Ofloxacin adsorption by calcined Verde-lodo bentonite clay: Batch and fixed bed system evaluation

Abstract

Due to the increasing consumption of antibiotic agents and the fact that conventional effluent treatment methods are inefficient in removing these compounds, new and more effective treatment processes need to be investigated and improved. This work evaluated the adsorption of the emerging contaminant ofloxacin (OFL, antibiotic) in static and dynamic systems using calcined Verde-lodo (CVL) bentonite clay. The use of CVL bentonite clay for this purpose has not been investigated, furthermore, there are no reported studies regarding OFL adsorption in a fixed bed system. The molecular structure of ofloxacin was obtained by molecular simulation showing a stable and minimum local energy structure. The characterization study before and after the adsorption process indicated the presence of OFL in the CVL clay. The analyzes indicated that the CVL clay exhibits a lamellar structure with some roughness, with pores of 80,000 nm larger than macropores (>50 nm). In addition, the thermogravimetric analysis indicated that the clay is thermally stabile up to 1000 °C. External mass transfer resistance and pseudo-second-order models best described the kinetic data. The Dubinin-Radushkevick model was best adjusted to the equilibrium assays, indicating heterogeneous adsorbent surface. The system reached a maximum Langmuir adsorption capacity (55 °C) of 0.445 mmol g−1 (160.81 mg g−1). Fixed bed assays indicated the occurrence of multilayer adsorption. Under operating conditions of 0.4 mL min−1 and 0.05 mmol L−1, the system operated for 140 h with practically 100% removal until the breakthrough time was achieved. The clay showed high reuse capacity, with removal efficiency >93% after 3 cycles.