BIOLOGICAL TREATMENT OF AGENT AND ENERGETIC HYDROLYSATES GENERATED FROM THE WASHOUT OF MUSTARD (HD) MUNITIONS

In August 2002, the Department of Defense (DoD) selected neutralization followed by biodegradation as the technology to be used to destroy chemical agent and energetics associated with assembled chemical weapons stored at the Pueblo Chemical Depot (PCD) in Colorado. DoD's decision was based in large part on technology evaluations and demonstrations carried out since 1997 by the Assembled Chemical Weapons Assessment (ACWA) program.The PCD stockpile consists entirely of projectiles and mortars filled with blister agents, the vast majority of which contain mustard agent HD (distilled β,β'-dichloroethylsulfide). Some munitions have mustard agent HT, a 60:40 eutectic mixture of HD and bis(2-[2- chlorethylthio]ethyl) ether. The munitions also contain one of two types of explosives, either tetryl or tetrytol, a 70:30 mixture of tetryl and TNT. Almost all of the mustard munitions have some degradation products and inorganic residues within the agent cavity that are commonly referred to as agent ‘heel’.The neutralization process for agent involves the acidic hydrolysis of sulfur mustard in hot (90°C) water, which yields a detoxified and biodegradable product typically containing from 80 to 90% thiodiglycol. Explosives are neutralized and destroyed using a base hydrolysis process that involves mixing the explosives in a hot (90°C) caustic (NaOH) solution. The products from both neutralization processes are called hydrolysates.Prior ACWA demonstration and engineering design study (EDS) testing validated biological treatment of a mixture of HD and tetrytol hydrolysates using Honeywell's patented Immobilized Cell Bioreactor (ICB™). The HD hydrolysate used in previous tests was made from neat agent obtained from ton containers stored at the Aberdeen Proving Ground (APG) in Maryland. Because the Pueblo stockpile consists of assembled munitions that contain both liquid agent and heel material, the HD hydrolysate used in previous ICB tests was not fully representative of hydrolysate that will be produced during full-scale operations at Pueblo. Therefore, ICB™ testing using HD hydrolysate prepared from liquid agent and heel material removed from actual chemical munitions (4.2” HD mortars) was conducted between January and May 2002. This paper presents the results of these tests, compares the results to those obtained in previous demonstration and EDS tests, and discusses their potential impact on the full-scale system design.