Nitrated energetics are widespread contaminants due to their improper disposal from ammunition facilities. Different classes of nitrated energetics commonly co-exist in ammunition wastewater, but co-removal of the classes has hardly been documented. In this study, we evaluated the catalytic destruction of three types of energetics using palladium (Pd0) nano-catalysts deposited on H2-transfer membranes in membrane catalyst-film reactors (MCfRs). This work documented nitro-reduction of 2,4,6-trinitrotoluene (TNT), as well as, for the first time, denitration of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and pentaerythritol tetranitrate (PETN) over Pd0 at ambient temperature. The catalyst-specific activity was 20- to 90-fold higher than reported for other catalyst systems. Nitrite (NO2-) released from RDX and PETN also was catalytically reduced to dinitrogen gas (N2). Continuous treatment of a synthetic wastewater containing TNT, RDX, and PETN (5 mg/L each) for more than 20 hydraulic retention times yielded removals higher than 96% for all three energetics. Furthermore, the concentrations of NO2- and NH4+ were below the detection limit due to subsequent NO2- reduction with > 99% selectivity to N2. Thus, the MCfR provides a promising strategy for sustainable catalytic removal of co-existing energetics in ammunition wastewater.
Keywords: Denitration; Hollow fiber membrane; Membrane catalyst-film reactor; Nitrated energetics; Palladium catalysis.
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