The principle of aerobic wastewater treatment is the use of aerobic microorganisms in suspended form (activated sludge) or in the form of biofilm (MBBR, MABR, Biostyr). These microorganisms decompose biodegradable substances (mainly organic compounds), nitrogen and phosphorus. A biological aerobic WWTP can be divided into up to three zones, anaerobic, anoxic and oxic.
The anaerobic zone (An) is designed for enhanced biological phosphorus removal. The inclusion of an anaerobic zone (without oxygen and without nitrate) leads to the development of phosphate accumulating bacteria and thus to an increased removal of phosphorus by its accumulation in biomass.
The anoxic zone (D - denitrification) is proposed for nitrogen removal. In an anoxic environment (without oxygen and with nitrate), nitrate is removed by microorganisms in so-called anoxic respiration.
The oxic zone (N - nitrification) is proposed for the removal of organic matter and for nitrification in an oxic environment (with oxygen).
Aerobic technologies have different arrangements of oxic, anoxic and anaerobic zones or different ways of supporting microorganisms, either by setting appropriate conditions or by trapping them in a biofilm.
