A comparative study of Cu(II) biosorption onto dried activated sludge of different sludge ages

Abstract This study compared the Cu(II) biosorption performance of dried activated sludge (DAS) of different sludge ages (5, 20 and 40 days). The influence of contact time, initial concentration, biosorbent dosage, pH, and sludge age on Cu(II) biosorption onto DAS was investigated. The optimal conditions for biosorption were identified as: 3-h contact time, pH 3–5, 0.1 g DAS dosage, and 100 mg/L initial Cu(II) concentration. The Langmuir isotherm and pseudo-second-order kinetics provided excellent fits to the experimental data. The adsorption capacity decreased with increasing sludge age, with maximum monolayer adsorption capacities of 40.32, 37.04 and 24.27 mg/g for DAS-5, DAS-20 and DAS-40, respectively. Thermodynamic analysis revealed that the Cu(II) biosorption onto DAS was a spontaneous and endothermic physisorption process with an increase in randomness. The Fourier Transform Infrared Spectroscopy analysis indicated the involvement of –OH, –NH, C=O, C–N and nitro and disulfide groups in Cu(II) biosorption. These findings demonstrate the potential of DAS as a cost-effective and sustainable biosorbent for copper removal.