Comparison of by-products as adsorbents for the removal of the antibiotics ciprofloxacin, trimethoprim and clarithromycin

Antibiotics in the environment are considered emerging pollutants, with special relevance and concern due to the proliferation of antibiotic-resistant bacteria and genes. Therefore, finding ways to remediate antibiotics-contaminated soil and water through the use of bio-adsorbents is imperative. In this research, we investigate three by-products (hemp waste, oak ash, and mussel shell) as potential low-cost bio-adsorbents for the antibiotics Ciprofloxacin (CIP), Clarithromycin (CLA), and Trimethoprim (TRI), using batch-type and stirred flow chamber experiments to study their retention and release. The results indicate that hemp waste has higher sorption capacity for CIP and TRI (20891.8 and 2481.6 μmol L^-1, respectively), while oak ash yields the highest retention for CLA (3078.4 μmol L^-1). In addition, it was shown that the pH value significantly influences the sorption of these pollutants onto hemp waste. Among the three antibiotics, CLA was the most mobile, given the release experiments (903.9-1758.9 μmol kg^-1), while ciprofloxacin (440.3-542.4 μmol kg^-1) and trimethoprim (639.4-1652.1 μmol kg^-1) are released less. Overall, the results of this research (the first of this kind including these antibiotics and sorbents simultaneously) suggest that while the individual antibiotics retention on each of the three by-products may not be entirely satisfactory, its potential combination (among them and/or with other low-cost sorbents) could significantly contribute to addressing antibiotics environmental pollution, favouring recycling and promoting a circular economy, which is a matter of global relevance.