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Do you understand the principles of the COD standard digester?

by:BOQU     2023-03-12
The COD standard digester is a cod heating and digestion reflux device set up according to the national standard water quality chemical oxygen demand determination (dichromate method), which is assembled by the original single electric furnace heating, iron stand and circulating water condenser. Now it can heat 8, 12 or 15 samples at the same time, the electric furnace becomes a glass-ceramic table, the circulating water becomes a double-fan air cooling, and the heating power can be easily adjusted, which solves many problems encountered in experiments trouble, making the operation more convenient. Product principle: Add a known amount of potassium dichromate solution and mercury sulfate solution into the water sample, and use silver sulfate as a catalyst in a strong acid medium. After 2 hours of boiling and refluxing, use 1,10-phenanthroline as an indicator Titrate the unreduced potassium dichromate in the water sample with ammonium ferrous sulfate, and convert the amount of ammonium ferrous sulfate consumed into the mass concentration of oxygen consumed, which is the apparent COD. Export the chlorine gas formed by the uncomplexed and oxidized chlorine ions in the water sample, absorb it with sodium hydroxide solution, add potassium iodide, adjust the pH to about 3-2 with sulfuric acid, and use starch as the indicator. Titrate with sodium thiosulfate standard titration solution, and convert the amount of consumed sodium thiosulfate into the mass concentration of oxygen consumed, which is the chloride ion calibration value. The difference between the apparent COD and the chlorine ion calibration value is the true COD of the measured water sample. Scope of application: This method is suitable for the determination of chemical oxygen demand (COD) in high-chloride wastewater with chloride ion content less than 20000mg/L. The detection limit of the method is 30mg/L. It is suitable for the determination of COD in wastewater such as oil fields, coastal refineries, oil depots, chlor-alkali plants, and wastewater deep-sea discharges. Steps for use: 1. Turn on the power switch on the right panel of the instrument (the JC-101C type switch is on the rear side), and the instrument will display"000""111""222"…"999", displaying the maximum set value of digestion time of 2 hours and 30 minutes, the fan is turned on at the same time, and the fan indicator light is on. 2. To change the set value of digestion time, press"timing"Press key to decrease the digestion time so that the set value is finally 2 hours. You can also set the digestion time value arbitrarily according to your needs. 3. Reflux digestion: press"start"key, the instrument starts to reflux digestion,"start"The indicator light is on, and the heating indicator light is on. After the digestion is complete, the instrument will display"000"and flashes,"start"The indicator light is off, and the heating indicator light is off. 4. Sample processing and analysis methods refer to the standard analysis method GB11914-89.
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