Decrease of the level of extractable polychlorinated biphenyls in soil microcosms: Influence of granular activated carbon and inoculation by natural microbial consortia

• A natural microbial consortium for PCBs biodegradation was selected from soil.
• Presence of Granular Activated Carbon modified bacterial communities in the inocula.
• Planktonic cell inoculum and inoculum with biofilm-coated GAC were tested.
• Total PCBs depletion was higher with planktonic cell inoculum.
• Early depletion was more rapid with biofilm-coated GAC inoculum.

Two bacterial consortia prepared from a polychlorinated biphenyl (PCB)-contaminated soil enrichment were used as inocula, for aerobic PCB-degradation experiments in soil microcosms. The consortia were prepared either as a planktonic culture, or as a biofilm attached to granular activated carbon (GAC). Both consortia were mainly composed of members of the α-, β- and γ-subclasses of the phylum Proteobacteria. The most abundant bacteria, belonged to the genera Pseudomonas, Achromobacter, Ochrobactrum and Halomonas which are commonly associated with soil contaminated with biphenyl or PCBs. The decrease of the level of extractable PCB congeners was assessed in microcosms containing the same PCB-polluted soil from which the consortia were prepared and it was spiked or not with Aroclor 1242. When Aroclor 1242 was added to soil, mainly low-chlorinated congeners were removed, whereas in non-spiked soil, decreases of extractable PCBs levels were observed for a broader range of congeners. The biofilm-coated GAC was less efficient than the planktonic cells to decrease the total amount of extractable PCBs. This limitation was possibly due to the differences in the bacterial composition of the two inocula and to the reduced bioavailability the GAC-adsorbed PCBs. Nevertheless, the biofilm-coated GAC accelerated the aerobic removal of the extractable PCBs during the first three months of incubation, albeit limited in terms of total PCB-removal.

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