Combined biological-chemical procedure for the mineralization of TNT

Contamination of ground and surface water with 2,4,6-trinitrotoluene (TNT) and its biological and chemical transformation products are a persisting problem at former TNT production sites. We have investigated the photochemical degradation of TNT and its aminodinitro-(ADNT) and diaminonitrotoluene (DANT) metabolites using OH-radical generating systems like Fenton and hydrogen peroxide irradiated with UV, in order to compare the degradation and mineralization rate of ADNT- and DANT-isomers with TNT itself. As a result, we find that the aminoderivatives were mineralized much faster than TNT. Consequently, as ADNTs and DANTs are the known dead-end products of biological TNT degradations, we have combined our photochemical procedure with a preceding biological treatment of TNT by a mixed culture from sludge of a sewage plant. This consecutive degradation procedure, however, shows a reduced mineralization rate of the ADNTa and DANTs in the biologically derived supernatant as compared to the pure substances, suggesting that during the biological TNT treatment by sludge competing substrates are released into the solution, and that a more defined biological procedure would be necessary in order to achieve an effective, ecologically and economically acceptable mineralization of TNT from aqueous systems.