Indigo blue method, under the condition of pH2.5, ozone can react quantitatively with indigo reagent. The blue indigo is bleached by ozone. The higher the concentration of ozone, the lighter the blue of the obtained indigo solution. Because the method is specific, it is recognized in ozone detection.
In the DPD method, ozone can react with KI in the DPD reagent to generate free iodine. In the pH range of 6.2-6.5, iodine immediately reacts with DPD to generate a red substance. This reaction complies with Lambert's law.
Test standard problems:
N,N-diethyl-p-phenylenediamine (DPD) can be oxidized by a variety of oxidizing disinfectants including ozone to produce red. Because there is no specific reaction to ozone, it is not listed as the standard for ozone detection in water in China method. Water disinfection of products for packaging drinking water and natural mineral water. Since no other types of disinfectants are introduced, only low-concentration ozone is used for disinfection, so DPD method can be used for detection, replacing traditional titration method or indigo colorimetric method, which can greatly save The inspection cost of factory production and quality control, shorten the inspection time, and further ensure the quality and safety of product water.
Comparison of two ways of generating ozone
High-pressure discharge is to directly dissolve oxygen in the air and dissolve it in water, because the oxygen in the air accounts for only 21%, and the conversion rate is poor. When dissolved in water, it will be blown off by a large amount of nitrogen, resulting in reduced solubility and another ozone. The content in the air is extremely low, and ozone is also relatively easy to overflow, resulting in a small amount of ozone actually dissolved in the water. If you want to increase the ozone content in the water, you need to pressurize and cool down. It is difficult to achieve high open ozone concentration. However, there are few ozone interferers in the form of high-voltage discharge. Generally, water purification plants adopt the form of high-voltage discharge.
The electrolyzed water is electrolyzed pure water and electrolyzed ordinary water. The ozone produced by electrolyzed water on the market is basically obtained in the form of electrolytic tap water to obtain an ozone aqueous solution. The chloride ions in tap water are preferentially electrolyzed into chlorine gas, and the chlorine gas is dissolved in water An aqueous solution of hypochlorite is formed, so the amount of ozone actually generated is relatively small, and there are many by-products. The basic formation of electrolytic purified water is mainly ozone.
The ozone generated by high voltage discharge can be measured by online measurement, DPD method and indigo method. The ozone generated by the electrolytic method cannot be detected online because there are many by-products and the ORP is negative. If the DPD method measures electrolyzed water, the interference is large, and ozone detection is not allowed.