“Hard COD” is the COD that resists a given treatment and more precisely hard COD is the COD resisting any biological treatment in the aqueous phase.
We can also say that the hard COD is the remaining one when there is no more BOD5 in the effluent.
Color is a special case of hard COD, in which the visual component makes it easily detectable in the environment. For this very reason, it has been subject to numerous complaints from residents and fishermen.
In the case of a flexographic ink operation,, we have succeeded in reducing the COD via 2 stages from 180,000 mg / l to 800 mg / l by significantly reducing the color being in the effluents.
