RDX degradation in bioaugmented model aquifer columns under aerobic and low oxygen conditions

Abstract

Degradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in laboratory columns following biostimulation and bioaugmentation was investigated using sediment and groundwater from a contaminated aquifer at a US Navy facility. No RDX degradation was observed following aerobic biostimulation with either fructose or lactate (both 0.1 mM) prior to bioaugmentation. Replicate columns were then bioaugmented with either Gordonia sp. KTR9, Pseudomonas fluorescens I-C (Ps I-C), or both strains. Under aerobic conditions (influent dissolved oxygen (DO) >6 mg/L), RDX was degraded following the addition of fructose, and to a lesser extent with lactate, in columns bioaugmented with KTR9. No degradation was observed in columns bioaugmented with only Ps I-C under aerobic conditions, consistent with the known anaerobic RDX degradation pathway for this strain. When influent DO was reduced to <2 mg/L, good RDX degradation was observed in the KTR9-bioaugmented column, and some degradation was also observed in the Ps I-C-bioaugmented column. After DO levels were kept below 1 mg/L for more than a month, columns bioaugmented with KTR9 became unresponsive to fructose addition, while RDX degradation was still observed in the Ps I-C-bioaugmented columns. These results indicate that bioaugmentation with the aerobic RDX degrader KTR9 could be effective at sites where site geology or geochemistry allow higher DO levels to be maintained. Further, inclusion of strains capable of anoxic RDX degradation such as Ps I-C may facilitate bimodal RDX removal when DO levels decrease.

Enhanced bioremediation of RDX and Co-Contaminants perchlorate and nitrate using an anaerobic dehalogenating consortium in a fractured rock aquifer

“…Although many RDX bioremediation studies have focused on biostimulation with an organic donor, recent studies have turned to bioaugmentation as an alternative bioremediation method to address the wide variety of site characteristics and the low cleanup goals for RDX. Initial bioaugmentation studies involved addition of aerobic RDXdegrading microbes (Crocker et al, 2015;Fuller et al, 2015Fuller et al, , 2017Michalsen et al, 2016). Achieving and maintaining aerobic conditions may be difficult in many contaminant plumes, however, especially when an organic donor source also needs to be added to support aerobic degradation.…”

“…Achieving and maintaining aerobic conditions may be difficult in many contaminant plumes, however, especially when an organic donor source also needs to be added to support aerobic degradation. Recent laboratory tests (Fuller et al, 2017) and a field test (Michalsen et al, 2020) used bioaugmentation with a combined inoculation of the aerobic RDX-degrading microbial species, Gordonia sp. KTR9, and a facultative RDX-degrading strain, Pseudomonas fluorescens strain I-C cells ("Strain I-C ′′ ) for degradation of RDX, without the presence of nitrate or perchlorate co-contaminants.…”

Right on target: using plants and microbes to remediate explosives

“…Despite encouraging initial results, both bacterial numbers of Gordonia sp. KTR9 and xplA levels declined over time (Crocker et al 2015;Michalsen et al 2016;Fuller et al 2017). Factors preventing the accumulation of sufficient numbers of xplAB-containing soil bacteria to remove RDX-contamination, preventing downstream contamination are unknown, but xplAB-engineered plant endophytic, and associated rhizospheric bacterial communities indigenous to a contaminated site would be predicted to successfully reestablish in that environment.…”

Effects of Perchlorate and Other Groundwater Inorganic Co-Contaminants on Aerobic RDX Degradation

“…Because the aerobic degradation of RDX does not produce toxic intermediates, the use of RDX-degrading strains, such as Gordonia KTR9, has been tested for the bioremediation of polluted water [ 27 , 28 , 29 ]. Those studies showed that in situ bioaugmentation and biostimulation of aerobic bacteria lead to rapid degradation of RDX in a polluted aquifer over a long period [ 30 ].…”