Regarding the determination of COD
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I would like to ask the teachers how to analyze solid COD.
Chemical oxygen demand (COD) refers to the amount of oxidant consumed when a water sample is treated with potassium dichromate as an oxidizing agent under strong acidic conditions and at elevated temperatures. It reflects the degree of contamination by reducing substances in water. Reducing substances in water mainly include: organic matter, sulfite salts, ferrous salts, sulfides, etc. Solids generally do not fall within the scope of COD determination. I assume what you need to determine is the content of organic matter in the solid insolubles? If that is the case, you can determine the ash content of the solid insolubles and use it to infer the organic content. With this method, inorganic salts remain in the ash. If one really wants to determine COD by treating solids as liquids, acid digestion does not achieve complete dissolution of the organic substances; there will likely be some deviation. I haven’t tried it, so I can’t give you a definite answer.
Use water or sulfuric acid as a solvent and then conduct the measurement; generally, there is no need to measure solid COD
The COD parameter refers to the amount of oxidizable substances in water; solid samples are not suitable for being expressed using COD.