COD testing method for high-salt wastewater
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Hello everyone. Recently, I’ve encountered a problem: the COD concentration in high-salt wastewater is estimated to be between 30,000 and 40,000. Those who are familiar with the potassium dichromate method for testing could please explain the specific steps involved, especially regarding the dilution process?
High-salt wastewater, COD of 30,000–40,000; what is the salt content approximately? Without shielding, the concentration of chloride ions might already reach 30,000–40,000. It is recommended to dilute the sample first, reducing the COD level to around 500–1000 before conducting the measurement; in other words, dilute it by a factor of 50, and add mercuric sulfate as a shielding agent ； Refer to HJ/T 399/2007
Hello, I haven’t measured the salt content in my wastewater; I estimate the concentration to be around 9%-10%. Can’t the dichromate method be used to determine the concentration of water with such a high salinity level? I saw that you mentioned the rapid digestion spectrophotometry method for testing
It’s best to measure the salt content; if it is 10%, or 100 g/L, then even after diluting it 50 times, the concentration will still be 2 g/L, which is equivalent to 2000 mg/L. According to HJ/T 399/2007, the chloride ion concentration should be below 1000 mg/L. The same requirement applies to chromate as well, per CJ/T 51-2004. Therefore, it’s necessary to dilute the water sample 100 times, add a masking agent, and then conduct the testing.
Hello, what you mean is: let me give an example. Test method: Take 20 ml of the water sample and dilute it to a total volume of 2000 ml in a volumetric flask. Then take 20 ml from this solution, add 0.4 g of mercury sulfate and 25 ml of potassium dichromate solution, as well as 30 ml of silver sulfate solution. Is the calculation done by dividing by 0.2 ml?
It is not clear what your testing method is; it is recommended to dilute the water sample 100 times and then conduct the test using the potassium dichromate method specified in CJ/T 51-2004 for the determination of chemical oxygen demand in urban wastewater.