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

Frontiers in Environmental Science

Dyllon Garth Randall¹  Prithvi Simha²  Björn Vinnerås²  Christopher Friedrich³ 

[1] Civil Engineering Department and the Future Water Institute, University of Cape Town, Cape Town, South Africa;Department of Energy and Technology, Swedish University of Agricultural Sciences, Uppsala, Sweden;Department of Sanitation, Water and Solid Waste for Development (SANDEC), Swiss Federal Institute of Aquatic Science and Technology (EAWAG), Dübendorf, Switzerland;

关键词: ammonia;    fertilizer;    nitrogen recycling;    urine source separation;    wastewater;    urine dehydration;   

DOI  :  10.3389/fenvs.2020.619901

来源: DOAJ

【 摘 要 】

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.

【 授权许可】

Unknown