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Research article - Peer-reviewed, 2021

Alkaline Dehydration of Human Urine Collected in Source-Separated Sanitation Systems Using Magnesium Oxide

Simha, Prithvi; Friedrich, Christopher; Randall, Dyllon Garth; Vinneras, Bjorn


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 degrees 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 degrees 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(-1)y(-1) and a cost of US$ 1.1 cap(-1)y(-1). Therefore, the use of sparingly soluble alkaline compounds like MgO in urine-diverting sanitation systems holds much promise.


ammonia; fertilizer; nitrogen recycling; urine source separation; wastewater; urine dehydration; sanitation; MgO

Published in

Frontiers in Environmental Science
2021, volume: 8, article number: 619901

Authors' information

Swedish University of Agricultural Sciences, Department of Energy and Technology
Friedrich, Christopher
Swiss Federal Institute of Aquatic Science and Technology (EAWAG)
Randall, Dyllon Garth
University of Cape Town
Swedish University of Agricultural Sciences, Department of Energy and Technology

Sustainable Development Goals

SDG6 Clean water
SDG12 Ensure sustainable consumption and production patterns

UKÄ Subject classification

Water Treatment

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