RESUMO
Pharmaceutical products and their byproducts which are present in wastewater and superficial water are becoming an environmental problem. A large effort has been made to introduce new and more efficient treatment processes for removing these emerging pollutants. Among them, activated carbon is currently being studied to be implemented in wastewater treatment plants. In the present study the equilibrium and kinetics of the adsorption of carbamazepine (Cbz) and sildenafil citrate (Sil) onto powdered activated carbon are presented. Batch experiments were performed to assess the potential of this kind of activated carbon for removing these recalcitrant pharmaceuticals from aqueous systems. In addition, its adsorption efficiency was compared with the granular activated carbon. The isotherms of Langmuir, Freundlich, Langmuir-Freundlich and Redlich-Peterson were applied. Pseudo-first and pseudo-second order models, as well as a combined model and an intraparticle diffusion model were assayed on the results obtained. Linear and non-linear analyses were carried out to compare the best fitting isotherms and kinetics. The Langmuir isotherm was a good fit for the adsorption of Sil, whereas the Redlich-Peterson isotherm described the adsorption of Cbz. The experimental results for both pharmaceuticals follow a kinetic of pseudo first order. Comparative studies preparing the solutions with distilled water, dechlorinated water and wastewater were performed. No significant differences were observed in these studies. When initial concentrations similar to those found in surface waters for both pharmaceuticals were evaluated, removal efficiencies greater than 85% were obtained. Therefore, the use of this kind of activated carbon seems to be an efficient tool for the removal of recalcitrant emerging pollutants, such as Sil and Cbz.
Assuntos
Poluentes Ambientais , Poluentes Químicos da Água , Adsorção , Carvão Vegetal , Cinética , PósRESUMO
Background: Sugarcane is one of the world's largest crop. It grows in the tropical and subtropical regions, and its harvest provides 80% of the world's sugar. In Latin America unrefined cane sugar is widely available and much less expensive than refined sugar. Sugarcane is a crop of great interest in Colombia due to the economic impact on the rural population and its application as sweetener agent. The powder of sugarcane (Saccharum officinarum L.) is widely used as a raw material in a wide range of industries such as foods, pharmaceutical, cosmetic and chemical. Objectives: The aim of the research work was the evaluation of the adsorption thermodynamics of sugarcane powder obtained by spray drying technology. Methods: The adsorption isotherms of sugarcane powder were evaluated at temperatures of 4 ± 0.1, 20 ± 0.2 and 30 ± 0.3 °C and its thermodynamic properties such as Gibbs free energy (G), differential heat of adsorption (∆H) and differential entropy (∆S) were calculated as a function of moisture content. Experimental data of adsorption isotherms were fitted to the GAB (Guggenheim Andersen - de Boer), BET (Brunauer Emmett - Teller), Henderson, Caurie, Smith, Hasley, Peleg, and Oswin models. Results: The results showed a type-II sigmoidal behavior, with temperature having a statistically significant effect. The GAB equation showed a better fit to the experimental data modeling (0.11≤aw≤0.87) although all models showed validity and goodness of fit to the experimental data. The net isosteric heat increased to a maximum value (57 kJ mol-1) and then decreased with the increase in moisture content. Conclusions: The sugarcane powder with maltodextrin, obtained by spray drying got low adsorption thermodynamic stability, as it required very low energy to occur this phenomenon, being obtained the maximum net isosteric heat when moisture content of 4.7% (d.b). This value is within the range of the monolayer moisture content found in the GAB and BET models.
