Kretsloppsteknik

We recently published a new paper on the use of Magnesium Oxide as an alkaline substrate for dehydrating urine in the journal Frontiers in Environmental Science.

https://www.frontiersin.org/articles/10.3389/fenvs.2020.619901/full

Abstract: 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 gL⁻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 NH⁺⁴ 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.

Contact: Prithvi Simha

The Urine Drying team at SLU (together with Sanitation360, Spiran and Gotlands Bryggeri) have been awarded 2.9 MSEK from JTI to test using our dehydrated urine as a fertilizer for barley destined for beer production.  The objective of the project is to produce a tailored dry fertilizer from urine and a new, more sustainably produced, beer that tastes exactly the same as conventional produced beer.