In contrast to phosphorus, nitrogen is an unlimited resource. 78% of the atmosphere consists of dinitrogen, which can be transformed into ammonium with the help of the Haber-Bosch process. In rural areas and in regions with a strong need for nitrogen fertilizer, direct recycling of urine to agriculture can be economical. In many urban areas, however, direct application of urine for nitrogen recovery is not economically interesting because of the lack of agricultural land and the need for costly transport out of urban areas.
For these reasons, we not only focus on nitrogen recovery but also on nitrogen removal from urine. In this project we investigate the one-stage nitritation/anammox process for decentralized nitrogen removal from urine. The process is resource-efficient and has been used in many wastewater treatment plants to remove nitrogen from digester supernatant. However, small on-site reactors pose new challenges. The process stability and resilience tends to be small because of low diversity within the different bacterial groups. An added challenge associated with urine is the high content of biodegradable organic substances, which fosters the growth of heterotrophic bacteria.