Biodegradation of glycerol trinitrate by activated sludge: Cosubstrate requirements, inhibition, and kinetics

Nitroglycerin or glycerol trinitrate (GTN) is an energetic and toxic substance with a wide range of military and pharmaceutical applications. Studies conducted with activated sludge showed that GTN is amenable to aerobic degradation only in the presence of a primary carbon source, such as glucose. Kinetic experiments indicated that GTN is an inhibitory substrate whose presence during biodegradation, reduces substantially the microbial yield and the apparent maximum specific growth rate coefficient of primary substrates. However, in the range of concentrations tested (50 to 200 mg/L of GTN) its inhibitory effects are reversible. The biodegradation mechanism proceeds via a set of successive denitration reactions to form isomers of glycerol dinitrate (1,2-GDN and 1,3-GDN) and glycerol mononitrate (1-GMN and 2-GMN), which are subsequently degraded. Significant regioselectivity was observed during denitration of GTN and 1,2-GDN favoring production of 1,3-GDN and 1-GMN. The rates of degradation of the metabolic products of GTN were slower at each denitration step with 2-GMN exhibiting the lowest denitration rate. Aerobic GTN degradation ceased upon exhaustion of the primary substrate. Although, cosubstrate requirements during aerobic bioconversion of GTN were relatively high, in field applications the need for addition of external carbon sources will be minimal since GTN waste streams usually contain high amounts of BOD.