Circular Economy

Urine Luck! Common Waste Streams Become Circular Gamechangers

In a circular economy, human urine can generate fertilizer, energy and wastewater-treatment solutions; shellfish waste becomes powerful carbon-capture tool.

Published 3 months ago | About a 7 minute read

Image: W. Zhong

From piddle to powerful: Human urine now a versatile circular resource

Don’t pee on seat
sign Image credit: Jaxn Blvd

Innovators have long been turning poop – both human and animal – into a plethora of waste-saving solutions – from biogas and fabric to beer ingredient. Now, Stanford researchers have developed a system upcycles human urine into a powerful tool for profitable and sustainable energy and agriculture in resource-limited regions.

The prototype — detailed in a study published this month in Nature Water — recovers a valuable chemical found in urine for use in organic fertilizer, using solar energy that can also provide power for other uses. In the process, the system provides essential sanitation — making wastewater safer to discharge or reuse for irrigation.

“This project is about turning a waste problem into a resource opportunity,” said study senior author William Tarpeh, an assistant professor of chemical engineering in the Stanford School of Engineering. “With this system, we’re capturing nutrients that would otherwise be flushed away or cause environmental damage and turning them into something valuable — fertilizer for crops — and doing it without needing access to a power grid.”

Nitrogen, a key component of commercial fertilizers, is typically produced using a carbon-intensive process and distributed globally from industrial facilities in wealthier nations — resulting in higher prices in low- and middle-income countries. Globally, the nitrogen in human urine could supply roughly 14 percent of annual fertilizer demand.

The prototype separates ammonia — a compound made up of nitrogen and hydrogen — from urine through a series of chambers separated by membranes, using solar-generated electricity to drive ions across and eventually trap ammonia as ammonium sulfate, a common fertilizer. Warming the system — using waste heat collected from the back of photovoltaic solar panels via an attached copper tube cold plate — helps speed up the process by encouraging ammonia gas production, the final step in the separation process. Solar panels also produce more electricity at lower temperatures, so collecting waste heat helps keep them cool and efficient.

“Each person produces enough nitrogen in their urine to fertilize a garden, but much of the world is reliant on expensive imported fertilizers instead,” said Orisa Coombs, the study’s lead author and a PhD student in mechanical engineering. “You don’t need a giant chemical plant or even a wall socket. With enough sunshine, you can produce fertilizer right where it’s needed — and potentially even store or sell excess electricity.”

The study shows that integrating waste heat from the solar panels to warm the liquid for the electrochemical process and managing the current supplied to the electrochemical system increased power generation by nearly 60 percent and improved ammonia recovery efficiency by more than 20 percent, compared to earlier prototypes that didn’t integrate these functions. The use of this waste heat is another benefit of the system: Roughly 80 percent of the sun’s energy that hits solar panels is lost, which can cause system overheating and efficiency slowdowns.

The researchers also developed a detailed model to predict how changes in sunlight, temperature and electrical configuration affect the system’s performance and economics. The model showed that in regions such as Uganda, where fertilizer is expensive and energy infrastructure is limited, the system could generate up to $4.13 per kilogram of nitrogen recovered — more than double the potential earnings in the US.

Coombs said she is working on a prototype that will have triple the reactor capacity, be capable of processing significantly more urine and process faster when more sunlight is available.

The researchers’ work to convert urine into fertilizer was supported by the Stanford Sustainability Accelerator in its first round of grants in 2022. The team built a lab-scale, electricity-driven reactor that could operate for up to 40 days — which inspired and enabled work on pairing electrochemical water treatment with solar panels; so, in addition to harvesting two valuable, previously wasted resources, the system could also help improve sanitation in less-developed regions.

According to the UN, more than 80 percent of wastewater goes untreated — much of it in low- and middle-income countries. Nitrogen in wastewater can contaminate groundwater and drinking water sources, and cause oxygen-depleting algal blooms that kill aquatic plants and animals. By removing nitrogen from urine, the prototype system makes the remaining liquid safer to discharge or reuse for irrigation. The ability to do this with a self-powered system could be a game changer in many countries where only a small percentage of the population is connected to centralized sewage systems.

The researchers see the win-win-win approach scaling to help farmers and communities around the world — recovering critical, costly resources while reducing water pollution.

“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,” Coombs said. “It’s clean, it’s scalable and it’s literally powered by the sun.”

Shrimp waste becomes versatile carbon-capture solution

shrimp
shells Image credit: W. Carter

Meanwhile, researchers at the UAE’s University of Sharjah have developed a method to transform shrimp waste — typically discarded by the ton by the seafood industry — into a valuable, carbon-sequestering product.

Processed shrimp, lobster and crab shells generate up to eight million tons of organic waste annually – which produces climate-changing methane when left to degrade in landfill. Innovators around the world have repurposed this waste into everything from plastic and foam packaging to solar cells; now, the Sharjah team — led by Dr. Haif Al-Jomard — has developed a process that utilizes shrimp shells, heads and intestinal tracts to produce activated carbon.

This material demonstrates excellent CO₂ adsorption capabilities — positioning it as a promising candidate for industrial carbon-capture applications for heavy-emitting industries including power generation, cement, steel manufacturing and petrochemicals.

“Our study turns shrimp waste into a high-performance carbon product. This not only addresses the environmental challenges posed by seafood waste but also contributes to global efforts to reduce greenhouse gas emissions and climate change mitigation,” Al-Jomard said.

Published in the journal, Nanoscale, the research outlines a process involving pyrolysis of shrimp waste to produce biochar — followed by acid treatment, chemical activation and ball milling. The resulting activated carbon exhibits strong CO₂ capture performance and long-term stability across multiple adsorption–desorption cycles.

“Our findings validate a scalable and sustainable strategy for shrimp waste valorization,” they write. “The combined thermal, chemical and mechanical treatments of shrimp waste enhance both the textural and chemical properties of the final activated carbon material — making it a viable solution for climate change mitigation.”

The study utilized white shrimp waste sourced from Souq Al Jubail in Sharjah, with the shrimp originally harvested in Oman.

“This approach offers a cost-effective route to producing activated carbon — turning a problematic waste stream into high-performance, efficient and environmentally friendly product with wide-ranging applications,” said Professor Chaouki Ghenai, co-author and expert in Sustainable and Renewable Energy at the University of Sharjah.

In addition to carbon capture, the research team says activated carbon derived from shrimp waste could also be utilized in air and water purification, solvent recovery, gold extraction and even medical applications.