Treatment to Remove High-Strength Contaminants in Wastewater Generated in the Destruction of VX Nerve Agent: Development of Technology and Demonstration of Environmental Quality

Shortly after the events of Sept. 11, 2001, the U.S. government accelerated efforts on eliminating potential terrorist threats across the U.S. – including those posed by storage of chemical warfare agents and weapons. As part of that effort, the U.S. Army is destroying its VX–nerve agent stockpile in Newport, Indiana. The Army has determined that elimination of this stockpile can be achieved best by on-site destruction of the VX-nerve agent in Indiana. The plan for the wastewater resulting from the destruction process – called Newport Caustic Hydrolysate (NCH) – would be to provide off-site treatment using an existing permitted commercial treatment facility. The NCH contains high concentrations of ethyl methyl phosphonate (EMPA), methyl phosphonate (MPA) and diisopropylaminoethylthiolate (“thiolamine”). At the Army's request, DuPont conducted studies that demonstrated that the NCH wastewater could be handled safely and in an environmentally sound manner in its Secure Environmental Treatment (SET) facility in Deepwater, New Jersey. However, concerns were raised that the phosphonate compounds were not substantially removed in the treatment process.In response to these concerns, DuPont undertook studies to develop enhanced removal of the phosphonate compounds. These studies demonstrated that chemical oxidation with sodium persulfate in the presence of air or hydrogen peroxide would yield nearly complete conversion of EMPA to MPA. The MPA generated during the oxidation and that initially present in the NCH could be removed using ferric chloride and lime. The study identified optimal doses of the treatment chemicals and identified destruction pathways for the trace impurities in the NCH. GC/MS analysis demonstrated that such impurities were destroyed in the pretreatment process. PACT® biotreatability studies were conducted to demonstrate that biotreatment operability would be maintained and effluent limitations would be achieved. A detailed set of whole effluent toxicity tests were performed, including both acute toxicity and chronic toxicity, on three species – Fathead minnow, Ceriodaphnia and green algae – using pretreated NCH samples with and without PACT® biotreatment. These tests demonstrated that there would be no toxic impacts in the receiving water, the Delaware River, after the NCH was subjected to the combined pretreatment process and PACT® biotreatment in the DuPont SET wastewater treatment plant.