Modelling, Simulation, and Life cycle Assessment of a Novel Sustainable Ammonia Production Process from Food Waste and Brown Water

To replace existing high impact ammonia production technologies, a new sustainability-driven waste-based process producing green ammonia with and without urea was devised using life cycle thinking and sustainable design principles, targeting efficiency, carbon emissions, water, and power use competitiveness.
Through this process, food waste and brown water are fed into a two-stage Dark Fermentation (DF) coupled with Anaerobic Digestion (AD)/AD-only bioreactors, resulting in the production of biogas. The biogas is then upgraded into hydrogen through a series of operating stages (emerging membranes) and reacts with nitrogen derived from the migration of air through a membrane in order to produce ammonia. This process is assessed via different scenarios, two hydrogen generating options are paired with four CO2 fates. For either an AD-centered process or a two-stage process, the resultant CO2 may be captured and injected, sold to the marketplace, released directly into the atmosphere, or converted to urea. An equation-based modular approach has been devised in Visual Basic for Applications for the new technology and family of configurations. Based on the said model, 72 assessed processes for the cradle-to-gate life cycle assessment model were generated to evaluate the potential efficiency and Greenhouse Gas (GHG) intensity.
Among the assessed technologies, coupling DF with AD and capturing CO2 for sequestration or later use is most efficient for GHGs, water, and energy, consuming 27% less energy and reducing GHGs by 98% compared to conventional ammonia production. In addition, water consumption is 38% lower than water electrolysis technology. The results indicate that leakage causes nearly all life cycle impacts, demonstrating that failing to prevent leakage undermines the effectiveness of these new technologies. The green ammonia/ammonia+urea process family as designed here can reduce waste and prevent the release of additional CO2 from ammonia production, while avoiding fossil-based alternatives and decreasing emissions from biogenic waste sources.