Field Testing a Pilot-Scale System for Alkaline Dehydration of Source-Separated Human Urine: A Case Study in Finland

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.

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

“…All the substrates apart from pure MgO had similar EC, approximately 25 mS•cm −1 when measured as 1:5 (substrate: urine) suspensions. Compared to the initial EC, the endproducts had higher EC because of accumulation of urine salts [Simha et al (2020a) for more information on the salt content of dried urine fertilizer]. The EC of the urine added to the treatment was 11.7 ± 1.2 mS•cm −1 .…”

“…Several promising technologies at various scales are being developed across the world for the on-site treatment of urine (Harder et al, 2019). One among these technologies is alkaline dehydration (Simha et al, 2020a;Simha et al, 2020b;Simha et al, 2020c), where urine is dried to produce a solid fertilizer with 10-30 times higher concentrations of plant nutrients than what is originally present in freshly excreted urine. The treatment involves alkalizing urine (pH ≥ 10) to inhibit the enzyme-catalyzed hydrolytic degradation of urea (Krajewska, 2009).…”

“…In previous studies, we have demonstrated that urease present in source-separated urine can be inhibited simply by increasing the pH of urine; according to Geinzer (2017), a pH above 10 is necessary for inactivation. To alkalize urine, wood ash (Dutta and Vinneras, 2016;Senecal and Vinneras, 2017;Senecal et al, 2018;Simha et al, 2018), Ca(OH) 2 (Dutta and Vinneras, 2016;Randall et al, 2016;Simha et al, 2020a;Simha et al, 2020b), KOH (Simha et al, 2018) and anion-exchange resin (Simha et al, 2018) can be used as alkalizing agents. While all the aforementioned can increase the pH of fresh urine, not all are equally effective as alkaline substrates for dehydrating urine.…”

The potential contribution of urine source separation to the SDG agenda – a review of the progress so far and future development options

“…Introducing a treatment with activated carbon between biological treatment and distillation resulted in a safe fertilizer product with a sufficiently low content of organic micropollutants to obtain an unlimited fertilizer allowance from the Swiss authorities, without co-removal of beneficial nutrients. 63 At the bathroom scale, Simha et al 64 tested alkaline dehydration at pilot-scale for the production of a volume-reduced dry, transportable fertilizer. With this technology, fresh urine is dehydrated by a forced air stream within an alkaline medium.…”

Circular Bio-economy—Paradigm for the Future: Systematic Review of Scientific Journal Publications from 2015 to 2021

“…They conclude that it is very much possible to ideally supply at least 20% of the total nitrogen demand for food production globally with urea recovery from urine. In a pilot study done in Finland, Simha et al (2020) [66] have shown that source-separated urine can be subjected to alkaline dehydration and converted to a dry, nitrogen-rich fertiliser. Such separation to recover nitrogen from human wastes upstream, instead of recovering just a part of it as ammonium sulphate at wastewater treatment plants [36], can lead to greater biomethane production when the relatively nitrogen-poor stream of human excreta is anaerobically digested.…”