From disposal problem to valuable product: the route of sewage sludge as an adsorbent for congo red removal

The present work is an attempt to address the feasibility of sewage sludge as a cost-effective adsorbent for the Congo Red (CR) elimination from a wastewater sample. The physicochemical properties of treated sewage sludge SS₄₀ were identified by using several techniques, such as Thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), zeta potential, and Fourier transform infrared spectroscopy (FTIR), Furthermore, to describe the adsorption balance, the experimental results were analyzed using the Langmuir, Freundlich, and Sips isotherms. The equilibrium was perfectly described by the Langmuir model, and the peak adsorption capacity in the monolayer was 25.10 mg. g⁻¹ at 40 °C. The kinetic data of adsorption were analyzed by the Pseudo-First Order (PFO), Pseudo-Second Order (PSO), and Elovich models. The results indicated that both Elovich and PSO models were the most appropriate for describing the adsorption of CR onto (SS₄₀) for all initial CR concentrations, indicating that the chemisorption controlled the dye retention by SS₄₀. The determination of thermodynamic parameters showed that ΔG⁰ was − 9.42 kJ.mol⁻¹ at 40 °C, ΔH⁰ was 10.64 kJ.mol⁻¹, and ΔS⁰ was 30.14 J.mol⁻¹. K⁻¹. The adsorption of CR on SS₄₀ was found to be feasible, spontaneous, and endothermic. The results of this study demonstrate that sewage sludge from the domestic wastewater treatment plant can be used advantageously as an economical, easy-to-handle, and eco-friendly sorbent for the elimination of CR as an emerging pollutant from aqueous solutions.