1

Introduction

Congress has directed the U.S. Army to dispose of its stockpile of chemical warfare agents in accordance with the Chemical Weapons Convention (CWC). At five of nine stockpile sites, the Army is using, or intends to use, high-temperature incineration as part of a baseline system to destroy the chemical agents in stored weapons. However, for two sites where chemical agents are stored solely in bulk containers, the Army has been pursuing alternative agent-destruction technologies that are more acceptable to the public than incineration. Several alternative technologies were evaluated intensively by the National Research Council (NRC, 1996a) and by the Army for use at these sites. Consistent with NRC recommendations in these evaluations, the Army chose to demonstrate one technology, chemical hydrolysis1 of the toxic agents, on a pilot scale (U.S. Army, 1996). The products of chemical hydrolysis (hydrolysate) will require further treatment to satisfy the requirements of the CWC and U.S. environmental regulations.

The chemical agents stored at the two bulk-only sites differ substantially (HD mustard agent at Aberdeen, Maryland, and VX nerve agent at Newport, Indiana). Therefore, different treatment process sequences were selected for use at the two sites. In both processes, the chemical bonds associated with agent toxicity will be destroyed by hydrolysis (with water for HD or aqueous sodium hydroxide for VX) (NRC, 1996a). However, in order to achieve rapid and complete hydrolysis, different reaction conditions will be used for each agent. Following hydrolysis, the processing steps for treating the hydrolysate for disposal will also differ greatly. At both sites, the stockpiled agents also contain significant concentrations of impurities, which had to be taken into account in the selection of postneutralization process steps (these impurities were examined in Review and Evaluation of Alternative Chemical Disposal Technologies [NRC, 1996a]). At the Aberdeen site, the HD stockpile also contains significant concentrations of volatile organic compounds (VOCs), chlorinated aliphatic hydrocarbons (which are common industrial solvents) that must be treated in the overall process.

The stockpile at Aberdeen Proving Ground, Maryland, consists of 1,625 tons of HD (mustard agent) stored in ton containers. HD, a blistering agent that produces painful, slow-healing burns on the skin, is toxic upon inhalation. The Army plans to detoxify HD by treatment with water slightly below the boiling point to produce an acidic aqueous solution of thiodiglycol (TDG). Although this solution is relatively nontoxic, TDG is regulated by the CWC because it could potentially be reconverted to mustard agent. Both to comply with the CWC and to ensure safe, environmentally responsible disposal, the HD hydrolysate will be made slightly alkaline and subjected to biological oxidation. Microorganisms will then be used to oxidize the TDG to carbon dioxide and an aqueous sulfate solution that can be safely discharged to a federally owned waste treatment facility on site. The resulting filter cake will be shipped to a commercial facility for disposal.

The Newport, Indiana, stockpile contains 1,269 tons of VX nerve agent, a relatively nonvolatile, persistent toxin that disrupts signal transmission in the central nervous system. VX can be hydrolyzed in hot aqueous sodium hydroxide solution. This process produces a strongly alkaline solution containing salts of methylphosphonic acid, its monoethyl ester, and a foul-smelling thiol amine compound. In 1996, the NRC recommended further evaluation of the Army's

1  

The Army refers to the destruction of chemical agent via hydrolysis as chemical neutralization. The term is derived from the military definition of neutralize, to render something unusable or nonfunctional. Hydrolysis is a reaction of a target compound with water, often catalyzed by an acid or a base, in which a chemical bond is broken in the target, and the components of water, OH− and H+, are inserted at the site of the bond cleavage. The technical definition of neutralization is a chemical reaction between an acid and a base to form a salt and water. Chemical agents are neither acids nor bases, however, so the use of the term neutralization is somewhat confusing. Nevertheless, in the literature on chemical demilitarization in aqueous systems, the terms neutralization and hydrolysis are used interchangeably.



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Integrated Design of Alternative Technologies for Bulk-Only Chemical Agent Disposal Facilities 1 Introduction Congress has directed the U.S. Army to dispose of its stockpile of chemical warfare agents in accordance with the Chemical Weapons Convention (CWC). At five of nine stockpile sites, the Army is using, or intends to use, high-temperature incineration as part of a baseline system to destroy the chemical agents in stored weapons. However, for two sites where chemical agents are stored solely in bulk containers, the Army has been pursuing alternative agent-destruction technologies that are more acceptable to the public than incineration. Several alternative technologies were evaluated intensively by the National Research Council (NRC, 1996a) and by the Army for use at these sites. Consistent with NRC recommendations in these evaluations, the Army chose to demonstrate one technology, chemical hydrolysis1 of the toxic agents, on a pilot scale (U.S. Army, 1996). The products of chemical hydrolysis (hydrolysate) will require further treatment to satisfy the requirements of the CWC and U.S. environmental regulations. The chemical agents stored at the two bulk-only sites differ substantially (HD mustard agent at Aberdeen, Maryland, and VX nerve agent at Newport, Indiana). Therefore, different treatment process sequences were selected for use at the two sites. In both processes, the chemical bonds associated with agent toxicity will be destroyed by hydrolysis (with water for HD or aqueous sodium hydroxide for VX) (NRC, 1996a). However, in order to achieve rapid and complete hydrolysis, different reaction conditions will be used for each agent. Following hydrolysis, the processing steps for treating the hydrolysate for disposal will also differ greatly. At both sites, the stockpiled agents also contain significant concentrations of impurities, which had to be taken into account in the selection of postneutralization process steps (these impurities were examined in Review and Evaluation of Alternative Chemical Disposal Technologies [NRC, 1996a]). At the Aberdeen site, the HD stockpile also contains significant concentrations of volatile organic compounds (VOCs), chlorinated aliphatic hydrocarbons (which are common industrial solvents) that must be treated in the overall process. The stockpile at Aberdeen Proving Ground, Maryland, consists of 1,625 tons of HD (mustard agent) stored in ton containers. HD, a blistering agent that produces painful, slow-healing burns on the skin, is toxic upon inhalation. The Army plans to detoxify HD by treatment with water slightly below the boiling point to produce an acidic aqueous solution of thiodiglycol (TDG). Although this solution is relatively nontoxic, TDG is regulated by the CWC because it could potentially be reconverted to mustard agent. Both to comply with the CWC and to ensure safe, environmentally responsible disposal, the HD hydrolysate will be made slightly alkaline and subjected to biological oxidation. Microorganisms will then be used to oxidize the TDG to carbon dioxide and an aqueous sulfate solution that can be safely discharged to a federally owned waste treatment facility on site. The resulting filter cake will be shipped to a commercial facility for disposal. The Newport, Indiana, stockpile contains 1,269 tons of VX nerve agent, a relatively nonvolatile, persistent toxin that disrupts signal transmission in the central nervous system. VX can be hydrolyzed in hot aqueous sodium hydroxide solution. This process produces a strongly alkaline solution containing salts of methylphosphonic acid, its monoethyl ester, and a foul-smelling thiol amine compound. In 1996, the NRC recommended further evaluation of the Army's 1   The Army refers to the destruction of chemical agent via hydrolysis as chemical neutralization. The term is derived from the military definition of neutralize, to render something unusable or nonfunctional. Hydrolysis is a reaction of a target compound with water, often catalyzed by an acid or a base, in which a chemical bond is broken in the target, and the components of water, OH− and H+, are inserted at the site of the bond cleavage. The technical definition of neutralization is a chemical reaction between an acid and a base to form a salt and water. Chemical agents are neither acids nor bases, however, so the use of the term neutralization is somewhat confusing. Nevertheless, in the literature on chemical demilitarization in aqueous systems, the terms neutralization and hydrolysis are used interchangeably.

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Integrated Design of Alternative Technologies for Bulk-Only Chemical Agent Disposal Facilities plans to use biological oxidation to destroy the organic components of this solution (NRC, 1996a). To date, attempts to treat VX hydrolysate by biological oxidation have not been successful. Therefore, the treatment of the hydrolysate by supercritical water oxidation (SCWO) is under development. Laboratory and bench-scale tests of the SCWO treatment have demonstrated nearly complete destruction of the organic compounds in VX hydrolysate. The combination of hydrolysis followed by SCWO would meet the regulatory requirements for the safe destruction and disposal of VX. However, more development and testing will be necessary to ensure the reliable operation of the SCWO processing step (NRC, 1998). The Stockpile Committee's statement of task for this study was as follows: The NRC study will accomplish the following: gather and review information on the 60-percent process design for the chemical agent demilitarization facilities to be constructed in Aberdeen, Maryland, and Newport, Indiana. Information to be evaluated will include the 60% process design documentation, testing, and evaluation data developed in support of the design development, relevant information contained in environmental permit applications, previous related NRC reports on chemical agent demilitarization, and briefings from the Army and its contractors. focus the evaluation on overarching issues in the process design which result from integration of the individual process steps, process safety, and process reliability. This evaluation will not include verification of specific design calculations or regulatory compliance. identify process design components which the Stockpile Committee believes warrant additional evaluation or action, including potential alternative configurations, options, or supporting information, prior to the Army finalizing the design for each facility. present the evaluation in a report which identifies each design issue, articulates the basis for the recommended further evaluation or action, and potential alternative approaches (where possible). In keeping with this statement of task, the committee gathered and reviewed information on the 60-percent process design2 for the chemical agent disposal facilities to be constructed at Aberdeen and Newport. The committee focused on the overarching issues resulting from the integration of individual processing steps, including process safety, reliability, and potential alternative configurations. An acquisition design package (ADP) is an approximately 60-percent completed design that is used as a basis for competitive bids for completion of the design, construction, and operation of each chemical agent destruction facility. The committee has reviewed the ADP designs for the Aberdeen and Newport facilities prepared by Stone and Webster Engineering Company (SWEC) (U.S. Army, 1998a, 1998b). As additional test data and design modifications suggested by the systems contractors became available, the committee reviewed them as well. No attempt was made to provide a detailed, comprehensive review of the process designs. Rather, this report reviews the major design changes, assesses the integration of processing steps, and identifies overarching issues that should be addressed. The committee also notes future development and tests that may be necessary. Chapter 2 presents the committee's evaluations, findings, and recommendations for the overall ADP designs for the disposal technologies at the Aberdeen and Newport chemical stockpile sites. Chapter 3 addresses issues related to the use of SCWO to treat VX hydrolysate at the Newport site. Chapter 4 focuses on the management of process and nonprocess wastes; Chapter 5 examines agent and nonagent monitoring; and Chapter 6 focuses on risk management. 2 The 60-percent design specifies the detailed design basis, primary process steps, process flow diagrams, major equipment components, monitoring requirements, facility requirements (e.g., building layouts, electrical and ventilation requirements), and preliminary operational strategies. Detailed final specifications of all process components, facilities, and operations are not complete.