Biotransformation of 2,4,6-trinitrotoluene in a continuous-flow Anabaena sp. system

Abstract

Reductive transformation of 2,4,6-trinitrotoluene (TNT) was observed in a continuous-flow system of Anabaena sp. operated for 33 d with a 5.7 d hydraulic retention time and a range of influent TNT concentrations of 1–58 mg/l. The TNT removal efficiency of the continuous-flow system at the highest influent TNT concentration of 58 mg/l was 96.7±1.7% (mean±95% confidence interval). Culture chlorosis and growth inhibition were not observed during this study. The pseudo-first order TNT transformation rate constant values corresponding to the system performance range (0.14–0.46/h) were lower than the values previously recorded for batch Anabaena sp. cultures with less than 10 mg/l initial TNT concentrations, possibly due to an inhibition of the TNT transformation process by either TNT and/or TNT transformation products. Heterotrophic bacterial populations developed in the continuous-flow Anabaena sp. cultures also transformed TNT, but at a much lower rate than the Anabaena sp. Less than 1% of the overall TNT transformation observed in the continuous-flow system was attributed to the heterotrophic bacterial populations. The only TNT reduction products identified in both the culture media and in biomass extracts were azoxytetranitrotoluene isomers and low levels of aminodinitrotoluene isomers. TNT and TNT transformation products identified in the culture effluent and the biomass extract accounted for only about 24% of the TNT added to the system (on a molar basis). Production of soluble, polar metabolites, uptake, partial mineralization and/or sequestration of TNT and its transformation products by Anabaena may be responsible for the relatively low contaminant recovery and mass balance observed in this study.