Adsorption of Rifampicin from Water Using Sawdust: Kinetics, Isotherms and Optimisation

Residual antibiotics pollution is one of the main drivers of antibiotic resistance, demanding effective and sustainable technologies for remediation. Adsorption was found to be an effective process for antibiotic contaminant remediation, particularly on surfaces of lignocellulosic materials, which have gained attention as low-cost adsorbents. This study investigated the adsorption mechanisms and the optimisation of rifampicin removal from water using sawdust. Adsorption mechanisms were proposed based on kinetic and isotherms, while response surface methodology (RSM) was employed to optimise and identify the critical operating parameters. The results revealed that the adsorption of rifampicin by both adsorbents could be best described by the pseudo-first-order model, while the experimental results fitted perfectly into the Temkin isotherm model, which suggests that the adsorption of rifampicin on sawdust occurred via multi-interaction on a varying, energetically heterogeneous surface. Optimal conditions resulting in an uptake of 0.71 mg/g were established as follows: initial concentration of 20 mg/L, an adsorbent dosage of 0.5 g per 40 mL, pH 6 and at 250 min. The initial concentration of rifampicin and the adsorbent dosage were found to be the most critical parameters that influenced its uptake. The findings revealed that sawdust is a sustainable and cost-effective material to remove rifampicin from water, with adsorption occurring mainly via physisorption on a varying, energetically heterogeneous surface.