Bioaugmentation of a soil bioreactor designed for pilot-scale anaerobic bioremediation studies

The aim of this work was to answer the following questions: (i) Can we realize a long-term dechlorination with a pure anaerobic strain in soil and (ii) can we monitor the process on an adequate scale with a controlled simulator of in situ conditions (soil bioreactor of a 500-L scale). The soil bioreactor was fed continuously with 3-chlorobenzoate (3-CB) as a model chloroaromatic compound. Bioaugmentation was carried out by inoculating Desulfomonile tiedjei in localized areas in the bioreactor. Temporal and spatial distribution of the 3-CB dechlorination activity was investigated with specific biological activity tests for approximately 4 months following the inoculation. These tests involved the minimally invasive sampling of geometrically distinct points in the reactor and their off-site handling within reconstructed microcosms, allowing the assessment of dechlorinating and methanogenic soil activities. Using autoclaved and nonautoclaved agricultural soil, the results showed a heterogeneous distribution of the dechlorination activity in the bioreactor. The autoclaved soil expressed a high microbial activity as reflected by biogas production and 3-CB dechlorination. Furthermore, durable establishment of D, tiedjei in both autoclaved and nonautoclaved soil was shown, although in the latter portion of the reactor the microorganism was maintained only at the top surface. Polymerase chain reaction (PCR) detection of the 16S rDNA gene of D. tiedjei was directly correlated with 3-CB dechlorination activity. Denaturing gradient gel electrophoresis (DGGE) analysis of PCR products demonstrated distinct bacterial community fingerprints in soil samples as a function of location and in response to process modifications. This investigation demonstrates for the first time the applicability and limitations of soil bioaugmentation with a pure anaerobic dechlorinating strain at a realistic pilot scare.