Researchers at the University of Patras have found that biochar made from a common brewery byproduct can substantially improve the ability of sand to retain Escherichia coli, pointing to a potential new use for brewing waste in water filtration and groundwater protection.
In laboratory column experiments, sand amended with 10% biochar removed 94.1% of E. coli, compared with only 17.8% removal by unamended sand. The study also revealed that adding more biochar changed how the bacteria were retained, shifting the dominant process from simple physical trapping to direct attachment to the biochar surface.
"Our results show that a low-cost byproduct from the brewing industry can be transformed into a functional material that strongly enhances bacterial retention in sandy media," said corresponding author Ioannis D. Manariotis of the Environmental Engineering Laboratory, Department of Civil Engineering, University of Patras. "This creates an opportunity to connect waste valorization with technologies designed to reduce microbial transport in water and soil systems."
The study, published in Biochar, investigated malt spent rootlets, a residual material generated during malt production. The researchers converted the rootlets into biochar through pyrolysis at 850 °C. The resulting material, known as malt spent rootlets biochar, or MSRB, had a highly porous and heterogeneous surface with a specific surface area of approximately 290 square meters per gram.
To understand how bacteria interact with the material, the team conducted both batch adsorption experiments and flow-through experiments using saturated sand columns. The experiments examined the behavior of E. coli CN-13 under different solution conditions and biochar application rates.
The batch tests showed that bacterial adsorption onto MSRB was well described by a pseudo-first-order kinetic model and a Freundlich isotherm. The researchers also accounted separately for the natural inactivation of E. coli, helping distinguish bacterial loss caused by cell inactivation from removal caused by adsorption onto biochar.
Solution chemistry mattered as well. Increasing ionic strength from 1 to 150 mM KCl reduced bacterial adsorption onto the biochar. The researchers attributed this behavior primarily to electrostatic shielding, which weakens attractive interactions between negatively charged bacterial cells and the positively charged MSRB surface under the experimental conditions.
The most striking results emerged from the sand column experiments. While physical straining dominated bacterial retention in unamended sand and sand containing 5% MSRB, numerical modeling showed that direct and irreversible attachment became the dominant retention mechanism when the biochar content reached 10% by weight.
This mechanistic shift suggests that biochar does more than simply reduce pore spaces and mechanically trap microorganisms. At sufficient concentrations, its surface can become an important attachment medium for bacterial cells.
The researchers note that the experiments were conducted under controlled laboratory conditions using sterilized quartz sand and simplified water chemistry. Natural soils and groundwater contain organic matter, minerals, competing microorganisms and other components that could alter biochar performance. The column experiments also involved a single run for each biochar application rate. Further testing under realistic environmental conditions and longer operating periods will therefore be needed before field-scale application can be recommended.
Even so, the findings provide proof-of-concept evidence that malt spent rootlets could be converted from an industrial residue into a useful biochar amendment for sand filtration and sandy agricultural soils, potentially combining microbial contamination control with more sustainable brewery waste management.
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Journal Reference: Giannopoulos, C.P., Kolotouros, C.A. & Manariotis, I.D. Sorption and transport of Escherichia coli CN-13 in saturated sand columns amended with biochar derived from malt spent rootlets. Biochar 8, 130 (2026).
https://doi.org/10.1007/s42773-026-00648-2
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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.
