Biological Treatment 2651 Mechanisms

Biological remediation of explosive wastes mainly occurs via compound oxidation and reduction. Oxidation takes place when oxygen is the reactant and oxygenase or peroxidase enzymes act as catalysts to cleave the aromatic ring. Reduction is the more common mechanism for nitroaromatics and occurs when the nitroaromatic compound is reduced to arylamines via hydrolytic deamination, acetylation, reductive deamination, and finally cyclization.

It was found that the Pseudomonas species degraded both DNT and TNT aerobically with supptemental glucose as a carbon source [16,17]. Reduction of the nitro groups took place only at the para position and proceeded through hydroxylamino-nitrotoluene to aminonitrotoluene. Haidour and Ramos [18] observed 2-hydroxylamino-4,6-dinitrotoluene, 4-hydroxylamino-2,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2-amino-4,6-dinitrotoluene, and 2,4-diamino-nitrotoluene as the products of TNT degradation with Pseudomonas sp. Boopathy et al. [19] reported the anaerobic degradation of TNT under different electron accepting conditions by a soil bacterial consortium. Hughes et al. [20] demonstrated the ability of Clostridium acetobutylicum to reduce TNT to 2,4-dihydroxylamino-6-nitrotoluene and then to phenol products via the Bamberger rearrangement. The transformation pathway is shown in Fig. 2 [20].

NHOH

Figure 2 Pathway of TNT transformation observed in Clostridium acetobutylicum crude cell extracts.

NHOH

Figure 2 Pathway of TNT transformation observed in Clostridium acetobutylicum crude cell extracts.

Biotransformation of RDX has been observed by a number of researchers. Young et al. [21] found a bacterial consortium in horse manure capable of degrading RDX at the rate of 0.022 L/g cells per hour. Most of the research in the biological degradation of RDX has been carried out under anaerobic conditions.

Kitts et al. [22] isolated three different genera of bacteria, which were able to degrade RDX. The most effective degrader of these three isolates was identified as Morganella morganii. One pathway for the biotransformation of RDX is a stepwise reduction of each of three nitro groups in RDX to form nitroso groups, as shown in Fig. 3 [22,23]. Detail of site remediation and ground water decontamination technologies are presented in another chapter by Wang [27].

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