The reducing of COD depends ...

The reducing of COD depends on load, flow rates, the type of compounds and applicable discharge standards. When the COD consists of heavy metals only, one solution is to work with a physical-chemical treatment of water system ("flocculation") or a water treatment plant electrocoagulation. If the effluent does not contain hydrocarbon and volumes are significant (from 5 m3 per day), an excellent solution is the Nano filtration.

An interesting solution is the treatment by chemical oxidation - oxidation-biochemical (biodegradation). If it is lightly loaded effluent, activated carbon can be an interesting solution.

As to the reduction of BOD, it is done by biological processes.

Hydrogen peroxide (H2O2) has been used to reduce the BOD and COD of industrial wastewaters for many years.While the cost of removing BOD and COD through chemical oxidation with hydrogen peroxide is typically greater than that through physical or biological means, there are nonetheless specific situations which justify the use of hydrogen peroxide. These include: Predigestion of wastewaters which contain moderate to high levels of compounds that are toxic, inhibitory, or recalcitrant to biological treatment (e.g., pesticides, plasticizers, resins, coolants, and dyestuffs);