Nitrate removal from aqueous solution: Screening of variables and optimization

The adverse effects caused by the increase in nitrate concentration in drinking water have prompted researchers to find green and economical methods for nitrate removal. Mineral materials are suggested for this purpose due to their economic and environmental benefits. In this study, Iranian natural zeolite was used for this purpose. An organic surfactant, HDTMA-Br, was used to modify the natural zeolite. Fourier-transform infrared spectroscopy (FTIR) verified that the surfactant was loaded on the zeolite surface. The influence of various parameters on adsorption was studied using the Taguchi method. They were screened by Taguchi’s L8 array, and four significant variables were determined: mass of adsorbent, particle size, contact time, and competing anion concentration. The Taguchi L9 array was used to determine the optimum condition of these significant variables. Analysis of the results showed that the concentration of the competing anion was the most significant variable on the nitrate adsorption by the surfactant modified zeolite (SMZ). In the optimum conditions, SMZ removed about 90% of nitrate from the aqueous solution obtained at a 20 mg/L initial nitrate concentration, 10 min contact time, 15 g adsorbent, and without any competing anion. The study of the adsorption isotherms showed that the nitrate adsorption process by SMZ from the aqueous solution fits well with the Freundlich and linear models.