Urine is relatively sterile and can be reused without further treatment (Wolgast, 1993). However, due to faecal contamination, pathogens have been found in yellow water; but in low concentration, which will pose low hygienic risk of using yellow water as a fertiliser, if it is stored at least for 6 months before being used in agriculture land (Jönsson et al., 1999; Hellström and Johansson, 1999). Since the practising of separated collection of yellow water, farmers in Sweden have been collecting it in underground storage tanks for applying to their agricultural land (Jönsson et al., 1999).

Figure 33: Practice of urine: storage and reuse or direct reuse

In Eco-village, Understenhöjden, Sweden, urine of 160 inhabitants is separated with urine separating toilets and collected in a collection tank. The collected urine is transported by tanker truck, once a year, to the storage tank, where it is sanitised prior to its use in agriculture. Similar to Eco-village Understenhöjden, 160 inhabitants in the Palsternacken housing state, Enskede in Sweden are connected to a urine separating system. Collected urine is transported once a year to a storage tank, where also the urine from eco-village, Understenhöjden is stored. Once the tank is full, it is closed and stored until it is ready for application in agriculture.

During the storage and transportation of urine, a large amount of unionised ammonia is formed due to decomposition of urea which also increases pH. The high pH causes precipitation of calcium, phosphate, struvite and calcite resulting 90 % of total nitrogen is present as ammonia, the pH is about 9 and 30 % of phosphorus is precipitated (Udert et al., 2003). The ammonia can evaporate while transportation and application in agriculture as fertiliser of urine solution (Hellström and Johansson, 1999). However, nitrogen loss can be prevented by ammonia oxidation; with the biological nitrification, urine can be stabilised (Udert et al. 2003). In the Pilot project Lambertsmuehle in Germany, urine from a family and museum visitors is separated with a newly developed sorting toilet where no water is needed for the urine flushing, a mechanical device closes the urine pipe when users stand up. The separated urine is collected and stored in the storage tank near the building until it is sanitised before it is applied in agriculture. Unlike in Sweden, in Lambertsmuehle, acidification is also used for sanitisation. In the storage tank the urine is acidified (pH< 5) with sulphuric acid to reduce microbial contamination, ammonia emissions and plant damage; however, it should not be used in excess to avoid yield losses due to high inputs of sodium choride (Simons and Clemens, 2003). Experiences from Sweden have shown that nitrogen loss during the storage is small and does not cause odour problem. The urine storage has been carried out without any extra conditioning.

In Mexico city, vegetables have been grown in containers using human urine as a fertiliser (Esrey et al., 1998). Urine is stored in a container for 3 weeks and is applied to the vegetables after diluting it with water on a ratio of 1:10. After several years of study it showed that plants fertilised with urine grew more rapidly and healthier than those grown with conventional agricultural techniques.

In a lab scale experiment, nutrient removal by different plants with different dilution of urine was studied (Prasapati and Gajurel, 2003). Results showed that Green Pea, Black Gram, Broad Bean, Cress, Spinach, Tintel, Mustard and Rape had high nutrients removal efficiency while using a ratio of 1:10 and 1:15. With the applied dilution, effluent still contained traces of N, P, K. Therefore, further dilution of source-separated urine could be applied for total nutrient recovery. This practice is good for a region where the farmland is near to the housing area; otherwise, transportation of large amounts of urine solution for longer distance has many negative environmental impacts (Hellström and Johansson, 1999).