BIOLOGICAL TREATMENT OF TNT CONTAMINATED SOIL - 2 - BIOLOGICALLY INDUCED IMMOBILIZATION OF THE CONTAMINANTS AND FULL-SCALE APPLICATION

Anaerobic treatment of originally contaminated soil from a former ammu nition plant was carried out in a laboratory slurry reactor. While fer menting glucose to ethanol, acetate, and propionate, the anaerobic bac teria completely reduced the nitro groups of 2,4,6-trinitrotoluene (TN T) and aminodinitrotoluenes, which led to a complete and irreversible binding of the reduced products to the soil. 2,4-Dinitrotoluene and he xahydro-1,3,5-trinitro-l,3,5-triazine were also reduced in the soil sl urry and were no longer detectable after the anaerobic treatment. To m ineralize the fermentation products, a subsequent aerobic treatment wa s necessary to complete the bioremediation process. This bioremediatio n process was tested in a technical scale at Hessisch Lichtenau-Hirsch hagen, Germany. A sludge reactor (Terranox system) was filled with 18 m(3) of contaminated soil (main contaminants were TNT, 2,4-dinitrotolu ene, hexahydro-1,3,5-trinitro-l,3,5-triazine)and 10 m(3) of water. The anaerobic stage was carried out by periodical feeding of sucrose. The sludge was subsequently dewatered and treated aerobically. Chemical a nalysis revealed an overall reduction of more than 99% of the contamin ants. Ecotoxicological tests performed with various aquatic systems (l uminescent bacteria, daphnids, algae) and terrestrial systems (respiri ng bacteria, nitrifying bacteria, cress plants, earth worms) showed th at residual toxicity could not be detected after the anaerohic/aerobic treatment.