Reduction of hydraulic conductivity and reactivity in zero-valent iron columns by oxygen and TNT

The degradation of 2,4,6-trinitrotoluene (TNT) and other explosives by zero-valent iron (ZVI) is rapid and, as a result, potentially useful for both ex situ ground water pump-and-treat systems and in situ permeable reactive barriers. However, the usefulness of ZVI in either configuration may be limited by reaction-induced reduction in both hydraulic conductivity (K) and reactivity (as represented by the surface area-normalized rate constant, k(sa)). The impacts of dissolved oxygen and TNT on K and ksa are examined here using field and laboratory columns. The data suggest that K reduction in ZVI columns can be significant when dissolved oxygen is present. However, when TNT is present at approximately the same concentration (10 mg/L), it does not cause significant reduction in K. In contrast, TNT causes a significant reduction in k(sa), while dissolved oxygen appears to have relatively little impact on the reactivity of the columns toward TNT.