Assessment of methylene blue adsorption on a composite based on cetyl tri-methyl ammonium bromide and sludge biochar: kinetic, mechanism, and cost estimation

Organic pollutants such as methylene blue (MB) dye are commonly found in industrial effluents and pose a threat to the aquatic environment. Adsorption is an effective, simple, and economical treatment method, especially when based on the use of porous biocomposite materials. This study aims to evaluate the kinetic, parametric, and economic performance of cetyl-trimethyl-ammonium bromide-sludge biochar (CTAB/SB) composite for MB removal. The CTAB/SB composite was synthesised by sludge calcination and CTAB impregnation and was characterised using SEM-EDX, FTIR, and XRD. Adsorption performance was assessed under various pH, adsorbent doses, and MB concentration, and modelled using Langmuir and Freundlich isotherms, as well as pseudo-first-order and pseudo-second-order kinetic models. MB adsorption at 20 mg L−1 reached 73.16 mg g−1 for a CTAB/SB dose of 0.2 g L−1 at pH 8, and the removal rate exceeded 97.10% at a CTAB/SB dose of 0.8 g L−1. The Langmuir isotherm (R2 = 0.9988) and the pseudo-second-order kinetic model (R2 = 0.9918) best describe the process, suggesting monolayer adsorption. The CTAB/SB composite is an effective, economical, and long-lasting adsorbent, enabling 1 L of MB to be treated for just $0.3. Prospects include its large-scale application and the study of its regenerability.HighlightsThe CTAB-sludge biochar (SB) composite is developed for methylene blue (MB) adsorption.The CTAB/SB material achieves a maximum adsorption capacity of 73.16 mg g−1 at pH 8 and a removal rate of 97.10%.The adsorption process of MB on CTAB/SB follows the Langmuir isotherm and the pseudo-second-order kinetic model.The composite offers an economical and sustainable solution, treating 1 L of methylene blue for just $0.3.