Efficiency of Different Bioremediation Methods for In Situ Clean-Up of Oil-Contaminated Sierozem Soil in Southern Kazakhstan

The efficiency of bioremediating oil-contaminated serozem (gray desert soil) of Southern Kazakhstan was investigated in the study. The first stage involved choosing hydrocarbon-degrading microorganisms suitable for the bioremediation of this desert soil. The second stage assessed the bioremediation potential of the selected microorganisms in laboratory microcosms. The final stage was a field trial experiment investigating oil removal under conditions of in situ natural attenuation, biostimulation (application of NPK fertilizer Nitroammophoska), reintroduction of indigenous oil-degrading microorganisms isolated from soils of the Aral Sea region and bioaugmentation using degrader strains from the laboratory collection. Additionally, the resulting native desert soil microbiomes were compared. Results showed that natural attenuation of the desert soil occurred over two months (with 68.5% of hydrocarbons removed), while biostimulation, reintroduction, and bioaugmentation were—as expected—also effective, achieving 89.4–97.0% oil removal. In the contaminated soil during the spring season, a significant increase in the proportion of Gammaproteobacteria within the soil microbiome was observed, with Alphaproteobacteria and Bacilli also representing significant fractions.