Urine separating wastewater systems experiences of design and nitrogen conservation

Sammanfattning: Urine separating (US) wastewater systems, where urine is collected and used as a fertiliser, may be a strategy to achieve a high degree of nutrient recycling from human waste to agriculture. The Swedish experiences of US systems show that the design of the toilets and the sewers are of great importance to achieve a working system. One study of the US system in the eco-village in Björsbyn also shows that special attention should be given to avoidance of leakage of water into the urine sewers. During storage of urine the main nitrogen constituent, urea, decomposes to ammonium. Thus, there is a risk nitrogen losses as ammonia evaporation. Several factors concerning the decomposition of urea has been studied in laboratory experiments. A one-time dosage of acid in the beginning of a storage cycle could inhibit the urea decomposition. One strategy to reduce the amount of urine solution produced in a US system may be to use nitrification in combination with drying. Results from a laboratory experiment showed that the method has a potential. However, the system used has to be modified in order to minimise the nitrogen losses.