Source separated urine-nutrient and heavy metal content, water saving and faecal contamination

Human urine is by far the largest contributor of nutrients to household wastewater. Source separation of urine can significantly decrease the nutrient load on the recipients. By recycling the urine to agriculture as a fertiliser, with very low levels of heavy metals, the nutrients are made into resources instead of becoming pollutants. The amounts and concentrations of nutrients and heavy metals in urine solution from a source separating sewage system were measured. The concentrations of nutrients were high. The ratio of nitrogen to phosphorus was close to the expected value, indicating that the system did not have any large nitrogen loss. The heavy metal concentrations in the urine were low, much lower than that in most chemical fertilisers. Per inhabitant and day, 1.34 litres of urine solution were collected. Of this, 0.34 litres was flush water. The low flush water volume was due to the double flush mechanism of the toilets, which saved 48% of the flush water compared with conventional water closets. Per inhabitant and day, 4.9 g of nitrogen and 0.42 g of phosphorus were collected, which was 86 and 81% respectively of the expected amount. The contamination level of faecal material in the source separated urine was low.