Abstract
Alkaline dehydration can treat human urine to produce a dry and nutrient-rich fertilizer. To evaluate the technology at pilot-scale, we built a prototype with capacity to treat 30 L urine d(-1)and field tested it for the first time at a military training camp in Finland. We operated the system for 3 months and monitored the recovery of nutrients, end-product composition, physicochemical properties and energy consumption. Results revealed that the system received less urine than anticipated, but achieved high dehydration rates (30-40 L d(-1)m(-2)), recovered 30 +/- 6% N, and yielded end-products with 1.4% N, 0.9% P, and 8.3% K. However, we demonstrated that the system had potential to recover nearly 70% N and produce fertilizers containing 13.2% N, 2.3% P, and 6.0% K, if it was operated at the design capacity. The energy demand for dehydrating urine was not optimized, but we suggested several ways of reducing it. We also discussed concerns surrounding non-essential heavy metals, salts, and micropollutants, and how they can be overcome to safely recycle urine. Lastly, we pointed out the research gaps that need to be addressed before the technology can be implemented at larger scale.
Highlights
In the field of wastewater management, the idea of separately collecting and treating different fractions of wastewater at the point where it is produced is rather innovative (Larsen et al, 2013)
To assess whether alkaline dehydration is a suitable on-site urine treatment technology, we focused on the following aspects – (i) the recovery of nutrients, nitrogen; (ii) the elemental composition of the endproduct; (iii) the concentrations of micropollutants and heavy metals; and, (iv) the energy demand for dehydrating urine
The present study explored this possibility by implementing urine source-separation and on-site treatment with alkaline dehydration
Summary
In the field of wastewater management, the idea of separately collecting and treating different fractions of wastewater at the point where it is produced is rather innovative (Larsen et al, 2013). A source-separating sanitation system treats various sub-streams of domestic wastewater according to their composition (Friedler et al, 2013) Such an approach allows resources present in wastewater to be recovered for reuse or recycling (e.g., plant-essential nutrients, water and heat). At the Swedish University of Agricultural Sciences we have opted for an alternative approach, one where fresh urine is dehydrated to concentrate nutrients within an alkaline medium, resulting in the production of a dry fertilizer. The system was designed to add fresh human urine continuously to a mixture of wood ash and calcium hydroxide (to prevent enzymatic ureolysis) and to concentrate the urine by hot air convective dehydration It was operated and monitored for a period of 3 months, the results of which are summarized in this paper. The present study explored this possibility by implementing urine source-separation and on-site treatment with alkaline dehydration
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