The public defence of the doctoral thesis for Prithvi Simha, entitled “Alkaline Urine Dehydration. How to dry source-separated human urine and recover nutrients?” is scheduled –
When? 2nd of June at 13:00 Where? Room Framtiden at MVM-hus at SLU in Uppsala and via Zoom Click this URL to join via Zoom: https://slu-se.zoom.us/j/69422000884 with Passcode: 732271
External reviewer: Professor Nancy Love, Department of Civil and Environmental Engineering, The University of Michigan, Ann Arbor, USA.
Examining committee: Professor Annelie Hedström, Luleå University of Technology, Luleå, Sweden; Docent Sebastian Schwede, Mälardalen University, Västerås, Sweden; and PhD Surendra Pradhan, University of Eastern Finland, Kuopia, Finland
The thesis is openly available at: https://pub.epsilon.slu.se/23473/1/simha_p_210511.pdf
Abstract
Human urine is a renewable resource from which water, nutrients and energy can be recovered and safely recycled. This thesis presents a novel on-site technology, called alkaline dehydration, for recovering nutrients from source-separated urine. To recover urea (the major nitrogenous compound in fresh urine) and prevent its urease enzyme-catalysed hydrolysis to ammonia, fresh urine was alkalised to pH ≥10 by anion exchange or use of alkaline substrates. To reduce the volume and concentrate the nutrients, the alkalised urine was dried in different substrates at temperatures of 40-60 °C. To evaluate alkaline urine dehydration at pilot-scale, a prototype dryer with capacity to treat 30 L urine d–1 was built and field-tested for three months at a military camp in Finland. More than 90% of the urine mass was reduced and dehydration rates of up to40 L urine d–1 m–2 were obtained. Up to 98% of the nitrogen (N) and 100% of the phosphorus (P) and potassium (K) in urine were recovered. A dry solid containing 10% N, 1.5% P and 6.0% K, with similar salt and heavy metal content to synthetic fertilisers available in Sweden was produced. At least 12.5 g Ca(OH)2 or 6.8 g MgO per litre of fresh urine was required to buffer the pH of urine against absorption of CO2 during dehydration. The energy demand for evaporating urine was similar to that of incineration toilets, but could be reduced if heat energy from the dryer’s exhaust air were recovered. Overall, this thesis shows that a new sanitation system that safely collects, treats, transports and applies urine as fertiliser could be created by integrating alkaline urine dehydration with existing infrastructure. If implemented globally, this system could recycle 31 Tg N y–1 and 2.8 Tg P y–1, which would reduce the transgression of the planetary boundary for N and P by 35% and 25%, respectively.
Contact: Prithvi Simha