Valorization of using agro-food waste as eco-friendly adsorbents for toxic dye removal from contaminated water

In this study, dried watermelon peels (DWP), an appropriate biological adsorbent, were employed to extract Acid Blue 193 (AB193) and Acid Orange 95 (AO95) from their aqueous solutions. These sorbents are affordable, safe for the environment, widely available, and very efficient.. A variety of analysis, such as Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDX) and Fourier transform infrared (FTIR), have been used to determine the surface physicochemical properties before and after the adsorption process. In general, the characterization investigations showed that the adsorbent chemical structure contained several types of oxygenated functional groups and had a suitable shape for dye removal. Experimental work was done to identify the ideal working conditions, which were 60 min contact time, 0.3 g adsorbent mass, 30 0C, and pH= 3. This range of initial dye concentration was 25-150 ppm., and the percentage of removal reached to 97.99 % and 95.51 % for AB193 and AO95 respectively. The Freundlich model was found to provide a good fit to the data in terms of equilibrium, while the thermodynamic parameters suggested that the process was spontaneous and exothermic in nature. Additionally, kinetic tests showed that the acidic dyes removal rate followed a pseudo-second-order model, indicating that the adsorption was controlled by either intra-particle diffusion or diffusion on the stationary layer covering the adsorbent particles. Finally, the information gathered in this study supported the interest in using agricultural waste products as inexpensive lignocellulosic sorbents that could replace other pricey adsorbents in wastewater treatment.