Solar-powered solution: turning wastewater into fertilizer

In a groundbreaking development, researchers at the University of New South Wales (UNSW), Sydney, Australia, have created an ‘artificial leaf’ that uses sunlight to convert nitrate wastewater into ammonium nitrate. This innovative approach has the potential to revolutionize fertilizer production by eliminating greenhouse gas emissions typically associated with the process.

Ammonia is essential for producing fertilizers, but traditional methods require high temperatures, high pressure, and hydrogen derived from fossil fuels. This conventional process contributes to about 5% of global greenhouse gas emissions. However, the new technology developed by UNSW engineers offers a greener alternative.

Led by Scientia Professor Rose Amal and Professor Xiaojing Hao, the research team has transformed a standard silicon solar panel into a device that mimics the natural process of photosynthesis. Just as leaves use sunlight to create energy, this artificial leaf uses sunlight to convert nitrate wastewater into ammonium nitrate. The key to this process is a nano-structured thin layer of copper and cobalt hydroxide on the panel, which acts as a catalyst.

The team demonstrated the effectiveness of this process, known as photoelectrocatalytics (PEC), with a 40 cm² artificial leaf system installed on the roof of UNSW’s Tyree Energy Technologies building. This system produced enough ammonium ions to fertilize approximately 1.49 m² of agricultural land. The researchers are now focused on scaling up the system to produce larger quantities of ammonia, providing a sustainable and decentralized solution for agricultural fertilization.

“We’re combining the expertise from UNSW’s School of Photovoltaics & Renewable Energy Engineering with our knowledge in chemical engineering to transform nitrate waste into valuable ammonia,” said Chen Han, the lead author of the study. “Our findings offer a clean, efficient, and cost-effective way to harness solar energy and repurpose chemical wastes to produce ammonia and other valuable products.”

This technology promises to reduce CO2 emissions not only from the ammonia production process but also from the transportation of fertilizers. By enabling onsite production of ammonia in agricultural areas, the system can decentralize the production process and minimize environmental impact.

The researchers are hopeful that once the nitrate wastewater is converted into ammonium nitrate, the processed water can be used for irrigation, promoting a circular economy. However, the wastewater must first be treated to remove organic matter and particulates before it can be utilized in the system.

Professor Amal highlighted the importance of collaborating with industry partners to scale up the device and develop a commercially viable system. “Achieving our emissions targets for 2030 and 2040, and ultimately reaching Net Zero by 2050, depends on innovations like this,” she said.