Deciphering the linear and non-linear biosorptive removal of the anti-inflammatory drug enrofloxacin

Abstract

The contamination of the hydrosphere through diverse human and veterinary medications has become a universal concern. The occurrence and outcomes of pharmaceutical micropollutant enrofloxacin (ENF) in freshwater bodies have been well-documented in a number of studies worldwide. In the current study, a biosorbent was developed from waste precursor sugarcane bagasse (Saccharum officinarum), which was activated physico-chemically with steam, followed by sodium hydroxide for the efficacious eradication of the anti-inflammatory drug ENF from contaminated water. Spectral analyses and characterisation of the biosorbent (SPCAB) were done using FTIR, SEM, and EDAX, which revealed the proper impregnation of the active agent on the adsorbent's surface and elucidated the adsorption mechanism. Response surface methodology (RSM) was exploited to attain optimal biosorption of ENF. The impact of distinct factors, such as pH (2–8), initial ENF concentration (5–40 mg L⁻¹), sorbent dose (0.005–0.2 g L⁻¹), duration (1–12 h), mixing intensity (100–180 rpm), and temperature (15–30 °C), on sorptive removal was probed, which resulted in the highest ENF removal of 94.78%. In kinetic and isotherm models, linear and nonlinear approaches were used to verify sorptive ENF removal. Regeneration experiments of the adsorbent proved good reusability till the 4th cycle with 80.07% ± 0.09% efficiency. The experimental equilibrium data were evaluated using the Langmuir, Freundlich, Temkin and Redlich–Peterson models. The pseudo first-order (PFO), pseudo second-order (PSO), intraparticle diffusion, Elovich, and Boyd kinetic models were studied. The PSO kinetic and Langmuir isotherm models proved to be the best fit with the obtained data. The thermodynamic study confirmed the spontaneous and exothermic nature of ENF sorption. Furthermore, the estimated cost of INR 309.034 per kg of tailored SPCAB ascertained its commercial feasibility. Therefore, the engineered SPCAB could be a proficient and cost-competent biosorbent for treating ENF-laden wastewater at a large scale.