What are the advantages and disadvantages of measuring COD by UV absorption method?

UV method online COD sensor is very suitable for online monitoring. Its advantage is that the UV absorption process can be completed in a few seconds, the data processor has fast data processing speed, and with the flushing time of the sample cell, a measurement process can be completed in about 1 minute. This is a traditional laboratory measurement. The methods are incomparable. Secondly, the interference of UV dual-wavelength measurement on water samples can be compensated for and subtracted from the results, and there is basically no need to preprocess the water sample. Regularly use the samples measured by the national standard potassium dichromate method to adjust the conversion coefficient to achieve low-cost online operation.

Although the UV method online COD analyzer has the characteristics of fast, economical and real-time monitoring, its measurement principle also determines its shortcomings, and its application is also greatly restricted. It can be seen from the working principle that there is a difference between the online CODuv value and the CODcr value. The CODuv value only reflects the measured value of the characteristic absorption of ultraviolet light by the comprehensive pollutants in the sewage sample. It is only effective for organic matter with absorbance at 254nm. Response, this type of organic matter is limited to organic matter with conjugated double bonds, other types of organic matter and inorganic reducing substances cannot be measured, and there is a certain error. Therefore, in order to realize online monitoring of the pollution status of reducing pollutants, it is necessary to convert the signal generated by the UV characteristic absorption of comprehensive pollutants into a signal reflecting the CODcr value. The UV method COD online sensor performs multi-point calibration on the CODcr value of the target water sample measured in the laboratory using the national standard method as the standard of the online analyzer. It is used as the conversion coefficient during online measurement to realize the conversion of the CODuv value to the CODcr value. The influence of other factors, such as turbidity and other interferences, is compensated by the conversion coefficient in dual-wavelength measurement and deducted from the indication result.

Because the UV method online COD analyzer indication value conversion CODcr value is achieved by using the water sample to be tested as a standard material, that is to say, the UV-based online COD analyzer calibrated by this water sample to be tested can only be suitable for monitoring This kind of water sample to be tested may be a water sample that has little collective change with this kind of water sample to be tested. Otherwise, the conversion coefficient adjusted by the water sample to be tested will be different. The greater the collective change of the water sample, the greater the conversion coefficient. The difference is even greater. This is because different water samples collectively have different absorption coefficients for UV absorption, not to mention that COD represents a comprehensive pollution index embodied by multiple reducing pollutants. Different water sample types have different categories of reducing pollutants.

The population and eating habits of a region are relatively stable, and general changes will not lead to collective changes in the main pollutants of urban domestic sewage. Moreover, urban domestic sewage also has the distinctive characteristics of large water volume and stable water quality. This stable water quality condition is exactly the working requirement of the UV method online COD analyzer, so that it can be used to monitor COD in various small and medium-sized sewage treatment plants.
Therefore, when using a COD sensor based on the UV absorption method, you need to pay attention to the application situation and, when necessary, combine multiple measurement methods to obtain accurate data. Delfino company focuses on the R&D and production of water quality analysis instruments. Our measurement parameters include pH, ORP, conductivity, TDS, salinity, dissolved oxygen, COD, ammonia nitrogen, turbidity, chlorophyll, blue-green algae, residual chlorine, and chlorine dioxide. wait. In addition to ORP sensors, our main products include pH ORP analyzer, conductivity analyzer, turbidity analyzer, COD analyzer, dissolved oxygen analyzer, ammonium analyzer, chlorine analyzer, etc.