Generally, the online cod detector is mainly used for monitoring various industrial wastewater such as sewage treatment, aquaculture, petrochemical, coking and so on, as well as monitoring livestock domestic sewage and leachate from garbage sites; And CDO monitoring of surface water quality such as rivers, lakes and seas.
The determination principle of online cod detector can be divided into two categories, one is chemical reagent method which is widely used, and the other is ultraviolet absorption method (electrode method) which has a short test time.
Principle of reagent method for online cod detector
Add a quantitative amount of potassium dichromate into the collected cod water sample. In an acidic medium, use silver sulfate as a catalyst. After high temperature digestion, potassium dichromate is reduced from hexavalent chromium (Cr6+) to produce trivalent chromium (Cr3+). The COD concentration in the water sample is proportional to the decrease of hexavalent chromium (Cr6+) and the increase of trivalent chromium (Cr3+). After the absorbance is detected by the corresponding light source, it is converted into the COD value of the water sample through software.Principle of electrode method for on-line cod detector
The electrode method of online cod detector can also be called ultraviolet absorption method. Its principle is based on the selective absorption characteristics of organic matter in water to specific wavelengths of ultraviolet and visible light, using the absorption of water sample to monochromatic light to determine the concentration of organic matter, and establishing the relationship between the absorbance of solution to specific wavelengths and COD value. The size of COD value mainly depends on the composition and concentration of organic substances, which have strong absorption at 254 nm. Determine the absorbance of sewage at the wavelength of 254 nm, and convert the COD concentration value through the established relationship between absorbance and COD concentration.Advantages and disadvantages of two cod on-line determination principles
The advantage of online cod detector reagent method is that the detection is more accurate and can be widely used for cod detection of various water quality. Of course, the disadvantage is also obvious. Because of the need for reagent, it needs to supplement the detection reagent regularly, and the waste liquid generated in the detection process also needs to be recycled by specialized personnel. Otherwise, it is easy to cause secondary pollution.
The advantages of ultraviolet absorption method of online cod detector lie in short test time, rapid electrode reaction, no need of any reagent and no secondary pollution. However, the disadvantages are also obvious, and the scope of application is limited. It is mainly used for conventional surface water, mariculture and other water bodies, and cannot cope with complex water environment. The change of water body is easy to affect the detection accuracy.
