Bioremediation of Glycerol Trinitrate (GTN) Explosive

Abstract

Bioremediation using living organisms, primarily microorganisms, offers the possibility to degrade or detoxify substances hazardous to human health and/or the environment. Explosives or ‘explosive waste’ fall into the category of energetic materials and are susceptible to initiation or self-sustained energy release, when present in sufficient quantities and exposed to stimuli such as heat, shock, friction, chemical incompatibility or electrostatic discharge. Explosives are classified as primary or secondary based on their susceptibility to initiation. The nitrate esters are classified as secondary explosives, as they are formulated to detonate only under certain conditions. Nitroglycerin or glycerol trinitrate (GTN) is manufactured for use as an explosive in the double-base gun and rocket propellants and as a pharmaceutical vasodilator. For most of its industrial history, GTN was considered either recalcitrant to microbial biodegradation or even inherently non-biodegradable and high concentrations of the ester (>900 ppm) were inhibitory to bacterial growth. Physicochemical methods of GTN destruction involve adsorption on activated carbon followed by reduction with inorganic chemicals or by alkaline hydrolysis, yielding glycerol and nitrite or nitrate. However, these techniques suffer from high operational costs, the presence of excess reactants that remain dissolved in the effluent and the necessity for secondary treatment to remove nitrogenous products. This review paper describes biotransformation and biodegradation of GTN using bacteria and fungi, which may offer a means of removal of GTN from waste streams and bioremediation of contaminated land sites. Possibilities of developing transgenic plants carrying microbial genes capable of metabolising GTN, and problems that can occur during the bioremediation of GTN, from the bacteria and fungi unable to adapt to the extreme anaerobic or anaerobic environment are also discussed in the paper.