| Trinitrotoluene (TNT), a nitroaromatic explosive, is a commonly encountered groundwater contaminant in the United States that poses a threat to human health even at aqueous concentrations in the part per billion level. This study assessed treatment techniques for TNT contamination that can be applicable in permeable reactive barrier technologies within the subsurface environment. Experimental investigations that involved batch kinetic tests of TNT with aqueous ferrous iron and six common minerals, as catalysts that can be incorporated in reactive barrier systems were carried out to test the reactivity of TNT in such systems. Further, column experiments were carried out to study the fate and transport of TNT through treatments that included minerals saturated with ferrous iron solution, and a geochemical model used to describe transport processes of TNT. Additionally, the sorption capability of geomembrane materials, which can be used for containment purposes, with TNT and four other commonly encountered groundwater contaminants was investigated.; Abiotic batch reactions involving combinations of TNT, ferrous iron (Fe 2+), six minerals and two pH buffers were performed. Unbuffered reactions between TNT, Fe2+, and calcite and siderite proceeded rapidly to completion; while, unbuffered reactions between TNT, Fe2+, and magnetite, pyrite, quartz, and goethite/quartz were non-reacive. Solution pH plays a significant role in the surface catalyzed reduction process of TNT with Fe2+. The presence of an excess Fe2+ concentration and a mineral surface or iron hydroxide coating was necessary for TNT reduction to proceed. Based on the results of the batch experiments, calcite and siderite were chosen as the mineral phase in the column experiments. Column breakthrough data achieved were modeled using the computer program PHREEQC. The high sorption parameters derived from modeled breakthrough curves allowed to decipher the possibility for TNT to undergo sorption to additional solid phases forming in the mineral treatment systems. Sorption and degradation are key processes that affect the transport of TNT in calcite and siderite minerals that are saturated with excess ferrous iron solution. Geomembranes have the capacity to uptake organic contaminants from solution through sorption processes. |
