Biochar-powered hydrogels boost solar water evaporation efficiency for sustainable desalination
Biochar Editorial Office, Shenyang Agricultural University
image:
Heat loss and water transport capacity regulation in hybrid evaporators
view moreCredit: Sihui Wang, Jiaqi Yang, Aijie Wang & Wenzong Liu
A new study reveals how combining biochar with advanced hydrogels can dramatically improve solar-driven water evaporation, offering a promising pathway for low-energy desalination and water purification technologies.
Freshwater scarcity is a growing global challenge, with most of Earth’s water locked in oceans or saline sources. Traditional desalination methods often require high energy input and infrastructure costs. Solar interfacial evaporation, which uses sunlight to convert water into vapor at the surface, has emerged as a cleaner and more energy-efficient alternative. However, improving its efficiency remains a key scientific challenge.
In a recent study published in Biochar, researchers developed a hybrid material that integrates biochar into a polyzwitterionic hydrogel, achieving a remarkable evaporation rate of 3.57 kilograms per square meter per hour under standard sunlight conditions. This performance is significantly higher than that of conventional hydrogels and highlights the potential of biochar-based materials in sustainable water treatment.
“By introducing biochar into the hydrogel network, we were able to simultaneously enhance light absorption, water transport, and energy efficiency,” said the study’s corresponding author. “This multi-functional synergy is key to achieving high-performance solar evaporation.”
The innovation lies in how biochar interacts with the hydrogel at both physical and molecular levels. Biochar, a carbon-rich material derived from biomass such as agricultural waste, is known for its porous structure and strong light-absorbing properties. When incorporated into the hydrogel, it transforms the material from transparent to dark, enabling it to capture more sunlight across a wide spectrum. According to experimental results, the hybrid hydrogel maintained over 95 percent light absorption across a broad wavelength range.
At the same time, the addition of biochar alters the internal structure of the hydrogel. Microscopic observations, shown in figures on page 4 of the paper, reveal a denser and more interconnected pore network. This structure improves the movement of water within the material, ensuring a continuous supply of water to the evaporation surface while minimizing heat loss to the bulk liquid.
Beyond photothermal effects, the study also uncovers a less explored mechanism involving water molecule behavior. The surface functional groups of biochar interact with the hydrogen bonding network inside the hydrogel, increasing the proportion of so-called intermediate water. This form of water requires less energy to evaporate compared to tightly bound water. As a result, the hybrid material significantly reduces the energy needed for evaporation, lowering the equivalent evaporation enthalpy to 877.79 joules per gram.
This dual enhancement, combining photothermal efficiency with molecular-level water activation, enables the hybrid hydrogel to outperform many existing materials. The system also demonstrates strong water transport capabilities even in saline conditions, making it particularly suitable for seawater desalination applications.
The researchers emphasize that biochar is not only effective but also sustainable and cost-efficient, as it can be produced from agricultural residues such as sorghum straw. This adds an important environmental advantage, aligning the technology with circular economy principles.
“Our findings provide new insights into how material design can address multiple bottlenecks in solar evaporation systems,” the authors noted. “This could guide the development of next-generation evaporators for clean water production in resource-limited settings.”
As global demand for freshwater continues to rise, innovations like biochar-enhanced hydrogels could play a critical role in delivering scalable, low-carbon water treatment solutions.
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Journal Reference: Wang, S., Yang, J., Wang, A. et al. Heat loss and water transport capacity regulation in hybrid evaporators. Biochar 8, 97 (2026).
https://doi.org/10.1007/s42773-026-00604-0
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About Biochar
Biochar (e-ISSN: 2524-7867) 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
Article Title
Heat loss and water transport capacity regulation in hybrid evaporators
Article Publication Date
27-Apr-2026
Turning “wastewater” into a resource: New insights on liquid fertilizer from hydrothermal carbonization
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Process water from hydrothermal carbonization: from waste to liquid fertilizer and soil health amendment in circular bioeconomy
view moreCredit: Qingnan Chu, Xiangyu Liu, Yanfang Feng, Detian Li, Shuai Yin, Chengrong Chen & Zhimin Sha
A growing body of research is redefining how scientists view a once-overlooked byproduct of biomass processing. A new review published in Biochar reveals that process water generated during hydrothermal carbonization, long treated as waste, could play a key role in sustainable agriculture and the circular bioeconomy.
Hydrothermal carbonization is an emerging technology that converts wet organic materials such as food waste, sewage sludge, and agricultural residues into a carbon-rich solid known as hydrochar. While much attention has focused on this solid product, the accompanying liquid fraction, called process water, has remained largely underutilized. According to the authors, this liquid can account for up to 70 percent of the original material and contains substantial amounts of nutrients and organic compounds.
“This process water is not just a byproduct. It is a nutrient-rich resource with significant potential for agriculture,” said the study’s corresponding author. “Our work highlights how it can be transformed from a disposal challenge into a valuable input for crop production and environmental management.”
The review synthesizes findings from recent studies on the composition and applications of this liquid. It shows that process water contains high levels of nitrogen, phosphorus, potassium, and organic carbon. These components are essential for plant growth and can support its use as a liquid fertilizer or soil amendment. In some cases, applying diluted process water has increased crop yields by up to nearly 30 percent and improved nutrient use efficiency by 15 to 30 percent in crops such as rice.
Beyond direct fertilization, the liquid can also be integrated into broader resource recovery systems. For example, nutrients can be extracted through processes such as struvite precipitation, which recovers phosphorus and nitrogen for reuse. The organic content can also be converted into energy through anaerobic digestion, producing methane-rich biogas. These approaches align with circular economy principles by reducing waste and maximizing resource efficiency.
However, the study also emphasizes that careful management is required before agricultural use. Process water can contain compounds such as organic acids, phenols, and salts that may inhibit plant growth if applied without treatment. Strategies such as dilution, co-application with other organic inputs, or pre-treatment methods like neutralization and filtration can significantly reduce these risks.
The authors note that operational conditions during hydrothermal carbonization strongly influence the quality of the process water. Factors such as temperature, reaction time, and feedstock type can be adjusted to tailor nutrient content and reduce harmful components. This opens the door to designing customized liquid fertilizers suited for specific crops and farming systems.
Importantly, the review highlights broader environmental benefits. Using process water as a fertilizer substitute can reduce reliance on synthetic fertilizers and lower greenhouse gas emissions. Life cycle assessments suggest that such substitution may cut global warming impacts by up to 50 percent under certain scenarios.
Despite these promising findings, the authors call for more long-term field studies and large-scale demonstrations. Questions remain about variability across feedstocks, long-term soil impacts, and regulatory frameworks for safe application.
Overall, the research signals a shift in perspective. What was once considered wastewater is now being reimagined as a multifunctional resource that supports sustainable agriculture, renewable energy, and waste reduction.
“This is a step toward closing nutrient loops and building more resilient agricultural systems,” the authors conclude.
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Journal Reference: Chu, Q., Liu, X., Feng, Y. et al. Process water from hydrothermal carbonization: from waste to liquid fertilizer and soil health amendment in circular bioeconomy. Biochar 8, 96 (2026).
https://doi.org/10.1007/s42773-026-00614-y
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About Biochar
Biochar (e-ISSN: 2524-7867) 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.
Follow us on Facebook, X, and Bluesky.
Journal
Biochar
Method of Research
Literature review
Article Title
Process water from hydrothermal carbonization: from waste to liquid fertilizer and soil health amendment in circular bioeconomy
Article Publication Date
27-Apr-2026
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