Efficient removal of tetracycline, ciprofloxacin, and amoxicillin by novel magnetic chitosan/microalgae biocomposites

Two new highly-efficient and eco-friendly biosorbents comprised of magnetite, chitosan and Chlorella vulgaris (MCC) or Arthrospira platensis (MCA) were prepared in such a way to be easily separated and reused for removing different classes of antibiotics such as tetracycline (TC), ciprofloxacin (CIP) and amoxicillin (AMX) from wastewater. They were characterized using SEM, FTIR and TGA. Biosorption experiments were performed to investigate the impact of pH, biosorbent dosage, initial antibiotic concentration, contact time, and concentration of background electrolytes (NaCl, KCl and CaCl2) on adsorption. Both biocomposites showed outstanding performance in antibiotics removal. Equilibrium data were modelled using Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherms, among which the first one gave the best fit, with maximum TC, CIP and AMX adsorption capacities of 834.0, 394.9, and 150.8 mg/g for MCA and of 831.1, 374.2, and 140.2 mg/g for MCC, respectively. To follow the adsorption time-evolution, the pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models were tested, the second of which proved to be the best-fitting one. Thermodynamic parameters revealed that adsorption was spontaneous and endothermic. Both biosorbents were regenerated through microwave-assisted treatment and reused repeatedly for up to four cycles, losing TC, CIP and AMX adsorption capacities at equilibrium by no >7, 4 and 9 %, respectively. This study suggests that both biocomposites may be effective and sustainable alternatives to commercial adsorbents for removing antibiotics from wastewater.