A Promising, Highly Effective Nitrate Sorbent Derived from Solid Olive Mill Residues

Abstract

Olive mill residues have been valorized by chemical modification with amines to improve their adsorption capacity and to be used as a low-cost bioadsorbent for nitrate removal. The Taguchi method was used to optimize the process. By performing a three-factor analysis with three levels, it was possible to significantly reduce the number of experiments to be performed and to obtain the best working conditions. The results of the Taguchi method showed that the highest adsorption capacity was 110 mg·g−1 with a functionalized biomass dose of 1 g·L−1 using an initial nitrate concentration of 500 mg·L−1. Field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the surface morphology and study the chemical changes that occurred in the biomass. For the best conditions of the Taguchi approach, the kinetic and equilibrium aspects of the adsorption process were analyzed. The adsorption isotherms obtained were successfully fitted to the Freundlich (R2 = 0.98) and Langmuir (R2 = 0.97) models. The kinetics of the process were studied, and the data obtained fit very well to the pseudo-second-order model (R2 = 0.99). The adsorption values obtained suggest that it is a bioadsorbent with great potential for nitrate retention in aqueous solutions.