Sorption and transport of Escherichia coli CN-13 in saturated sand columns amended with biochar derived from malt spent rootlets

Pathogenic microorganism transport through sandy soils and engineered sand filtration systems represents a significant groundwater contamination risk; biochar amendment of these media offers a sustainable retention strategy. This study investigated the sorption and transport of Escherichia coli ( E. coli ) CN-13 in saturated sand columns amended with biochar derived from malt spent rootlets (MSRB) pyrolyzed at 850 °C. Batch experiments were conducted to quantify inactivation and adsorption kinetics under varying ionic strengths (1 and 150 mM KCl). E. coli inactivation was best described by the Weibull model, while adsorption kinetics and isotherms followed the pseudo-first-order (PFO) and Freundlich models, respectively. Increasing ionic strength was found to hinder adsorption capacity, likely due to electrostatic shielding and increased competition for active sorption sites. Column transport experiments demonstrated that amending sand with MSRB significantly enhanced bacterial retention, with removal efficiencies increasing from 17.8% in unamended sand to 94.1% in sand containing 10% (w/w) biochar. Numerical modeling using the one-dimensional biocolloid transport equation (1D-BTE) revealed that while physical straining dominated removal in unamended and 5% biochar columns, direct attachment became the governing mechanism at 10% biochar application rate. The attachment of bacteria to MSRB was found to be irreversible. These results indicate that MSRB is a promising low-cost amendment for enhancing pathogen retention in sandy porous media, with direct relevance to engineered sand filtration and applications in agricultural sandy soils, while simultaneously addressing brewery waste disposal challenges.