- 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.