Chemical Oxygen Demand COD
The parameter "chemical oxygen demand" or COD is comprised of all oxidizable substances, including those that are not included in the BOD (biological oxygen demand). In contrast to BOD, COD delivers no information on the degradability of the detected substances.
COD is determined by adding a strong oxidizing agent (potassium dichromate K₂Cr₂O₇). The relationship between BOD₅ and COD delivers an indication about the degradability of the waste water. For municipal wastewater, typical COD / BOD ratios are found to be around 1.5 to 2.0, while industrial wastewaters have much higher ratios, all depending on their origin.
In the effluent of a municipal wastewater treatment plant, typical COD / BOD ratios are usually between (5 ... 10) / 1.


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