Modeling of Phenol Adsorption in Fixed- and Fluidized-Bed Columns Using Coal-Based Activated Carbon

The removal of phenol from wastewater is crucial due to its harmful effects on human health and the environment. This study investigates phenol removal using a sulfuric acid-activated coal-based adsorbent in fixed- and fluidized-bed columns, evaluating the effects of initial phenol concentration, flow rate, and bed height. In the fixed-bed adsorption, the optimum operating conditions were determined to be a bed height of 3.2 cm, a flow rate of 1.75 mL/min, and an initial phenol concentration of 100 mg/L based on the analysis of the mass transfer zone heights and removal efficiencies. While higher removal efficiencies were observed at lower flow rates and higher initial phenol concentrations, increasing the bed height did not improve removal efficiency due to increases in the unused bed heights. In the fluidized-bed column, higher phenol removal efficiencies were achieved with increased contact time at lower flow rates. The optimum operating flow rate was determined to be 18.38 mL/min depending on the minimum fluidization velocity. In contrast to fixed bed, it was determined that the initial phenol concentration did not have a significant effect on removal efficiency in the fluidized-bed column due to the presence of mixing. When the bed heights were equal, the fluidized bed reached saturation faster at higher flow rates compared with the fixed bed, allowing for the treatment of larger volumes of water in shorter periods. In the modeling studies, the Adams–Bohart, Wolborska, Thomas, and Yoon–Nelson models were fitted to the experimental data, and the model predictions were compared with breakthrough curves. Thomas and Yoon–Nelson models showed the best fit to the experimental data, but the predicted removal efficiencies were lower than those of the experimental data. The discrepancy was attributed to neglecting diffusion mass transfer in the models.