Novel biological nitrogen-removal processes: Applications and perspectives

Since the requirement for nutrient removal is becoming increasingly stringent, a high efficiency of nitrogen removal is necessary to achieve a low total nitrogen concentration in the effluent. Biological nitrification and denitrification processes are generally employed to remove nitrogen from wastewater. Unfortunately, these processes are not suitable to treat wastewater with a low COD/N ratio because it involves the addition of an external organic carbon source and, therefore, an increase of the operational costs. Several alternative processes for nitrogen removal can be applied in order to reduce partially ("nitrite route") or totally (anammox, autotrophic denitrification) the organic matter required. Such processes suppose not only an economical way to treat these wastewaters but they are also more environmentally friendly technologies (lower production of CO2, N2O and sludge; lower energy consumption). Up to now, they were basically applied to the return sludge line of municipal wastewater treatment plants (WWTPs). However, these processes could even be implemented in the actual WWTPs in order to achieve more compact and energy efficient systems. Their potential advantages can make them also feasible technologies to treat polluted ground water or to remove nitrogen compounds from recirculating aquaculture systems.