New System Captures Fertilizer from Urine with Solar Energy

A Stanford-led study published in Nature Water explains a newly developed system to capture ammonia from urine efficiently, using solar energy. The prototype separates ammonia 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. “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.”