Could urine be the perfect fertilizer for your garden?

Krista Wigginton has been working with the Rich Earth Institute in Vermont to figure out a way to not put human waste to waste. They have many reasons, but one big one is to save water. 

“The way we handle urine is we flush it down the toilet,” says the assistant professor of civil and environmental engineering at the University of Michigan. “We [flush urine] with water that’s been treated to a drinking water standard. And we flush a lot of water. We flush several times a day — gallons of water every time. Most of those [gallons] are for flushing urine down, and so especially in places like California where all of that water is so precious, it really doesn’t make sense to be flushing so much down the drain." 

Besides the fact that flushing urine wastes water, scientists also say that urine contains valuable nutrients. 

“Urine contains a lot of nitrogen and phosphorus and potassium. In fact, if you look at what we excrete, more than half of the nitrogen and phosphorus and potassium excrete comes out in our urine, and that tends to be what we add to plants to fertilize them. So we’re interested in capturing those nutrients and turning it into a fertilizer product, rather than, ‘I’m sending it to the wastewater treatment plant where it’s treated in different ways,’” Wigginton says. 

She and a group of researchers have been collecting urine to reuse as fertilizer on a community-wide scale in Brattleboro, Vermont. Before they can use the collected human waste in gardens, however, they have to put the liquid through a strenuous treatment process. 

“There’s things in urine that we probably don’t want to be applying directly to plants and to the soil. Urine can contain pathogens and it can contain pharmaceuticals, so we’re looking at how to remove those and turn it into a safe and practical fertilizer,” Wigginton says. 

Wigginton and her fellow researchers focus on two main things when they treat urine: condensing their product, and ridding it of harmful pharmaceuticals and organisms. 

“It’s not very practical to truck large volumes of urine around, so it’s better to concentrate the nutrients down to smaller volumes or even as precipitates. So concentrating it, that makes it cheaper and easier to move around,” Wigginton says, adding, “And then the other thing is we need to get rid of the pharmaceuticals and organisms that are in it. … There’s lots of different ways you can treat it. But it’s all about concentrating and getting rid of some of the constituents.”

The Rich Earth Institute has been collaborating with the EPA, the Water Environment Research Foundation, University of Buffalo, Hampton Road Sanitation district in Virginia and others on the “Peecycling” project. They hope their research will help the EPA come up with guidelines and policies on what should be done with urine before it’s applied to plants and soils. 

Wigginton and her colleagues have made progress in turning urine into a safe fertilizer. The results of their work are currently being used to fertilize experimental crops of carrots and lettuce. The biggest obstacle they face, however, is coming up with ideas on how to change the infrastructure in the US to accommodate new ways of treating and reusing human waste. 

“The number one thing that’s holding it up right now is infrastructure. I mean we have a great sanitation system in the United States. But there’s definitely some inefficiencies,” Wigginton says. 

Still, she thinks the project will gain ground quickly. 

“I definitely expect in the next 10-20 years people are going to hear more about this,” Wigginton says, adding, “And we’re already seeing some buildings. Our partners at HRSD in Virginia, they’ve taken their headquarters and put in source-separating toilets and they’re collecting [urine] in a tank outside for their research.”

Wigginton has been turning her work into recommendations for the EPA, but she stops short of advising people to use urine they’ve collected themselves in their own gardens. 

“I don’t think I’m in a position to tell people what to do at the household level. but it’s being done and there are lots of websites out there where people can get help on what they should do before they apply it to their yards,” she says. 

This article is based on an interview that aired on PRI's Science Friday with Ira Flatow.