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How to control the by-products of chlorate disinfection to make drinking water safer?

Mar. 22, 2021

   The outbreak of the new coronavirus in 2020 has greatly increased the importance of people around the world on disinfection and sanitation. This is not only reflected in surface disinfection and environmental disinfection in daily life, but also in water disinfection. Especially when Paris revealed that 4 out of 27 tap water sampling points detected the presence of the new coronavirus, the topic of safe and efficient water disinfection was once again heatedly discussed.

   Although there are auxiliary disinfection methods such as ozone and ultraviolet in recent years, the disinfection technology for drinking water plants still use the"chlorine-based disinfectant": liquid chlorine, sodium hypochlorite, and chlorine dioxide are three mainstream disinfectants.Compared with the other two disinfectants, sodium hypochlorite has been gradually adopted by more and more water plants in recent years,because of its good disinfection effect and safer operation and management.

   Sodium hypochlorite disinfection is divided into two methods: finished sodium hypochlorite and on-site preparation of sodium hypochlorite by electrolysis.The on-site preparation method does not require the transportation and storage of hazardous chemicals, and is better than the finished sodium hypochlorite in terms of safety and operating costs.

   Today we will talk about another major advantage of the on-site preparation of sodium hypochlorite technology: the disinfection by-product chlorate is lower.

How to control the by-products of chlorate disinfection to make drinking water safer?cid=3

   Chlorate is a highly oxidized form of chlorine. It can be introduced into the water source in the form of industrial or agricultural pollutants, and it can also enter the production water of drinking water plants in the form of disinfection by-products (DBP).

   Chlorate is a highly oxidized form of chlorine. It can be introduced into the water source in the form of industrial or agricultural pollutants, and it can also enter the water produced by drinking water plants in the form of disinfection by-products (DBP).

   The limit requirements of various countries for the concentration of chlorate

   At present, many countries have no clear standard for the limit of chlorate concentration in drinking water.

   European Union BS EN 901-2013 requires that the ratio of chlorate to available chlorine in domestic water treatment should not exceed 5.4%.

   The United States does not currently regulate chlorate, nor does it have an enforced maximum pollutant concentration limit. However, chlorate is listed as a chemical substance that can cause potential health hazards and is listed in the United States Environmental Protection Agency (EPA). The third list of chemical pollutants (CCL3), and 0.21mg/L is determined as the healthy reference level of chlorate content.

The maximum pollutant concentration limit set by Canada is 1.0 mg/L

WHO recommends a chlorate concentration limit of 0.7 mg/L

Factors affecting the formation of chlorate

How to control the by-products of chlorate disinfection to make drinking water safer?cid=3

The following factors will affect the concentration of chlorate produced. The longer or the higher the degree of any one of these factors, the greater the amount of chlorate formed:

Storage time: The longer the storage time, the higher the chlorate concentration.

Storage temperature: The higher the storage temperature, the faster the chlorate concentration will increase Concentration of hypochlorite.

In order to prevent the formation of chlorate as much as possible, it is recommended that users of finished sodium hypochlorite need:

Sodium hypochlorite should be stored indoors as much as possible, avoid sunlight, and store in a cool and dry environment, especially avoid direct sunlight. The storage time in summer should not exceed 10 days.

Cool the storage room of sodium hypochlorite to slow down the degradation caused by high temperature.

The manufacturer of the finished sodium hypochlorite is required to provide the production date of the chemical to ensure its freshness.

Limit the storage capacity of the finished sodium hypochlorite. The sodium hypochlorite in the storage tank should be added after it is used up to avoid the residual liquid from being stored for too long and continuously decomposing.

Purchase a lower concentration of finished sodium hypochlorite to reduce degradation.

If you are buying high-concentration sodium hypochlorite, it must be diluted once it is transported to the site.

All of the above must be done will increase the owner's operating costs. Therefore, it is necessary for the water plant to pay enough attention to use the corresponding technology as much as possible to optimize the operating cost while ensuring that the water quality reaches the standard.