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In this study, we explored why urine recycling systems have failed to gain wide-scale expansion despite their high potential for food and fertilizer security. Additionally, we examined the future perception of urine recycling in Sweden and Switzerland, as these two countries are at the forefront of technological advancement. Along with identifying barriers, we also proposed pathways for overcoming those barriers and achieving the upscale. The analysis was conducted using the technological innovation (TIS) approach, which is technology-focused, i.e., revolves around emerging technologies. Additionally, the study provides a methodological contribution to the innovation systems research by employing the Delphi method in conjunction with urine recycling experts to enforce transparency and prevent bias in the analysis. For urine recycling to overcome its current challenges, actors must work collectively. There needs to be a combination of top-down and bottom-up efforts to achieve the upscaling pathways. Lobbying and knowledge provision are necessary to adjust the current regulatory framework in a manner that provides public and private incentives. For urine recycling to diffuse and break into the mainstream market, we must move beyond enthusiasts, innovators, and niche markets into the mass market (ordinary people); dedicated service providers can facilitate this process. Pilot projects have been found integral to urine recycling upscaling. Future work could conduct life cycle assessments on existing pilot projects to understand the environmental and economic performance of urine recycling systems when scaled up. [Display omitted] [ABSTRACT FROM AUTHOR]

Life cycle assessment (LCA) is a commonly used method for assessing environmental impacts of systems, but cannot produce absolute values, i.e. a comparison with existing calculated values, which represents limits of what can be emitted into the environment. Therefore, absolute environmental sustainability assessments have been developed to assess impacts against the planetary boundaries (PBs) of the safe operating space for humanity. Since PB-LCAs are novel, it is useful to analyze both results from this method and conventional LCAs, something which has not been done before. This study applied both methods to two full-scale sanitation systems in the city of Helsingborg, Sweden. The current conventional system for handling wastewater with active sludge and food waste to biogas production was compared with the novel project H+ source separation system with three pipes (food waste, grey and black water) with increased resource recovery through anaerobic digestion, ammonia stripping, struvite precipitation and pelletization. The Planetary Boundaries LCA (PB-LCA) results showed that both systems exceeded eight of the assigned shares of PBs, including climate change and biogeochemical flows of nutrients. Traditional LCA (ReCiPe impact assessment) showed net savings for the H+ system in a few categories and considerable reductions in several impacts, e.g., global warming potential (GWP), stratospheric ozone depletion, terrestrial acidification, and water consumption. In PB-LCA the H+ system gave additional impacts in both assessments for a few categories, mostly due to high consumption of chemicals in the ammonium stripping process used for nutrient recovery. In conclusion, the combined assessments highlight hot-spots for process optimization in the H+ system. From a methodological standpoint, PB-LCA still needs improvements to better reflect avoided burdens and results from traditional LCA should be fully transparent and analyzed carefully. The assessment methods complement each other and can be combined to better represent environmental performances of systems. [Display omitted] • Planetary Boundaries LCA was compared to the traditional LCA for sanitation systems. • Source separation in 3 streams in Sweden performed better in 10 categories in Recipe. • Eight of the Boundaries were exceeded but the avoided burdens are not represented. • Electricity and chemicals played major roles in the systems assessed. • Improvements are needed in PB-LCA to also reflect the benefits of the systems. [ABSTRACT FROM AUTHOR]

Adopting urine-recycling technologies can support a transition to circular nutrient management systems. Although these technologies have been developed since the 1990s, their large-scale implementation remains limited. From a technological innovation system (TIS) perspective, "knowledge development and diffusion" is a critical function in the development phase. Yet, available methods in the literature to evaluate this function are not standardized. Hence, this study aims to fill this literature gap by developing a novel multi-criteria framework for evaluating knowledge functions. Several characteristics of emerging technologies are reflected in the criteria, including the rate of growth, novelty, diffusion, and relationship to incumbent systems. The knowledge base was measured by bibliometric analysis of publications obtained from comprehensive mapping. Results showed that the rate of publications and knowledge diffusion increased sharply in 2011–2021 compared to 1990–2010. However, the function still has insufficiency in some criteria. The lack of innovation in scientific research and the diversification of technologies were found to be impediments. The analysis also identified the lock-in of conventional technologies and centralized infrastructures in terms of publication dominance as another impediment. For the TIS to be legitimate and to grow, more pilot-scale implementations at a higher level are recommended to demonstrate that the technology works in practice. [ABSTRACT FROM AUTHOR]