Biodegradation of RDX-contaminated wastes in a nitrogen-deficient environment

A feasible biological treatment process for RDX-contaminated wastes was demonstrated in a bench-scale system, using real wastewater of a munitions factory. The wastewater mixture tested included the nitramine RDX together with high levels of nitrate and various organic solvents such as cyclohexanone and acetone. The purpose of the study was to remove both RDX and nitrate in order to prevent groundwater contamination. A two-stage reactor system including an anoxic stage followed by an aerobic one was tested. The anoxic stage was aimed at removing nitrate by denitrification, using available carbon sources present in the waste mixture. Additional supply of carbon source (acetone) was required to support complete removal of nitrate. Further removal of residual organic was achieved in the aerobic stage together with total mineralization of RDX. Complete removal of nitrate in the anoxic stage was found to be crucial to RDX mineralization in the aerobic stage, since RDX was used solely as a nitrogen source. Additional carbon source (cyclohexanone) was also required in the aerobic stage to assure complete removal of RDX. The treatment scheme tested may be a cost-effective alternative to physico-chemical treatments such as carbon adsorption and UV destruction, commonly applied for explosives-contaminated wastes.