Valorization of Municipal Sewage Sludge into Activated Carbon for Cationic Dye Removal

Abstract

This study demonstrates the potential of municipal sewage sludge collected from the wastewater treatment plant of Sidi Bel Abbès, Algeria, as a low-cost precursor for the production of activated carbon for the removal of Bezacryl Red GRL 180, a cationic textile dye, from aqueous solutions. The prepared material exhibited a synthesis yield of 69.3%, a low residual moisture content of 0.98%, an ash content of 1.9%, and an iodine number of 1129.5 mg g⁻¹, indicating promising characteristics for adsorption applications. FTIR and EDS analyses further revealed modifications in the surface functional groups following carbonization and phosphoric acid activation, while confirming the persistence of certain inorganic constituents in the resulting material.The adsorption experiments demonstrated that the removal efficiency depended on the adsorbent dosage, contact time, and solution pH. Under the investigated conditions, a dosage of 0.30 g of activated carbon achieved approximately 98% dye removal from a solution containing 0.05 g L⁻¹ Bezacryl Red, with the adsorption process reaching an apparent equilibrium after approximately 30 min. High removal efficiencies were also observed under acidic conditions, highlighting the importance of solution pH in the adsorption process. Kinetic modeling showed that the pseudo-second-order model provided the best fit among the investigated kinetic models, with coefficients of determination ranging from 0.97 to 0.98. Regarding adsorption equilibrium, the Langmuir and Freundlich models both described the experimental data well, with reported coefficients of determination of approximately 0.98, while the Temkin model showed a slightly lower value. The thermodynamic results reported in this study were consistent with a spontaneous and exothermic adsorption process over the investigated temperature range, although the thermodynamic parameters should be verified for internal consistency before final publication. Taken together,the findings highlight the potential of sewage-sludge-derived activated carbon as an alternative adsorbent for cationic dye removal and demonstrate the environmental value of converting a wastewater-treatment residue into a useful material. This approach could contribute to more sustainable sludge management while supporting the development of accessible treatment materials for dye-contaminated water. Further work should include detailed textural characterization, assessment of the influence of coexisting pollutants, regeneration and reuse tests, and evaluation of potential metal leaching from the sludge-derived material before its application in real textile wastewater treatment.