BIODEGRADATION OF ENERGETIC COMPOUNDS IN ANAEROBIC FLUIDIZED BED REACTORS
Abstract:Two anaerobic fluidized bed reactors (AFBRs) were used to study the biological degradation of organic energetic compounds. During the first half of the study, the synthetically produced wastewater contained 95 mg/L of the compound 2,4,6-trinitrotoluene (TNT), which was co-metabolized with 560 mg/L ethanol. During the second half of the study, the TNT was replaced with 16 mg/L hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 1.1 mg/L octahydro-1,3,5,7- tetranitro-1,3,5,7-tetrazocine (HMX). Granular activated carbon (GAC) was selected as attachment medium for the first AFBR, which was preloaded with 200 g of TNT, before addition of the seed culture. During the first three weeks of operation, the ethanol was completely degraded, although no methane production was observed. Analysis of the effluent inorganic carbon content, however, indicated equivalent conversion of the ethanol to dissolved inorganic carbon, with accumulation of carbon dioxide in the reactor headspace. Once the oxygen from the nitro groups of the preloaded TNT was depleted, methane production started. The TNT degradation intermediates which were observed were 2,4,6-triaminotoluene (TAT), 2,4-diamino- 6-nitrotoluene (2,4-DA-6-NT), 2,6-diamino-4-nitrotoluene (2,6-DA-4-NT), 2-amino-4,6- dinitrotoluene (2-A-4,6-DNT), and 4-amino-2,6-dinitrotoluene (4-A-2,6-DNT). After operating for a period of 200 days, no TAT, or any other intermediates, was observed in the AFBR effluent for a period of 60 days, at which point the AFBR was disrupted for the extraction of GAC. From this point onward, TAT was again constantly observed. It is possible that TAT was being degraded anaerobically during this period, although the phenomenon did not repeat itself. Less complete degradation of TNT, RDX and HMX was consistently observed on the sand attachment medium AFBR than on the GAC-AFBR. This could be attributed to the superior microbial attachment properties of the GAC, or to catalytic properties of the GAC surface. A secondary activated sludge treatment step followed both AFBRs, which aerobically degraded all residual TNT, RDX, HMX and intermediates.
Document Type: Research Article
Publication date: 2000-01-01
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