Removing urine from wastewater and using it as fertilizer has the potential to decrease nutrient loading in water bodies and boost sustainability by making use of a common waste material.

The key here is that if the urine is urine only, it’s ready to go as a nitrogen- and phosphorus-rich fertilizer the moment it leaves the body. But getting a good separation is important. Feces are the main source of pathogens in the collected urine, according to Björn Vinnerås, environmental engineering professor at the Swedish University of Agricultural Sciences. Urine-diverting toilets aren’t perfect, he said, and some mixing is unavoidable.

If it can be separated, urine can act to partly sterilize itself. The nitrogen in urine leaves the body as urea, a simple organic compound. Bacteria in pipes typically break down urea into ammonia. When urine is sitting in a container, the ammonia raises the pH of the solution to about eight or nine. The high pH environment kills any pathogens from the body that might have entered the urine, Vinnerås said.

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Urine diversion fits into a circular water economy by connecting some of the dots. The water people drink and excrete may come back around to fertilize the vegetables prepped for a salad. For it to be more widely accepted by gardeners and farmers alike, shifts in both mentality and plumbing are important next steps.

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