Enhanced Degradation of TNT and RDX by Bio-reduced Iron Bearing Soil Minerals

Abstract

We demonstrated that reductive degradation of 2,4,6-Trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (Royal Demolition Explosive, RDX) can be enhanced by bio-reduced iron-bearing soil minerals (IBSMs) using Shewanella putrefaciens CN32 (CN32). The degradation kinetic rate constant of TNT by bio-reduced magnetite was the highest (0.0039 <TEX>$h^{-1}$</TEX>), followed by green rust (0.0022 <TEX>$h^{-1}$</TEX>), goethite (0.0017 <TEX>$h^{-1}$</TEX>), lepidocrocite (0.0016 <TEX>$h^{-1}$</TEX>), and hematite (0.0006 <TEX>$h^{-1}$</TEX>). The highest rate constant was obtained by bio-reduced lepidocrocite (0.1811 <TEX>$h^{-1}$</TEX>) during RDX degradation, followed by magnetite (0.1700 <TEX>$h^{-1}$</TEX>), green rust (0.0757 <TEX>$h^{-1}$</TEX>), hematite (0.0495 <TEX>$h^{-1}$</TEX>), and goethite (0.0394 <TEX>$h^{-1}$</TEX>). Significant increase of Fe(II) was observed during the reductive degradation of TNT and RDX by bio-reduced IBSMs. X-ray diffraction and electron microscope analyses were conducted for identification of degradation mechanism of TNT and RDX in this study. 4-amino-dinitrotoluene were detected as products during TNT degradation, while Hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine, Hexahydro-1,3-dinitroso-5-nitro-1,3,5triazine, and Hexahydro-1,3,5-trinitroso-1,3,5-triazine were observed during RDX degradation.