ADSORPTION OF BISPHENOL-A AT ENVIRONMENTAL CONCENTRATIONS: RICE HUSK ASH AS AN ALTERNATIVE ADSORBENT TO ACTIVATED CARBON

Abstract

The presence of micropollutants in aquatic matrices has become a relevant environmental concern, since conventional wastewater treatment plants are not designed to remove them efficiently. Among these compounds, bisphenol-A (BPA), an endocrine disruptor of wide occurrence, stands out. This work evaluated the efficiency of adsorptive processes in removing BPA at concentrations in the order of ng L⁻¹, comparing rice husk ash (RHA), an agro-industrial residue, to commercial activated carbon (AC). The adsorbents were characterized for particle size distribution, surface area, specific mass, morphology, chemical composition, functional groups, pH and point of zero charge. Batch kinetic tests evaluated contact time (0–60 min), initial BPA concentration (50, 500 and 1000 ng L⁻¹) and adsorbent dosage (0.5, 5.0 and 10 g L⁻¹). Experimental isotherms were fitted to Langmuir and Freundlich models, and BPA quantification was performed by liquid chromatography coupled to mass spectrometry (UHPLC-MS). RHA, with macroporous structure, promoted rapid adsorption with equilibrium tendency at 60 min and efficiencies greater than 99%. The pseudo-second-order model best described the kinetics for both adsorbents, suggesting chemisorption as the rate-determining step. BPA removals ranged from 7.5% to 99.7% for RHA and 16.5% to 99.2% for AC. The results indicate the potential of rice husk ash as an alternative low-cost adsorbent for BPA removal.