From sewage to super soil: Dual
breakthrough in phosphorus recycling
unveiled by Chinese research teams
Innovative hydrochar technology led by Dr. Wei Guo at Beijing University of Technology and Dr. Xiaohui Liu at Ocean University of China transforms sewage sludge into smart phosphorus fertilizers—tailored for long-term soil health or rapid crop growth
image:
Soil–plant-microbial evidence for the available phosphorus generation and utilization of Ca/Mg salts conditioned hydrochar from sewage sludge
view moreCredit: Qian Zhao, Wei Guo, Yuhan Zhu, Dongyue Li, Xiaohui Liu, Minda Yu, Dongyang Li, Xiang Gao, Xishi Tai & Jun Li
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
- Calcium-based hydrochars formed slow-release phosphorus compounds like hydroxyapatite and chlorapatite—rock-stable minerals that lock in P for the long haul. These compounds increased by 48.6% to 86.3% compared to untreated sludge, making Ca-hydrochars a long-term reservoir of phosphorus, perfect for building soil fertility over years.
- Magnesium-based hydrochars, especially those with MgO, produced easily soluble phosphorus forms like Mg₃(PO₄)₂. Though their total P increase was lower (0–50.7%), they released nutrients rapidly—ideal for giving crops a quick boost.
“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:
- Mg-modified hydrochars, especially MgO, led to faster plant growth, higher chlorophyll levels, and better photosynthesis. Mung beans grown with Mg-hydrochar absorbed more phosphorus—proof that the nutrients were not just present, but usable.
- Ca-modified hydrochars didn’t push rapid growth, but they transformed the soil microbiome. They enriched bacteria like Skermanella and RB41, known for breaking down organic matter and cycling minerals—helping unlock phosphorus over time.
- In contrast, Mg-hydrochars boosted P-solubilizing powerhouses like Pseudomonas and Bacillus, which actively dissolve phosphorus into plant-usable forms.
“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:
- Use Ca-based hydrochars for long-term soil restoration, carbon sequestration, and slow nutrient release.
- Use Mg-based hydrochars when crops need a fast start—like in degraded soils or early growth stages.
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.
- The National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology at Beijing University of Technology is pioneering the transformation of urban waste into high-value resources.
- The Key Laboratory of Marine Environment and Ecology at Ocean University of China is expanding the frontier of nutrient cycling and soil-microbe interactions in coastal and agricultural systems.
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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- Title: Soil–plant-microbial evidence for the available phosphorus generation and utilization of Ca/Mg salts conditioned hydrochar from sewage sludge
- Keywords: Sewage sludge; Hydrothermal carbonization; Calcium/magnesium salts; Phosphorus species; Plant growth; Microbial community
- Citation: Zhao, Q., Guo, W., Zhu, Y. et al. Soil–plant-microbial evidence for the available phosphorus generation and utilization of Ca/Mg salts conditioned hydrochar from sewage sludge. Carbon Res. 4, 64 (2025). https://doi.org/10.1007/s44246-025-00228-2
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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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Journal
Carbon Research
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Soil–plant-microbial evidence for the available phosphorus generation and utilization of Ca/Mg salts conditioned hydrochar from sewage sludge
Smart hormone technologies could help sugarcane survive droughts and floods
Biochar Editorial Office, Shenyang Agricultural University
image:
Application of phytohormones exogenously to ameliorate sugarcane's response to water stress
view moreCredit: Varucha Misra, Ashutosh Kumar Mall
As climate extremes become more frequent, sugarcane growers face a double challenge: droughts that parch their crops and floods that drown them. A new review highlights how applying plant hormones from outside the plant, rather than waiting for natural processes—can strengthen sugarcane’s ability to cope with both too little and too much water.
The study, published in Agricultural Ecology and Environment, examines how exogenous phytohormones such as abscisic acid (ABA), gibberellins (GA), and auxins can improve sugarcane’s drought and waterlogging tolerance. These tiny signaling molecules regulate growth, photosynthesis, and stress defenses. When sprayed on leaves or delivered to roots, they can trigger the same internal mechanisms that help plants conserve water, maintain photosynthetic activity, and repair cellular damage.
For instance, external ABA applications have been shown to boost the plant’s antioxidant defenses and osmotic balance, limiting damage from reactive oxygen species that accumulate during drought. GA helps sustain shoot and root growth under stress, while auxins support root development in flooded soils. Together, these treatments could help stabilize yields in regions facing erratic rainfall.
However, traditional application methods, such as uniform field spraying—are often inefficient and poorly timed. The authors point to emerging technologies that can deliver hormones precisely when and where they are needed. Robotic systems equipped with sensors can detect early signs of stress and apply hormones directly to affected plants. Meanwhile, nanotechnology is being developed to encapsulate phytohormones in tiny carriers that release them gradually over time, protecting the compounds from degradation and providing longer-lasting protection during prolonged stress.
These “smart delivery” systems may transform how crops like sugarcane are managed under changing climates. By combining robotics, nanotechnology, and plant biochemistry, scientists hope to create precision tools that use minimal resources while maximizing plant resilience.
“Understanding and manipulating hormone signaling offers one of the most promising ways to protect high-value crops such as sugarcane from water stress,” the authors note. “Integrating advanced delivery systems can make these approaches scalable and sustainable for real-world farming.”
The review calls for more field-based studies to refine hormone dosages, timing, and combinations tailored to different sugarcane varieties and environments. With continued innovation, exogenous phytohormones and smart delivery technologies could help ensure a more reliable sugar supply in the face of global climate uncertainty.
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Journal Reference: Misra V, Mall AK. 2025. Application of phytohormones exogenously to ameliorate sugarcane's response to water stress. Agricultural Ecology and Environment 1: e006 https://www.maxapress.com/article/doi/10.48130/aee-0025-0006
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About Agricultural Ecology and Environment:
Agricultural Ecology and Environment is a multidisciplinary platform for communicating advances in fundamental and applied research on the agroecological environment, focusing on the interactions between agroecosystems and the environment. It is dedicated to advancing the understanding of the complex interactions between agricultural practices and ecological systems. The journal aims to provide a comprehensive and cutting-edge forum for researchers, practitioners, policymakers, and stakeholders from diverse fields such as agronomy, ecology, environmental science, soil science, and sustainable development.
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Method of Research
Literature review
Subject of Research
Not applicable
Article Title
Application of phytohormones exogenously to ameliorate sugarcane's response to water stress
Article Publication Date
23-Oct-2025
Sustainable use of woody biochar boosts soil carbon and crop yields in pepper fields
image:
Sustainable woody biochar application for improving net ecosystem carbon budget, yield and soil properties in red pepper cropping systems: a two-year field study
view moreCredit: Sohee Yoon, Yeomyeong Lee, Hyerin An, Jasmin Melendez & Sang Yoon Kim
Applying woody biochar to farmland could help farmers grow healthier crops while locking more carbon into the soil, according to a new study published in Biochar. Researchers from Suncheon National University found that carefully managed applications of biochar significantly improved soil quality, crop yield, and carbon balance in red pepper fields over two growing seasons.
Biochar is a carbon-rich material made by heating plant matter under low-oxygen conditions. When added to soil, it can store carbon for long periods and enhance soil fertility. However, the ideal amount of biochar for sustaining both crop production and carbon storage has remained unclear.
To address this gap, the team tested different application levels of woody biochar, derived from conifer wood, on red pepper fields in South Korea. They applied 0, 2.5, 5, and 10 metric tons of biochar per hectare each year and measured greenhouse gas emissions, soil properties, and plant growth. They also analyzed how much carbon entered and left the system to calculate the annual net ecosystem carbon budget (NECB), a key measure of carbon sustainability.
The study found that biochar applications improved the NECB, soil structure, and organic carbon content. Fields that received higher levels of biochar produced up to 18 percent more red pepper fruit compared with untreated plots. Soils became less dense, more nutrient-rich, and better able to retain carbon. The researchers determined that optimal biochar application rates ranged from about 7 to 11 metric tons per hectare when crop residues were removed after harvest, and 2 to 7 tons per hectare when residues were returned to the soil.
“Our findings show that woody biochar can make agriculture more sustainable by improving soil health and helping to offset carbon losses,” said lead author Sohee Yoon. “Using the right amount of biochar not only enhances crop productivity but also contributes to climate change mitigation.”
The results provide new guidance for farmers and policymakers seeking to balance productivity with environmental stewardship. By identifying optimal biochar application levels, the study offers a practical pathway to enhance soil resilience, reduce greenhouse gas emissions, and support long-term carbon sequestration in agricultural systems.
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Journal Reference: Yoon, S., Lee, Y., An, H. et al. Sustainable woody biochar application for improving net ecosystem carbon budget, yield and soil properties in red pepper cropping systems: a two-year field study. Biochar 7, 112 (2025). https://doi.org/10.1007/s42773-025-00494-8
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About Biochar
Biochar is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
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Journal
Biochar
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Sustainable woody biochar application for improving net ecosystem carbon budget, yield and soil properties in red pepper cropping systems: a two-year field study
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