Sequential anaerobic-aerobic treatment of soil contaminated with weathered Aroclor 1260

Soil contaminated with weathered Aroclor 1260 was bioremediated by sequential anaerobic and aerobic laboratory-scale treatment. The initial concentration was 59 microg of PCBs/g of soil. Following 4 months of anaerobic treatment with an enrichment culture, all of the major components in Aroclor 1260 were completely or partially transformed to less chlorinated PCB congeners. The major products of reductive dechlorination were 24-24-tetrachlorobiphenyl and 24-26-tetrachlorobiphenyl, and the average chlorine substituents per PCB molecule decreased from 6.4 to 5.2. The molar concentration of PCBs did not decrease during the anaerobic treatment. All of the major products formed during the anaerobic treatmentwere degraded in the subsequent aerobic treatment using Burkholderia sp. strain LB400. After 28 days of the aerobic treatment, the concentration of PCBs was reduced to 20 ug/g of soil. PCBs were not significantly removed in aerobic treatments unless they were bioaugmented with LB400. Also, PCB degradation was not detected in soil bioaugmented with LB400 without prior anaerobic treatment. These results confirm the potential for extensive biological destruction of highly chlorinated, weathered PCB congeners in soil.