INITIAL-PHASE OPTIMIZATION FOR BIOREMEDIATION OF MUNITION COMPOUND-CONTAMINATED SOILS

We examined the bioremediation of soils contaminated with the munition compounds 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5 -triazine, and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine by a procedure that produced anaerobic conditions in the soils and promoted the biodegradation of nitroaromatic contaminants. This procedure cons isted of flooding the soils with 50 mM phosphate buffer, adding starch as a supplemental carbon substrate, and incubating under static condi tions. Aerobic heterotrophs, present naturally in the soil or added as an inoculum, quickly removed the oxygen from the static cultures, cre ating anaerobic conditions. Removal of parent TNT molecules from the s oil cultures by the strictly anaerobic microflora occurred within 4 da ys. The reduced intermediates formed from TNT and hexahydro-1,3,5-trin itro-1,3,5-triazine were removed from the cultures within 24 days, com pleting the first stage of remediation. The procedure was effective ov er a range of incubation temperatures, 20 to 37-degrees-C, and was imp roved when 25 mM ammonium was added to cultures buffered with 50 mM po tassium phosphate. Ammonium phosphate buffer (50 mM), however, complet ely inhibited TNT reduction. The optimal pH for the first stage of rem ediation was between 6.5 and 7.0. When soils were incubated under aero bic conditions or under anaerobic conditions at alkaline pHs, the TNT biodegradation intermediates polymerized. Polymerization was not obser ved at neutral to slightly acidic pHs under anaerobic conditions. Comp letion of the first stage of remediation of munition compound-contamin ated soils resulted in aqueous supernatants that contained no munition residues or aminoaromatic compounds.