This research investigated the possibility of transferring phosphorus from human urine into a concentrated form that can be used as fertilizer in agriculture. The community of Siddhipur in Nepal was chosen as a research site, because there is a strong presence and acceptance of the urine-diverting dry toilets needed to collect urine separately at the source. Furthermore, because the mainly agricultural country is landlocked and depends on expensive, imported fertilizers, the need for nutrient security is high. We found that struvite (MgNH(4)PO(4)·6H(2)O) precipitation from urine is an efficient and simple approach to produce a granulated phosphorus fertilizer. Bittern, a waste stream from salt production, is a practical magnesium source for struvite production, but it has to be imported from India. Calculations show that magnesium oxide produced from locally available magnesite would be a cheaper magnesium source. A reactor with an external filtration system was capable of removing over 90% of phosphorus with a low magnesium dosage (1.1 mol Mg mol P), with coarse nylon filters (pore width up to 160±50 μm) and with only one hour total treatment time. A second reactor setup based on sedimentation only achieved 50% phosphate removal, even when flocculants were added. Given the current fertilizer prices, high volumes of urine must be processed, if struvite recovery should be financially sustainable. Therefore, it is important to optimize the process. Our calculations showed that collecting the struvite and calcium phosphate precipitated spontaneously due to urea hydrolysis could increase the overall phosphate recovery by at least 40%. The magnesium dosage can be optimized by estimating the phosphate concentration by measuring electrical conductivity. An important source of additional revenue could be the effluent of the struvite reactor. Further research should be aimed at finding methods and technologies to recover the nutrients from the effluent.

Source-separated urine contains most of the excreted nutrients, which can be recovered by using nitrification to stabilize the urine before concentrating the nutrient solution with distillation. The aim of this study was to test this process combination at pilot scale. The nitrification process was efficient in a moving bed biofilm reactor with maximal rates of 930 mg N L−1 d−1. Rates decreased to 120 mg N L−1 d−1 after switching to more concentrated urine. At high nitrification rates (640 mg N L−1 d−1) and low total ammonia concentrations (1,790 mg NH4-N L−1 in influent) distillation caused the main primary energy demand of 71 W cap−1 (nitrification: 13 W cap−1) assuming a nitrogen production of 8.8 g N cap−1 d−1. Possible process failures include the accumulation of the nitrification intermediate nitrite and the selection of acid-tolerant ammonia-oxidizing bacteria. Especially during reactor start-up, the process must therefore be carefully supervised. The concentrate produced by the nitrification/distillation process is low in heavy metals, but high in nutrients, suggesting a good suitability as an integral fertilizer.

Urine contains about 50 % of the phosphorus (P) and about 90 % of the nitrogen (N) excreted by humans and is therefore an interesting substrate for nutrient recovery. Source-separated urine can be used to precipitate struvite or, through a newly developed technology, nitrified urine fertilizer (NUF). In this study, we prepared 33P radioisotope- and stable 15N isotope-labeled synthetic NUF (SNUF) and struvite using synthetic urine and determined P and N uptake by greenhouse-grown ryegrass (Lolium multiflorum var. Gemini) fertilized with these products. The P and N in the urine-based fertilizers were as readily plant-available in a slightly acidic soil as the P and N in reference mineral fertilizers. The ryegrass crop recovered 26 % of P applied with both urine-based fertilizers and 72 and 75 % of N applied as struvite and SNUF, respectively. Thus, NUF and urine-derived struvite are valuable N and P recycling fertilizers.Electronic supplementary materialThe online version of this article (doi:10.1007/s13280-014-0616-6) contains supplementary material, which is available to authorized users.

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In recent years, a large number of urine-diverting dehydration toilets (UDDTs) have been installed in eThekwini to ensure access to adequate sanitation. The initial purpose of these toilets was to facilitate faeces drying, while the urine was diverted into a soak pit. This practice can lead to environmental pollution, since urine contains high amounts of nutrients. Instead of polluting the environment, these nutrients should be recovered and used as fertiliser. In 2010 the international and transdisciplinary research project VUNA was initiated in order to explore technologies and management methods for better urine management in eThekwini. Three treatment technologies have been chosen for the VUNA project. The first is struvite precipitation, a technology which has already been tested in multiple projects on urine treatment. Struvite precipitation is a simple and fast process for phosphorus recovery. Other nutrients, such as nitrogen and potassium, remain in the effluent and pathogens are not completely inactivated. Therefore, struvite precipitation has to be combined with other treatment processes to prevent environmental pollution and hygiene risks. The second process is a combination of nitrification and distillation. This process combination is more complex than struvite precipitation, but it recovers all nutrients in one concentrated solution, ensures safe sanitisation and produces only distilled water and a small amount of sludge as by-products. The third process is electrolysis. This process could be used for very small on-site reactors, because conversion rates are high and the operation is simple, as long as appropriate electrodes and voltages are used. However, nitrogen is removed and not recovered and chlorinated by-products are formed, which can be hazardous for human health. While urine electrolysis requires further research in the laboratory, struvite precipitation and nitrification/distillation have already been operated at pilot scale.