Biodegradation of high explosives on granular activated carbon [GAC]: Enhanced desorption of high explosives from GAC -- Batch studies

Abstract

Adsorption to GAC is an effective method for removing high explosives (HE) compounds from water, but no permanent treatment is achieved. Bioregeneration, which treats adsorbed contaminants by desorption and biodegradation, is being developed as a method for reducing GAC usage rates and permanently degrading RDX and HMX. Because desorption is often the limiting mass transfer mechanism in bioregeneration systems, several methods for increasing the rate and extent of desorption of RDX and HMX are being studied. These include use of cosolvents (methanol and ethanol), surfactants (both anionic and nonionic), and p-and y-cyclodextrins. Batch experiments to characterize the desorption of these HEs from GAC have been completed using Northwestern LB-830, the GAC being used at Pantex. Over a total of 11 days of desorption, about 3% of the adsorbed RDX was desorbed from the GAC using buffered water as the desorption fluid. In comparison, about 96% of the RDX was extracted from the GAC by acetonitrile over the same desorption period. Ethanol and methanol were both effective in desorbing RDX and HMX; higher alcohol concentrations were able to desorb more HE from the GAC. Surfactants varied widely in their abilities to enhance desorption of HEs. The most effective surfactant that was studied was sodium dodecyl sulfate (SDS), which desorbed 56.4% of the adsorbed RDX at a concentration of 500 mg SDSL. The cyclodextrins that were used were marginally more effective than water. Continuous-flow column tests are underway for further testing the most promising of these methods. These results will be compared to column experiments that have been completed under baseline conditions (using buffered water as the desorption fluid). Results of this research will support modeling and design of further desorption and bioregeneration experiments.

Enhanced Desorption of RDX from Granular Activated Carbon

“…In baseline desorption tests with buffered water, 57.7% (76.5 mg) of the initially adsorbed RDX was desorbed by 36 500 BV of buffered water over 2.9 days. The HSDM predictions matched the experimental data very well (model results not shown; Morley, 2000 ), providing further evidence that RDX reversibly adsorbs to GAC. Results of desorption with water are included in Figures 2 and 3 for comparison with other enhanced desorption methods.…”

“…For all simulations related to this research, 12 axial and 3 radial collocation points were used. Further details of the algorithms and computer solution methods are presented by Crittenden et al (1986) and Friedman (1984) , and additional details of the modeling are included in Morley (2000) .…”

An Overview of Treatment Approaches for Octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocine (HMX) Explosive in Soil, Groundwater, and Wastewater

“…The adsorption technique has been extensively employed in the removal of hazardous pollutants and is acknowledged to be a very promising approach owing to its high selectivity and cost-efficacy [ 53 , 54 , 55 , 56 , 57 ]. The commercially available and synthesized activated carbon-based adsorption of toxic pollutants has been reported by many researchers [ 58 , 59 ]. Various low-cost materials have also been examined to develop efficient activated carbon [ 58 ].…”

“…Different types of GACs were selected for this study and among all, the Calgon F400 sample was found to be very effective in HMX removal. Explosive-loaded GAC was regenerated by using bio-regeneration where explosive-loaded GAC was degraded in a bioreactor [ 59 ]. It was noted that HMX reduced from 0.6 mg/L to 0.4 mg/L in 4 days.…”