Rapid biotransformation of the insensitive munitions compound, 3-nitro-1,2,4-triazol-5-one (NTO), by wastewater sludge

As the use of the new insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO) increases, wastewaters, runoff and groundwater containing NTO will be generated. Little is known about the fate of NTO during biological wastewater treatment. The objective of this study was to explore the ability of wastewater sludges to promote the biotransformation of NTO. Three different sludges, i.e., anaerobic granular sludge, anaerobic digested sludge, and return activated sludge, were used to study the biotransformation of NTO under anaerobic conditions. Three different electron donor amendments were compared- hydrogen, ethanol, and acetate. Mixed microbial communities in each of the three sludge sources were effective in the reductive biotransformation of NTO. 3-amino-1,2,4-triazol-5-one (ATO) was observed as the major product of NTO biotransformation. The highest maximum specific rate of NTO reduction, about 120 mg NTO/g volatile suspended solids/d, was observed in anaerobic granular sludge with hydrogen or ethanol supplied as electron donors. NTO biotransformation to ATO by anaerobic digested sludge was also studied under denitrifying conditions. In this case, reduction of NTO started only after complete denitrification of added nitrate. An important implication of this paper is that sludge from wastewater treatment plants can rapidly and readily reduce NTO to ATO. Graphic abstract