for testing.
What are the disinfection methods for tap water?
A: The main methods used in the world for disinfection of drinking water include: chlorination, chlorine dioxide disinfection, UV disinfection and ozone disinfection. Among them, the chlorine disinfection method is the longest and most widely used disinfection method, and generally includes disinfecting reagents such as chlorine gas or free chlorine. Chlorine dioxide disinfection generally involves the direct addition of chlorine dioxide powder or the use of chlorine dioxide generator, using the principle of sodium chloride and hydrochloric acid to form chlorine dioxide. This method has good sterilization effect, but it is easy to produce chlorate or The problem of chlorite exceeding the standard. Ultraviolet and ozone disinfection and sterilization effects are also very good, but can not guarantee the killing of pathogenic bacteria in the pipe network, so it is generally combined with the method of adding chlorine before leaving the factory.
What are the forms of residual chlorine in tap water?
What is the national standard?
A: The residual chlorine form in water includes free residual chlorine and combined chlorine. Free residual chlorine is included in the form of chlorine, hypochlorous acid, and hypochlorite ions. Chlorinated compounds include monochloramine, dichloramine and trichloramine. China's "Sanitary Standard for Drinking Water GB5749-2006" requires that the disinfectant index be: if chlorine or free chlorine is used as the disinfection method, then the residual amount in the factory water should not be less than 0.3mg/L, not higher than 4mg/L. At the same time, the balance of the end of the pipe network is not less than 0.05mg / L; if the disinfection with monochloramine is used, the total chlorine in the factory water should not be less than 0.5mg / L, not higher than 3mg / L, while the end of the pipe network The amount is not less than 0.05 mg/L. If the water plant does not use monochloramine disinfection, the total chlorine at the end of the pipe network can represent the cleanliness of the raw water to a certain extent.
What are the hazards of disinfection by-products and the factors that affect their formation?
A: Studies have shown that disinfection by-products can have an impact on human health. There are many factors affecting the disinfection by-products in drinking water, including the following aspects: 1) The type and concentration of precursors. Generally, surface water pollution is serious, and there are many types of pollutants, and the types and concentrations of by-products formed by chlorine oxidation are much higher than those of deep-rooted pollution. 2) The pH value, water temperature and bromide ions in water can affect the formation of disinfection by-products to varying degrees. The increase in the content of these three will increase the probability of trihalomethane formation in the water. 3) The amount of chlorine can affect the concentration of disinfection by-products and the distribution of its species. In addition, disinfection procedures, chlorine contact time, residual chlorine, season, and metal ions all affect the formation of disinfection by-products.
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