Use of bioaugmentation for continuous removal of carbon tetrachloride in model aquifer columns

The feasibility of sustained removal of carbon tetrachloride (CT) by Pseudo monas stutzeri KC was evaluated in two 2 meter-long columns packed with aqu ifer material from a CT-contaminated aquifer at Schoolcraft, MI. CT-contami nated groundwater was pumped continuously through both columns until the aq ueous and adsorbed CT had equilibrated. CT transformation was initiated by inoculating an 8 cm-wide alkaline-adjusted zone near the upstream end of bo th columns with groundwater containing strain KC and acetate. CT-contaminat ed groundwater was then pumped continuously through the columns. Both colum ns received weekly acetate additions in the bioaugmentation zone. Base and phosphate additions were performed weekly in one column and twice weekly in the second column. A CT-transforming zone developed in the bioaugmentation zone of both columns, with 97% removal of CT in the column receiving weekl y base additions and 93% removal in the column receiving twice-weekly base additions. Strain KC was detected on the solids of both columns. When aceta te and base additions were discontinued, CT transformation decreased, and c hloroform (CF) production was observed in the column that had received twic e-weekly base additions (no CF was detected in the other column). The resul ts indicate that efficient CT removal without CF production is possible ove r extended periods. The results also suggest that microbial populations ind igenous to the Schoolcraft aquifer can convert CT to CF, and that such popu lations were selected by twice-weekly base additions. Weekly base additions evidently failed to select such populations.