Urine accounts for less than 1% of our waste water, but it contains 50-80% of the nutrients in the waste water. For this reason, it is extremely burdensome for our sewer water purification installations. In fact, it is illogical to allow such a dirty waste water flow to mix with other waste water, as has occurred in our sewers for more than a hundred years. There is growing support therefore for collecting and purifying urine separately. By separating urine, phosphate and nitrogen are more effectively removed. Phosphate can even be reclaimed as a raw material. Urine accounts for at least 50% of the phosphate in waster waste, (with phosphate being a raw material of limited availability), and for 80% of the nitrogen found in the waste water.
In Sweden and other countries, experiments have been conducted involving separate urine-collections. Delft University of Technology PhD candidate Jac Wilsenach researched – supported by a STOWA grant – the possibilities and consequences of following this principle in the Netherlands. He concluded that if 50% of the urine is separately purified, it would save 25% of the energy needed for the entire purification system. Moreover, the stench of the sewer will be lessened, environmental pressure on the surface water will be reduced, and sewer pipes will be better protected against rot.
A requirement for separating urine is an appropriate toilet (on which men also sit to urinate) or a dry urinal, both of which are commercially available. The urine is collected in tanks on a per building or neighbourhood basis and must then be - preferably as undiluted as possible - periodically transported to a special purification installation. It is also possible to process the urine in a decentralized manner - concepts for this were developed in the research.