Remoção do corante reativo azul 5g de um efluente sintético com separação por membrana e adsorção em casca de pinhão

Abstract

The textile industry is recognized for its high level of water consumption, which results in a large quantity of wastewater containing high concentration of dyes. Due to the toxic character of these compounds, diverse methods were developed for the treatment of effluents. The pine nut shell, commonly discarded as a residue, is a viable biosorbent, because of its lignocellulosic composition. This work aimed at applying the methods of membrane separation and adsorption on pine nut shells to remove the reactive blue 5G dye from synthetic effluents. The dye was characterized in terms of particle size and functional groups. In the membrane separation process, polyethersulfone and regenerated cellulose membranes were utilized in a dead­end membrane module. For the adsorbent’s characterization, PCZ, BET, FTIR, MEV and TGA analysis were carried out. Equilibrium isotherms were performed at 30, 40 and 50ºC temperature, and adsorption kinetics in the concentration of 10, 50 and 90 ppm. The combined process of membrane separation followed by adsorption on the pine nut shell was applied considering the best operating conditions found. During the dye’s characterization, the size of the particle grew with the concentration increase only at 30ºC and pH 2. The regenerated cellulose membrane provided the best results, with a hydraulic permeability of 158,10 kg h­1 m­2 bar­1 and maximum dye removal of 35,9%. This was performed with a 50 ppm concentration, 0,5 bar pressure and agitation. The cleaning process was efficient for the two membranes, and the permeated flow was fully recovered. In the adsorbent’s characterization, a 5,6 PCZ was found. The material showed a structure that was mostly macroporous, with an specific area of 5,14 m2 g-­1. The FTIR analysis of the dye and the adsorbent before and after the adsorption, suggested that the hydroxyl and carboxyl are the main functional groups associated with the adsorption. After analysing the influence of pH, the best adsorption result was achieved at pH 2. All of the isotherms were favorable, and the best results were obtained at 50ºC, with a maximum adsorption capacity of 83,38 mg g-­1, and 85% of dye removal for the initial concentration of 50 ppm, whereas 75% for the 70 ppm concentration. The Freundlich model was shown as the best adjustment. In adsorption kinetics, the increase in concentration shifted the equilibrium, which was achieved in 4 hours, at most. The pseudo­second order model was the one that best described the process. The thermodynamic parameters revealed that the adsorption on pine nut shells is a physical and endothermic process that occurs spontaneously. The combined process of membrane separation followed by adsorption on pine nut shells obtained the final concentrations of 0,6 and 5,4 mg L-­1 for the initial concentrations of 50 and 70 mg L­-1, respectively, demonstrating that these processes combination is efficient in removing the reactive blue 5G dye from textile effluents and it is an environmentally and economically viable alternative.