Urine separating sewage systems--environmental effects and resource usage.

Effects of urine separation on the environment and resource usage were estimated using the simulation package ORWARE. Measurements on the urine-separating system in the housing district Palsternackan in Stockholm and on the fertilising effect of the urine were used in the simulations. The tenants were at home 65% of the time and separated 65% of the urine. Under these conditions, urine separation decreased the waterborne emissions of nitrogen and phosphorus by 55% and 33% respectively. Compared to the conventional system, urine separation increased the flow from the wastewater system to agriculture of plant-available nitrogen by a factor of 28, phosphorus by a factor of 1.35 and potassium by a factor of 23. Urine is a well-balanced complete fertiliser with very low concentrations of heavy metals. Urine separation conserved energy as long as the urine was transported distances shorter than 221 km to the field with a truck and trailer. If all the urine had been separated and transported only 1 km, the energy saving would have been 36%. In this and in previous studies, urine separation proved to be an improvement over the conventional system as regards environmental effects and resource usage.