In a newly published paper in the journal Biochar, researchers Christos P. Giannopoulos, Christos A. Kolotouros, and Ioannis D. Manariotis investigated how converting brewery waste into an engineered soil amendmentA soil amendment is any material added to the soil to enhance its physical or chemical properties, improving its suitability for plant growth. Biochar is considered a soil amendment as it can improve soil structure, water retention, nutrient availability, and microbial activity.   More can safeguard vital groundwater resources from bacterial contamination. The downward migration of disease-causing microorganisms through coarse sandy soils and engineered filtration systems represents a persistent hazard to public drinking water supplies worldwide. Standard quartz sand filters often provide limited protection because wide pore spaces permit microscopic pathogens to migrate freely. To address this vulnerability, the authors examined how biochar produced by heating malt spent rootlets at elevated temperatures alters the transport, retention, and survival of bacteria within water-saturated sand columns.

The experimental outcomes revealed that incorporating malt spent rootlet biochar significantly enhances the ability of sand filters to trap bacteria. Plain sand without biochar achieved a bacterial removal efficiency of only 17.8 percent, allowing the vast majority of cells to pass through the column. Adding just five percent biochar by weight doubled the filtration performance, yielding a 35.1 percent removal rate. When the biochar content reached ten percent by weight, the filter achieved a remarkable 94.1 percent bacterial removal rate, representing a more than fivefold improvement over unamended sand.

Beyond simply measuring overall removal, the study uncovered a fundamental shift in how the filtration system captures microbes. In pure sand and low-dose mixtures, physical straining served as the primary mode of removal, where cells were merely wedged into narrow junctions between sand grains. At the ten percent biochar application rate, direct chemical and physical attachment took over as the dominant mechanism. Mathematical modeling demonstrated that the attachment rate coefficient increased more than thirteenfold in the ten percent biochar mixture compared to plain sand. Furthermore, the bacteria remained firmly anchored to the biochar particles without detaching, preventing the microbes from breaking free and washing downstream.

Batch testing provided deeper insight into the surface forces driving this exceptional retention. Microscopic imaging showed that the high-temperature pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More process creates an intricate, honeycomb-like matrix filled with microscopic ridges and crevices. This complex architecture delivers an extensive surface area that presents abundant energetic landing spots for passing cells. Because the biochar surface carries a slight positive electrical charge under typical water conditions while bacterial cell walls carry a negative charge, electrostatic attraction draws the microbes directly onto the carbon framework. Strong water-repelling forces between the carbon rings and bacterial outer membranes further lock the cells in place.

The researchers also evaluated how background water chemistry influences performance by testing solutions with low and high salt concentrations. Natural bacterial die-off accelerated under saltier conditions because osmotic stress destabilizes outer cell membranes. However, elevated salt concentrations also weakened bacterial sorption onto the biochar, decreasing the maximum adsorption capacity. In salty water, dissolved ions shield the opposing electrical charges on the biochar and bacterial surfaces, reducing the electrostatic pull that draws them together.

Overall, the findings demonstrate that malt spent rootlet biochar serves as a powerful, cost-effective, and environmentally sustainable filter medium for municipal water treatment and agricultural runoff control. Turning brewing residues into high-performance filtration materials addresses industrial waste disposal while providing a reliable barrier against waterborne disease outbreaks.

Source: Giannopoulos, C. P., Kolotouros, C. A., & Manariotis, I. D. (2026). Sorption and transport of Escherichia coli CN-13 in saturated sand columns amended with biochar derived from malt spent rootlets. Biochar, 8, 130.