Abstract
Nutrient recovery from source-separated human urine has been identified by many as a viable avenue towards the circular economy of nutrients. Moreover, untreated (and partially treated) urine is the main anthropogenic route of environmental discharge of nutrients, most concerning for nitrogen, whose release has exceeded the planet’s own self-healing capacity. Urine contains all key macronutrients (N, P, and K) and micronutrients (S, Ca, Mg, and trace metals) needed for plant growth and is, therefore, an excellent fertilizer. However, direct reuse is not recommended in modern society due to the presence of active organic molecules and heavy metals in urine. Many systems have been proposed and tested for nutrient recovery from urine, but none so far has reached technological maturity due to usually high power or chemical requirements or the need for advanced process controls. This work is the proof of concept for the world’s first nutrient recovery system that powers itself and does not require any chemicals or process controls. This is a variation of the previously proposed microbial electrochemical Ugold process, where a novel air cathode catalyst active in urine conditions (pH 9, high ammonia) enables in situ generation of electricity in a microbial fuel cell setup, and the simultaneous harvesting of such electricity for the electrodialytic concentration of ionic nutrients into a product stream, which is free of heavy metals. The system was able to sustain electrical current densities around 3 A m–2 for over two months while simultaneously upconcentrating N and K by a factor of 1.5–1.7.
Highlights
Nutrient management in the modern world is reaching a tipping point
Human urine was collected in the male toilets of the Advanced Water Management Centre (University of Queensland, Brisbane, QLD, Australia) using 15 L drums fitted with a large funnel that acted as a waterless urinal
Once the drums contained 10 L of urine, they were swapped for empty ones, and the collected fresh urine was left to hydrolyze in the drums for 3 to 7 d through the action of naturally occurring ureolytic bacteria
Summary
Nutrient management in the modern world is reaching a tipping point. Most of the nitrogen needs are covered by the Haber–Bosch process, which uses fossil energy to fix atmospheric nitrogen into the ammonia molecule, and can be used as a fertilizer, or more frequently converted to urea or salts before land application. The excessive loss of nitrogen from land application is a cause for disruption of natural balances and has recently exceeded its planetary boundary [4], implying that the Earth has passed its natural capacity to deal with anthropogenic nitrogen release. The phosphorus needed for fertilizers is produced from minerals locked in phosphate rock mines, of which there are limited stocks that are expected to reach critically concerning low levels within a century [1,5]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
