Operating capacity of GAC adsorbers—dissolved oxygen and extended service life

Abstract

ABSTRACT: The effect of molecular oxygen on the adsorptive capacity of activated carbon was evaluated in this study. It was determined that the capacity of granular activated carbon (GAC) for o‐cresol under oxic conditions can be more than 2.5‐fold the capacity attainable under anoxic conditions. This increase in the GAC adsorptive capacity under oxic conditions cannot be attributed to biological activity. The observed phenomenon was found to result from carbon mediated polymerization reactions of o‐cresol that occur in the presence of molecular oxygen. The rate of adsorbate polymerization was slower than the rate of adsorption and the presence of molecular oxygen did not affect adsorption kinetics during the initial phase of adsorbent‐adsorbate contact. However, the presence of molecular oxygen was demonstrated to have a significant impact on the breakthrough of o‐cresol from 5 GAC adsorbers operated in series (total bed length = 4 m, total GAC mass = 1 kg). During the first phase of the experiment, which was conducted under anoxic conditions, breakthrough of o‐cresol from all 5 adsorbers was accurately predicted using a plugflow homogeneous surface‐diffusion model and independently determined kinetic and capacity parameters. Furthermore, the effluent profiles collected under anoxic conditions exhibited almost no tailing during the later part of breakthrough as saturation was approached. On introduction of oxygen to this system the effluent o‐cresol concentration dropped significantly (from 200 mg/L to only 6 mg/L). The total exhibited GAC adsorptive capacity for the entire experiment was accurately predicted by the oxic adsorption isotherm.