Adsorptive removal of anionic dyes from aqueous solutions using spent mushroom waste

The removal of hazardous dyes has become a major economic and health concern to treat wastewater. In this study, efficient, low-cost, and eco-friendly spent mushroom waste (SMW) showed great potential for removing the anionic dyes, namely Direct Red 5B (DR5B), Direct Black 22 (DB22), Direct Black 71 (DB71), and Reactive Black 5 (RB5). The mechanisms of adsorption could be controlled by both physical and chemical adsorption. Scanning electron microscope analysis showed that SMW surface is porous and irregular. The kinetic study could be described well with the pseudo-second-order kinetic model, whereas the best representation of the equilibrium isotherm is the Langmuir model. The maximum adsorption capacities of SMW were found to be 18 mg g⁻¹ for DR5B, 15.46 mg g⁻¹ for DB22, 20.19 mg g⁻¹ for DB71, and 14.62 mg g⁻¹ for RB5. The analysis of thermodynamic study of ΔG°, ΔH°, and ΔS° proved that the adsorption of the tested dyes onto SMW was endothermic and spontaneous. Based on these results, SMW can be considered as high potential adsorbent for the removal of dyes from wastewater.