Influence of adsorption on phenol transport through soil-bentonite vertical barriers amended with activated carbon

The potential for enhanced containment of phenol by soil-bentonite (SB) vertical barriers amended with activated carbon (AC) was investigated. Results of batch equilibrium adsorption tests on model SB backfills amended with 0-10 wt.% granular AC (GAC) or powdered AC (PAC) illustrate that the backfills exhibited nonlinear adsorption behavior that was described well by both the Freundlich and Tóth adsorption models. The AC amended backfills exhibited enhanced phenol adsorption relative to unamended backfill due to hydrophobic partitioning to the AC. Adsorption capacity increased with increasing AC content but was insensitive to AC type (GAC versus PAC). Results of numerical transport simulations based on the measured adsorption behavior show that the Tóth model yielded similar or lower phenol breakthrough times than the Freundlich model for the range of source concentrations (C(o)) considered in the simulations (0.1-10 mg/L). Breakthrough time decreased with increasing C(o) but increased with increasing AC content. Predicted breakthrough times for an SB vertical barrier amended with 2-10 wt.% AC increased by several orders of magnitude relative to the theoretical case of a nonreactive (non-adsorbing) barrier. The findings suggest that AC may be a highly effective adsorption amendment for sustaining the containment performance of SB vertical barriers.