Harnessing a carbon-based material from food waste digestate for dye adsorption: the role of hydrogel beads in enhancing the material stability and regenerative capacity

Abstract

This study focuses on both ecological and economic gains from food waste treatment. Accordingly, anaerobic digestion and adsorption have been combined to achieve these goals, resulting in synergistic effects that improve productivity. Firstly, a considerable amount of methane (energy source) was produced by the anaerobic digestion of food waste (FW) under mesophilic conditions (38 °C), resulting in a biologically activated digestate. Secondly, the residue of anaerobic digestion (digestate) was utilized as raw material to design two types of low-cost adsorbents for dye removal: a carbon-based material (CM-HNO₃) and an alginate encapsulated carbon-based material (CM-HNO₃@Alginate beads). We evaluated the adsorption capacity of the designed carbon materials to eliminate the target pollutant methylene blue (MB) from aqueous solutions. The results show that the CM-HNO₃ and CM-HNO₃@Alginate beads present maximum dye adsorption capacities of 303.03 mg g⁻¹ and 212.77 mg g⁻¹, respectively. Further, the adsorption process was found to fit best to the Langmuir and pseudo-second-order kinetic models for both the adsorbents. In addition, the CM-HNO₃@Alginate beads exhibited good long-term stability, regenerative ability, and high mass recovery, indicating that this absorbent is suitable for frequent usage.