Use of hexahydro-1,3,5-trinitro-1,3,5-triazine as a nitrogen source in biological treatment of munitions wastes

The purpose of this study was to develop a biological treatment process for the degradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a nitramine explosive present in munitions manufacturing and processing wastes. A real waste mixture containing RDX, nitrate and nitrite (NO_x), and several solvents (primarily cyclohexanone and acetone) was used as basic feed for bench-scale experiments. Pure culture experiments indicated that bacteria can use RDX as a nitrogen source and organic solvents as carbon sources under aerobic conditions. In addition, it has been found that inorganic nitrogen compounds might interfere with the use of RDX as a nitrogen source. Because NO_x are problematic constituents that should be removed anyway, anaerobic microbial denitrification was applied as a pretreatment stage to simultaneously remove NO_x and organics and to form a nitrogen-deficient environment for further aerobic degradation of RDX and residual organics. This conceptual approach was performed using two reactor systems: a two-stage anaerobic-aerobic system and a single reactor with anaerobic and aerobic stages in its operation cycle. All laboratory reactors were operated in the sequencing batch reactor mode. Both systems achieved complete NO_x removal in the denitrification stage with acetone serving as the carbon source and complete aerobic biodegradation of RDX with cyclohexanone serving as the carbon source.