Evaluation of a sequential anaerobic-aerobic membrane bioreactor system for treatment of traditional and insensitive munitions constituents

Anaerobic sequencing batch reactor for concurrent removal of multiple recalcitrant munition compounds

Large-scale production, use, and disposal of munitions has resulted in widespread environmental contamination. A laboratory-scale anaerobic sequencing batch reactor (AnSBR) was initiated in this study to investigate the concurrent removal of multiple energetic compounds that comprise modern munition formulations. The AnSBR achieved high removal efficiencies of 2,4-dinitroanisole (DNAN, >99%) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX, 84 ± 16%), along with the partial removal of 1-nitroguanidine (NQ, 30 ± 27%). Specific DNAN, RDX, and NQ removal rates of 17.0 ± 0.1 µmol DNAN/g VSS/d, 22.0 ± 0.8 µmol RDX/g VSS/d, and 2.0 ± 0.3 µmol NQ/g VSS/d were recorded in the AnSBR under steady-state conditions, respectively. Long-term operation of the AnSBR selected Actinobacteria (2 - 58%) and uncultured Actinomycetaceae (1 - 58%) as the most abundant phylum and genus, respectively. Results from this study provide valuable insights into the development of anaerobic bioreactors for the remediation of sites impacted by modern munitions.

Combined sorption-biodegradation for removal of energetic compounds from stormwater runoff

Munition constituents (MC) in stormwater runoff have the potential to move these pollutants into receiving bodies at military installations. Here we present further evaluation of a passive and sustainable biofilter technology for removal of dissolved MC from simulated surface runoff by combined sorption-biodegradation processes under dynamic flow conditions. Columns were packed with MC sorbents Sphagnum peat moss and cationized (CAT) pine shavings with and without wood-based biochar. Some columns also received biodegradable polymers as a slow-release carbon source and MC degrading bacterial cultures. MC removal was greater under combined sorption-biodegradation conditions than under sorption only conditions, ranging from 2.5-fold for 2,4,6-trinitrotoluene (TNT) to > 25-fold for hexahydro-1,3,5-trinitro-s-triazine (RDX). Biochar improved removal for some MC, which was attributed to it acting as a buffer by its ability to sorb/degrade these compounds, thus delaying their elution from the columns until the biodegradation activity increased. It was also found that labile carbon source availability, rather than microbial culture viability, was responsible for the apparent reduction in energetic removal over time. These results provide a foundation for further development of technologies for remediation of energetic compounds in military range stormwater runoff.

Carbon and Nitrogen Isotope Fractionations During Biotic and Abiotic Transformations of 2,4-Dinitroanisole (DNAN)

2,4-Dinitroanisole (DNAN) is a main constituent in various new insensitive munition formulations. Although DNAN is susceptible to biotic and abiotic transformations, in many environmental instances, transformation mechanisms are difficult to resolve, distinguish, or apportion on the basis solely of analysis of concentrations. We used compound-specific isotope analysis (CSIA) to investigate the characteristic isotope fractionations of the biotic (by three microbial consortia and three pure cultures) and abiotic (by 9,10-anthrahydroquinone-2-sulfonic acid [AHQS]) transformations of DNAN. The correlations of isotope enrichment factors (ΛN/C) for biotic transformations had a range of values from 4.93 ± 0.53 to 12.19 ± 1.23, which is entirely distinct from ΛN/C values reported previously for alkaline hydrolysis, enzymatic hydrolysis, reduction by Fe2+-bearing minerals and iron-oxide-bound Fe2+, and UV-driven phototransformations. The ΛN/C value associated with the abiotic reduction by AHQS was 38.76 ± 2.23, within the range of previously reported values for DNAN reduction by Fe2+-bearing minerals and iron-oxide-bound Fe2+, albeit the mean ΛN/C was lower. These results enhance the database of isotope effects accompanying DNAN transformations under environmentally relevant conditions, allowing better evaluation of the extents of biotic and abiotic transformations of DNAN that occur in soils, groundwaters, surface waters, and the marine environment.

Isolation and characterization of nitroguanidine-degrading microorganisms

Nitroguanidine (NQ) is a component of newly developed insensitive munition (IM) formulations which are more resistant to impact, friction, heat, or sparks than conventional explosives. NQ is also used to synthesize various organic compounds and herbicides, and has both human and environmental health impacts. Despite the wide application and associated health concerns, limited information is known regarding NQ biodegradation, and only one NQ-degrading pure culture identified as Variovorax strain VC1 has been characterized. Here, we present results for three new NQ-degrading bacterial strains isolated from soil, sediment, and a lab-scale aerobic membrane bioreactor (MBR), respectively. Each of these strains -utilizes NQ as a nitrogen (N) source rather than as a source of carbon or energy. The MBR strain, identified as Pseudomonas extremaustralis strain NQ5, is capable of degrading NQ at a rate of approximately 150 μmole L-1 h-1 under aerobic conditions with glucose as a sole carbon source - and NQ as a sole N source. The addition of NH4+ to strain NQ5 during active growth with NQ as a sole N source slowed the growth rate for several hours, and the strain released NH4+, presumably from NQ. When NO3- was added as an alternate N source under similar conditions, the NO3- was not consumed, but NH4+ release into the culture medium was again observed. Strain NQ5 was also able to utilize guanylurea, guanidine, and ethyl allophanate as N sources, and - tolerate salt concentrations as high as 4 % (as NaCl). The other two stains, NQ4 and NQ7, both identified as Arthrobacter spp., grew significantly slower than strain NQ5 under similar culture conditions and tolerated only ∼1 % NaCl. In addition, neither strain NQ4 nor strain NQ7 was able to degrade guanlyurea or ethyl allophanate, but each degraded guanidine. These strains, particularly strain NQ5, may have practical applications for in-situ and ex-situ NQ bioremediation.