Fixed-bed column and batch reactors performance in removal of diazinon pesticide from aqueous solutions by using walnut shell-modified activated carbon

Abstract

Abstract This paper evaluates adsorption of diazinon pesticide from aqueous solution onto walnut shell-modified activated carbon using fixed-bed column and batch system. Contact time, initial concentration, and pH were considered as variable parameters to obtain maximum adsorption capacity using batch technique. The pseudo-first-order, the pseudo-second-order, and Webber and Morris models were chosen to analyze adsorption kinetic data. The results indicated that adsorption process followed closely the pseudo-second-order kinetic model. The equilibrium adsorption data fitted the Freundlich isotherm well, with K f = 53 . 82 , n = 1.98, and R 2 = 0 . 9966 . For continuous fixed-bed column studies, the effect of inlet concentration (15–40 mg.lit−1), flow rate (9.5–16.5 lit.h−1), and bed height (10–30 cm) was investigated. Results showed that increase in inlet concentration and also bed height lead to increase of bed capacity. In addition, changes in flow rate from 9.5 to 14.5 lit.h−1 caused a decrease in bed capacity. However, a minor increase in bed capacity was observed via an increase in flow rate from 14.5 to 16.5 lit.h−1. The highest bed capacities were 34.98 and 34.31 mg.g−1 for the same initial concentration of 40 mg.lit−1, flow rates of 12 and 9.5 lit.h−1, and bed heights of 30 and 20 cm, respectively. Dynamic behavior of column was investigated by Bohart–Adams and Yoon–Nelson models. According to obtained results, Yoon–Nelson model can describe well the adsorption process. The findings of the current study show that the walnut shell-modified activated carbon can be successfully applied to remove diazinon pesticide from aqueous solution.