Optimization of Adsorption Parameters for Removal of Carbaryl Insecticide Using Neem Bark Dust by Response Surface Methodology

Abstract

Adsorptive removal of carbaryl from aqueous solutions by neem bark dust (NBD) was investigated in a batch method under laboratory conditions. At first, the effects of particle size, stirring rate, and contact time on the adsorption process were studied. The optimum value of particle size, stirring rate, and contact time were 200 μm, 250 rpm, and 25 min, respectively. Subsequently, response surface methodology (RSM) was applied to investigate the effects of other operating parameters such as solution pH (2–10), adsorbent dose (0.01–1 g), and initial concentration (5–20 ppm). The optimization of the process parameters and calculation of the effects and interactions of process variables were done by using Box-Behnken design (BBD) which is a subset of RSM. The independent variables were precisely optimized by making use of an objective function called “desirability function.” Based on the adsorption capacity and economical use of adsorbent, the input parameters were optimized by setting two different sets of criteria (I and II). The desirability of two different sets were 1.00 and 0.822, respectively, which explains that the estimated function can well represent the experimental model. The optimized result revealed that the NBD can be an effective adsorbent for the removal of carbaryl from an aqueous system. The adsorption of carbaryl on NBD was best analyzed with the Langmuir isotherm and the pseudo-second order kinetic model. From the kinetic study, the maximum adsorption capacity was found to be 142.85 mg g−1. Thermodynamic data confirmed the feasibility and spontaneous nature of the adsorption process.