Effect of suspended solids on COD measurement
The impact of suspended solids on COD (chemical oxygen demand) measurement is mainly reflected in the following aspects:
1.Interference determination accuracy:
The organic matter in the suspended solids will directly consume the oxidant, resulting in high COD measurement results. During the measurement of COD, strong oxidants such as potassium dichromate or potassium permanganate are usually used to oxidize organic matter in the water. If the suspended solids contain organic components that can be oxidized, this part will be included in the measurement of COD. Results are in progress.
2.Physical interference:
High concentrations of suspended solids may cause sample turbidity, increase background absorption in photometric measurements, and affect the accuracy of photometer or colorimeter readings, especially when COD is measured using spectrophotometric methods.
3.Suitability of the determination method:
For standard laboratory measurement methods, it is generally required to pre-process the sample and remove suspended matter by filtration or centrifugation to avoid its impact on the measurement results. Due to structural limitations, online monitoring instruments may use filters and other methods to block part of the suspended solids, but this may also result in the inability to fully reflect the true COD level of the sample.
4.Oxidant consumption:
Although the inorganic substances in the suspended solids themselves are not contributors to COD, if they react with oxidants (such as some sulfur- and nitrogen-containing inorganic substances), they may also cause non-specific consumption of oxidants, which will lead to biased COD measurement results. high.
5.Determination deviation:
Because of the above reasons, the presence of suspended solids may lead to significant differences between laboratory measurements and online monitoring instrument measurement results. According to relevant technical specifications, the allowable relative errors are different for different concentrations of COD.
In summary, in order to obtain accurate COD data, when the content of suspended solids in the water sample is high, pretreatment should be carried out according to relevant standard methods, such as sedimentation, centrifugation or filtration before COD measurement is performed to eliminate the interference of suspended solids. effect. At the same time, appropriate adjustment and calibration are also required during online monitoring to ensure the reliability of measurement results.
AM-D-UVCOD Online COD Sensor
