The Effect of Regeneration on the Adsorptive and Mechanical Properties of WG-12 Granular Activated Carbon Used in Water Treatment: A Case Study

This study evaluated the effectiveness of regenerating WG-12 granular activated carbon used in drinking water treatment, based on a case study of the “Miedwie” Water Production Plant supplying the city of Szczecin, Poland. The investigation was conducted using samples collected from eight adsorption beds after five years of operation. Thermal regeneration was performed in a steam atmosphere at 600–850 °C for 20 min, and the regenerated samples were subsequently demineralized using a 1.75% HCl solution. The effectiveness of the process was evaluated using changes in the iodine number, BET specific surface area, bulk density, mechanical strength, regeneration mass yield, and an adsorption–mechanical trade-off index. Thermal regeneration substantially improved the adsorption properties of the spent carbon. The mean iodine number increased from 528.2 mg/g to 858.1 mg/g after regeneration at 800 °C, while the specific surface area increased from 480.4 to 806.9 m2/g. The application of demineralization further enhanced process efficiency. In the 800 °C + 1.75% HCl variant, an iodine number of 903.9 mg/g and a specific surface area of 883.6 m2/g were obtained, corresponding to recoveries of 95.1% and 98.2% of the reference values for virgin carbon, respectively. The improvement in adsorption properties was accompanied by a decrease in bulk density and a moderate reduction in mechanical strength. The most favorable process variant was regeneration at 800 °C combined with HCl demineralization, for which the adsorption–mechanical trade-off index reached 93.7%. The results indicate that regeneration of WG-12 effectively restores the adsorption potential of the material and may reduce the need for complete bed replacement while maintaining acceptable mechanical durability. The analysis also indicates that increasing the temperature to 850 °C is not technologically justified because it does not improve adsorption performance and simultaneously increases material loss, which is important from both economic and sustainability perspectives. The proposed ISM index should be regarded as a supplementary screening tool for comparing regeneration variants within the same experimental system, whereas mass yield and cost-related aspects should be evaluated separately to avoid overstating the universality of the index.