Laboratory evaluation of bioaugmentation for aerobic treatment of RDX in groundwater

Abstract

The potential for bioaugmentation with aerobic explosive degrading bacteria to remediate hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) contaminated aquifers was demonstrated. Repacked aquifer sediment columns were used to examine the transport and RDX degradation capacity of the known RDX degrading bacterial strains Gordonia sp. KTR9 (modified with a kanamycin resistance gene) Pseudomonas fluorescens I-C, and a kanamycin resistant transconjugate Rhodococcus jostii RHA1 pGKT2:Km+. All three strains were transported through the columns and eluted ahead of the conservative bromide tracer, although the total breakthrough varied by strain. The introduced cells responded to biostimulation with fructose (18 mg L(-1), 0.1 mM) by degrading dissolved RDX (0.5 mg L(-1), 2.3 µM). The strains retained RDX-degrading activity for at least 6 months following periods of starvation when no fructose was supplied to the column. Post-experiment analysis of the soil indicated that the residual cells were distributed along the length of the column. When the strains were grown to densities relevant for field-scale application, the cells remained viable and able to degrade RDX for at least 3 months when stored at 4 °C. These results indicate that bioaugmentation may be a viable option for treating RDX in large dilute aerobic plumes.

Evaluation of microbial transport during aerobic bioaugmentation of an RDX-contaminated aquifer

“…Bioaugmentation of UMCD sediment columns with known aerobic RDX degrading strains was successful at increasing the RDX degradation rate tenfold following the addition of a suitable carbon source (Fuller et al 2015). The transport, survival, and long-term activity of the aerobic RDX degraders in the repacked sediment column experiments provided a proof-of-concept that UMCD is a suitable site for aerobic RDX bioaugmentation.…”

“…Bioreactors were amended with 50 lg L -1 of kanamycin for the growth of RHA1 Km R and KTR9 Km R . After the required cell density (5 9 10 14 total cells) was achieved, each culture was concentrated by cross-flow filtration and tangential flow centrifugation according to Fuller et al (2015). Each culture was resuspended and starved in approximately 18 L of UMCD artificial groundwater (AGW; Fuller et al 2015) which was split between two, 20-L soda kegs that were pressurized with air to maintain aerobic conditions.…”

“…After the required cell density (5 9 10 14 total cells) was achieved, each culture was concentrated by cross-flow filtration and tangential flow centrifugation according to Fuller et al (2015). Each culture was resuspended and starved in approximately 18 L of UMCD artificial groundwater (AGW; Fuller et al 2015) which was split between two, 20-L soda kegs that were pressurized with air to maintain aerobic conditions. Kegs were stored at 4°C prior to being shipped, which was shown previously to maintain culture viability and RDX degrading activity for at least 6 months (Fuller et al 2015).…”

“…Each culture was resuspended and starved in approximately 18 L of UMCD artificial groundwater (AGW; Fuller et al 2015) which was split between two, 20-L soda kegs that were pressurized with air to maintain aerobic conditions. Kegs were stored at 4°C prior to being shipped, which was shown previously to maintain culture viability and RDX degrading activity for at least 6 months (Fuller et al 2015). The kegs were sealed with top cross-bars to maintain a watertight seal and packed into coolers equipped with ice packs for shipment.…”

“…Native UMCD sediments contain low levels of the xplA gene (10 2 -10 4 copies g -1 ) and accordingly, aquifer column and microcosm studies with site samples degraded RDX at low rates (first order coefficients = 0.08-0.17 d -1 ) or not at all under typical aquifer conditions (Crocker et al 2012;Fuller et al 2015). Bioaugmentation of UMCD sediment columns with known aerobic RDX degrading strains was successful at increasing the RDX degradation rate tenfold following the addition of a suitable carbon source (Fuller et al 2015).…”