Development of fungal degrading system to detoxify 2,4,6-Trinitrotoluene (TNT) in liquid phase bioreactors

Abstract

This project was designed to explore the potential of white-rot fungi to detoxify TNT contamination in liquids, and to define the optimum conditions for TNT detoxification. All the selected fungal strains, Phanerochaete chrysosporium, Phanerochaete sordida, Phlebia brevispora and Cyathus stercoreus were able to completely remove the added TNT (90 mg/1) within three weeks of incubation. The major TNT metabolites were 2 and 4-amino-dinitrotoluenes, which were also degraded. The fungal treatment resulted in up to 94% reduction of the medium mutagenicity induced by TNT and its metabolites. Moreover, these fungi did not produce mutagenic metabolites during growth period. Fungal treatment for 36 days under nitrogen-limiting conditions resulted in a limited mineralization of TNT. Mass balance data show that approximately 40% to 60% of the initial [14C] remained in the liquid medium, 35% to 55% of [14C] was trapped in fungal biomass, and less than 10% of [14C] was mineralized. This study examined the effects of growth substrates, culture pH, incubation temperatures, and TNT concentrations on TNT detoxification. The data indicate that supplementation of starch to the growth media was critical to fungal growth and TNT detoxification. The fungi grew best and resulted in the highest TNT detoxification at pH of 4 and 5, and were able to degrade TNT at TNT. concentrations up to 92 mg/I. Nevertheless, the effect of incubation temperature on TNT degradation was found to be minor. This work demonstrates that the selected white-rot fungi are capable of degrading, mineralizing, and detoxifying TNT in liquid medium. To achieve the best result, an extra growth substrate must be supplied. The system should be maintained at pH of 4.0 to 5.0, TNT concentration should be controlled below 90 mg/I, and a low nitrogen concentration should be maintained in the fungal culture medium.