Adsorção de bisfenol-a utilizando cinza de casca de arroz e carvão ativado

Abstract

Currently, the focus of studies on contaminants in water and effluent matrices deals with the presence of micropollutants and their effects on the environment and public health. The problem involved is due to evidence that conventional Wastewater Treatment Plants (WWTP) are not efficient in removing these pollutants. Therefore, there is a need to implement advanced technologies to polish the treatment. Among several techniques under study, adsorption processes stand out as a viable alternative for reducing contaminants, such as the endocrine disruptor Bisphenol A (BPA), which is the subject of this work. In this sense, this work aimed to study the efficiency of adsorptive processes to reduce BPA concentrations in aqueous solutions. Rice Husk Ash (RHA) was tested as an alternative adsorbent to Activated Carbon (AC). The AC was characterized through analysis of granulometric distribution, surface area, specific mass, hydration capacity, pH, zero load test, loss on ignition, total carbon, elemental chemical composition, determination of functional groups and image analysis. Kinetic and equilibrium adsorption studies (isotherms) were performed with standard BPA solutions, quantified by Liquid Chromatography coupled to Mass Spectrometry. In the adsorption kinetics, the following variables were evaluated: contact time (15, 30, 45 and 60 minutes); initial adsorbate concentration (50, 500 and 1000 ng L-1) and adsorbent dosage (0.5, 5.0 and 10 g L-1). The kinetic models of Pseudo-first order and Pseudo-second order were fitted to the experimental data, as well as the obtained experimental isotherms were fitted to the Langmuir and Freundlich models. The characteristics of activated carbon showed a uniform microstructure formed by micro and mesopores and the presence of functional groups such as carboxylic acids, alcohols and phenols. Differently, RHA has macroporous structures, which allowed a fast adsorption, tending to equilibrium after 60 minutes, with removal efficiencies above 99.0%. Among the kinetic models, the pseudo-second order linear model fitted better to BPA adsorption, for both adsorbents, reaching k2 up to 0,99 for RHA and AC. The adsorption isotherms were linear, with the Freundlich isotherm as a reference for adjustments for BPA adsorption using RHA, while for the AC, no model showed unanimity. BPA removal values with RHA ranged from 7,5% to 99,7%; and for activated carbon between 16,5% and 99,2%. These results indicate the potential of using rice husk ash as an alternative adsorbent for BPA adsorption.