A silver lining in sewer sludge: Volatile fatty acids
By Leah Shaffer
Many sewage treatment plants are equipped to process waste using anaerobic digestion, in which the sewage sludge is held in an oxygen-free chamber to ferment and break down. As part of that degradation, biogas such as methane can be reclaimed from that sludge. But the process can be expensive because it requires electric generators to convert the biogas to a more useful form such as electricity, and such conversion may not be economically viable when biogas production is at a small scale.
Jason He, the Laura and William Jens Professor of Energy, Environmental and Chemical Engineering at Washington University in St. Louis, wanted to find more efficient ways to get riches out of the rubbish.
“Can we recover something potentially of higher value than biogas?” he asked.
He and his team looked at short-chain volatile fatty acids (VFA), a common intermediate compound for many materials, including bioplastics.
VFAs can also serve as the feedstock to clean the sewage at lower cost. Treatment facilities could use VFAs from their own sewage to serve as a carbon source for the nitrogen converters and for biological phosphorus removers, He said.
Along with reducing the expense of sewage cleanup, VFAs can be reclaimed in liquid form and potentially sold for use in manufacturing and agricultural processes to further recoup sewage treatment costs.
In work published in Water Research, the McKelcey School of Engineering team shows how using hydrogen peroxide on the sewage will inhibit methanogenesis and send sewage down the path of VFA production instead.
Hydrogen peroxide is a low-cost addition that leads to more than 30 times the VFA production in sludge compared to controls. Even further efficiencies emerged when Jiasi Sun, He’s PhD student and the paper’s first author, noticed how light exposure further improved the efficiency of the process.
Sun saw that two identical reactors were producing different results. She thought at first it was a measurement error, but then realized the one reactor was closer to a light source.
“I realized that light was accelerating the breakdown of hydrogen peroxide into reactive species. That small observation completely changed how I understood the process of reclaiming VFAs,” she said.
The bit of scientific serendipity is sending the team down a new research rabbit hole: bringing light back to the dark fermentation tanks.
“With light, the hydrogen peroxide dosage can be greatly reduced,” He added.
For now, they are exploring the addition of LED lights to the reactors and tinkering with reactor design to push the efficiencies even farther.
“It’s all coming from these unexpected results,” He said.
Sun J, He Z. Light stimulated H2O2 inhibition on methanogenesis during anaerobic digestion towards enhanced VFAs production. Water Research, Volume 286. https://doi.org/10.1016/j.watres.2025.124229
This work was financially supported by the U.S. National Science Foundation (award # 2150613).
Originally published on the McKelvey Engineering website
Journal
Water Research
Steel sludge transformed into powerful water cleaner for antibiotic pollution
image:
Peroxydisulfate activation by one-step pyrolysis iron-rich sludge biochar for tetracycline removal in water: performance, mechanism and degradation pathway
view moreCredit: Xunli Bao, Lu Zhou, Bei Liu, Guanhao Zhang, Yi Fang & Yulin Zeng
Researchers have developed an innovative way to turn steel industry waste into a low-cost material that can clean antibiotics out of water, offering a promising solution to one of today’s growing environmental challenges.
Steel mills generate large volumes of iron-rich sludge during wastewater treatment. Traditionally, this sludge has been disposed of through landfilling or incineration, raising concerns about waste management and heavy metal contamination. Now, a team led by scientists from Changsha University of Science and Technology has found a way to convert this industrial byproduct into a valuable resource: a special form of biochar that can break down tetracycline, one of the world’s most widely used antibiotics.
Tetracycline is frequently detected in rivers, groundwater, and even drinking water sources due to its heavy use in medicine, livestock, and aquaculture. Persistent antibiotic residues in the environment not only harm aquatic life but also contribute to the spread of antibiotic resistance – a pressing public health concern worldwide.
In the new study, the researchers produced iron-rich biochar by heating steel sludge in an oxygen-limited environment, a simple “one-step pyrolysis” process. When combined with peroxydisulfate – a powerful but stable oxidant – this biochar acted as a catalyst, triggering chemical reactions that generated reactive oxygen species capable of degrading tetracycline.
The team found that biochar produced at 450 °C (called FSB450) was especially effective. Under optimal conditions, it removed more than 85% of tetracycline from water in just two hours. The breakdown occurred through both radical and non-radical chemical pathways, ultimately reducing the antibiotic to smaller, less toxic molecules. Importantly, toxicity tests suggested that the treated water posed lower risks to aquatic organisms such as fish, algae, and daphnia.
Beyond its effectiveness, the iron-rich biochar showed strong magnetic properties, allowing it to be quickly separated from water with a magnet and reused multiple times with only minor performance loss. This feature makes the approach both practical and environmentally safe.
“Our study shows that steel sludge, once considered an industrial waste problem, can be transformed into a powerful tool for water purification,” said lead author Dr. Xunli Bao. “This not only helps tackle antibiotic pollution but also provides a sustainable way to recycle industrial byproducts.”
The research highlights a dual benefit: turning waste into a valuable resource while addressing the urgent need for cost-effective technologies to clean up contaminated water. With further development, this approach could be scaled up for real-world wastewater treatment applications.
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Journal Reference: Bao, X., Zhou, L., Liu, B. et al. Peroxydisulfate activation by one-step pyrolysis iron-rich sludge biochar for tetracycline removal in water: performance, mechanism and degradation pathway. Biochar 7, 87 (2025). https://doi.org/10.1007/s42773-025-00471-1
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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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Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Peroxydisulfate activation by one-step pyrolysis iron-rich sludge biochar for tetracycline removal in water: performance, mechanism and degradation pathway
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