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

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

Sammanfattning

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.

Nyckelord

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

Publicerad i

Frontiers in Environmental Science
2021, Volym: 8, artikelnummer: 619901
Utgivare: FRONTIERS MEDIA SA

      SLU författare

      • Globala målen

      SDG6 Säkerställa tillgången till och en hållbar förvaltning av vatten och sanitet för alla
      SDG12 Säkerställa hållbara konsumtions- och produktionsmönster

      UKÄ forskningsämne

      Vattenbehandling

      Publikationens identifierare

      DOI: https://doi.org/10.3389/fenvs.2020.619901

      Permanent länk till denna sida (URI)

      https://res.slu.se/id/publ/110779