Sorptive and reactive scavenger-containing sandwich membranes as contaminant barriers

The barrier properties of composite membranes containing either zero-valent iron nanoparticles or powdered activated carbon mixed into an aqueous clay suspension and sandwiched between two sheets of high-density polyethylene were measured using carbon tetrachloride and trichloroethylene as model contaminants. The lag time to trichloroethylene breakthrough increased 17-fold when 24 wt % powdered activated carbon was mixed into the 400-μm -thick center layer of the composite. Zero-valent iron was successful in extending the lag time for carbon tetrachloride but not for trichloroethylene, presumably because the latter reaction with zero-valent iron is slow relative to diffusion. Approximately 30% of the total iron in the composite membrane was consumed before carbon tetrachloride breakthrough, a major improvement over the 2-3% reported previously for single-layer high-density polyethylene membranes containing iron nanoparticles. Simplified multilayer membrane models used to describe contaminant breakthrough are consistent with the experimental results.