Treatment of Hydrolysates of the High Explosives Hexahydro‐1,3,5,‐Trinitro‐1,3,5‐Trianize and Octahydro‐1,3,5,7‐Tetranitro‐1,3,5,7‐Tetrazocine Using Biological Denitrification

Abstract

Alkaline hydrolysis byproducts of the high explosives hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) and octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX), consisting of acetate, formate, formaldehyde, and nitrite, were treated in a denitrifying (anoxic) packed‐bed upflow reactor. Additional nitrite or nitrate was added to match the carbon oxidation requirement. In a 2‐year study, more than 90% removal of the organic compounds and nitrite were observed in a reactor with a 3‐hour retention time. Removal was quantified by measuring actual compound concentrations and total organic carbon. The stoichiometry of the experimental results closely matched the predicted stoichiometry. Formaldehyde and acetate were preferentially removed over formate. The system removed N (nitrite):C (acetate):C (formaldehyde):C (formate) in a relative ratio of 1:0.07:0.36:0.50, respectively. The volumetric removal rate was as high as 170 mg/L of nitrite‐nitrogen per day with existing carbon sources. The observed cell yield (mass basis) of nitrite reduction with acetate/formate was 0.21 mg cells/mg total organic carbon or 0.16 mg cells/mg chemical oxygen demand at 20 °C. This culture was also capable of biodegrading RDX and HMX when using nitrate as an electron acceptor.