Eggshell Waste as a Sustainable Adsorbent for Effective Removal of Direct Dyes from Textile Wastewater

Abstract

This study aims to evaluate the performance of calcined eggshells (CES) for removing pollutants across three textile effluent types with increasing complexity (aqueous, reconstituted, and real effluent), highlighting its potential as an adsorbent for a wide range of pollutants. The results indicate that dye adsorption capacities in aqueous, reconstituted, and real effluents were 80.1, 36.3, and 64.8 mg g⁻¹, respectively. CES is most effective at removing turbidity from real effluent, achieving a 98% removal efficiency. However, the COD removal efficiency by CES is relatively low, reaching only 33%, and is at least five times slower than dye removal, requiring a higher CES dose. Dye adsorption follows the Langmuir isotherm and pseudo-second-order kinetics, with an endothermic and spontaneous process. Desorption studies confirm CES reusability. All characterizations indicated that adsorption occurred through physisorption, electrostatic forces, hydrogen bonding, van der Waals interactions, and ion exchange, with the release of calcium. Overall, this research demonstrates the potential of calcined eggshells as a cost-effective and efficient solution for removing dyes, turbidity, and some COD from textile wastewater. However, the release of calcium ions in the treated effluent requires additional treatment, such as nanofiltration.