U.S. Army and DoD facilities generate perchlorate (ClO_4~- ) from munitions manufacturing and demilitarization processes. Ammonium perchlorate is one of the main constituents in Army’s new main charge melt-pour energetic, PAX-21. In addition to ammonium perchlorate, RDX and 2,4-dinitroanisole (DNAN) are the major constituents of PAX-21. Biological treatment of DNAN and RDX is inefficient due to the presence of electron-withdrawing nitro constituents in these energetic compounds, and microbial per- chlorate reduction requires a constant supply of electron donors for perchlorate reducing bacteria (PRB). The objective of this study is to develop an innovative treatment process to chemically reduce and biologically remove both perchlorate and energetic compounds from PAX-21 wastewater. It was hypothesized that the pretreatment of PAX-21 wastewa- ter with Fe(0) would convert energetic compounds to products that are more amenable for biological oxidation and that these products can also serve as electron donors for PRB. Results of batch experiments showed that DNAN was completely reduced to 2,4- diaminoanisole (DAAN) and RDX was completely reduced to formaldehyde in the pres- ence of cast iron granules within 2h. Anaerobic batch experiments were conducted to investigate the bio-oxidation of Fe(0)-treated DNAN and RDX solutions by perchlorate as the electron acceptor. Batch biodegradation experiments showed that perchlorate in iron-treated PAX-21 wastewater was decreased to an undetectable level after 5 days of incubation. In contrast, negligible perchlorate was removed in control bottles containing untreated PAX-21 wastewater. Anaerobic batch experiments demonstrated that complete reduction of perchlorate in iron-treated PAX-21 wastewater can be achieved without add- ing an exogenous electron donor. This study confirmed that iron pretreatment not only removed energetic compounds, but also transformed the energetic compounds to products that can serve as the source of electrons for perchlorate respiring bacteria.
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