Adsorptive removal of Methylene Blue using novel adsorbent from palm oil mill effluent waste activated sludge: Equilibrium, thermodynamics and kinetic studies

Waste activated sludge (WAS) from palm oil mill effluent (POME) treatment plant was used to adsorb Methylene Blue (MB) in a batch system. The WAS was prepared at lower temperature compared to the previous studies. Parameters such as initial MB concentration, pH, and temperature were studied for their effects on the adsorption process. Results showed that the uptake of MB increased with an increase in both the initial MB concentration and the pH, and decreased with an increase in temperature. Both the Langmuir and the Freundlich Isotherms are fit to explain the MB adsorption on WAS. The maximum monolayer adsorption capacity of WAS was found to be 66.23 mg/g at 30 °C. The kinetic data for this study fit well the pseudo-second-order kinetic with a R2 more than 0.95. Thermodynamic analysis was performed by evaluating the Gibbs Free Energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) of the process. The evaluation showed that the MB adsorption process onto WAS is an exothermic process and is spontaneous in nature. Hence, this work reveals that the use of POME WAS is an innovative application of a local waste product as an adsorbent for MB removal.

► Waste activated sludge (WAS) from palm oil mill effluent treatment plant turned into adsorbent via chemical activation without high thermal treatment.
► Obeys both Langmuir and Freundlich Isotherm with maximum monolayer adsorption capacity of 66.23 mg/g.
► Adsorption kinetics fits the pseudo-second order model.
► Methylene Blue (MB) adsorption onto WAS is exothermic and spontaneous.
► MB adsorbed onto WAS by electrostatic attraction.