Estimated read time: 3.5 minutes

Nitrogen-based chemical fertilizer, the bedrock of industrial agriculture, feeds the world, but hurts the planet. This fertilizer is made using planet-warming fossil fuels, and its runoff pollutes waterways across the world causing algae blooms, harming fish and aquatic life. But it doesn’t have to be like this: scientists and farmers have slowly begun to tap into a far more climate-friendly source of fertilizer — human urine. And for subsistence farmers, this freely available liquid is a welcome way to grow more food. 

Human urine is flush with nutrients— nitrogen, phosphorus and potassium—the “NPK” of plant fertilizers. Early research into urine fertilizer found it performed on par with conventional fertilizers and could replace those made using fossil fuels. But switching from polluting synthetic fertilizers to pee wholesale is not always easy. Both social and technological barriers have slowed the uptake of urine fertilizers. It’s hard to switch, but researchers around the globe tackle these challenges and give hope for this liquid gold to create a more sustainable food system. 

In rural Niger, where fertilizer is expensive and soils are depleted of nutrients, female subsistence farmers are often left with infertile land to grow pearl millet to feed their families. An essentially free fertilizer, urine, could make a big difference for these farmers. At first, social barriers kept farmers from tapping into this resource. It took a rebranding urine to overcome the stigma. Now, it’s called oga, which roughy translates to “boss” in the local Igbo language.

“Oga is urine that you collect, store, transport it and apply it to the crop, that it's become fertilizer,” said Ali Maman Aminou. “Urine is what you left in the toilet.” Aminou is an agronomist and director of a farmer’s union federation called Fuma Gaskiya, in Maradi, Niger, which supports farmer-led research into ecological and affordable farming practices in the region.

In addition to the rebrand, Aminou’s group spoke with local religious leaders and medical professionals to ensure urine reuse was acceptable to both. It was. Now, use of urine fertilizer is spreading and around five thousand farmers use it in the region. A trial from 2021, showed that urine boosted crop production by 30 percent. 

Farmers collect urine from homes in small plastic containers, which are then poured into larger plastic jugs for storage. Some farmers even give a piece of candy to kids in exchange for their pee. After sitting for two months, farmers carry the jug to the fields, dilute the urine with water and apply it to the crops.  

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From pee to products

Tapping into urine fertilizer looks very different across the world in the city of Portland, Oregon. Dense urban living with no nearby farmland poses new challenges, mainly how to separate, collect, and transport urine to where it’s needed. One company, Nutrient Recovery Systems, has a solution: extract the nutrients out of urine and leave behind the 95 percent that is just water.

Their inaugural system is in a five-story building in Portland, Oregon. It’s the home of PAE, an ecological engineering firm. Called the PAE Living Building, it was designed to keep urine separate from wastewater through urinals and composting toilets. Urinals and leachate from the toilet drain to a 1500 gallon tank before processing. The system then extracts both nitrogen and phosphorus from the liquid and generates commercial fertilizer products.

After a bumpy start, with the COVID 19 pandemic preventing the new building from being occupied, now, “it’s going really well,” said Pat Lando, the co-founder of Nutrient Recovery Service. That’s good news since this is the first building in the world to create such carbon-neutral fertilizers from human waste.

The system concentrates nutrients through distillation. In this process, heat evaporates nitrogen compounds in urine and separates them from the rest of the liquid. Phosphorus is left behind in a slurry, which is dried in an oven and turned into a white powder called struvite — a slow-release, phosphorus-rich fertilizer. These products are packaged and sold in retail garden stores for people to use in their home gardens. 

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Community-scale pee collection

Of course, most buildings are not designed with this sort of nutrient recovery in mind. That’s why separating urine from the rest of the wastewater stream is a challenge. A nonprofit called the Rich Earth Institute in Brattleboro, Vermont, addresses this issue through education and community engagement. 

The Urine Nutrient Reclamation Project, started in 2011, is the first and only community-scale pilot project in the United States, collecting urine for use on local farms. Some community members bring jugs of urine to a drop off site, others have large tanks installed in their homes to store urine, which is later pumped out. The liquid is sanitized then trucked to fertilize nearby farms. Each year they collect around 10,000 gallons of urine. 

To expand urine recycling, the Rich Earth Institute also works to overcome another barrier: Regulations. 

Right now, most plumbing codes are not designed to allow these nutrient recovery systems. But with code updates, it will be easier to get the necessary permits. Last spring, Mathew Lippincott, a collaborator with Rich Earth, led efforts to include a urine-diverting provision into the International Plumbing Code. The approval process is ongoing, but the proposal was favorably received, says Lippincott. If approved, urine diverting toilets will be included in the next version of the plumbing code.  

Another perk to separating urine is the water savings. The Rich Earth Institute estimates their urine collection programs have saved over two million gallons of water by avoided flushing. 

Back in Niger, when farmers first learned of urine reuse, they set up a trial and the plants spoke for themselves.  The urine-free control plot ended with patches of sandy tan soil between scraggly plants. And the urine-fertilized plot was covered with bright green pearl millet shoots, taller than the farmers, reaching for the sun.

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Laura Allen is a writer and educator based in Oregon. She co-founded Greywater Action, where she teaches people how to transform their homes to reuse water. She authored the books, The Water Wise Home: How to Conserve, Capture and Reuse Water in Your Home and Landscape, and Greywater, Green Landscape. Her article, For a better brick, just add poop, won the Gold Award in Children’s Science News from the AAAS Kavli Science Journalism Awards (2023). Her favorite pastimes include gardening, hiking, reading and visiting eco-toilets.