Avaliação da remoção de fármacos por processos adsortivos: estudos isotérmico, cinético e termodinâmico

Abstract

Sodium diclofenac (DCF) is an anti-inflammatory with high toxicity and frequently detected in effluents and wastewater treatment plants. Ciprofloxacin (CIP) is an antibiotic that is widely used in clinical and veterinary treatment to prevent bacterial infections, with a high polluting potential. Adsorption using activated carbon has been widely used to remove micropollutants, but this adsorbent requires an expensive and inefficient phase separation step, compromising the efficiency and cost of the adsorptive process. Thus, an innovative and unprecedented process based on ionic flocculation-assisted adsorption (IFAA) using the surfactant sodium dodecanoate was proposed, aiming to increase the adsorption capacity of the process and facilitate phase separation. In the context of the search for bioadsorbents, the potential of sweet sorghum bagasse (NSB) and chemically treated with sulfuric acid (TSB) as adsorbents was also evaluated, aiming to remove DCF and CIP from synthetic wastewater. The efficiency of the processes of adsorption and adsorption assisted by ionic flocculation was evaluated from a kinetic study, equilibrium isotherms, thermodynamic properties and for activated carbon as adsorbent, the kinetics of separation through the sedimentation process was studied. In the study of direct adsorption and IFAA using activated carbon as adsorbent and DCF as a contaminant, the adsorption kinetics followed the pseudo-second order model in both processes. From the equilibrium isotherms, the maximum adsorption capacity obtained was 49.43 and 51.85 mg.g-1 in direct adsorption and IFAA, respectively, being best represented by the Langmuir model. In the sedimentation analysis, it was noticed that the higher the surfactant concentration, the higher the compaction height, the higher the decantation speed and the shorter time to obtain the clarified effluent. In the adsorption of DCF and CIP in NSB and TSB, the chemical treatment carried out in the NSB modified the lignocellulosic composition of this material, reducing the percentage of lignin by 35%, hemicellulose by 26% and increasing the alpha-cellulose content by 20%. The pseudo-second order model was the one that best fitted the adsorption kinetics of DCF and CIP in both adsorbents, as evidenced by the correlation coefficients and the sum of squares of the residues. The equilibrium isotherms obtained with the adsorbents (NSB and TSB) and the CIP were better fitted with the Langmuir model (R² > 0.98). In the case of DCF adsorption, the Freundlich model provided the best fit (R² > 0.99). The thermodynamic analysis revealed that the processes occurred spontaneously, exothermically and that there is a reduction in randomness at the solid-solution interface. The use of IFAA proved to be effective by increasing the adsorption capacity of the DCF, promoting a better phase separation of the constituents (adsorbent and DCF), making the separation faster and more efficient. The ability of NSB and TSB to adsorb DCF and CIP from water was evidenced, highlighting its potential as an efficient, environmentally friendly and low-cost bioadsorbent.