Hexahydro-1,3,5-trinitro-1,3,5-triazine mineralization by zerovalent iron and mixed anaerobic cultures

Soil microcosms were used to evaluate the potential benefits of an integrated microbial-Fe-0 system to treat groundwater contamination by RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine). Microcosms amended with both Fe-0 filings and municipal anaerobic sludge mineralized RDX faster and to a greater extent than separate treatments, with up to 51% (CO2)-C-14 recovery after 77 d. The nitroso byproducts 1,3-dinitro-5-nitroso-1,3,5-triazacyclohexane (MNX), 1,3-dinitroso-5-nitro-1,3,5-triazacyclohexane (DNX), and 1,3,5-trinitroso-1,3,5-triazacyclohexane (TNX) were detected in all microcosms, although these compounds never accumulated above 5% of the added RDX on a molar basis. A soluble intermediate that was tentatively identified as methylene-dinitramine [(O2NNH)(2)CH2] was relatively persistent, although it accumulated to a much lower extent in combined-treatment reactors than in sets with Fe-0 or sludge alone. Some of the radiolabel was bound to soil and Feii and could not be extracted with CH3CN. This fraction, which was recovered by combustion with a biological oxidizer, was also found at lower concentrations in combined-treatment reactors. This work suggests that permeable reactive Fat barriers might be an effective approach to intercept and degrade RDX plumes and that treatment efficiency might be enhanced by biogeochemical interactions through bioaugmentation.