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1 Background Under the direction of the Department of Defense (DOD), BRIEF DESCRIPTION OF THE PCAPP PROCESS the U.S. Army Element known as the Assembled Chemical A detailed description of the PCAPP process can be found Weapons Alternatives (ACWA) program will destroy the in earlier National Research Council (NRC) reports, Assess- remaining U.S. stockpile of chemical weapons in storage at ment of Agent Monitoring Strategies for the Blue Grass and the Pueblo Chemical Depot (PCD) in Colorado and at the Pueblo Chemical Agent Destruction Pilot Plants (2012) and Blue Grass Army Depot in Kentucky. Review of Secondary Waste Disposal for the Blue Grass and The chemical agent stockpile at the PCD contains 105-mm Pueblo Chemical Agent Destruction Pilot Plants (2008). and 155-mm artillery projectiles along with 4.2-inch mortar Figure 1-1 depicts a block diagram of all the main process rounds. Together, these number approximately 780,000 steps for biotreatment and water recovery used at PCAPP that munitions and contain a total of about 2,600 tons of mustard are the subject of this report. The process for munition disas- blister agent. All the projectiles and more than three-quarters sembly and agent destruction includes the following steps: of the mortar rounds contain distilled mustard agent (HD). The remaining mortars contain HT, which is a mixture of 1. Munitions are removed from their pallets. mustard agent and 20 to 40 wt. percent of T (bis[2-chloro- 2. Propellant is separated from the projectiles and sent ethylthioethyl] ether), which was simultaneously produced off-site for disposal. during the synthesis process (NRC, 2001). 3. Bursters are removed at the linear projectile/mortar The facility constructed to destroy the chemical ­ eapons w disassembly machine and also sent off-site. stored at the PCD is called the Pueblo Chemical Agent 4. Mustard agent is washed out of the projectile bodies Destruction Pilot Plant (PCAPP). Construction was essen- by the munition washout system (MWS) with a high- tially completed in late 2012. Its operational readiness to pressure water stream. begin destroying agent is expected to be achieved by the 5. Mustard agent and MWS wash water is sent to the first half of 2015, and it will continue in operation for 3 to agent hydrolysis reactors where the agent is hydro- 5 years. PCAPP will robotically disassemble the projectiles, lyzed with hot water (194°F). remove the energetic materials, destroy the chemical agent 6. After the agent hydrolysis is completed and the by ­hydrolysis with hot (194°F) water, and decontaminate the hydrolysate has been determined to contain no more mustard agent projectile casings by heating them to 1,000°F than 20 ppb HD or no more than 200 ppb HT, it is for more than 15 minutes. The Army refers to the hydrolysis transferred and treated in immobilized cell bioreac- step as neutralization. The product stream from this neu- tors (ICBs) in the biotreatment area where the main tralization step is called hydrolysate, and it must be further product of the hydrolysis, TDG, will be degraded by treated to conform to requirements of the Chemical Warfare microorganisms. Convention treaty, to which the United States is a signatory. 7. If a munition is leaking or contaminated with agent, The major component in the product stream is ­hiodiglycol t the whole munition will be detonated by using explo- (HOCH2CH2SCH2CH2OH) (TDG), which is listed as a sive destruction technology (EDT).1 Schedule 2 compound in the Chemical Weapons Convention treaty because it is a precursor for the synthesis of mustard 1In agent. The DOD and ACWA have selected biotreatment for general, an EDT is a sealed chamber in which chemical munitions this second treatment step. that are otherwise difficult to process are destroyed by detonation and/or deflagration. A variant EDT technology developed by the U.S. Army, the explosive destruction system uses shaped charges in a sealed chamber to 6

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BACKGROUND 7 Overview of the PCAPP Biotreatment System and WRS-BRS ICBs WRS BRS GAC Wastes other Off-gas than Vent Condensate hydrolysate GAC condenser r Off-gas Munitions ICB Hydrolysate Blending CO pH Munitions processing feed ICBs 2 Evaporator Biomass, Tank stripping adjustment tank dissolved organics, Filtrate Brine Process inorganic RO reject, water, Process solids Blowdown NaOH water, nutrients water Belt filter Crystallizer Condensate Cake to GAC landfill Process water FIGURE 1-1  Overview block diagram of the PCAPP biotreatment, water recovery, and brine reduction systems. NOTE: BRS, brine reduction system; GAC, granular activated carbon; ICB, immobilized cell bioreactor; RO, reverse osmosis; WRS, water recovery system. Figure 1-1 The ICBs are designed to remove at least 95 percent of the The BRS consists primarily of two unit operations. The influent TDG. The TDG is mineralized to CO2, sulfuric acid, liquid stream from the WRS flows to an evaporator where and water, and a large quantity of biomass resulting from distillate water is produced, leaving a more concentrated TDG degradation is produced. The biotreatment process brine. The brine concentrate (BC) from the evaporator is sent is described and reviewed in detail in Chapter 2. Table 1-1 to the crystallizer, which concentrates the brine further and indicates the distribution of the water recycled from the water recovery and brine reduction systems (WRS-BRS). The TABLE 1-1  Summer and Winter Quantities and Percentages ­liquid effluent from the ICBs is blended with boiler and cool- for the Units Using the Recycled Water at PCAPP ing tower blowdown water and reject water from a reverse osmosis process that provides highly purified water for uses Percentage Process Water Use Flow rate (gpd) of total (%) such as the feed for the high-pressure spray nozzles of the munitions washout system and the boilers. The ICBs also Summer generate vapors possibly containing toxic volatile organic Biotreatment system 116,000 79.7 Reverse osmosis system 14,300 9.7 compounds (VOCs), which will be collected and routed to Off-gas treatment scrubbers 2,000 1.4 an off-gas treatment system containing granular activated Agent hydrolyzers 830 0.57 carbon (GAC). BRS and miscellaneous 1,600 1.11 The WRS and BRS are described and reviewed in detail in Cooling tower basin 11,000 7.5 Chapter 3. The WRS-BRS is designed to treat approximately TOTAL 145,000 145,000 gallons per day (gpd). The WRS collects and mixes Winter ICB effluent with other wastewater streams and provides Biotreatment system 115,000 79.6 equalization of the collected liquid streams before the com- Reverse osmosis system 24,800 17.2 Off-gas treatment scrubbers 2,000 1.4 bined stream is delivered to the BRS. The recovered water Agent hydrolyzers 830 0.58 is transferred to process water storage tanks from which it is BRS and miscellaneous 1,600 1.12 reused by the facility. The WRS-BRS is expected to be able TOTAL 144,000 to recycle 80 percent of the water used in PCAPP operations. NOTE: BRS, brine reduction system. SOURCE: Adapted from Calculation 24851-RD-M5C-B17-M0001, Basic open the munition and then the agent is neutralized with an appropriate Utilities Water Balance for PCAPP, Appendix A (Summer) and Appendix solvent reagent. B (Winter).

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8 REVIEW OF BIOTREATMENT, WATER RECOVERY, AND BRINE REDUCTION SYSTEMS FOR PCAPP produces more distillate water. The distillate stream (water) and planned operating conditions for the biotreatment from the evaporator and the crystallizer both pass through process as well as the water recovery and brine reduc- carbon filters for removal of any residual constituents that tion systems (WRS and BRS), and recommend activities would prevent the water from meeting permit requirements. that should be performed as part of systemization at the Pueblo Chemical Agent Destruction Pilot Plant (PCAPP) The remaining slurry is passed to a belt filter press where to provide additional confidence in the opera­ ional readi- t the solids are concentrated and the filtrate is returned to the ness of the plant. crystallizer. The filter cake is sent off-site to a hazardous waste disposal site. After passing through the carbon filters, the BRS effluent must be of sufficient quality to enable it to SCOPE be recycled in the plant. As noted earlier, the committee recognizes that PCAPP has been designed and that construction is completed. While STATEMENT OF TASK this facility is identified as a pilot plant, it is intended to func- tion as the vehicle for destruction of the entire stockpile at Because the PCAPP WRS-BRS is technology that has not PCD. The current approach to biotreatment, water recovery, been used at chemical munitions destruction facilities before, and brine reduction has not had the benefit of a more tradi- the Program Executive Officer for ACWA (PEO-ACWA) tional smaller-scale pilot evaluation. The committee limited requested the NRC initiate a study to review the PCAPP its concerns, findings, and recommendations to address prob- water recovery system and the brine reductions system that lems that might occur during systemization (pre-operational are already installed. After the originally constituted commit- testing) and operations and offers suggestions regarding how tee had already met three times, in October 2012, PMACWA PCAPP might respond to these problems. requested that the statement of task be expanded to include a The committee visited the PCAPP site during its first review of the biotreatment area. The expanded statement of meeting in May 2012. Upon examining the WRS-BRS task for what became the Committee on Review of Biotreat- installation that was nearing completion, the committee ment, Water Recovery, and Brine Reduction Systems for decided there was no benefit to be gained in visiting another the Pueblo Chemical Agent Destruction Pilot Plant is given installation using this technology, because the feed stream below: at PCAPP is unique and feeds of similar composition have never been treated before. However, the committee did hold The National Research Council will establish an ad hoc committee to: a teleconference and discussion with Veolia Water Solutions & Technologies, the technology provider of the BRS. Original Tasks: The stipulations pertaining to the rules under the Fed- eral Advisory Committee Act by which the NRC performs • Obtain information from the equipment vendor on BRS s ­tudies (other than those involving classified materials) installations that treat comparatively similar biotreatment require that all reference materials used to support study effluents, and determine that operability of these systems reports must be made available to the public by a Freedom has been acceptable. of Information Act request. Consequently, the committee • Review materials of construction for the WRS and BRS was limited in the information that it could use, because the to judge whether or not performance can be expected to BRS system technology provider, Veolia Water Solutions & be adequate over the anticipated operational life of the Technologies, considered the design of its process equip- plant. • Ascertain the likelihood that the quality of the recycled ment to be proprietary. Moreover, the technology provider’s water will meet requirements for its use as plant process reports on testing of surrogate feeds that led to the BRS water at PCAPP. design were also labeled proprietary and were not available • Address the possibility of fouling of the WRS and BRS to the committee.2 Thus, the committee depended on receiv- equipment due to migration of microorganisms from the ing responses to its questions from the PCAPP contractor bioreactors. and the BRS technology provider. Such responses include, for example, the information on materials of construction New Tasks: given in Table 4-1. After the statement of task was extended, six members • Review the results of mustard agent-only hydrolysate of the committee, including four newly appointed members, biotreatment studies carried out prior to 1999, including visited the PCAPP site in November 2012. The revised the ICB-based bench-scale study reported in ERDEC- TR-497 and prior SBR-based bench-scale studies. Also, statement of task requested the committee to review vari- reexamine the results from the 1999-2004 mixed agent ous former studies conducted between 1994 and 2006 on and energetics testing in light of current plans to biotreat mustard agent-only hydrolysate. 2Permission was granted by Veolia Water Solutions & Technologies to • Review the current design, systemization approach, use two figures from one of the company’s reports as the basis for two of the figures in Chapter 3.

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BACKGROUND 9 biotreatment processing of mustard hydrolysate. Many of as requested in the expanded statement of task. Chapter 3 these studies used both agent and energetics hydrolysate as describes and reviews in detail the WRS-BRS system design. feed to the bioreactors. Also, the scale and nature of the tests As mentioned above, the descriptions are based on the draw- varied from 1-liter sequencing batch reactor (SBR) bench- ings and presentations given to the committee at its first scale studies to 1,000-gallon pilot ICB bioreactors. To meet meeting and the responses to question sets that were given the statement of task, these studies were reviewed by the to the PCAPP contractor and its BRS technology provider. members of the committee and those deemed relevant have Chapter 4 reviews the materials of construction being used, been cited in Chapter 2 when appropriate. The committee taking into consideration the expected 3- to 5-year usage of does not present specific reviews of any of these studies but the plant. has considered the results in its review and analysis of the PCAPP biotreatment process. REFERENCES NRC (National Research Council). 2001. Analysis of Engineering Design ORGANIZATION OF THIS REPORT Studies for Demilitarization of Assembled Chemical Weapons at Pueblo Chemical Depot. Washington, D.C.: The National Academies Press. This chapter provides brief background information on NRC. 2008. Review of Secondary Waste Disposal for the Blue Grass and the PCAPP plant design, the statement of task for this study, Pueblo Chemical Agent Destruction Pilot Plants. Washington, D.C.: The introductory descriptions of the biotreatment, water recov- National Academies Press. ery, and brine reduction systems processes, and the scope NRC. 2012. Assessment of Agent Monitoring Strategies for the Blue Grass and Pueblo Chemical Agent Destructions Pilot Plants. Washington, of the committee’s review. Chapter 2 describes prior testing D.C.: The National Academies Press. and reviews the design of the biotreatment ICB processes,