Biological and chemical treatments of high explosive contaminated waters: Application of a packed-bed reactor, membrane bioreactor, and fenton oxidation

In the first part, the application of biological denitrification for treating hydrolysis byproducts of 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 packed-bed upflow reactor. Over 90% removal of the organic compounds and nitrite were observed in a reactor with a three-hour retention time. The stoichiometry of the experimental results closely matched the predicted stoichiometry. The volumetric removal rate was as high as 170 mg/L of NO₂ −-N per day with existing carbon sources. This culture was also capable of biodegrading RDX and HMX when using nitrate as an electron acceptor.; In the second part, a membrane bioreactor (MBR) system, consisting of a bioreactor coupled to a ceramic crossflow ultrafiltration (UF) module, was evaluated. This system was used to treat a synthetic wastewater containing same hydrolysates of high explosive RDX. The bench-scale anoxic MBR system effectively treated these wastewaters. The permeation flux was between 0.15 and 2.0 m3/m2/day and was restored to original flux after backwashing. Heterotrophic bacteria counts method showed that the membrane was very efficient in retaining biomass, which had resulted in the production of a clear final effluent. The reactor was operated over a range of transmembrane pressure, temperature, suspended solids concentration, and organic loading to evaluate the influence on the permeation flux and optimize its treatment.; In the third part, the feasibility of the Fenton oxidation of RDX and HMX was investigated as another option to treat RDX and HMX in acidic environment. It was found that the oxidation of RDX and HMX by Fenton's reagent is rapid at between 20 and 50°C at pH 3. All experimental data could be fit to a pseudo first-order rate equation. The temperature dependence follows the Arrhenius correlation. The activation energy using Arrhenius equation was determined to be 51.3 (RDX) and 48.6 (HMX) kJ.mol−1 , respectively. Experimental results show that there exists an optimal pH at 3 for the Fenton treatment process. The reaction rate coefficient was also strongly dependent on both H₂O₂ and Fe2+ concentrations. Finally, the byproducts of the Fenton oxidation of RDX and HMX were discussed.