Brewery-waste biochar for antibiotic removal: Modeling, BAC column enhancement, and microbial analysis

ABSTRACT Conventional wastewater treatment plants incompletely remove antibiotics, contributing to antimicrobial resistance and demanding improved tertiary treatments. However, integrated evaluations of brewery-waste-derived biochar in hybrid systems for antibiotic removal remain scarce. This study evaluated malt bagasse (MB) biochar for levofloxacin (LEV) removal via batch adsorption, fixed-bed columns, and a biological activated carbon (BAC) column for tertiary treatment. MB biochar exhibited an acidic surface and specific surface area (8.0 m 2 g -1 ). LEV adsorption reached equilibrium after 4,880 min, with 2.96 mg g⁻¹ of maximum capacity. A Mass transfer model was proposed and fitted to experimental kinetic data to estimate the convective mass transfer coefficient (4.63×10 -5 g L -1 min -1 ), suggesting that internal diffusion may play an important role in adsorption. Conventional kinetic models were tested, with Elovich and Mass transfer models yielding the lowest AIC/BIC values and, therefore, the best statistical performance among the evaluated models. Equilibrium results were well described by Langmuir and Freundlich isotherms. Kinetic and isotherm models were also statistically compared using nonlinear parameter estimation and R 2 . MB biochar columns saturated rapidly (40–66 min), achieving LEV removals of 10–12%. In contrast, the BAC column did not reach saturation after 15 days and achieved 22.6% removal (2.5 times higher than adsorption alone). Microbial analysis revealed enrichment of Proteobacteria (84%) in the BAC biofilm, with Burkholderia (65%) dominating (associated with fluoroquinolone transformation pathways). Overall, integrating MB biochar into a BAC system improved LEV attenuation, highlighting its potential as a complementary treatment for pharmaceutical-containing effluents while extending column lifetime.