Utilização de resíduos poliméricos para a remoção de surfactantes de águas residuais

Abstract

A constant challenge in the treatment of industrial and domestic effluents is the removal of surfactants, a class of high complexity due to their high concentration and limited removal efficiency. The composition of the main commercial detergents is dominated by anionic surfactants, specifically, the sodium linear alkylbenzene sulfonate (LAS). The average concentration found in domestic effluents varies from 14.0 mg L1 to 27.0 mg L1and in industrial effluents around 50.0 mg L1. When released into the water body without adequate treatment, surfactants have a high polluting potential. Its presence reduces the surface tension of the water and, consequently, its evaporation rate, thus favoring eutrophication, causing excessive growth of aquatic vegetation, organisms such as algae and cyanobacteria and reduction of oxygen concentration, which causes the death of other beings. alive. Thus, the search for the efficient removal of surfactants, in addition to being fundamental for the ecosystem, becomes a constant challenge. This work aims to remove surfactants (LAS and dodecyl pyridinium chloride, DPC) by the adsorption method using polymeric residues, polyurethane (PU) and polyamide (PA), generated in large quantities as residues and with a low recycling rate. As it is a thermoplastic, PU is hardly recycled to be used in a plastic material of the same type, and PA, even with chemical recycling processes, in addition to being costly, generates new waste to the environment. The solution presented in this work is the direct use of polymeric residues to remove surfactants by means of adsorption, providing adequate disposal and generating aggregated value to the residue. Firstly, the adsorbents were characterized via Fourier Transform Infrared Spectroscopy with Attenuated Reflectance and zero charge potential (pHPCZ). The influence of experimental parameters pH (lower level 4.0 and upper level 10.0), temperature (lower level 20 and upper level 40 °C) and contact time (lower level 20 and higher level 120 min) on the adsorption capacity of the adsorbents was evaluated by facecentered central composition design. Four experimental conditions were optimized, which were used in the evaluation of isotherms and adsorption kinetics. The adsorption isotherms adjusted better to the Sips model, indicating the heterogeneity of the system, with maximum adsorption capacities between 9.5 and 91 mg g1. The obtained values were satisfactory when compared to the data in the literature. The adsorption kinetics using PU as adsorbent reached equilibrium in 60 minutes and followed pseudosecond order (LAS) and diffusion (CDP). The results obtained were satisfactory, indicating that the polymeric residues can be used as adsorbents for the removal of surfactants in wastewater. However, more studies should be carried out in order to optimize the parameters and evaluate ways of rapid removal. In any case, this work opens up new possibilities for the use, recovery and added value of polymeric waste.