The mean oxidation number of carbon (MOC)—a useful concept for describing oxidation processes

When characterizing real waste waters and sludges, usually collective parameters like COD and TOC are used. Detailed protocols (USEPA, APHA, DIN) concerned with the analytical determination of these parameters exist. However, some difficulties may arise when interpreting the measured values. Waste waters may contain substances refractory to the COD determination, or high concentrations of easily oxidizable inorganic salts may be mistaken for organic matter. When treating waste waters and sludges using physical, chemical or biological processes, there may be unexpected phenomena apparently contributing to a reduction or even concentration of the dissolved substances: adsorption effects (on reactor walls, catalyst, biomass), stripping of volatile organics, sedimentation, complexation, precipitation, or evaporation of water. When monitoring only COD or TOC, one cannot conclude whether a change of these values is due to a chemical degradation process or to a purely physical elimination like stripping. In this paper the concept of the mean oxidation number of organic carbon (MOC) is presented. By combining TOC (or DOC) and COD measurements, one can obtain valuable additional information concerning the reaction development during waste water treatment processes, especially when oxidative transformations are involved. The applicability of the MOC concept is demonstrated using the wet oxidation of pyridine, stripping of toluene, decarboxylation of malonic acid, and wet oxidation of phenol as well as the wet oxidation of sewage sludge as an example of a real system.