New Scientist asks, “So how do standard sewage systems deal with urine?“
The problem with urine is that it is the main source of some of the chemical nutrients that have to be removed in sewage treatment plants if they are not to wreck ecosystems downstream.
Despite making up only 1 per cent of the volume of waste water, urine contributes about 80 per cent of the nitrogen and 45 per cent of all the phosphate.
Peeing into the pan immediately dilutes these chemicals with vast quantities of water, making the removal process unnecessarily inefficient.
What do we do?
The first step is to filter the sewage to remove large objects such as condoms, tampons and a random assortment of dead goldfish and false teeth. What remains flows into settlement tanks, to allow the faeces to sink to the bottom. This solid sludge is separated off and stored in oxygen-free tanks, which are gently warmed for about two weeks. Bacteria break it down, generating methane gas that can be burned to produce electricity. The end product is an inert solid that is usually burned or dumped in landfill.
Sewage sludge is a biomass fuel that contains about as much heat as lower grade coal. Increasingly, municipal wastewater treatment plants are drying sewage sludge to use as a green energy source, reducing operating costs and keeping sludge off the ground.