Self-Powered Bioelectrochemical Nutrient Recovery for Fertilizer Generation from Human Urine

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.

Development of a Self-Sustaining Wastewater Treatment with Phosphorus Recovery for Small Rural Settlements

“…Table 2 shows the composition of stored urine from the Reinighof (28 samples) in comparison to values from the literature [1, 3,5,11,[30][31][32]. In all samples, the pH reaches values around 9, which is in accordance with literature data, although fresh urine is conveyed daily into the urine tank.…”

Urine in Bioelectrochemical Systems: An Overall Review

“…More recently and based on the same concept, Freguia et al . (2019) reported the use of a bio‐electroconcentration cell similar to their previous work reported by Ledezma et al . (2017) but using an air‐breathing cathode.…”

“…This energy demand is quite high compared with electroconcentration cells using bioanodes (8.6 MJ kg N À 1 ). [118] More recently and based on the same concept, [119] reported the use of a bio-electroconcentration cell similar to their previous work reported by Ledezma et al (2017) [20] but using an air-breathing cathode. Unlike previously, in this work, real human urine was used to feed the system.…”

Taking the water out of “wastewater”: An ineluctable oxymoron for urban water cycle sustainability

“…Membranes (reverse osmosis, microfiltration, and nanofiltration) have also shown potential, at the laboratory scale, to concentrate phosphates, ammonia, calcium, and magnesium in a liquor source to facilitate the recovery of magnesium ammonium phosphate or hydroxyapatite (Qiu & Ting, 2014). Preliminary studies on P recovery with microbial extraction by microbial fuel cells (MFCs) with simultaneous energy recovery have also shown positive laboratory results (Almatouq & Babatunde, 2016; Freguia et al, 2019; You, Greenman, Melhuish, & Ieropoulos, 2014).…”