Environmentally sustainable removal of methylene blue, Congo red, naphthalene, and phenanthrene using chitosan tea waste composite beads

Abstract

In this study, chitosan tea waste composite (CS/TW) bead-based adsorbent was prepared by coalescing tea waste and chitosan for wastewater treatment. The composite was characterized using XRD, FTIR, SEM, TGA, and BET to assess its structure, surface morphology, thermal stability, and surface area. The sorption performance has been examined using methylene blue (MB), Congo red (CR), naphthalene (Naph), and phenanthrene (Phen) as model pollutants. The adsorption of dyes was very rapid, especially for MB, which achieved equilibrium within one minute, whereas PAHs showed slower adsorption kinetics. Kinetic analysis indicated that MB and PAHs followed the pseudo-second-order model, while CR fit well with both the pseudo-first-order and pseudo-second-order models. Isothermal studies indicated that the Sips model best described the adsorption of CR and PAHs, whereas MB was a better fit in Freundlich model. The maximum adsorption capacities for MB, CR, Naph, and Phen were 395.01, 173.51, 96.32, and 14.51 mg g^-1, respectively. The adsorbent demonstrated pH dependence in removal efficiency and various responses to salt and humic acid interferences. Even after five regeneration cycles, CS/TW maintained over 95.43 % removal efficiency for MB, and a moderate decrease was noted for Naph, indicating good reusability and stability. The composite beads also removed target pollutants from real water samples collected from the Baltic Sea, Vistula River, and municipal sources. These findings highlight the potential of CS/TW beads as an economical and environmentally friendly material for efficient and reusable wastewater treatment approaches.

Keywords: Adsorption; Chitosan composite beads; Dyes; Polycyclic aromatic hydrocarbons; Real wastewater treatment.