What is the principle of optical UV absorption COD sensor?

Chemical oxygen demand is also called chemical oxygen demand, or COD for short. COD is an important indicator of water pollution. The unit of COD is mg/L. At present, the principles of measuring COD mainly include chemical titration (potassium dichromate method, potassium permanganate method), electrochemical measurement method and UV method.

The COD content was determined by chemical titration. The disadvantages are that the measurement time is too long, the operation and maintenance are complicated, the operation cost is high, and secondary pollution will be generated at the same time.

When the organic matter in the water is oxidized on the surface of the working electrode, there will be a current change on the working electrode. When the potential balance of the working electrode is fixed, the change of the current is linearly related to the water quality parameters in the water. The water quality can be measured by calculating the change of the current parameter. Its main features are fast measurement speed and simple instrument structure. The disadvantage is that the electrode current changes produced by different electrochemical methods only have a linear relationship with one alternative parameter, and have a nonlinear relationship with other water quality parameters. Therefore, the online analyzer based on the principle of electrochemical method can only measure one water quality parameter.

Principle of UV ultraviolet absorption method

The amount of organic matter in water represents the amount of COD in water. Although various organic matter has its own absorbance, the absorbance of each wavelength of light is different, but we found that most of the organic matter has a wavelength of There is a strong absorption at 254nm, so it has great accuracy to measure sewage COD in the ultraviolet region with a wavelength of 254nm. However, in fact, most of the sewage samples we usually make are relatively turbid, which contain a large amount of suspended matter and some colloids, which will have a certain impact on the determination of COD during the measurement process, and will make the measurement The result is too large, so we must correct the COD amount measured at this time. That is to say, we should also measure the turbidity of the water at this time, and the turbidity of the water can be measured in the visible light region with a wavelength of 546nm. In this way, the difference between the two measurements is the COD content in the water. Our COD351 online COD Sensor adopts this optical UV absorption method.

Our company focuses on the R&D, production and sales of water quality analysis instruments. Our main products include online pH ORP analyzer, conductivity analyzer, turbidity analyzer, dissolved oxygen analyzer, COD analyzer, ammonia analyzer, etc. If you need water treatment related products, please contact us.