Closing the active carbon cycle: Regeneration of spent activated carbon from a wastewater treatment facility for resource optimization

This study focusses on the regeneration of spent activated carbon sourced from a wastewater treatment facility using both conventional and microwave reactors with similar reaction parameters. The active carbon was characterized by iodine and methylene blue adsorption as a measure of micro- and mesoporosity. The process parameters were adjusted to identify the influence of intensifying operating parameter on the effectiveness of the regeneration process. Optimal activity was observed in the sample regenerated at 600 °C for 2 h in CO₂. There was a 17.1 % and 141 % increase in iodine and methylene cyanine adsorption values, respectively, versus the spent activated carbon. This indicates restoration of ∼83 % and ∼90 % of the adsorptive capabilities of fresh activated carbon. The adsorption properties of regenerated carbon are enhanced in microwave reactors under CO₂ atmosphere due to the benefits of microwave heating in expediting the thermal desorption of adsorbates via devolatilization and partial oxidation with minimal disruption to the carbon's pore structure. This demonstrates the feasibility and advantage of microwave reactors for reactivating spent active carbon and the importance of reaction parameter optimization for obtaining regenerated active carbon with enhanced quality.