Bench-scale evaluation of bioaugmentation to remediate carbon tetrachloride-contaminated aquifer materials

Pseudomonas sp, strain KC is a denitrifying bacterium that, under iron-limited conditions and in the presence of sufficient quantities of growth substrate, rapidly transforms carbon tetrachloride (CCl4) to carbon dioxide and nonvolatile products without production of chloroform, Bench-scale laboratory methods were used to evaluate the feasibility of bioaugmentation with strain KC to remediate aquifer materials from an aquifer of documented CCl4 contamination at Schoolcraft, Michigan. Nine glass columns packed with uncontaminated aquifer materials from the site were used to simulate aquifer conditions, Columns were alternately exchanged with ground water from the site in a rapid (20-30 minute) displacement of the pore fluid, then incubated under static conditions for a period of days to weeks, The exchange and incubation procedure continued until CCl4 removal began to plateau, indicating equilibration of the sorbed CCl4 with CCl4 in the pore fluid, Information obtained during this period was used to evaluate porosity (total and effective) and CCl4 sorption, In subsequent exchanges, base, acetate, and phosphorus were added to the exchange fluids to create conditions favorable for growth of strain KC and expression of its CCl4 transformation activity (niche adjustment). Three columns were inoculated with strain KC; three were not inoculated; and three were chemically disinfected with thimersol. Strain KC was transported more rapidly than the average linear velocity of the exchange fluids in the inoculated columns, Protein levels measured in the effluent of the inoculated columns during subsequent exchanges indicated that niche adjustment enabled rapid growth and colonization of the aquifer solids by strain KC. Little or no protein was detected in the effluent of uninoculated columns. CCl4 mass balances on the inoculated, noninoculated, and chemically disinfected columns indicated that niche adjustment and inoculation with strain KC created conditions favorable for CCl4 removal from the aquifer solids, Up to 70% removal of soluble CCl4 (30-50 mu g/l) occurred in inoculated columns over a period of seven to nine days.