Life cycle assessment of ammonium sulfate recovery from urban wastewater

Anthropogenic nitrogen fluxes are profoundly altering the global biogeochemical nitrogen cycle. Better management of these nitrogen fluxes is essential. Recovering nitrogen from urban wastewater reduces both the energy and resources required to produce nitrogen-based fertilizer and to remove nitrogen from wastewater collected. Nitrogen can be recovered from wastewater in the form of ammonium sulfate, a common nitrogen-based fertilizer. In the urban setting, the technology can be applied to target source-separated urine or municipal wastewater. To assess the environmental sustainability of this approach, this study compared the life cycle environmental impacts of ammonium sulfate recovered from urban wastewater (through nine different recovery technology trains) and ammonium sulfate produced by six different industrial processes. The results show that wastewater-derived ammonium sulfate generally has lower potential environmental impacts than industrially produced ammonium sulfate in most of the impact categories assessed. The impact of the membrane technology-based recovery train is the smallest. The contribution analysis shows that energy use is the major contributor, while the background inventory analysis shows that the results can be sensitive to the choice of region-specific background inventory. In the future, nitrogen recovery from urban wastewater is promising for the circular economy in cities.