Bioaugmentation and biostimulation as strategies for the bioremediation of a burned woodland soil contaminated by toxic hydrocarbons: A comparative study

• Bioremediation of a burned forest soil with an average C12-40 hydrocarbon content of 110 mg kg−1 was conducted.
• Bioaugmentation and biostimulation by using two commercial products were applied.
• Biostimulation resulted in an abatement of 70% for C12-40 and 100% for PAHs compounds in 60 days.
• It took one year for natural attenuation to give results comparable to those achieved with biostimulation.
• A series of bacterial and fungal isolates from the burned forest soil were able to decolorize polynuclear dyes in vitro.

In this work, the natural attenuation strategy (no soil amendments done) was compared with two different bioremediation approaches, namely bioaugmentation through soil inoculation with a suspension of Trichoderma sp. mycelium and biostimulation by soil addition with a microbial growth promoting formulation, in order to verify the effectiveness of these methods in terms of degradation efficiency towards toxic hydrocarbons, with particular attention to the high molecular weight (HMW) fraction, in a forest area impacted by recent wildfire in Northern Italy. The area under investigation, divided into three parcels, was monitored to figure out the dynamics of decay in soil concentration of C12-40 hydrocarbons (including isoalkanes, cycloalkanes, alkyl-benzenes and alkyl-naphthalenes besides PAHs) and low molecular weight (LMW) PAHs, following the adoption of the foregoing different remediation strategies. Soil hydrocarbonoclastic potential was even checked by characterizing the autochthonous microbial cenoses.Field experiments proved that the best performance in the abatement of HMW hydrocarbons was reached 60 days after soil treatment through the biostimulation protocol, when about 70% of the initial concentration of HMW hydrocarbons was depleted. Within the same time, about 55% degradation was obtained with the bioaugmentation protocol, whilst natural attenuation allowed only a 45% removal of the starting C12-40 hydrocarbon fraction. Therefore, biostimulation seems to significantly reduce the time required for the remediation, most likely because of the enhancement of microbial degradation through the improvement of nutrient balance in the burned soil.

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