Removal of BOD and COD from Wastewater

BOD and COD removal: the need in water treatment

Civil and industrial wastewater may contain a number of organic pollutants, which can be measured by the parameters BOD (Biochemical Oxygen Demand) and COD (Chemical Oxygen Demand).

Both BOD and COD are two “indirect” measures of the amount of organic matter, thus composed of carbon, that must be degraded to purify water. In fact, since direct measurement of carbon is difficult, the two values are calculated as follows (both are expressed in mg/l).

• The BOD value is the amount of oxygen, dissolved in water, that is consumed by aerobic bacteria that degrade a certain amount of organic material in a water sample. All this is done under well-determined temperature and time conditions: 5 days of incubation at 20 °C. In fact, it is more properly referred to as BOD5.
• In contrast, the COD value indicates the amount of oxygen required to chemically oxidize the totality of organic matter in the reference water sample. Indeed, it should be specified that aerobic bacteria cannot degrade all organic matter: instead, COD considers all that can be oxidized (and is therefore always higher, as a value, than BOD).

Wastewater, particularly industrial wastewater, can vary in BOD and COD content: as with other pollutants, each sector and each process line has specific needs to be studied by testing with pilot units.