Bioaugmentation of PAH-contaminated soils: A novel procedure for introduction of bacterial degraders into contaminated soil

[Display omitted] •A novel bioaugmentation method for PAH contaminated soil was suggested and tested.•Principle is a stepwise use of pre-inoculated soil for inoculation of a larger amount.•The results showed that the ratio 1:1000 resulted in 73% PAH removal.•NGS method proved that Acinetobacter was the dominant bacterial species.•The results indicate suitability of the approach for use in full-scale applications. An innovative method of inoculation of contaminated soils tested under laboratory conditions resulted in increased efficiency of PAH biodegradation in an aged industrial soil by almost 40% compared to biostimulation alone. The process encompassed inoculation of a small amount of contaminated soil with exogenous degraders. This first step was followed by a necessary propagation period of the introduced microbes. The material was further used as the inoculant for next step of the bioaugmentation procedure for a larger amount of contaminated soil in various ratios from 1:200 to 1:1000 and the process was repeated once more. The results showed that even the most diluted soil sample was very successful in terms of biodegradation of PAHs, resulting in 72.9% removal of PAHs including substantial biodegradation of heavy 4–5 ring PAHs. The employed next generation sequencing method provided evidence that one of the bioaugmentation strains, Acinetobacter calcoaceticus, was the dominant bacterial species in the soil and the results documented its involvement in the successful bioremediation experiment. The novel bioaugmentation method seems to be a promising strategy avoiding complications connected with the large-scale production of inoculant in bioreactors.