Sustainability assessment of urine concentration technologies

Sammanfattning: The majority of the nutrients in household wastewater are found in the urine and in order to facilitate the use the nutrients in the urine as fertilizer, the urine can be can be concentrated. To extract the nutrients from the urine, various technologies for urine concentration are being developed today. As the technologies are relatively new, urine concentration systems have not been installed on a larger scale. In this study, sustainability of three different urine concentration technologies was evaluated through a fictional case study for 2100 people that took inspiration from a planned residential area in Malmö, Sweden, where technology for urine concentration will be implemented in at least one of the buildings. The technologies were evaluated through a multi-criteria assessment (MCA), where different criteria within sustainability categories environment, technical, economic and health were determined based on the Sustainable Development Goals (SDGs). The technologies examined were alkaline dehydration, nitrification-distillation and ion-exchange using a pre-step of struvite precipitation. For the alkaline dehydration technology, fresh urine is added to an alkaline medium, in order to prevent nitrogen losses, and then dried. In the nitrification-distillation technology, stored urine is treated by first being stabilized by a partial nitrification and then distilled in order to reduce the volume. For the ion-exchange and struvite precipitation system, phosphorus is first precipitated from stored urine and nitrogen is then extracted through ion-exchange. The urine concentration technologies were assumed to be installed in semi-centralized treatment plants in basements in the residential area. The other household wastewater was assumed to be treated in the local wastewater treatment plant (WWTP). The results showed that all three urine concentration technologies may contribute to a significant increase in nitrogen recovery from the household sewer. However, this may come at the expense of increased annual costs for the population. Before it is possible to determine whether urine concentration can be an alternative as a complement to the existing wastewater treatment, further studies of the urine concentration technologies and their sustainability are required. However, this study indicated that urine concentration technologies perform well in many of the sustainability criteria examined and therefore have potential to contribute to the SDGs, especially regarding nitrogen recovery. This study can therefore be an incentive for further studies, where the sustainability of an implementation of urine concentration in Sweden is addressed.