Remediation of dinitrotoluene contaminated soils from former ammunition plants: soil washing efficiency and effective process monitoring in bioslurryreactors

A pilot-scale bioslurry system was used to test the treatment of soils high ly contaminated with 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2 ,6-DNT). The treatment scheme involved a soil-washing process followed by t wo sequential aerobic slurry reactors augmented with 2,4-DNT-and 2,6-DNT-mi neralizing bacteria. Test soils were obtained from two former army ammuniti on plants, the Volunteer Army Ammunition Plant (VAAP, Chattanooga, TN) and the Badger Army Ammunition Plant (BAAP, Baraboo, WI). Soil washing was used to minimize operational problems in slurry reactors associated with large particulates. The Eimco, slurry reactors were operated in a draw-and-fill m ode for 3 months and were monitored for the biodegradation of 2,4-DNT and 2 ,6-DNT, nitrite production, NaOH consumption, and oxygen uptake rate. Resul ts show that soil washing was very effective for the removal of sands and t he recovery of soil fines containing 2,4-DNT and 2,6-DNT. Bioslurry reactor s offered rapid and nearly complete degradation of both DNT isomers, but re quire real time monitoring to avoid long lag periods upon refeeding. Result s found a significant discrepancy between the measured DNT concentrations a nd calculated DNT concentrations in the slurry reactors because of solids p rofiles in the slurry reactors and the presence of floating crystal of DNTs . Based on the actual amount of dinitrotoluene degradation, nitrite release , NaOH consumption, and oxygen uptake were close to the theoretical stoichi ometric coefficients of complete DNT mineralization. Such stoichiometric re lationships were not achieved if the calculation was based on the measured DNT concentrations due to the heterogeneity of DNT in the reactor. Results indicate that nitrite release, NaOH consumption, and oxygen uptake rates pr ovide a fast assessment of 2,4-DNT degradation and microbial activity in a slurry reactor, but could not be extended to a second reactor in series whe re the degradation of a much lower concentration of 2,6-DNT degradation was achieved. (C) 2001 Elsevier Science B.V. All rights reserved.