Biotechnology Laboratory

Center for Innovation, Inc.

TNT and Other Nitro Aromatic Compounds

Many Unites States Army, and other Department of Defense (DoD) sites, are contaminated with a variety of contaminants including highly energetic compounds, such as 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), chlorinated aliphatics (trichloroethylene,TCE) and chlorinated aliphatics. These compounds often persist in soil or groundwater for extended periods of time and present a toxicological risk to humans and the environment. Three microbial strains known to degrade nitroaromatics and other environmental contaminants were tested by CFI researchers for their ability to degrade TNT in pure culture biofilms and as members of a complex biofilm community derived from a TNT contaminated soil. The pure cultures’ ability to form biofilms alone and as part of an undefined, mixed, consortium was compared to the TNT degradation ability of the soil biofilm consortium alone.

 

In detail, it was shown that pure culture and mixed-species biofilm communities derived from TNT contaminated soil could be established that completely degraded 50 µM TNT (approx. 11 mg/L TNT) with a contact time of about 10 hours. The pure cultures that we tested consisted of a common soil bacterium of the genus Cellulomonas (Sani, Peyton et al., 2002; Borch, Gerlach et al., 2004; Borch, Inskeep et al., 2004), the saprophytic Mycobacterium fortuitum that is known to be very resistant to environmental stresses (Campbell, Srinivasan et al., 1999; Holman, Nieman et al., 2002), and the white-rot fungus Phanerochaete chrysosporium, which is a well known producer of strongly oxidative lignolytic enzymes and known to be a key contributor to the removal of TNT and other persistent environmental contaminants in unsaturated soils and composting operations (Lestan and Lamar, 1996; Reddy, 1995). At the higher influent concentration of approximately 250 µM, the mixed-species biofilm communities derived from TNT-contaminated soil were more efficient in degrading TNT than the three biofilms formed by each of the pure cultures tested. The mixed species biofilm communities removed TNT so efficiently that only a fraction of the added TNT was detected as metabolites in the effluent. The remainder was either transformed to non-aromatic or other non-detectable1 aromatic metabolites, which are likely to be more biodegradable than TNT. Augmenting the mixed-species biofilms with one or all of the three tested strains did not significantly improve the degradative capabilities of the formed biofilms, indicating that the soil consortia from TNT-contaminated sites were well adapted to degrade TNT. However, the addition of the tested strains allowed us to influence the hydraulic properties of the formed biofilms, thus providing us with a way to control biofilm properties. The addition of the pure culture strains prevented the plugging of the columns. This

finding is important in view of commercial applications since it can provide us with an additional technique to manipulate the hydraulic properties of subsurface biofilm barriers according to specific site conditions or contaminants.

 

Center for Innovation staff together with their Montana State University collaborators have completed preliminary investigation of the effect of thermal treatment on biological and abiotic processes in DNAPL contaminated soils. Research has confirmed that there is a loss of TCE at temperatures well below the temperature at which TCE would be evaporated and that both biological and abiotic processes are at involved and seem to have optimal temperature regimes. The results of this preliminary work promises to lead the way toward significant cost reductions in the application of thermal treatment to remove and/or destroy DNAPLS. Through an understanding of the factors that contribute to biotic and abiotic transformations it is possible to assess the impact of thermal treatments of DNAPL contaminated soils, and to promote the rationale design of strategies for accelerating remediation of soil and groundwater impacted by chlorinated solvents.

2,4,6-trinitrotoluene

hexahydro-1,3,5-trinitro-1,3,5-triazine

trichloroethylene