Dried sewage sludge as an efficient adsorbent for pollutants: cationic methylene blue removal case study

Sewage sludge valorization must be the favored solution of management for a residue that does not present the desired improvement in terms of wastewater treatment. The objective of this research work was to study the dye fixation capacity of the adsorbents produced from sewage sludge. The dried sewage sludge (DSS) was used as an adsorbent to remove a cationic dye, methylene blue (MB), from an aqueous solution in a batch system, as a function of contact time, pH, temperature and initial concentration. The proposed adsorbent was characterized using several techniques such as scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The adsorption equilibrium of MB was described using Langmuir, Freundlich and Sips equations. The equilibrium is perfectly adapted to the Langmuir model with a maximum adsorption capacity of 44.39 mg g−1 on a single layer. In order to study the adsorption mechanisms, first- and second-order kinetic models were used. The adsorbent produced from the sludge was capable of absorbing MB from the solution, with the expression of the second-order rate being preferred to that of the first order. In addition, the thermodynamic parameters were evaluated, demonstrating that the adsorption process is spontaneous and endothermic. Thus, this study convinced that the DDS proved to be an alternative, attractive, effective, economic, and environmentally friendly adsorbent for MB dye removal from aqueous solution. Graphic abstract: Schematic illustration of the prepared dried sewage sludge adsorbent for the removal of methylene blue from aquatic samples [Figure not available: see fulltext.].