Regeneration of Granular Activated Carbon (GAC) Columns Used for Removal of Lead

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Abstract
Granular activated carbon (GAC) columns that were used for Pb removal were regenerated using several regeneration schemes. Acid type (HCl and HNO 3 ), regenerant concentration (0.1 N or 1 N), acid reuse, and a NaOH-only rinse were studied. Column performance was assessed using the Pb surface loading (X/M) at exhaustion, and the number of bed volumes (BVs) treated at breakthrough and exhaustion. The type of acid used did not affect column performance. Increasing the regenerant concentrations from 0.1 N to 1 N increased the surface loading at exhaustion and the BVs treated at breakthrough by 20% and 25%, respectively. Acid reuse did not significantly affect column performance, although desorption efficiencies decreased with the run number. The insensitivity of Pb removal to desorption efficiency indicates that the dominant removal mechanism is precipitation on the carbon surface or in the carbon pore, not adsorption. All measures of column performance deteriorated slightly when base-only regeneration was employed. However, column performance for the 1 N NaOH experiments were similar to the 0.1 N HCl-0.1 N NaOH studies.