With systemization, the testing phase of the Pueblo Chemical Agent-Destruction Pilot Plant (PCAPP), 93 percent complete, focus is on Biotreatment Area (BTA) Risk Reduction.

A major step in the risk reduction process is surrogate testing, which involves starting up the Immobilized Cell Bioreactors (ICB), said Dr. Jim Earley, chief scientist, PCAPP.

During agent destruction operations, hydrolysate, the byproduct of the chemical agent neutralization process, will be pumped into the ICBs to be further broken down by biomass, or microorganisms. A surrogate feed consisting of Thiodiglycol (TDG), the primary component of hydrolysate, and nutrients will be used to test the biotreatment process as part of the risk reduction testing program prior to the start of agent operations, Earley said.

In preparation for the testing, five isotainers of TDG, manufactured by BASF of Ludwigshafen, Germany, were delivered to the PCAPP site this fall. Each was placed in one of the 30-day storage holding tanks where it was diluted with process water.

“The TDG is diluted to less than 30 weight percent, as required by treaty, and will be further diluted during surrogate testing,” said Earley.

During surrogate testing, one module, consisting of four ICBs, will be started up simultaneously. This will allow for Standard Operating Procedures to be written concisely, Earley said.

Biomass, approximately 4,500 gallons of waste-activated sludge, will be added to each ICB unit and water will be added to fill one compartment of the unit. Each ICB will be aerated and the pH will be controlled by adding bicarbonate, which will serve as a buffer during the initial batch mode operation, said Earley.

The initial feed will consist of TDG, diammonium phosphate and urea. During continuous feed operations, the TDG loading to the ICBs will be incrementally increased from 12.5 percent to 100 percent of design in order for the microbes to become fully acclimated to the TDG. The startup and acclimation process will take two to four weeks, during which TDG concentration will need to be reduced by at least 85 percent before more feed will be added. Samples will be taken daily, Earley said.

“The risk reduction testing is designed to reveal challenges,” said Walton Levi, deputy site project manager, PCAPP. “It will allow PCAPP staff to understand failure modes and hence, develop corrective actions.”