Sorption of distillery spent wash onto fly ash: Kinetics, mechanism, process design and factorial design

Batch and continuous experiments were performed for the sorption of distillery spent wash onto fly ash particles. The Freundlich and pseudo-second order equation were found to fit the equilibrium data perfectly. The Weber-Morris intraparticle diffusion isotherm equation was used to predict the sorption mechanism and the predicted equation for 10% dilution of spent wash sorption is qt = 1.1344t0.5 + 33.304. The optimization using 23 factorial design of experiments provides optimal removal of color of 93% for dilution (5%), dosage of adsorbent (10 g) and temperature (293 K). The actual color removal at optimal conditions was 92.24%, confirms close to the factorial design results. The complete error analysis using six non-linear error functions: Chi-square (χ2); sum of square errors (SSE); composite fractional error function (HYBRD); derivative of Marquardt's percent standard deviation (MPSD); average relative error (ARE); sum of absolute errors (EABS) were calculated. Free energy of adsorption at 293 K (ΔG0 = −1574.67 J), enthalpy change (ΔH0 = −32.5487 KJ) and entropy change (ΔS0 = 105 J/K) were calculated to predict the nature of adsorption. Adsorption studies in a packed column were evaluated using Bed depth service time model, Thomas model and Adams-Bohart model.