%A Simha,Prithvi
%A Friedrich,Christopher
%A Randall,Dyllon Garth
%A Vinnerås,Björn
%D 2021
%J Frontiers in Environmental Science
%C
%F
%G English
%K Ammonia,fertilizer,Nitrogen recycling,Urine source separation,Wastewater (WW),Urine dehydration,Sanitation,MgO
%Q
%R 10.3389/fenvs.2020.619901
%W
%L
%M
%P
%7
%8 2021-January-20
%9 Original Research
%#
%! Alkaline urine dehydration using MgO
%*
%<
%T Alkaline Dehydration of Human Urine Collected in Source-Separated Sanitation Systems Using Magnesium Oxide
%U https://www.frontiersin.org/articles/10.3389/fenvs.2020.619901
%V 8
%0 JOURNAL ARTICLE
%@ 2296-665X
%X Fresh human urine, after it is alkalized to prevent the enzymatic hydrolysis of urea, can be dehydrated to reduce its volume and to produce a solid fertilizer. In this study, we investigated the suitability of MgO to alkalize and dehydrate urine. We selected MgO due to its low solubility (<2 g·L−1) and relatively high saturation pH (9.9 ± 0.2) in urine. Using a laboratory-scale setup, we dehydrated urine added to pure MgO and MgO mixed with co-substrates (biochar, wheat bran, or calcium hydroxide) at a temperature of 50°C. We found that, dehydrating urine added to a mixture of MgO (25% w/w), biochar, and wheat bran resulted in a mass reduction of >90% and N recovery of 80%, and yielded products with high concentrations of macronutrients (7.8% N, 0.7% P and 3.9% K). By modeling the chemical speciation in urine, we also showed that ammonia stripping rather than urea hydrolysis limited the N recovery, since the urine used in our study was partially hydrolyzed. To maximize the recovery of N during alkaline urine dehydration using MgO, we recommend treating fresh/un-hydrolysed urine a temperature <40°C, tailoring the drying substrate to capture NH4+ as struvite, and using co-substrates to limit the molecular diffusion of ammonia. Treating fresh urine by alkaline dehydration requires only 3.6 kg MgO cap−1y−1 and a cost of US$ 1.1 cap−1y−1. Therefore, the use of sparingly soluble alkaline compounds like MgO in urine-diverting sanitation systems holds much promise.