Electrolytic Alkaline Decomposition of a Munition Constituent (RDX) Contaminated Groundwater

Abstract

Combined use of electrolysis and alkaline hydrolysis is explored for in-situ decomposition of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in laboratory experiments with simulated groundwater. Alkaline medium generated by water electrolysis at the cathode under direct electric currents will develop a permeable alkaline barrier for in-situ decomposition of RDX. Pseudo-first order transformation rate coefficients were developed from alkaline hydrolysis and electrolytic batch experiments for RDX decomposition with time. The results provided a target pH of 12 and a current density of 1 mA/cm2 for treatment of RDX under groundwater flow column experiment. The results from the one-dimensional sand-filled alkaline hydrolysis columns (5-cm ID) were used to develop reaction rate coefficients used in designing a large scale-up one-dimensional column to test the electrolytic generation of hydroxide (10-cm ID). The rate coefficient from the 5-cm alkaline columns (0.46 per hr) was used to calculate a column length (160 cm) for complete removal of RDX and its nitroso-substituted products under groundwater flow rate of 30 cm/day. Effluent RDX concentrations from the 10-cm scale-up column (4,000 μg/L influent) were less than 0.1 μg/L for 36 days of treatment. The study concludes that cathodes placed at the down-gradient of groundwater RDX plume can perform as an effective permeable alkaline hydrolysis barrier for decomposition of RDX to levels below EPA drinking water advisory limits.