Oily sludge stimulates microbial activity and changes microbial structure in a landfarming soil

• Oily sludge increased microbial activity of landfarming soil in microcosm.
• Hydrocarbons degradation was quantified and correlated with bacterial taxa.
• Microbial community of different bioremediation strategies was revealed.
• Minimal management and bioaugmentation reduced soil hydrocarbons.

We aimed to evaluate the microbial community structure in microcosms containing a soil collected at a landfarming (LF) site and which was artificially contaminated with oily sludge from the same site. In addition we have examined the hydrocarbons degradation under different bioremediation conditions. The experiment was conducted during 60 days in microcosms containing 300 g of LF soil and 18 g of oily sludge. The treatments employed were: a) LF soil without oily sludge addition (control); b) minimal management (LF soil + oily sludge adjusted to pH 7.0 and aerated); c) bioaugmentation (LF soil + oily sludge + pH 7.0 + aeration + inoculation of an adapted bacterial consortium); d) Biostimulation (LF soil + oily sludge + pH 7.0 + aeration + addition of N and P); e) native forest soil (to compare with the microbial community from LF soil). CO2 released from the microcosms was captured and quantified. Fifteen aliphatic hydrocarbons (C15-C29) and 17 PAHs were quantified by gas chromatography mass spectrometry. Microbial communities were analyzed using next generation sequencing and the results were correlated with the hydrocarbon degradation rates. Bacterial families Sphingomonadaceae, Xanthobacteraceae, Pseudomonadaceae, Ectothiorhodospiraceae, Xanthomonadaceae, and Comamonadaceae were the most abundant in all microcosms. The treatments involving biostimulation and minimal management removed 40% and 60% of the aliphatic hydrocarbons in the respective microcosms, and the those involving minimal management and bioaugmentation removed 50 and 40% of [PAHs] at the end of the respective treatments. In all treatments, phenanthrene, methylphenantrene, and pyrene were not removed.

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