Thesis (Ph.D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Dr. Joseph B. Hughes; Committee Member: Dr. Jian Luo; Committee Member: Dr. Jim C. Spain; Committee Member: Dr. Patricia Sobecky; Committee Member: Dr. Spyros G. Pavlostathis

Abstract not available

Contamination of soils and groundwater with nitroaromatic compounds such as 2,4,6-trinitrotoluene (TNT) and dinitrotoluenes (DNTs) has drawn considerable attention due to widely distributed contamination sites and substantial efforts for cleanup. Two isomers of DNT, specifically 2,6-dinitrotoluene (2,6-DNT) and 2,4-dinitrotoluene (2,4-DNT), occur as soil and groundwater contaminants at former TNT production sites. The discovery of bacteria that use DNT isomers as electron donors has encouraged bioremediation at contaminated sites. Current work is extending the existing engineered bioremediation to naturally occurring in situ biodegradation and focuses on the application of natural attenuation (NA) as a remediation strategy for residual DNT at contaminated sites. More specifically this research evaluated factors influencing in situ bioremediation of DNTs and TNT in surface soils, vadose zones, and saturated medium. Applications involving surface soils and vadose zones investigated the potential of water infiltration to promote in situ bioremediation. Studies in saturated media were more applicable to NA. Factors that were also considered in studies conduced included: 1) the presence and distribution of degrading microbes in field soils (Barksdale, WI); 2) the dissolution and bioavailability of contaminants in historically contaminated soils; and 3) the effect of mixtures of contaminants (i.e., DNTs and TNT) on biodegradation processes. This research provided information useful for practitioners considering an in situ bioremediation NA as a remedial solution for contaminated sites. Under the condition simulating downflow of surface waters or rainwater, the rapid rate of DNT degradation could be facilitated by the availability of oxygen in the soil gas without concern of toxicity (i.e., nitrite evolution and pH drop) and addition of nutrients. As a result, in situ bioremediation or NA should be strongly considered as a remedial option for Barksdale soils and similar sites where relatively low concentrations of DNT isomers are present as contaminants. At TNT contaminated sites TNT was not mineralized by indigenous microorganisms despite oxidative biotransformation, and mixed culture capable of growth on DNT also could not develop the mineralization of TNT during DNT degradation. This suggests that the mixtures of contamination did not improve the potential for in situ TNT bioremediation.

Factors influencing natural attenuation of dinitrotoluenes (DNT) in surface soils and the application of monitored natural attenuation (MNA) as a remediation strategy were examined using contaminated soils from Badger Army Ammunition Plant (BAAP). Based on the previous research involving contaminated media obtained from locations at BAAP, and the fact that groundwater at the site is not contaminated, it seemed likely that aerobic biodegradation of DNT is active without intervention, and that natural attenuation may be an effective strategy for managing the contamination that exists at BAAP. Microcosms showed that microbes indigenous to soils are capable of 2,4-DNT mineralization and that DNT will adsorb reversibly and become bioavailable. In column studies 2,4-DNT biodegradation was observed and the nitrite evolved during DNT degradation was presumably removed due to oxidation by nitrite oxidizers. The use of simulated rainwater as influent with no nutrient amendments suggests that nutrients do not limit the biodegradation of low concentrations of DNT in the soil tested. In the chemostat study carried out to study effect lowering of temperature (22㬠15㬠10㬠7.5㠡nd 4㩠on biodegradation of DNT at hydraulic retention time of 2.5 days, no sustained change in the DNT substrate removal was observed with change in temperature, but it had a large effect on the nitrite oxidizers. This suggests that the seasonal fluctuations in temperature will have minimal effect on the DNT removal via biodegradation at temperatures above 0㮠Nitrite oxidizers were active at 22㬠their activity decreased at 15㠡nd ceased at temperatures 10㠡nd lower. Nitrite is generally taken as a line of evidence for biodegradation of DNT. The results from the soil column study and chemostat showed that nitrite measurement should not be always taken as a conclusive indicator of DNT degradation. It should be taken into consideration that absence of nitrite does not necessarily mean absence of DNT biodegradation (probably at high temperatures).