What if the key to feeding the world didn’t come from a factory, but from a wastewater treatment plant?
In a groundbreaking leap for sustainable agriculture, two leading Chinese research teams have turned one of the most overlooked waste streams, sewage sludge , into a powerful new resource for farming. Not just fertilizer, but precision-engineered fertilizer.
Published on September 17, 2025 , in the open-access journal Carbon Research , this innovative study reveals how modified hydrochar , a carbon-rich material made from treated sewage sludge, can be fine-tuned to deliver phosphorus (P) to crops in a smarter, more sustainable way. And the secret lies in a simple choice: calcium or magnesium .
Led by Dr. Wei Guo from the National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology at Beijing University of Technology and Dr. Xiaohui Liu from the Key Laboratory of Marine Environment and Ecology at Ocean University of China , this research bridges environmental engineering, soil science, and microbiology to tackle one of agriculture’s biggest challenges: phosphorus scarcity.
The Phosphorus Problem—And a Waste-Based Solution
Phosphorus is essential for plant growth. But global reserves of phosphate rock, the source of most commercial fertilizers—are dwindling, and excessive use leads to pollution and eutrophication. Meanwhile, sewage sludge, rich in organic matter and nutrients like phosphorus, is often discarded or incinerated.
This study flips the script: instead of waste, it’s raw material .
By treating sewage sludge at 260°C for 2 hours in water (a process called hydrothermal carbonization), the team created hydrochar —a stable, soil-enhancing material. But they didn’t stop there. They boosted its performance by adding calcium (Ca) or magnesium (Mg) salts, CaO, CaCl₂, MgO, and MgCl₂, before processing.
The result? Two distinct types of hydrochar, each with a unique phosphorus personality.
Calcium vs. Magnesium: The Great Phosphorus Divide
“This isn’t just recycling, it’s reprogramming,” says Dr. Wei Guo of Beijing University of Technology . “We’re not just returning phosphorus to the soil. We’re controlling how and when it becomes available.”
Plants, Microbes, and Real-World Results
To test their hydrochars, the team grew mung beans (Vigna radiata) in pot experiments and used the advanced DGT (Diffusive Gradients in Thin-films) technique to measure bioavailable phosphorus in real time.
The findings were clear:
“It’s a beautiful synergy,” explains Dr. Xiaohui Liu from Ocean University of China . “The hydrochar doesn’t just feed the plant, it feeds the soil microbiome, which in turn feeds the plant. We’re seeing a whole ecosystem response.”
A Smart Strategy for Sustainable Farming
This study doesn’t just offer a new fertilizer, it offers a strategy :
It’s a dual-path approach to phosphorus management, born from waste, guided by science, and ready for real-world impact.
Beijing University of Technology and Ocean University of China: Leading the Green Revolution
At the heart of this innovation are two of China’s top environmental research institutions.
Together, their collaboration shows how interdisciplinary science can turn pollution into productivity.
The Future of Fertilizer is Circular—and Smart
So next time you flush, think beyond waste. Think resource . Think phosphorus cycling . Think soil health .
Thanks to visionary scientists like Dr. Wei Guo and Dr. Xiaohui Liu , and their teams at Beijing University of Technology and Ocean University of China , we’re not just closing the loop on waste, we’re opening a new chapter in sustainable agriculture.
One hydrochar pellet at a time, we’re building a world where nothing is wasted, and everything has purpose.
Stay tuned for more breakthroughs from these dynamic research groups, where sewage becomes soil gold, and science grows a greener future.
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About Carbon Research
The journal Carbon Research is an international multidisciplinary platform for communicating advances in fundamental and applied research on natural and engineered carbonaceous materials that are associated with ecological and environmental functions, energy generation, and global change. It is a fully Open Access (OA) journal and the Article Publishing Charges (APC) are waived until Dec 31, 2025. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon functions around the world to deliver findings from this rapidly expanding field of science. The journal is currently indexed by Scopus and Ei Compendex, and as of June 2025, the dynamic CiteScore value is 15.4.
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Carbon Research
Experimental study
Not applicable
Soil–plant-microbial evidence for the available phosphorus generation and utilization of Ca/Mg salts conditioned hydrochar from sewage sludge
17-Sep-2025