In nature, ”biological waste water treatment“ ideally takes place by itself. Organic and inorganic wastewater ingredients, such as excreta or dead plant parts, are converted to biomass by the metabolic activity of microorganisms. This process usually requires oxygen. Therefore, the right oxygen content of the wastewater is an important prerequisite for aerobic biological wastewater treatment. Only when the oxygen content decreases, anaerobic conditions can cause the collapse of water bodies in nature and the production of fouling materials. When talking about aerobic biological waste water treatment in the industrial sectors, it means the addition of oxygen in order to degrade carbonaceous (organic) wastewater ingredients. Aerobic wastewater treatment can also be used efficiently in the industrial sector in combination with other waste water treatment processes. It always pays off when there are high values of COD and BOD.
What are COD, BOD, and TOC/DOC values?
The organic load of the waste water is described with the parameters COD (=chemical oxygen demand), BOD (=biological oxygen demand) and the TOC/DOC value (=total/dissolved organic carbon). The COD indicates the amount of oxygen that would be required for a chemical oxidation of the existing dirt particles; the BOD indicates the amount of oxygen required for biological degradation. The TOC/DOC value represents the sum of total and dissolved organic carbon in a wastewater sample. It serves as a parameter for assessing the amount of organic pollutants in the wastewater, but it does not indicate biological degradability. This also applies to the COD value. The BOD-COD ratio allows an initial assessment of biodegradability. Better statements can be made using the Zahn-Wellens test – a laboratory test which determines aerobic biodegradability using activated sludge in a 4-week trial.
If calculation also takes into account COD-dependant surcharges, COD limits or COD load limits, the biodegradation process can significantly reduce the overall costs of industrial wastewater disposal: the disposal costs are lower and it is much easier to carry out the final stage of purification.