Red-fleshed pitaya peels (Hylocereus polyrhizus) as a biosorbent for removal of hormone 17α-methyltestosterone in aqueous medium.

Residual shells of the red-fleshed pitaya (Hylocereus polyrhizus) in natura (IN) and post-alkaline treatment (AT) were investigated for the efficiency of removal of the endocrine disrupting hormone 17α-methyltestosterone (MT) in aqueous solution. The characterizations of the biosorbents pointed to changes on the surface of the material after alkaline treatment, in which the formation of micropores was observed, in addition to alterations on the composition and thermal stability of the biomass. FTIR analysis of the biosorbents after adsorption revealed important role of hydroxyl and carboxylic groups in the hormone adsorption. The mass transfer process occurred quickly reaching equilibrium in up to 120 min, following a kinetics of pseudo-second order at temperatures of 25, 35 and 45 °C. It is suggested that the slow step of the adsorptive process correspond to the formation of intermolecular interactions of greater intensity, such as hydrogen bonds. Equilibrium studies revealed a better percentage of removal at low concentrations of the hormone and at room temperature. The optimum pH for MT removal increased from 3 to 7 after alkaline treatment, with q_max of 1.93 and 1.23 mg g⁻¹ for the IN (at pH 3) and AT (at pH 7), respectively. The isothermal models suggested that the adsorption occurred in homogeneous sites with monolayer formation and enthalpically directed. These results, associated with the low concentrations in which the emerging contaminants are found, indicate that the biosorbent of pitaya may be a potentially advantageous and low-cost alternative for removal of the hormone from aqueous effluents. [ABSTRACT FROM AUTHOR]