Anaerobic Degradation Of TNT By Escherichia Coli

As a kind of energy-containing material, trinitrotoluene is widely used in military and civil aspects. It is usually used in the production of explosive, dyestuff, medicine and reagent. It is characteristic of great toxicity and lower biodegradability. Thus the treatment of TNT wastewater is important. This paper aimed to investigate the degradation of TNT by Escherichia coli.The results indicated that the best degradation performance of TNT reduction was found at pH 5.0,35℃. The specific degradation rate increases with the increasing of initial TNT concentration when it is lower than 80.32 mg/L. The maximal specific degradation rate is 32.12 mg/(g·h) with 80.32 mg/L TNT. The specific degradation rate decreases with the increasing of initial TNT concentration when it is higher than 80.32 mg/L. This maybe due to the toxicity of TNT to microorganism with the concentration of TNT attains to certain value. The degradation rate of TNT increased first and then decreased with the increasing of concentration of 2-hydroxyl-1,4-naphthoquinone, which was used as redox mediator.The degradation of TNT by E. coli is a cometabolism processes.Malic acid, sucrose, glucose, galactose, lactose monohydrate, lemon acid, sodium acetate and starch soluble can serve as cometabolism substrate, among which glucose was found to be the best substrate with an optimal concentration of 0.5 g/L. Supplemented nitrogen source is not necessary for TNT degradation. E. coli can obtain nitrogen source from the process of the TNT degradation.The Andrews inhibition equation was used to describe TNT degradation kinetics. Using non-linear regression, the kinetic parameters q_msx, K_s and K_i were found to be 13.72 mg/(g·h), 157.59 mg/L and 1.52 mg/L, respectively. With the presence of growth substrate, the raised metabolism level has positive effects on the degradation of TNT. The kinetic parameters q_max, K_s and K_i were found to be 217.47 mg/(g·h), 200.18 mg/L and 22.41 mg/L, respectively. The experimental data verification for the model equation is satisfactory.Crude cell extracts obtained by ultrasonic disruption was used as crude enzyme. The crude enzyme has strong degradation ability to TNT between pH 6-7. The optimal pH value is 7. The activity of reductase was enhanced with the increase of temperature between 20 and 60℃. The optimal temperature is 60℃. The enzymatic reaction was accordant with Michaelis-Menten kinetics, with K_m and V_max values of 0.0249 mmol/L and 0.2810 U/mg, respectively. The enzyme activity was stimulated by the presence of trace amount of Mn²⁺ and Mg²⁺. However, this stimulation tended to be limited when the ion concentrations increased to certain extent. The enzyme activity declined along with the increasing of the ion concentrations of Zn²⁺ and Cu²⁺.The putative TNT transformation pathway was studied using LC/MS. E. coli reduced TNT to hydroxylaminodinitrotoluenes and aminodinitrotoluenes at first, which was finally transformed to diaminonitrotoluene.