Abstract

Source separating the human urine and using it as a fertiliser on cereal fields might be a simple way to make both the sewage system and agriculture more sustainable. Several evaluations of urine separation have been done, however they have not been based on measured performance of urine separating systems. In order to increase the knowledge about such systems, measurements were done on two urine separating systems. The measurement on the system in the eco-village Understenshöjden is based on 4480 person days while the measurement of the system in Palsternackan is based on 1653 person days. The collected urine solution in Understenshöjden contained 4.9 grams of nitrogen, 0.42 g phosphorus and 1.34 g potassium per person and day. These amounts corresponds to 78, 74 and 95% respectively of the expected amounts. The corresponding values for Palsternackan were 4,2 grams of nitrogen, 0.30 g phosphorus and 1.14 g potassium. These amounts corresponds to 59, 61 and 70% respectively of the expected amounts. The expected amounts were calculated from the average per person excretion as given by the Swedish Environmental Protection Agency. These values were adjusted for how much the persons were at home per day and for the percentage of children (younger than 13 years) among the inhabitants. In Understenshojden the inhabitants were on average at home 13.9 hours per day and in Palsternackan 15.9 hours per day. The reason for the lower collection in Palsternackan is probably that those inhabitants were not as careful as those in Understenshojden to use the toilet in a way that maximised the separation. The concentrations of heavy metals in the urine were very low. When using urine as a fertiliser the amounts of heavy metals spread with a normal dosage of urine per hectare were much below the amounts allowed when using sewage sludge as a fertiliser. The urine separating toilets uses only a small amount of water (approximately 0.1 litre) to flush away the urine. This feature was calculated to save 14 litres per inhabitant and day in Understenshöjden and 6.8 litres per inhabitant and day in Palsternackan, 48% and 20% respectively of the flush water consumption of conventional 6 litre per flush toilets. Almost all of the nitrogen in the collected urine solution was in the form of ammonium, which suggests an active biofilm in the urine pipes. Analyses were made on the urine entering the collection tank from the pipes. Of the nitrogen in Understenshojden 2.6% was in the form of urea. In Palsternackan 1.3% of the nitrogen was organic. Nitrate was detected only in one analysis, which means that the risk of nitrogen loss via denitrifikation is negligible. In Understenshöjden a small amount of fast sedimenting sludge was observed. This indicates that thorough mixing is needed when taking representative samples. It is important that the whole urine system, both piping and collection tank, is easy to inspect and clean and that no water can leak into it. If the piping system is completely tight against surrounding ground water, if the amount of water used for flushing away the urine is less than 0.15 litres per time and if the inhabitants are at home no more 14-16 hours per day, then the urine system can be dimensioned for 1.5 litre per person and day.

Keywords

urin; växtnäring; kväve; fosfor; uppsamlad mängd; antal spolningar; spolvatten; stor spolning; liten spolning; hemvaro

Published in

Rapport - Sveriges lantbruksuniversitet, Institutionen för lantbruksteknik
1998,
Publisher: Institutionen för lantbruksteknik, Sveriges lantbruksuniversitet

Permanent link to this page (URI)

https://res.slu.se/id/publ/125801