Halophilic Biodegradation of 3-Nitro-1,2,4-Triazol-5-One in Brine

Abstract

Production of insensitive munitions (IM) creates wastewater containing 3-nitro-1,2,4-triazol-5-one (NTO). Because NTO is an anion in neutral pH wastewaters, it can be removed via ion exchange (IX), released during IX brine recharge, and may be subsequently degraded by halophiles. IX brine regeneration through halophilic NTO biotransformation was observed over 210 cycles in a sequencing batch reactor (SBR) and averaged 64.8%±20.2% NTO removal. NTO formed 3-amino-1,2,4-triazol-5-one (ATO) under sulfate- and nitrate-reducing conditions. Variable NTO reductions were observed over four phases including anoxic enrichment (80.5%±7.7%, Cycles 0 to 41); anoxic followed by aerobic (42.2%±23.5%, Cycles 42 to 81); anoxic supplemented with nitrate (64.7%±21.5%, Cycles 82 to 177); and anoxic stress test with nitrate and perchlorate (91.0%±9.7%, Cycles 178 to 210). Sequencing results showed 69% of the genera to be halophiles and sulfate-reducing bacteria and archaea including Desulfovibrio and Halanaerobium. ATO reduction in each cycle was shown to be correlated with the abundance of genus Alkalibacterium. The presence of the potential cocontaminants in munitions wastewater IX brine, nitrate and perchlorate, were shown to either increase or not interfere with NTO transformation, respectively. The results of these studies demonstrate that NTO biotransformation by halophiles in brine solutions is feasible and could be utilized for IX brine regeneration. Explosive production and munitions manufacturing in the US creates wastewater containing explosive contaminants. Treatment of this wastewater to remove the explosives is required before the water can be released to the environment. IX can remove the explosive NTO from munitions manufacturing wastewater, but to be economical, the resins need to be reused many times. Regeneration of the IX resin for reuse generates brine that contains the explosive NTO. To remove NTO from the brine so it can be reused, salt-tolerant bacteria were grown that biodegrade NTO. The bacteria were able to biotransform NTO over for 210 cycles and over 500 days from a synthetic IX brine. After optimization of the treatment system, the bacteria were degrading 91.0%± 9.7% of the NTO in each cycle. This system, IX with brine regeneration, for munitions wastewater treatment is potentially more economical and sustainable than current wastewater treatment methods.