Adsorptive removal of fluoroquinolones using bamboo culm biochar in a single and multi-component system

Abstract

Adsorption of three different, second-generation fluoroquinolone molecules ofloxacin (OFL), ciprofloxacin (CIP), and levofloxacin (LEV), using bamboo culm biochar, was systematically analyzed. The morphological and functional characteristics of the prepared bamboo biochar revealed the presence of a porous structure with higher charge density, specific surface area, and pore volume. The point of zero charge of biochar was determined as 9.5, aiding the process to effectively adsorb positively charged fluoroquinolones at lower pH levels, through cation exchange and π-π interactions. One variable at a time (OVAT) approach was used to study the effects of operating variables, i.e., contact time, pH, adsorbent dosage, antibiotic concentration, and temperature. The maximum adsorption of these antibiotics was achieved around 5 min of contact time, acidic to the neutral range of pH, 0.2 g of adsorbent dose, and at a higher antibiotic concentration (350 to 400 mg/L) and temperature of 55°C. Adsorption kinetics suggested that the adsorption of OFL was controlled by physisorption, and the adsorption of CIP and LEV was controlled by a chemisorption-based adsorption mechanism. The Langmuir isotherm model exhibited the best fit for OFL and LEV, indicating monolayer adsorption of antibiotics. While, the Freundlich isotherm model exhibits the best fit for CIP, suggesting multilayer adsorption. OVAT approach for the multi-component system depicted that the maximum removal of a mixture of three fluoroquinolones was achieved at a contact time of 5 min, pH of 5.0, adsorbent dose of 0.2 g, and at an initial concentration of 400 mg/L. Overall, the study depicted the potential of using bamboo biochar as an efficient adsorbent for removing fluoroquinolone antibiotics from aqueous solutions.