Untreated anaerobically digested sewage sludge was used for the first time as a biosorbent for removing phenol from aqueous solution. Results showed that adsorption capacity was influenced by the pH of the aqueous solution with an observed maximum phenol removal at pH around 6–8. The adsorption equilibrium of phenolic compounds was obtained after almost two hours with an adsorption of approximately 90% of the phenolic compounds. A sorbent concentration of 1.8 g/L was found to insure the best removal percentage and the best sorbent capacity. Both Langmuir and Freundlich models have provided reasonable fittings for the data of phenol adsorption. The experimental data fitted the pseudo-second-order kinetic model and the intraparticle diffusion model. The values of change in Gibbs free energy (Δ
°), enthalpy (Δ
°) and entropy (Δ
°) were calculated. The thermodynamic study of adsorption process showed that the process was exothermic in nature.
Keywords: adsorption, phenol, anaerobically digested sludge, ADS, kinetics, thermodynamics