Advances in nitrogen removal and recovery technologies from reject water: Economic and environmental perspectives

This review critically assesses nitrogen removal technologies applied in the reject water treatment, across different stages of technological development, with a focus on their economic and environmental impacts. The prevalent use of biological processes raises concerns due to potential environmental impacts caused by N₂O emissions. However, partial nitritation-anaerobic ammonium oxidation demonstrated economic benefits and the potential for positive environmental outcomes when properly operated and controlled. Furthermore, reject water, in many cases, provides sufficient nitrogen concentrations for nitrogen recovery processes, such as ammonia stripping, substituting production of industrial fertilizers and contributing to a circular economy. Nonetheless, their financial competitiveness is subject to various conditions, including the nitrogen concentration or reject water flow. As the environmental benefits of bioprocesses and economic benefits of nitrogen recovery processes may vary, it is crucial to further optimize both and investigate novel promising technologies such as electrochemical systems, denitrifying anaerobic methane oxidation or direct ammonia oxidation.