Question: Activated carbon for decreasing NOM, TOC, COD

Question: Activated carbon for decreasing NOM, TOC, COD

What should be the thickness of the activated carbon layer on gravity filter mixed with sand? Activated carbon for removing "Natural organic matter 20 ppm" ,TOC =15ppm ,colour 13 ,COD range "10-15" ,TSS=0-10 """. The source of this water is Tertiary sewage effluent "TSE Water". Thank you!