Sustainable Detoxification of Methylene Blue in Wastewater via Tea Residue Adsorption: Optimization and Kinetics

Abstract

This study investigates the adsorption efficiency of Methylene Blue (MB) dye using tea waste as a cost-effective and environmentally friendly adsorbent. The impact of various parameters on MB removal was assessed, including solution pH, adsorbent dosage, pollutant concentration, and contact time. Optimal conditions were identified as pH 10, a dosage of 4 g/L, a concentration of 100 mg/L, and a contact time of 2 h, achieving nearly 99% removal efficiency at 25 °C. At pH 10, the highest adsorption capacity was 24.4 mg/g, and increasing the initial concentration to 500 ppm resulted in an adsorption capacity of 119 mg/g. Contact time showed a stable effect, and increasing the dosage enhanced MB adsorption. The adsorption isotherms were modeled by the Temkin, Freundlich, and Dubinin-Radushkevich (D-R) equations. The Freundlich model indicates favorable multilayer adsorption on heterogeneous surfaces. The Sips model confirms significant heterogeneity. The Temkin model, which assumes that the heat of adsorption decreases linearly with coverage due to adsorbent-adsorbate interactions, aligns strongly with the data. The D-R model provides insights into the adsorption mechanism. The Temkin and Freundlich models are most suitable, while the D-R model offers valuable insights, and the Sips model is less satisfactory. Moreover, the adsorption kinetics conformed to the pseudo-second-order model, indicating the process's efficiency and suggesting that chemisorption is the rate-limiting step. These findings underscore the potential of tea waste as a sustainable adsorbent for dye removal from wastewater, contributing to environmental remediation and water purification efforts.

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