This project validated a biodegradation process for treatment of hazardous industrial wastewater containing ammonium perchlorate (AP). While much of the AP generated at U.S. Department of Defense (DoD) installations from demilitarization and disposal of solid rocket motors, remanufacturing, and standard propellant handling operations can be recovered, it is neither technically feasible nor cost-effective to recover low concentrations completely. Secondary perchlorate brine waste streams may contain more than 1percent perchlorate, more than 2 percent salts (Na+, K+, Cl-, NO2-, NO3-, SO42-) and rocket motor components. The biotreatment process employs a strain of the Wolinella succinogenes bacterium to degrade the perchlorate anion (ClO4-) completely and anaerobically to simple chloride. A prototype stirred-tank reactor design was first tested at Tyndall AFB, FL, and then integrated into the Thiokol production plant near Brigham City, UT.
During 1999, the prototype successfully was fed 84,000 gallons of perchlorate brine wastewater, representing a 500-fold scale-up over laboratory systems. Dilution of the feed to 5-20 percent of full strength was necessary to overcome inhibition of the bacteria by the high salt content. Perchlorate concentrations were reduced at 10-20 hours residence time from 2,000-6,000 ppm (optimum 4,000 ppm) to below the detection limit of 0.5 ppm prior to direct sewer discharge. Stable operation was maintained and the process was not impacted detrimentally by low concentrations of co-contaminants from rocket-motor manufacturing operations. Using a low-cost carbohydrate food-processing by-product reduced nutrient costs by more than 90 percent compared to a brewer's yeast/cheese whey mixture. Post-treatment of residual chemical oxygen demand and suspended solids may be required by local sewer authorities.
Biodegradation is an environmentally sound treatment process that facilitates the recovery and reuse of propulsion system components and propellant ingredients, greatly reduces operating costs, and enables regulatory compliance. The Minuteman III remanufacture program and the Titan solid rocket motor disposal program will benefit directly from this technology. Perchlorate brine effluents could be treated for $0.35-$1.00 per gallon depending on their dissolved salt content. Comparable conventional treatment (activated carbon, ion exchange) costs would be more than $1 per gallon. The cost estimate for a 1-gpm brine treatment system was $500k installed.
It is thought that engineering modifications would allow optimized processing of the diluted perchlorate feed stream at 4-8 hours residence time and reduce treatment costs to as low as $0.15 per gallon of brine, or $0.85 per pound of perchlorate destroyed. Cost savings compared to conventional treatment would yield a payback of 2.5 to 6.5 years. The prototype system was designed with two stirred-tank reactors in parallel to provide flexibility in case of process upset and loss of biological activity, but a two-step series operation was more efficient. A patent has been granted on this process, which also has potential for application to AP-contaminated groundwater streams. (Project Completed - 2000)