Role of adsorption in granular activated carbon‐fluidized bed reactors

A granular activated carbon‐fluidized bed reactor (GAC‐FBR) was used to treat groundwater contaminated with toluene. The performance of the reactor and the amount of adsorbed toluene on the GAC were investigated during start‐up, under pseudo‐steady‐state conditions, during a step‐increase in the applied organic loading rate (OLR) and after the OLR was returned to the initial level. Under constant, organic loading rate conditions (5.4 kg chemical oxygen demand/m3 day), 99.4% removal of an inlet toluene concentration of 2.7 mg/L was observed. The amount of adsorbed toluene was measured at various points in time by performing a solvent extraction on samples of GAC carrier removed from the FBR system. There were significant changes in the amount of toluene adsorbed onto the GAC during non‐steady state (start‐up and step OLR periods). This confirms the interpretation from previous biological activated carbon (BAC) studies that adsorption serves to dampen concentration changes in the system, thereby providing improved stability effluent quality and overall system efficiency compared with systems employing only biodegradation. The results also conclusively demonstrate that bioregeneration occurs in BAC systems such as the GAC‐FBR process configuration.