The Pueblo Chemical Agent-Destruction Pilot Plant, known as PCAPP, safely destroyed the stockpile of chemical weapons stored at the U.S. Army Pueblo Chemical Depot, now known as the U.S. Army Chemical Materials Activity-West, in Colorado. A two-step technology – neutralization followed by biotreatment – was the primary process selected to destroy the chemical weapons.
The Program Executive Office, Assembled Chemical Weapons Alternatives (PEO ACWA) was responsible for the safe and environmentally compliant destruction of the 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. The last chemical weapon in the Colorado stockpile was destroyed June 22, 2023. PEO ACWA is now focused on the safe and environmentally protective closure of the plant.
Neutralization
During the neutralization process, munitions were taken apart and energetics (explosives and propellants) were removed. The chemical agent was drained, and the munitions bodies were rinsed. The agent was then mixed vigorously with hot water and sodium hydroxide, which neutralized it. The resulting wastewater product, known as hydrolysate, was tested to ensure agent destruction before proceeding to the biotreatment process.
Biotreatment
Following confirmation of agent destruction, the hydrolysate was treated in the Immobilized Cell Bioreactor (ICB) system, which had 16 rectangular reaction tanks. Each tank was an aerobic, fixed-film bioreactor packed with two-inch polyurethane foam cubes containing biological organisms.
Four reactors were grouped together to form an ICB module. Each module was 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 broke down thiodiglycol, also called TDG, and other organics in the hydrolysate, converting them to carbon dioxide, water and minerals (chlorides and sulfides). The resulting biotreated water was transferred to three Brine Concentrator Feed Tanks.
Environmental Conservation
During operations at PCAPP, the Pueblo plant recovered, recycled and reused approximately 80 percent of the water required to complete destruction of the stockpile.
Brine Reduction System
The Brine Reduction System (BRS) played an important
role in PCAPP’s conservation efforts. It incorporated three technologies: evaporation, crystallization and solids dewatering.
Biotreated effluent was held in the Brine Concentrator Feed Tanks prior to pumping it to the BRS for further processing. An 86-foot-tall evaporator was used to boil water from the biotreated effluent and recover the water through condensation. The water was filtered and then recycled back into the plant.
After evaporation, the concentrated brine was pumped to a crystallizer to further reduce its volume and prepare this salt slurry for filtration. With additional evaporation in the crystallizer, the concentration of the dissolved salt increased to a critical point where salt crystals formed.
As in the evaporator, the water vapor was condensed and recovered water was filtered and sent to the Process Water Tank. The salt crystals and other solids in the concentrated slurry were filtered out and compressed. The resulting filtered “salt cake” was shipped to an off-site permitted hazardous waste disposal facility. Approximately 5,000 tons of salt cake were produced during the project.
Secondary Wastes
Secondary wastes, which included both solid and liquid products from PCAPP’s Static Detonation Chamber units, were stored in either a less-than-90-day hazardous waste accumulation area or a permitted storage area, then shipped to permitted Treatment, Storage and Disposal Facilities for further treatment and/or ultimate disposal.