Is Human Urine the Future of Fertiliser?

By Sarah Zhang on at

Among the things I found mortifying about my parents when I was a teenager was their habit of leaving buckets of urine in the bathroom. Instead of flushing all that phosphorous-nitrogen-rich liquid down the toilet, they saved it for our backyard vegetable garden. Urine as fertiliser has since become a hip idea among some eco-minded backyard farmers.

Thinking bigger, Sam Brasch at Modern Farmer investigates the possibility of bringing this process to large-scale industrial agriculture.

At the centre of the nascent urine movement in the USA is the Rich Earth Institute in Vermont. REI talks about "closing the food nutrient cycle:" from food to pee to fertiliser and back to food again. It's a fair proposition to consider because the fertilisers we dump on our food are not renewable resources. Phosphorous, for example, is mined—from guano before we exhausted it and now from rocks in places like Morocco. And the nitrogen in fertiliser is captured through a process that requires natural gas. So instead of letting all the nutrients go to waste, what if we could recapture it?

That's why REI has been collecting human urine—3,000 gallons of it so far. A successful preliminary study finding urine-fertilised fields to be more productive than unfertilised fields won the organisation a $10,000 USDA grant. They're the only project to legally experiment with urine for fertiliser in the US right now.

At this point, you might be wondering about urine versus fecal matter as fertilizer. The solid waste industry is looking a lot more, ummm, solid; almost 50 per cent of "human biosolids" is already used on farmland in the United States. This is in spite of the fact that bacteria-filled fecal matter requires a lot more processing for safety than usually-sterile urine.

To collect urine on a large scale, we need to go beyond the buckets of urine my parents left around. We need a whole new gizmo: the urine-diverting toilet. It already exists, but are widely available globally. A division in the toilet bowl diverts urine down the front into a holding tank while solid waste and toilet paper fall down the back for composting. That's if you have your own septic system—city-wide reengineering would have to happen on a different, more massive scale entirely.

Is Human Pee the Future of Fertilizer?

Urine-diverting toilets from Sweden. Credit: World Health Organization

The Swedes, who pioneered urine diversion 15 years ago, have found challenges scaling up. A survey from 2006 found only 10,000 urine-diverting toilets in the the country and 10 to 15 larger municipal systems. A backlash in the early 2000s after problems with the first systems put a damper on efforts, though the study's authors are optimistic.

In the US, the urine diversion moment is more nascent, and perhaps those early mistakes can be avoided. Even if infrastructure hurdles are surmounted, though, advocates still have to deal with a weird quirk of urine-diverting toilets: Men have to sit down to use them.

But hey, toilets are already forcing us into inherently unnatural bathroom positions anyway. When it comes to bowel movements, we really should be squatting like our toilet-less ancestors rather than sitting. If men can learn to sit while they poop, perhaps men can learn to sit while they wee, too? [Modern Farmer]

Lead image: Africa Studio/Shutterstock and Pixelbliss/Shutterstock