A Stanford-led research team has developed a system that converts human urine into fertilizer using solar power. The prototype offers a sustainable solution for sanitation, agriculture, and energy generation in regions with limited resources.
The system separates ammonia from urine through electrochemical chambers powered by solar energy. That ammonia is then captured as ammonium sulfate, a common fertilizer.
By integrating waste heat from solar panels, the process speeds up and increases efficiency. The approach also cools solar panels, improving their performance.
William Tarpeh, senior author of the study and assistant professor of chemical engineering at Stanford, said the project focuses on turning waste into opportunity.
He explained that the system captures nutrients that would otherwise be lost or cause environmental harm and converts them into fertilizer for crops. Importantly, it does this without requiring a power grid.
Nitrogen, a key ingredient in fertilizers, is typically produced in carbon-intensive facilities. Many of these are located in wealthier countries, driving up costs elsewhere.
Human urine contains enough nitrogen to meet about 14% of global fertilizer demand.
Boosting efficiency with waste heat
The Stanford team’s prototype shows major improvements over earlier designs.
By using copper tubing behind solar panels to capture waste heat, researchers boosted power generation by nearly 60% and improved ammonia recovery by more than 20%.
The innovation also prevents overheating, which reduces solar panel efficiency.
Orisa Coombs, the study’s lead author and a Ph.D. student in mechanical engineering, noted that each person produces enough nitrogen in their urine to fertilize a garden. She added that the system makes it possible to create fertilizer directly where it is needed, using only sunshine.
The process could even allow communities to store or sell excess electricity, eliminating reliance on large chemical plants or grid connections.
The researchers developed a model to predict how sunlight, temperature, and electrical settings affect performance.
In regions such as Uganda, where fertilizer is costly and electricity is scarce, the system could generate up to $4.13 per kilogram of nitrogen recovered. That is more than double the potential earnings in the U.S.
Addressing sanitation challenges
The technology offers more than agricultural and energy benefits. By removing nitrogen from urine, the system makes wastewater safer to discharge or reuse for irrigation.
More than 80% of global wastewater goes untreated, much of it in low- and middle-income countries. Untreated nitrogen often contaminates groundwater and causes algal blooms that damage ecosystems.
Coombs said the innovation solves several challenges at once. “We often think of water, food, and energy as completely separate systems, but this is one of those rare cases where engineering innovation can help solve multiple problems at once,” she said. “It’s clean, it’s scalable, and it’s literally powered by the sun.”
The research team is already working on a larger prototype with triple the reactor capacity.
The upgraded system will process more urine and run faster in strong sunlight. Lessons from this project could also apply to industrial sites, such as wastewater treatment plants, that could capture waste heat for other uses.
The study is published in the journal Nature Water.
Aamir Khollam Aamir is a seasoned tech journalist with experience at Exhibit Magazine, Republic World, and PR Newswire. With a deep love for all things tech and science, he has spent years decoding the latest innovations and exploring how they shape industries, lifestyles, and the future of humanity.