Biodegradation of Energetic Compounds Under Varying Co-Substrate Loading Conditions (original) (raw)

2001, Proceedings of the Water Environment Federation

Two anaerobic fluidized-bed reactors (AFBRs), the first with sand and the second with granular activated carbon (GAC) were utilized in the biodegradation of 2,4,6trinitrotoluene (TNT) with ethanol as co-substrate. The ethanol loading was systematically lowered beyond the critical point, and the degradation phenomena observed. The point at which the production of methane ceased corresponded well to the theoretical point at which no excess ethanol was available to the system. The complete reduction of TNT to 2,4,6-triaminotoluene (TAT) was observed up to the critical ethanol loading point. A third AFBR with GAC as the attachment medium was utilized under identical operating conditions. In addition to TNT, it received the energetic compounds hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7tetrazocine (HMX). In this reactor too the theoretical ethanol requirement corresponded well to the point at which methane production ceased, and the point up until which complete TNT reduction was observed. Through the operation of laboratory scale reactors, these observations are important practical verifications of the assumed TNT reduction mechanisms. Improved biodegradation was observed on the GAC medium AFBRs compared to the sand medium AFBR. Interestingly, the GAC medium AFBR receiving RDX and HMX was able to degrade the aromatics to a lower concentration than the GAC medium AFBR receiving only TNT. It is possible that the presence of these two energetic compounds may be stimulating some biological degradation process. The activated sludge reactors lowered the effluent DOC further, but were unable to remove TAT completely. Through batch tests with GAC, TNT and varying concentrations of ethanol some inhibition of the methanogens was observed in the presence of TNT. Sufficient ethanol was available to completely transform TNT to TAT, but the higher the presence of excess ethanol the more complete removal of TAT was observed.