The study applied microbial molecular biological techniques to show that 2.5% to 3.0% (w/w) of diesel in the soil reduced the types and number of bacteria in the soil and destroyed the microbial communities responsible for the nitrogen cycle. In the meantime, the alkane degradation gene alkB and polycyclic aromatic hydrocarbons (PAHs) degradation gene nah evolved in the contaminated soil. We evaluated four different remediation procedures, in which the biostimulation-bioaugmentation joint process reached the highest degradation rate of diesel, 59.6 ± 0.25% in 27 days. Miseq sequencing and quantitative polymerase chain reaction (qPCR) showed that compared with uncontaminated soil, repaired soil provides abundant functional genes related to soil nitrogen cycle, and the most significant lifting effect on diesel degrading bacteria γ-proteobacteria. Quantitative analysis of degrading functional genes shows that degrading bacteria can be colonized in the soil. Gas chromatography-mass spectrometry (GC-MS) results show that the components remaining in the soil after diesel degradation are alcohol, lipids and a small amount of fatty amine compounds, which have very low toxicity to plants. In an on-site remediation experiment, the diesel content decreased from 2.7% ± 0.3 to 1.12% ± 0.1 after one month of treatment. The soil physical and chemical properties returned to normal levels, confirming the practicability of the biosimulation-bioaugmentation jointed remediation process.
Diagnosing bioremediation of crude oil-contaminated soil and related geochemical processes at the field scale through microbial community and functional genes