Removal of persistent COD

For the removal of organic waste water constituents, biological process steps are preferably combined and used for waste water treatment.
However, the organic compounds present in waste water, measured as chemical oxygen demand (COD), often cannot be biologically degraded, or are degraded only partially. Therefore, organic residues remain in the treated waste water, which cause a non-degradable COD, also known as persistent COD.
In order to remove these impurities, further processing steps are required, for example oxidation with a strong oxidising agent or adsorptive separation.

The oxidative attack on these compounds can lead to partial or, if necessary, complete degradation, the so-called mineralisation. If the degradation is incomplete, the organic compounds are converted into bioavailable fragments. These can then be removed from the waste water stream in a downstream biological stage, for example in a biofilter.


Oxidation with ozone is one way of partially degrading these compounds. Depending on the origin and composition of the waste water, however, stronger oxidation conditions based on radical reaction mechanisms may also be required. For the selection of the appropriate Advanced Oxidation Process (AOP), the organic constituents must be further analysed and the degradability must be checked.

Our References

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