Statistical optimization study of adsorption parameters for the removal of glyphosate on forest soil using the response surface methodology

The present study highlights the use of forest soil for glyphosate removal from aqueous solutions under different experimental conditions through batch mode and optimizing the process conditions. Maximum glyphosate adsorption (161.29 mg/g) occurred at pH 12. Experimental data of glyphosate biosorption onto forest soil fitted well to Langmuir isotherm model in comparison with the Freundlich and D-R model. Kinetic studies were carried out to get useful information on the rate of glyphosate adsorption onto the forest soil, which was found to follow pseudosecond-order model. Four important process parameters including glyphosate concentration (5-30 mg/L), pH (2-14), contact time (5-120 min) and dose (0.05-1.5) were optimized to obtain the best response of glyphosate removal using the statistical Box-Behnken design. Optimized values of initial glyphosate concentration, pH, contact time and dose were found as 25.74 mg/L, 12.0, 119.99 min and 0.05 g, respectively, with the 87.8% removal efficiency. The efficiency of the operating variables was also assessed by the percent contribution and Pareto analysis. Thermodynamics data suggest that glyphosate adsorption is spontaneous in nature. The results revealed that forest soil can be used as an effective and low-cost adsorbent to remove glyphosate from aqueous solutions.