Thermodynamics, Non-Linear Isotherms, Statistical Modeling and Optimization of Phosphorus Adsorption from Wastewater

Abstract

Palm Kernel Shell (PKN), an eco-friendly biomass, was carbonized and activated for the removal of phosphorus from wastewater through batch adsorption process. The studies evaluate the effects of pH, particle size, dosage and contact time on the adsorption capacity of the prepared adsorbent. The equilibrium concentration data and the amount of adsorption were described using non-linear regression analysis of the curve fitting toolbox of MATLAB 7.0. The mechanism of adsorption was determined through thermodynamic properties such as change in free energy ΔG (KJ mol^-1) and change in entropy ΔS (Jmol^-1K^-1). Statistical modeling via Central Composite Design (CCD) for process optimization was carried out. The obtained results showed that, adsorption data conformed to Freundlick Isotherm. The positive values of ΔH (KJ mol^-1) and ΔS (J mol^-1 K^-1) indicate the endothermic character of the reaction and the increased randomness at the solid-solution interface respectively during the adsorption process. The most significant main effect for performance of the adsorbent is contact time (P_value = 0.0000). Based on the result of the optimization of response surface model fit to experimental data, PKN reduced the effluent concentration from 373 to 24.095 mg L^-1, a performance of 93.54%. The minimum pH2, dosage (1000 mg) and particle size (0.2 mm) are local while the contact time (4.1 h) is a global optimum.