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Anaerobic Degradation of TNT by Escherichia Coli

Author: ChenZuo
Tutor: ZhouJiTi
School: Dalian University of Technology
Course: Environmental Engineering
Keywords: Escherichia coli TNT Intracellular crude enzyme Cometabolism Degradation pathway
CLC: X703
Type: Master's thesis
Year: 2008
Downloads: 110
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Abstract

2,4,6 - trinitrotoluene (trinitrotoluene, TNT) is a military and civilian aspects of the most widely used of energetic materials commonly used in the manufacture of explosives, also used in the manufacture of dyes, pharmaceuticals, reagents, and its toxic The poor biodegradability characteristics, it is particularly important to the degradation of its wastewater. The purpose of this paper is to study the Escherichia coli TNT degradation of performance. The experiments show that the E. coli bacterial cells Degradation of TNT optimum pH value of 5.0, and the optimum temperature of 35 ° C. Seen by comparing different initial concentrations of TNT degradation rate, when TNT concentration <80.32 mg / E ratio of the rate of degradation with initial concentration increases with increasing concentration of 80.32 mg / L when the degradation rate achieve maximum 32.12mg / (g · h); when TNT concentration> 80.32 mg / L, a decreasing trend than the rate of degradation. This may be because TNT have some toxicity to microorganisms produce inhibition, when the concentration reaches a certain value to be interested in the degradation process. With different concentrations of redox mediator, TNT degradation rate as the redox mediator concentration increases first increases and then decreases. Strains of E.coli by microbial metabolic mechanism of degradation of TNT. Malic acid, sucrose, glucose, lactose, galactose, citric acid, sodium acetate, sodium starch can be used as the TNT degradation of substrate metabolism, glucose is the preferred substrate of the present study, the optimum substrate concentration of 0.5 g / L . NITROGEN ADDITION TNT degradation rate did not improve further, no applied nitrogen source, E.coli can still total metabolic degradation of TNT, to show that E.coIi get their own needs in the process of decomposition of TNT nitrogen source. Choice Andrews inhibition model described anaerobic TNT degradation kinetics, nonlinear fitting of the experimental data fit better. When there is no growth substrate, obtained the model parameters q _max the K _s and K _i 13.72 mg / (g · h) 157.59 mg / L and 1.52 mg / L, when the presence of the growth substrate, improved reductase metabolite levels, has played a positive role in TNT degradation the q _max K _s and K _i were 217.47 mg / (g · h), 200.18 mg / L and 22.41 mg / L. By ultrasonic crushing microbial cells obtained by the method crude intracellular enzyme, an enzyme at pH = 6 to 7 range, the TNT has a strong ability to degrade at pH = seven o'clock maximum enzyme activity. Within the range of 20 ~ 60 ℃ enzyme activity increased with the rise in temperature of 60 ° C the enzyme activity greatest. The enzymatic reaction kinetics of the Michaelis-Menten equation, K _m 0.0249 mmol / L, V _max .2810 U / mg. Different metal ions, different from the effect on the enzyme activity, the trace Mn ^{2 and Mg ^{of 2 the presence can improve the activity, but with the ion concentration is increased to a certain extent, this right the improved activity tends to be limited; the Zn ^{2 and of Cu ^{, 2 's presence can inhibit the activity of ion concentration increases, the reaction rate gradually decreased. E.coli pathway of degradation of TNT by LC / MS inferred, TNT was first reduced to dinitrotoluene hydroxylamino, amino dinitrotoluene, and eventually converted to the diamino nitrotoluene.}}}}

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