Anaerobic biodegradation of RDX and TCE: Single- and dual-contaminant batch tests

Several sites in the United States have groundwater contaminated with mixtures of high explosives and chlorinated solvents. This research examined the ability of two microbial cultures (anaerobic sludge and a facultative enrichment culture) to biodegrade single- and dual-contaminant mixtures of trichloroethene (TCE) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) under anaerobic conditions. In single component batch tests, both cultures degraded 0.6-1mgRDX/L and its nitroso metabolites to below detection limits in <7days. During initial 9-day TCE biodegradation tests, the anaerobic sludge did not transform TCE, whereas the facultative culture transformed approximately 10% of the initial 1.4mgTCE/L. Prior to dual-contaminant batch tests, both cultures were grown in the presence of TCE. Subsequently, both acclimated cultures rapidly biodegraded mixtures of RDX and TCE. Both cultures degraded RDX and RDX-nitroso compounds to below detection limits in <4days. In the same tests, TCE-acclimated anaerobic sludge converted TCE primarily to cis-dichloroethene (cis-DCE), while the acclimated facultative culture produced cis-DCE and other chlorinated metabolites. These preliminary results demonstrate that anaerobic bioremediation may be part of a feasible groundwater remediation alternative for mixtures of TCE and RDX.