Muhammad Ikhwan Razak: hardly to answer your question when we do not know, what the target COD concentration is (0 ppm or 199 ppm?) and which chemical compounds form COD or what kind of industrial wastewater should be treated.
It would be nice to have some background about the path of the effluent until you get a COD of 200. I would say you may consider a biological treatment stage (if not yet included) or membrane filtration. However, for more accurate advice we need more info.
Entesar Kareem: I am not sure that your solution is correct. COD is formed by organic content as well as by inorganic one. In addition, when the rest concentration of COD is 200 ppm it is very probable that this rest COD is not biologicaly degradable at all.
mr. Vit thank you for comment .if we measur BOD and find the BOD/COD ratio this will helpfull for decide the source of COD for the same sample so,the aeration method will be for high BOD/COD ratio i think.do you agree with me or not?
Entesar Kareem : YES, basically I agree with you. But it is a quite different story, in your previous answer there was no mention on BOD and BOD/COD ratio.
Yes, I agree with your opinion, Dr. Vit. We should have some information like the type of industrial wastewater, the target COD concentration etc. Hence, the best method for reducing COD can be used.