Use of solvent extraction-indigenous microbial degradation technology to repair soils contaminated by high concentrations of mechanical oil

Remediation of soils contaminated by mechanical oil has become a difficult problem worldwide. In this study, soil contaminated by mechanical oil was repaired by domestication and inoculation of microorganisms collected from the contaminated site, and soil quality and plant growth indexes were evaluated to verify the efficacy of our solvent extraction-indigenous microbial degradation technology. Solvent extraction of the contaminated soil removed 97.03% mechanical oil, increased soil water-holding capacity by 68.20%, and improved root activity and soluble sugar content of alfalfa plants. However, solvent extraction depleted 82.98% of the soil organic matter. Screening and domestication of strain TB-6 from the contaminated site revealed that it is an Enterobacter with obvious degradation effects on petroleum hydrocarbons (C15-C28). After the solvent-extracted soil was inoculated with TB-6 for 30 days, the soil structure became loose; degradation rate of residual mechanical oil was 19.45%; and soil organic matter content, water-holding capacity, alfalfa root activity, and soluble sugar content increased by 35.00%, 9.01%, 44.60%, and 7.03%, respectively. These results indicate that TB-6 has a good repairing effect on the soil after solvent extraction, and the combined technology efficiently removed mechanical oil from the soil and reduced the damage caused by the solvent.