Adsorptive removal of biophenols from olive mill wastewaters (OMW) by activated carbon: mass transfer, equilibrium and kinetic studies

In this study, the removal of biophenols from olive mill wastewater by activated carbon of different particle sizes has been carried out using the batch adsorption technique. The effects of the sorbent specific surface area and concentration, temperature, initial biophenols concentration, and contact time on the adsorption efficiency have been analyzed independently. The sorbent yields higher removal efficiency of biophenols as its specific surface area increases. When increasing the sorbent concentration from 10 to 50 g L-1, the sorbent uptake capacity increases from 20% to 41%, and it reaches a maximum value of 65 mg g(-1) at 298.2 K. Adsorption of olive mill wastewater biophenols is moderately rapid, being about 38% to 40% of the initial phenolic content after 120 min. Kinetic analysis shows that the adsorption process can be approximated by a pseudo-second-order model for which pore diffusion is the essential rate-controlling step. Equilibrium modeling by linearized adsorption isotherms reveals that a Langmuir-type isotherm with a preferable monolayer sorption would likely proceed. Calculated thermodynamic parameters such as Gibbs energy, enthalpy, entropy, activation energy, and sticking probability indicate that adsorption is a typical endothermic yet spontaneous process with a preferable physisorption mechanism. An external mass transfer coefficient model has been developed to determine the rate of adsorption controlled initially by the boundary layer film, with particular focus on its predictive performance. Copyright (C) 2016 Curtin University of Technology and John Wiley & Sons, Ltd.