| The biological removal of 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) through a multiple stage treatment approach was investigated. The reduction of TNT to 2,4,6-triaminotoluene (TAT) and the removal of RDX and HMX in first stage anaerobic fluidized-bed reactors (AFBRs) were achieved. Ethanol served as the electron donor, and two types of attachment media were utilized, namely sand and granular activated carbon (GAC). More complete removal of TNT, RDX and HMX was achieved with GAC as attachment medium. A GAC-AFBR successfully reduced the TNT contained in industrial pretreated pinkwater to TAT, and removed RDX and HMX. Near complete reduction of TNT to TAT and removal of RDX and HMX was achieved in sand and GAC medium AFBRs at very low ethanol loadings. The theoretical ethanol loadings required to achieve this could be calculated with the proposed stoichiometric. An ethanol to TNT loading of 3.6:1 on a molar basis was provided as a practical operating guideline for a laboratory scale AFBR. An empty bed contact time (EBCT) of 1.82 hours was shown to be sufficient for a GAC-AFBR operating under these conditions.; Second stage activated sludge reactors were shown to lower influent TAT concentrations significantly, although complete removal was not accomplished. The extent of TAT removal attributable to biological oxidation is uncertain since TAT polymerizes under aerobic conditions. Residual dissolved organic carbon (DOC) concentrations indicate some removal of TAT can be attributed to oxidation.; A second stage denitrifying fluidized-bed reactor (FBR) was incapable of utilizing TNT and incompletely reduced intermediates as electron donor. With the addition of ethanol these energetic compounds competed for ethanol, and may have been toxic to denitrifying microorganisms. Ethanol was utilized preferentially over TAT for the reduction of nitrate. TAT did not polymerize under denitrifying conditions, and was utilized as electron donor under ethanol insufficient operating conditions.; Methanogenesis was observed to be inhibited by the presence of TNT in batch tests. RDX and HMX at various concentrations neither enhanced nor inhibited the biological reduction of TNT. Hydrogen served as electron donor for TNT reduction at a loading of 147% of the theoretical requirement. Sulfide was shown to abiotically reduce TNT to TAT. |
