Insights into oil recovery, soil rehabilitation and low temperature behaviors of microwave-assisted petroleum-contaminated soil remediation

As an environmental contaminant, petroleum-contaminated soil will pollute water, stunt agricultural growth, and cause serious harms to human health if it wasn't safely disposed and remediated. Here, low-temperature microwave-assisted treatment of petroleum-contaminated soil was developed for simultaneous soil rehabilitation, oil recovery and revegetation. The results indicated the concentration of petroleum contaminant was decreased to regulatory standard after 20 min treatment at 250-300 degrees C. 91.6% of the oil was recovered, and it mainly consisted of C-11-C-30 hydrocarbons. Using the soil remediated at 250 degrees C for plant growth test, no adverse effect or fertility loss was observed and an optimal clover germination rate was reached. The results of microwave thermogravimetric analysis, dielectric property and EDX mapping revealed that the efficient remediation was attributed to the presence of hot spots, and the efficient heat /mass transfer during microwave heating. A three-stage petroleum removal mechanism was proposed, where the hydrocarbons were gradually removed via steam stripping, thermal desorption, and pyrolysis/carbonization as the temperature increased.