Brewery waste biochar traps bacteria in filters

Researchers at the University of Patras have demonstrated that biochar derived from brewery byproducts can significantly enhance the retention of Escherichia coli in sand, suggesting a novel application for brewing waste in water filtration and groundwater protection.

In laboratory experiments, sand mixed with 10% biochar achieved a 94.1% removal rate of E. coli, compared to only 17.8% with unamended sand. The study found that increasing biochar content altered the bacteria retention mechanism from physical trapping to direct attachment on the biochar surface.

Ioannis D. Manariotis of the Environmental Engineering Laboratory at the University of Patras stated, "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." This approach could link waste valorization with technologies aimed at reducing microbial transport in water and soil systems.

The study, published in the journal Biochar, focused on malt spent rootlets, a byproduct of malt production. These rootlets were converted into biochar through pyrolysis at 850 °C, resulting in a material with a porous surface and a specific surface area of approximately 290 square meters per gram.

To investigate bacterial interactions with the biochar, the researchers conducted batch adsorption and flow-through experiments using saturated sand columns. These experiments assessed the behavior of E. coli CN-13 under various solution conditions and biochar application rates.

Batch tests indicated that bacterial adsorption onto the malt spent rootlets biochar (MSRB) followed a pseudo-first-order kinetic model and a Freundlich isotherm. The study also distinguished bacterial loss due to cell inactivation from removal by adsorption onto biochar.

Solution chemistry played a role in bacterial adsorption. Increasing ionic strength from 1 to 150 mM KCl reduced bacterial adsorption onto the biochar, attributed to electrostatic shielding, which weakens interactions between negatively charged bacterial cells and the positively charged MSRB surface.

The sand column experiments revealed that while physical straining was the primary retention mechanism in unamended sand and sand with 5% MSRB, direct attachment became dominant at 10% biochar content. This shift indicates that biochar can serve as an effective attachment medium for bacterial cells at higher concentrations.

The researchers caution that these experiments were conducted under controlled conditions with sterilized quartz sand and simplified water chemistry. Natural soils and groundwater, with their organic matter, minerals, and competing microorganisms, may affect biochar performance. Further testing in realistic environmental conditions is necessary before field-scale applications can be recommended.

Nonetheless, the findings provide proof-of-concept that malt spent rootlets can be transformed from industrial residue into a valuable biochar amendment for sand filtration and sandy agricultural soils, potentially integrating microbial contamination control with sustainable brewery waste management.