Largest UK study uncovers hidden chemical risks in waste-to-energy residues
New research from the University of East London highlights environmental behaviour of little-understood by-products from modern waste treatment plants
Energy-from-waste facilities are often positioned as a cleaner alternative to landfill, transforming rubbish into electricity and reducing the UK’s waste burden. But new research suggests there may be a hidden cost to this process: potentially hazardous chemical residues that remain largely out of public view.
A major study from the University of East London (UEL) has uncovered new evidence about the risks posed by air pollution control residues (APCr) – a fine, highly alkaline powder produced when harmful pollutants are captured from incinerator flue gases.
Drawing on one of the most comprehensive UK analyses to date, researchers examined 42 samples from 22 energy-from-waste facilities nationwide, revealing fresh insights into the complex chemical make-up of these materials and how they behave in the environment.
The findings raise important questions about how safely these residues are currently managed and whether they could pose longer-term environmental risks, particularly if reused or disposed of without a full understanding of their chemical properties.
Energy-from-waste facilities, which burn rubbish to generate electricity, use advanced filtration systems to remove harmful substances from exhaust gases before release. The study, led by Dr Bamdad Ayati from UEL’s Sustainability Research Institute (SRI), analysed APCr samples from UK facilities to examine their chemical composition, mineral structure and behaviour under environmental conditions such as exposure to air and water.
The findings show these residues are highly alkaline and rich in soluble salts, influencing how they react in landfill and their suitability for recycling or reuse. Researchers identified 45 mineral phases, including 21 not previously reported, and detected trace metals and compounds that may become mobile under certain conditions. This behaviour is critical for assessing long-term environmental risks, particularly in disposal or construction applications.
Using a range of analytical techniques, the study provides a clearer picture of APCr’s chemical and physical properties, helping to inform waste management practices, regulatory approaches and the development of safer reuse options within the growing energy-from-waste sector.
Dr Ayati said the research highlights the importance of fully understanding the by-products created by modern waste treatment systems.
“Energy-from-waste facilities play an important role in reducing landfill and recovering energy from materials that would otherwise be discarded,” he said. “However, the residues produced during air pollution control contain complex mixtures of minerals and trace elements. Understanding their physicochemical properties is essential if we want to manage them safely and explore sustainable options for reuse.”
As energy-from-waste capacity continues to expand across the UK, the amount of APCr produced each year is also increasing. Studies such as this provide critical data to ensure that these materials are handled responsibly while supporting efforts to move towards more circular approaches to waste management.
“Our work provides a clearer scientific foundation for evaluating how these residues behave and how they might be treated or stabilised,” Dr Ayati added. “With the right knowledge, we can reduce environmental risks while identifying opportunities for more sustainable material management.”
The research, “Comprehensive study of physicochemical and environmental properties of air pollution control residues from UK energy-from-waste facilities”, is published in the journal Waste Management.
Journal
Waste Management
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Comprehensive study of physicochemical and environmental properties of air pollution control residues from UK energy-from-waste facilities
Jeonbuk National University researchers reveal safer way to manage chemical sewage sludge using pyrolysis
Study shows how controlling pyrolysis temperature can help reduce environmental risks of chemical sewage sludge, supporting sustainable sewage treatment
image:
An appropriate thermal treatment process is necessary for effective CEPT sewage sludge management and reducing environmental risks.
view moreCredit: Professor Kitae Baek from Jeonbuk National University, Republic of Korea
To handle increasing wastewater loads, sewage treatment plants are adopting more advanced treatment processes. However, many of these approaches require additional space and energy, highlighting the need for more efficient alternatives. Chemical-enhanced primary treatment (CEPT), which uses chemicals, instead of microorganisms, to promote flocculation and coagulation of sewage, has attracted significant attention for reducing energy consumption and operation costs in sewage treatment plants.
The sewage sludge produced during treatment can be further processed through pyrolysis, a high-temperature process that can reduce sludge volume, degrade pollutants, and produce value-added materials. However, biochar, which is product of pyrolysis, derived from CEPT sewage sludge (CS) differs from that produced by conventional biological treatment sewage sludge (BS). These differences can influence how heavy metals behave and remain stable in the biochar, potentially increasing environmental risks. Until now, limited information has been available on heavy metal behavior in CS-derived biochar.
To address this gap, a research team led by Professor Kitae Baek from the Department of Environment and Energy and Soil Environment Research Center, Jeonbuk National University, Republic of Korea, investigated the properties of heavy-metals in CS-derived biochar with those of conventional BS-derived biochar. Their study was made available online on December 18, 2025, and published in Volume 206 of Process Safety and Environmental Protection on January 15, 2026.
“While CEPT can reduce energy consumption, it is necessary to consider not only treatment performance but also the environmental impact of its byproducts. Our study clarifies the potential risks associated with CS-derived biochar and highlights the need for appropriate countermeasures as CEPT adoption increases,” says Prof. Baek.
The researchers collected CS and BS samples from two sewage treatment plants in Hong Kong. Both sludge types were pyrolyzed at different temperatures, and the resulting biochars were analyzed to compare their heavy metal content and stability.
The biochar yield of CS ranged between 32.1% and 40.9%, notably lower than that of BS, which ranged between 43.9% and 75.2%. Heavy metal content analysis showed that a smaller proportion of heavy metals remained trapped in CS-derived biochar across all temperatures. This suggests that thermal treatment of CS can lead to secondary heavy metal pollution in the surrounding environment.
Further tests revealed that CS-derived biochar had lower heavy metal stability, especially at high temperatures above 800 °C. At such high temperatures the mobility of heavy metals also increased significantly and could be easily leached out, increasing environmental safety concerns. Based on these results, the researchers recommend using lower pyrolysis temperatures when treating CEPT sludge.
Interestingly, at an optimized temperature of 550 °C, heavy metals in both types of biochar showed long-term stability. This suggests that, when properly treated, CS-derived biochar can be safely used for applications such as soil amendment or fertilizer, similar to biochar from conventional sludge.
“Our findings show that an appropriate thermal treatment is necessary to enhance sustainability of the CEPT process. With proper sludge management, CEPT can support efficient sewage treatment while reducing carbon emissions and environmental impacts. This will have a long-term positive impact on people's lives and environmental conservation,” concludes Prof. Baek.
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Reference
DOI: 10.1016/j.psep.2025.108338
About Jeonbuk National University
Founded in 1947, Jeonbuk National University (JBNU) is a leading Korean flagship university. Located in Jeonju, a city where tradition lives on, the campus embodies an open academic community that harmonizes Korean heritage with a spirit of innovation. Declaring the “On AI Era,” JBNU is at the forefront of digital transformation through AI-driven education, research, and administration. JBNU leads the Physical AI Demonstration Project valued at around $1 billion and spearheads national innovation initiatives such as RISE (Regional Innovation for Startup and Education) and the Global University 30, advancing as a global hub of AI innovation.
Website: https://www.jbnu.ac.kr/en/index.do
About the Author
Dr. Kitae Baek is a Professor in the Department of Environmental Engineering & Department of Environment & Energy, Jeonbuk National University where he has been a faculty member since 2012. He is also the Director of Environmental Education and Research Center for Glocal Resources Circulation (BK21 Four). He received his B.S., M.S., and Ph.D. degrees from the Korea Advanced Institute of Technology, Republic of Korea. His group has published more than 220 peer-reviewed articles. His main research interests include electrokinetic or electrochemical remediation, soil washing, adsorption of arsenic, geochemistry, and fate of arsenic in agricultural soils and remediation of mining area including acid mine drainage and mine tailings.
Journal
Process Safety and Environmental Protection
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Stability assessment of heavy metals in sewage sludge pyrolysis biochar based on the chemical-enhanced primary treatment (CEPT) process
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