Drying fresh human urine in magnesium-doped alkaline substrates: Capture of free ammonia, inhibition of enzymatic urea hydrolysis & minimisation of chemical urea hydrolysis

[Display omitted] •Complete nutrient recovery by drying fresh urine in Mg-based alkaline substrates.•Urea recovered by inhibiting enzymatic hydrolysis and minimising chemical hydrolysis.•Ammonia recovered by shifting [Mg]:[NH4]:[PO4] molar ratio in urine to form struvite.•Solid fertiliser containing 11% N, 2% P and 3% K produced by dehydrating urine. Recycling urine can reduce the flux of reactive nitrogen in the environment. This paper presents a novel approach to recover all N (Ntot) from urine, including ammonia (TAN; about 5% of Ntot), which is usually volatilised when alkalised urine is dehydrated. As analytical methods for measuring N have a standard deviation of at least 5%, real fresh urine was fortified with ammonia (urineN) or ammonia and phosphate (urineNP) so that TAN comprised 10% of Ntot. The urine was then added to different magnesium-based alkaline substrates (MgO, Mg(OH)2, MgCl2 + Mg(OH)2) and dried at 38 ˚C. Chemical speciation modelling suggested that, irrespective of the substrate, >98% of Ntot in urineNP was recovered and 86% of TAN was precipitated as struvite. Experimental results showed that