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Analyze the principles and characteristics of sewage COD detection methods

by:BOQU     2022-03-17

Summary of sewage COD detection methods:

COD is an indispensable item in water quality monitoring. Its meaning refers to the number of oxidants consumed when treating water samples with strong oxidants under certain conditions. It is expressed in mg/L of oxygen. The chemical oxygen demand reflects the water Degree of contamination by reducing substances. In the process of detection and analysis, Cl- in water samples is easily oxidized by oxidants, and a large amount of Cl- makes the determination result on the high side. The determination of high-chlorine and low-COD wastewater is a difficult problem now. In actual monitoring, it is found that many kinds of wastewater, such as chemical wastewater, monosodium glutamate wastewater, seafood processing wastewater, etc., have high Cl- content, and the COD measurement needs to be measured after Cl- is shielded. The majority of environmental monitoring workers have done a lot of work on the interference of Cl- on COD determination. The following will describe the influence of Cl- and the existing methods of eliminating Cl- interference.

Working principle of sewage COD detection method:

A quantitative potassium dichromate solution was added to the sample, and in a strong acid medium, using silver sulfate as a catalyst, after digestion at high temperature and high pressure, the COD concentration was determined by spectrophotometry.

Measure the absorbance of trivalent chromium (Cr3+) produced by the reduction of potassium dichromate at a wavelength of 600nm. The COD concentration of the sample has a linear relationship with the absorbance of trivalent chromium (Cr3+). According to this relationship, the absorbance of trivalent chromium (Cr3+) can be converted into the COD concentration value of the sample.

Characteristics of sewage COD detection method:

1. The background light compensation mechanism is adopted to reduce the influence of the drift of the LED output light intensity with time, improve the accuracy and repeatability of the measurement, and reduce the detection limit of the instrument.

2. The temperature compensation mechanism is adopted to reduce the influence of environmental temperature changes on the measurement, improve the accuracy and repeatability of the measurement, and reduce the detection limit of the instrument.

3. The low-pass noise reduction algorithm is adopted, which improves the accuracy and repeatability of the measurement and reduces the detection limit of the instrument.

4. The electrical control and operation unit is based on the embedded system framework, the mainboard adopts an industrial-grade ARM9 chip, the operating system is Linux, and the driver board adopts an industrial-grade Cortex-M3 chip.

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