The Pueblo Chemical Agent-Destruction Pilot Plant, known as PCAPP, is safely destroying a stockpile of chemical weapons currently stored at the U.S. Army Pueblo Chemical Depot (PCD). A two-step technology – neutralization followed by biotreatment – is the process selected to destroy the chemical agent stored at PCD.
The Program Executive Office, Assembled Chemical Weapons Alternatives, is responsible for the safe and environmentally compliant destruction operations of the remaining U.S. chemical weapons stockpile in Colorado and the Blue Grass Army Depot in Kentucky, by the Chemical Weapons Convention treaty commitment of Sept. 30, 2023. U.S. public law mandates stockpile destruction by Dec. 31, 2023.
During the neutralization process, munitions are taken apart and energetics (explosives and propellants) are removed. The chemical agent is drained, and the munitions bodies are rinsed. The agent is then mixed vigorously with hot water and sodium hydroxide, which destroys or neutralizes the agent. The resulting wastewater product, known as hydrolysate, is held and tested to ensure agent destruction before proceeding to secondary treatment. The process was the same during the 105mm and 155mm campaigns.
Following confirmation of agent destruction, the hydrolysate is treated in the Immobilized Cell Bioreactor (ICB) system — a system composed of 16 rectangular reaction tanks. Each tank is an aerobic, fixed-film bioreactor packed with two-inch polyurethane foam cubes where biological organisms reside.
Four reactors are grouped together to form an ICB module. Each module is equipped with a feed tank, aeration system, nutrient addition system, pH control system, effluent tank and an off-gas treatment system. A mix-culture of bacterial microorganisms attached to the ICB foam cubes break down thiodiglycol, also called TDG, and other organics in the hydrolysate, converting them to carbon dioxide, water and minerals (chlorides and sulfides). The resulting effluent (biotreated water) then goes to three Brine Concentrator Feed Tanks.
Chemical weapons destruction at PCAPP includes the conservation of water, a precious commodity in Colorado’s arid terrain. During its life cycle, the Pueblo plant will recover, recycle and reuse the equivalent of 80 percent of its water.
Brine Reduction System
The Brine Reduction System, or BRS, plays an important role in PCAPP’s conservation efforts. It is a process that incorporates three technologies: evaporation, crystallization and solids dewatering. Biotreated effluent is held in the Brine Concentrator Feed Tanks prior to pumping it to the BRS for further processing. An 86-foot-tall evaporator is used to boil water from the biotreated effluent and recover the water through condensation. The water is filtered and then recycled back into the plant.
After evaporation, the concentrated brine is pumped to a crystallizer to further reduce the brine volume and to prepare this salt slurry for filtration. With additional evaporation in the crystallizer, the dissolved salt concentrations increase to a critical point where salt crystals form.
As in the evaporator, the water vapor is condensed and recovered water is filtered and sent to the Process Water Tank. The salt crystals and other solids in the concentrated slurry are filtered out and compressed. The resulting filtered “salt cake” is shipped to an off-site permitted hazardous waste disposal facility. Approximately 5,000 tons of salt cake are expected to be produced during the life of the project.
Secondary wastes, which include both solid and liquid products coming from PCAPP’s Static Detonation Chamber (SDC), are stored in either a less than 90-day hazardous waste accumulation area or a permitted storage area, pending shipment to Treatment, Storage and Disposal Facilities for further treatment and/or ultimate disposal.