The Program Executive Office, Assembled Chemical Weapons Alternatives (PEO ACWA), the U.S. Army Pueblo Chemical Depot and the surrounding communities worked together to select neutralization followed by biotreatment to destroy the chemical weapons stored at the depot. PEO ACWA was responsible for completing stockpile destruction operations by the Chemical Weapons Convention treaty commitment of Sept. 30, 2023. U.S. public law mandated stockpile destruction by Dec. 31, 2023.
In September 2002, the Bechtel Pueblo Team was awarded a contract to design, construct, test, operate and close the facility that would utilize this technology: the Pueblo Chemical Agent-Destruction Pilot Plant (PCAPP). Neutralization followed by biotreatment used hot water to neutralize the chemical agent, effectively destroying the mustard agent molecules. The resulting hydrolysate was mostly water and thiodiglycol, a common industrial chemical that was readily biodegradable. Ordinary sewage treatment bacteria, or microbes, consume the organics in the hydrolysate. Besides being a common phenomenon in nature, the science of using microbes to help dispose of hazardous waste has existed for decades. Sewage treatment facilities across the country use microbes every day to help break down raw sewage.
Pilot testing in the main plant began on Sept. 7, 2016, with the gradual introduction of actual agent-filled munitions into the automated system.
Pilot testing in the main plant was completed in compliance with all safety requirements. Environmental permits are pending. The remaining agent-filled projectiles are being destroyed.
Operations at the Pueblo plant reflect that the plant performed as it was designed, with munitions being destroyed using neutralization followed by biotreatment. The main plant functioned as a fully operational facility under a Resource Conservation and Recovery Act Part B Permit.
How Neutralization Followed by Biotreatment Works
Step 1: Removing the Energetics
Robotic equipment will remove the weapon’s energetic components, including the fuze and the burster. Removing these parts first makes the remaining processes safer. The energetics are destroyed in the Static Detonation Chamber (SDC) unit in Anniston, Alabama.
Step 2: Removing the Mustard Agent
Once the energetic components are removed, the 4.2-inch mortar round body containing mustard agent is processed. To remove the agent, the body is robotically accessed, and then the agent is washed out with pressurized water. The first step in this process removes the burster well from the mortar round and rinses it. The Improved Cavity Access Machine (ICAM) moves the burster well to a punch site, where holes are punched to vent any pressure while the munition body goes through a final thermal treatment process. The second step of the ICAM takes the mortar round to a wash water-station, where a wash wand, or drain tube, vacuums agent from the upright mortar round. Wash water is then sprayed inside the mortar round to rinse out any residual agent.
Step 3: Neutralization of Mustard Agent
The mustard agent is vigorously mixed with hot water to break down agent. A caustic solution is then added to raise the pH and prevent the reaction from reversing. The product from this neutralization process is called hydrolysate and has a high pH.
Step 4: Biotreatment
The hydrolysate generated in step three is blended with chemicals and additional water. It then goes through the biotreatment process, which consists of large tanks containing microbes that digest and further break down the solution.
Water released from the process will be recycled, leaving various salts and biosludge. Biosludge is made up of microbe waste products and other bacterial matter. The salts and biosludge are filtered to remove water and disposed of at an off site, permitted Treatment, Storage and Disposal Facility.
Step 5: Disposing of Metal Parts
The final step is treating the weapon’s metal parts. Although the metal parts were cleansed of energetics and agent in step one and step two, they still may contain traces of contamination, and need to be decontaminated to a higher level. To reach this level of decontamination, the metal parts will be heated to 1,000 degrees Fahrenheit for 15 minutes in a Munitions Treatment Unit.