text: Nutrient removal is one of the main concerns in modern wastewater treatment, especially, in areas that are sensitive to eutrophication. Nitrogen (N) is a pollutant present in wastewater that must be eliminated for multiple reasons: it reduces dissolved oxygen in surface waters, is toxic to the aquatic ecosystem, poses a risk to public health, and together with phosphorus (P), are responsible for the excessive growth of photosynthetic organisms like algae. All these factors make its reduction focus on wastewater treatment. In wastewater, nitrogen can be present in multiple forms.
  Like in the conventional activated sludge process, currently, the most widely applied technology for N-removal from municipal wastewater is nitrification combined with denitrification, carried out by bacteria nitrifying and the involvement of facultative organisms.
  Besides phosphorus precipitation, enhanced biological phosphorus removal can be implemented which requires an additional anaerobic process step. Some characteristics for membrane bioreactor technology render enhanced biological phosphorus removal in combination with post-denitrification an attractive alternative that achieves very low nutrient effluent concentrations.
  For this, a membrane bioreactor improves the retention of solids, which provides a better biotreatment, supporting the development of slower-growing microorganisms, especially nitrifying ones, so that it makes them especially effective in the elimination of N (nitrification).