What if one of the world’s most overlooked waste products could be turned into a valuable resource?
A team of researchers led by Stanford University has developed a new system that does just that—transforming urine into fertilizer and renewable energy.
Their prototype, recently published in Nature Water, shows how human waste can become a powerful tool for farming, sanitation, and sustainability, especially in parts of the world where resources are limited.
For decades, scientists have known that human urine contains nitrogen, a key ingredient in fertilizers.
In fact, the total amount of nitrogen in urine worldwide equals about 14% of the fertilizer needed each year.
Normally, this nitrogen gets flushed away, where it can pollute rivers, lakes, and groundwater, or cause harmful algal blooms.
At the same time, commercial nitrogen fertilizers are expensive to produce and distribute. The process is energy-intensive, releases carbon pollution, and often concentrates production in wealthier nations, leaving low- and middle-income countries paying higher prices.
The Stanford-led team wanted to find a way to recover this “liquid gold” directly from human waste, in a way that would also improve sanitation.
Their solution was a solar-powered device that separates ammonia from urine and captures it as ammonium sulfate, a common fertilizer. The system works by running urine through chambers divided by membranes, while solar electricity drives the movement of ions that eventually trap the ammonia.
The innovation doesn’t stop there. The researchers also designed the system to capture waste heat from the solar panels.
Usually, about 80% of the sun’s energy that hits a solar panel is lost as heat, which can actually make panels less efficient. By attaching copper tubing behind the panels, the team used this excess heat to warm the liquid inside the urine-processing system.
Heating the liquid encourages the release of ammonia gas, which speeds up the separation process. At the same time, cooling the panels with the heat-transfer system makes them produce more electricity. The result is a clever two-in-one system: more efficient solar panels and a faster way to recover fertilizer.
According to the study, combining these functions increased power generation by nearly 60% and improved ammonia recovery by more than 20% compared to earlier versions of the device.
The researchers also developed a computer model to predict how sunlight, temperature, and electrical settings affect performance. In countries like Uganda, where fertilizer is costly and electricity is scarce, the model showed the system could generate over $4 per kilogram of nitrogen recovered—more than twice the potential value in the United States.
Beyond the economics, the system addresses an urgent sanitation problem. The United Nations estimates that more than 80% of wastewater worldwide goes untreated. In many developing regions, this means nitrogen-rich waste pollutes drinking water supplies and ecosystems. By removing nitrogen at the source, the prototype makes the remaining liquid safer to discharge or reuse for irrigation—an important step in improving health and water security.
Lead researcher Orisa Coombs, a Ph.D. student at Stanford, explained it simply: “Each person produces enough nitrogen in their urine to fertilize a garden. With enough sunshine, you don’t need a giant factory or even a wall socket. You can make fertilizer right where it’s needed, and even produce extra electricity.”
The team is already working on a larger version of the prototype with three times the reactor capacity. They believe the system could be scaled up to serve farms and communities worldwide, turning a universal waste product into a sustainable source of food and energy.
As senior author William Tarpeh put it: “This project is about turning a waste problem into a resource opportunity.”
