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Summary Under the direction of the Department of Defense, the U.S. combined water recovery system. The combined water Army Element known as the Assembled Chemical Weapons recovery system (WRS) and brine reduction system (BRS) Alternatives (ACWA) program will destroy the remainder will process approximately 145,000 gallons per day (gpd) of the outdated U.S. stockpile of chemical weapons that are of the combined ICB effluent from the biotreatment system in storage at two sites: the Pueblo Chemical Depot (PCD) and utility wastewaters. The BRS is designed to produce in Colorado and the Blue Grass Army Depot in Richmond, high-quality water for reuse in upstream processes. PCAPP Kentucky. The PCD stockpile consists solely of mustard intends to recycle at least 80 percent of the water back into blister agent in the distilled mustard agent (HD) and distilled the process after treatment. mustard mixed with bis(2-chloroethylthioethyl) ether (HT) The WRS-BRS consists of two major unit operations. The forms. This agent resides in 105-mm and 155-mm projec- blended feed stream flows to an evaporator where recycled tiles and in 4.2-inch mortar rounds. Together, these number water is produced, leaving a more concentrated brine. The approximately 780,000 munitions that contain a total of about brine concentrate (BC) from the evaporator is sent to the 2,600 tons of agent. crystallizer, which concentrates the brine further and pro- The Pueblo Chemical Agent Destruction Pilot Plant duces more recycled water. The distillate (water) from the (PCAPP) is named a pilot plant because many of the pro- evaporator and the crystallizer both pass through carbon fil- cesses used for destroying the agent and munition bodies have ters for removal of any residual constituents. Solids produced not been used before. Chemical neutralization (­ ydrolysis) h in the crystallizer are dewatered in a filter press and are sent with hot (194°F) water will be used to destroy the mus- off-site to a hazardous waste disposal site. tard agent. The primary product present in the resulting The product water from the BRS must be of sufficient h ­ ydrolysate is thiodiglycol (TDG), a Schedule 2 compound quality to enable it to be recycled in the plant. Permitting that must be destroyed to comply with the requirements of requirements mandate that the product water must be ade- the Chemical Weapons Convention treaty. The hydrolysate quate as a substitute for well water, indicated by the ability will subsequently undergo biotreatment in immobilized cell of the water to meet primary drinking water standards. bioreactors (ICBs), and the effluent from those units will Because the PCAPP water recovery system is a technol- undergo further treatment for purposes of water recovery. ogy that has not been used at chemical munitions destruction The feed streams to the ICBs and to downstream processes facilities before, the program executive officer for ACWA will be first-of-a-kind applications of the technologies used. (PEO-ACWA) requested that the National Research Coun- Agent destruction operations are planned to begin in the first cil (NRC) initiate a study to review the PCAPP WRS-BRS half of 2015 and continue for 3 to 5 years. that had already been installed at PCAPP. This study had The ICBs are designed to remove at least 95 percent of been in progress for 5 months when in October 2012, after the produced TDG in the hydrolysate. Besides the TDG the originally constituted  committee had already met three that is mineralized to CO 2, sulfuric acid, and water, a times, PEO-ACWA requested and sponsored an expansion of large quantity of precipitates and biomass associated with the statement of task to include a review of the biotreatment bacteria metabolizing the TDG is also produced (2,500 area (BTA). The expanded statement of task for what became to 3,300 lb/day). The effluent from the ICBs, including the Committee on Review of Biotreatment, Water Recovery, biomass and other suspended solids, will be blended with and Brine Reduction Systems for the Pueblo Chemical Agent boiler and cooling tower blowdown water and reject water Destruction Pilot Plant is given below: from a reverse osmosis process during introduction to the 1

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2 REVIEW OF BIOTREATMENT, WATER RECOVERY, AND BRINE REDUCTION SYSTEMS FOR PCAPP The National Research Council will establish an ad hoc committee. Thus, for the review and analysis of the BRS in committee to: particular, the committee depended on the PCAPP contractor and the technology provider for responses to its questions. Original Tasks: The committee identified several overarching concerns, findings, and recommendations that are expressed through- • Obtain information from the equipment vendor on BRS out the report. These are as follows: installations that treat comparatively similar biotreatment effluents, and determine that operability of these systems has been acceptable. • The feed, consisting of hydrolysate and recycled pro- • Review materials of construction for the WRS and BRS cess water, is unique, complex, and not well defined. to judge whether or not performance can be expected to This may present challenges and require PCAPP to be adequate over the anticipated operational life of the be particularly flexible and proactive in the operation plant. of the plant. • Ascertain the likelihood that the quality of the recycled • Insufficient or inconsistent information limited the water will meet requirements for its use as plant process committee’s ability to provide a thorough review of water at PCAPP. some aspects of the plant. • Address the possibility of fouling of the WRS and BRS • Consequently, a conservative approach of starting the equipment due to migration of microorganisms from the ICB units sequentially instead of simultaneously is bioreactors. strongly urged. New Tasks: • Continuous and extensive process monitoring throughout the BTA-WRS-BRS is required to prevent • Review the results of mustard agent-only hydrolysate system failure. A comprehensive corrosion monitor- biotreatment studies carried out prior to 1999, including ing program is also necessary. the ICB-based bench-scale study reported in ERDEC- TR-497 and prior SBR-based bench-scale studies. Also, reexamine the results from the 1999-2004 mixed agent BIOTREATMENT SYSTEM and energetics testing in light of current plans to biotreat Figure S-1 is a diagram illustrating the configuration of a mustard agent-only hydrolysate. PCAPP biotreatment ICB unit during planned normal opera- • Review the current design, systemization approach, tion. A total of 16 ICB units will be installed in four parallel and planned operating conditions for the biotreatment process as well as the water recovery and brine reduc- modules with four units per module. The ICBs are expected tion systems (WRS and BRS), and recommend activities to remove at least 95 percent of the influent TDG and 85 that should be performed as part of systemization at the percent of the chemical oxygen demand. In the ICB process, Pueblo Chemical Agent Destruction Pilot Plant (PCAPP) biomass grows on a surface and forms a biofilm. The com- to provide additional confidence in the opera­ ional readi- t mittee believes this immobilization of the biomass permits ness of the plant. excellent retention and accumulation without the need for separate biomass recovery devices and biomass recycling. In PCAPP had been designed over the course of the prior comparison to a suspended growth process, advantages for decade, and construction was essentially completed by this application include greater resiliency during fluctuating autumn of 2012; therefore, the committee limited its con- loading, faster recovery from off-normal conditions, and cerns, findings, and recommendations to problems that longer biomass residence time. might occur during systemization (pre-operational testing) The committee makes the following major observations and during agent processing, with a focus on how PCAPP regarding the biotreatment system: might respond to operational circumstances and problems that might occur. • ICB start-up. Start-up is the most critical phase in The stipulations pertaining to the rules under the Federal establishing stable operation of the ICBs. Satisfac- Advisory Committee Act by which the NRC performs ­studies tory operation will hinge on the ability of the bacteria (other than those involving classified materials) require that to adapt to and tolerate initially high and potentially all reference materials used to support study reports be made inhibitory influent concentrations of TDG. The cur- available to the public upon a Freedom of Information Act rent plans are to start up the ICBs over a period of request. Consequently, the committee was limited in the 30 days. PCAPP staff should consider a longer start- information that it could use, because the BRS technology up period to avoid system failure and provide more provider, Veolia Water Solutions & Technology, considered time for the organisms to acclimate to the hydrolysate the design of its process equipment to be proprietary. Also, feed. the technology provider’s reports on testing of surrogate • Toxicity concerns. TDG can be inhibitory to the feeds that led to the BRS design were also labeled proprietary biotreatment system at high concentrations. Once and, except for two block diagrams, were not available to the at steady state, biodegradation and dilution of the

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SUMMARY 3 FIGURE S-1  Conceptual diagram for the 16 immobilized cell bioreactor (ICB) units during planned normal operation.  SOURCE: Adapted from George Lecakes, Chief Scientist, PCAPP, “PCAPP’s Water Recovery System and Brine Reduction System Briefing,” presentation to the committee, May 1, 2012. Figure 2-1 and S-1 Bitmapped influent hydrolysate should maintain sub-inhibitory limitations. PCAPP should consider adding piping concentrations of TDG. During start-up or off-normal to feed the influent directly to the second and third periods, however, TDG toxicity/inhibition may occur. chambers in addition to the first chamber. This would • Solids buildup issues. Solids may build up in the reduce the mass-loading rate to the first chamber and ICBs. Precipitation during treatment may produce would decrease the potential for oxygen-limited con- iron-containing solids; furthermore, overaccumu- ditions in the biofilm in the first chamber. The addi- lation of biomass within the packing of the ICB tion of nitrate as a supplemental electron ­ cceptor a units may occur. The buildup of either could hinder would also mitigate sulfidogenesis. biotreatment efficiency. The solids will flow into the effluent tank and suspended solids may have an effect WATER RECOVERY AND BRINE REDUCTION SYSTEMS on the WRS-BRS system. Conducting ongoing solids balance calculations, collecting composite samples The WRS collects and mixes the ICB effluent and other to characterize the effluent, possibly using a settling wastewater streams and provides equalization before the tank, avoiding excessive FePO4 and diammonium combined stream of approximately 145,000 gpd is delivered phosphate use, and pre-operational testing with a to the BRS. Figure S-2 is a block diagram of PCAPP’s BRS, benign and common substrate such as molasses, are which is the main system for water recovery at PCAPP. The possible ways for controlling solids. BRS consists primarily of two unit operations. The liquid • Monitoring. Extensive monitoring should be done, stream from the WRS flows to an evaporator where distil- particularly during start-up, to ensure that the sys- late water is produced, leaving a more concentrated brine. tem is robust and that the operators have an accurate The BC from the evaporator is sent to the crystallizer, which understanding of oxygen use, pH control, nutri- concentrates the brine further and increases the amount of ent supply, TDG degradation, and the solids mass distillate. The distillate streams (water) from the evapora- balance. tor and the crystallizer both pass through carbon filters for • Downstream effects. The precise composition and removal of any residual constituents that would prevent the character of the effluent and off-gas are unknown. It water from meeting primary drinking water requirements. is unclear to the committee how this might change Monitoring of the granular activated carbon filters for the with time and how this might affect downstream presence of these constituents is essential. The remaining processing. The monitoring data for the composition slurry is passed to a belt filter press where the solids are and character of the effluent and off-gas during start- concentrated and the filtrate is returned to the crystallizer. up should be closely examined to anticipate potential The filter cake is sent off-site to a hazardous waste disposal long-term concerns for downstream processing. site. After passing through the carbon filters, the BRS efflu- • Oxygen demand issues. Although the air supplied to ent must be of sufficient quality to enable it to be recycled the ICBs exceeds the overall stoichiometric oxygen in the plant. demand, a shortage of oxygen supply may occur in The committee makes the following major observations the first chamber, which receives the full organic regarding the WRS-BRS: loading. In addition, the development of sulfidogenic conditions within the pores of the elastomer foam • The modeled concentrations of organic compounds media used as packing could occur due to oxygen flux and suspended solids in the PCAPP crystallizer dis-

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4 REVIEW OF BIOTREATMENT, WATER RECOVERY, AND BRINE REDUCTION SYSTEMS FOR PCAPP Off gas To process H2SO4 NaOH water tank to OTS Hot evaporator Deaerator Brine BRS Evaporator feed (from distillate water recovery Steam carbon Concentrated brine Distillate filters system) Distillate Crystallizer Neutralized feed Crystallizer Slurry Belt feed tank filter Steam Belt filter filtrate Filter cake FIGURE S-2  Block diagram of the brine reduction system. NOTE: OTS, off-gas treatment system. SOURCE: Adapted from Veolia Water Solutions & Technologies, Bench Scale Evaporation of Waste Brine and Filter Testing, 2010. Used with permission. Figure 3-1 tillate are uncertain and may not be achieved. If the initial operation, as well as for operator training, can concentrations of organic compounds of concern are be helpful in this effort. higher than expected, the activated carbon will need to be replaced more frequently than planned. If the MATERIALS OF CONSTRUCTION suspended solids concentration is too high, excessive backwashing of the carbon filter may be required. As part of its study, the committee reviewed the materials The concentrations of the organic compounds and of construction (MOC) provided to them. The biotreatment, suspended solids in the distillate from the PCAPP water recovery, and brine reduction systems include a large crystallizer should be carefully monitored. If they number of different items that are constructed from a wide prove to be unacceptably high, consideration should spectrum of materials, including carbon steel, high-nickel be given to upgrading the de-entrainment device in alloys, fiber-reinforced plastic, epoxy-coated carbon steel the crystallizer. and titanium, and austenitic and duplex stainless steels, with • Much uncertainty remains whether the product the latter two being used extensively. water from the distillate activated carbon filters of The committee makes the following major observations the PCAPP BRS will meet permit requirements that regarding the MOC: conform to drinking water quality standards. There is insufficient detail available on the composition of • The materials of construction selected for the PCAPP the total organic carbon in the filter influent water to biotreatment and WRS-BRS process equipment determine with confidence what the effluent quality appear to be generally appropriate for the service will be. PCAPP operators should, therefore, monitor conditions anticipated, based on the information the carbon filter effluent for compounds of concern. available to the committee. • Primary drinking water standards were developed • The combination of high chloride concentrations and based on the need to protect public health; water elevated temperatures creates highly corrosive condi- that is recycled for non-potable use should not have tions, even when the pH is near 7. to meet stringent drinking water standards. PCAPP • Heat transfer surfaces are vulnerable to corrosion, should renegotiate the permitting requirements to especially under deposits. Standard operating proce- better reflect that the recycled water is intended for dures should be implemented to ensure that appro- non-potable use within the plant. priate surface cleaning is performed regularly for • The brine reduction system for PCAPP will be a first- the PCAPP biotreatment system and the WRS-BRS. of-a-kind system because a similar feed has never • Properly designed and implemented protocols to been treated before. The PCAPP WRS-BRS process monitor the occurrence of corrosion in components will require a high level of monitoring and operator of the PCAPP biotreatment system and WRS-BRS intervention. Enlisting the assistance of the technol- enables the identification of problems before equip- ogy provider of the WRS-BRS during start-up and ment failures occur, and such protocols should be

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SUMMARY 5 designed and implemented. This provides a basis corrosion, and stress corrosion cracking is needed for selecting alternative materials if the original not only for tanks but for other equipment as well. selections prove to be inadequate, or for modifying • No corrosion monitoring plan has been developed for operating practices to minimize the corrosion risk. equipment other than tanks. PCAPP should develop a • The proposed tank corrosion monitoring plan for corrosion monitoring plan for equipment other than PCAPP relies on ultrasonic inspection and external tanks that includes, as a minimum, internal inspection visual inspection. This approach would provide no and corrosion testing. This plan should include provi- warning of pitting attack prior to wall penetration. sions for detecting general corrosion, pitting/crevice Internal visual inspection of the equipment when it is corrosion, and stress corrosion cracking. out of service between destruction campaigns would • The Assembled Chemical Weapons Alternatives reduce the probability of such failures. A monitoring program leadership and PCAPP site contractor man- plan that includes both external and internal inspec- agement should strongly support implementation of a tion for detecting general corrosion, pitting/crevice comprehensive corrosion-monitoring program. This should be a priority.