(272c) Geomembranes Containing Powdered Activated Carbon for the Isolation of Polychlorinated Biphenyl Contamination

Many hydrophobic solutes easily diffuse through the high-density polyethylene geomembranes used for storage or isolation of contaminated sediments. The goal of this work was to develop geomembrane barriers with improved performance in terms of both the flux and the lag time of contaminants. Breakthrough across high-density polyethylene was measured for two potential sediment contaminants, 1,2,4-trichlorobenzene and 2,3',4',5-tetrachlorobiphenyl. Addition of powdered activated carbon (0.14 g carbon/cm³ membrane) reduced pseudo-steady-state flux through thin membranes (145 μm) by approximately 60%. Flux of 2,3',4',5-tetrachlorobiphenyl through a composite membrane with layers of poly(vinyl alcohol) with 0.05 g carbon/cm³ and high-density polyethylene (~130 μm each) was 69% lower than expected for a similar layered membrane without the sorptive scavenger. Breakthrough curves were compared to different models for scavenger-containing membranes and were best described by the model in which sorption kinetics within the membrane were limited by the rate of diffusion from the membrane matrix to the carbon particle surfaces. With this assumption, the reduced flux of these contaminants through a field-scale high-density polyethylene barrier (2000 μm thickness) containing activated carbon was estimated. The field-scale estimates show a drastic reduction in flux compared with pure high-density polyethylene and a sorption capacity that is not exausted for a century or more.