| Nitroglycerin or glycerol trinitrate, a toxic substance, is widely used in the production of explosives and is one of the main components of gun and rocket propellants. In addition to military applications, this compound is used in the manufacturing of drugs to treat high blood pressure and heart diseases. Due to these industrial activities, the compound is abundantly found in munitions and pharmaceutical wastewater as well as in wastewater from the nitroglycerin manufacturing plants thus causing significant environmental pollution. Bioremediation of this compound has been previously tested with partial success. In this study, the complete degradation of nitroglycerin has been studied in microcosm vials, batch reactors, and immobilized packed bed reactors under both aerobic and anaerobic conditions. Mixed bacterial consortia from activated sludge, and the white rot fungus, Phanerochaete chrysosporium are the microorganisms used to study the aerobic degradation of nitorglycerin. Mixed bacterial culture from digester sludge was used in anaerobic studies. Preliminary studies showed that a cosubstrate, such as glucose, is necessary to aerobically degrade nitroglycerin whereas anaerobic bioconversion can be carried out without external carbon sources. However, the degradation rate substantially increases in the presence of glucose. The biodegradation results showed that denitration occurs in a stepwise manner resulting in the production of dinitro and mononitro glycerin isomers. Based on the results obtained, a complete microbial degradation pathway of nitroglycerin is formulated and the regioselectivity for the denitration products are described. The rate of bioconversion was found to decrease at each denitration step. A mathematical model has been developed to describe the cometabolic aerobic degradation behavior of this compound by mixed bacterial cultures. To enhance the degradation rate, a novel immobilized packed bed reactor was configured and operated in a flow through mode. The degradation rate was enhanced by an order of magnitude compared to the degradation obtained in the batch reactor. |
