Remediation Of Petroleum-contaminated Soil By Ex-situ Washing

Ex-situ washing is a commonly-used method for remediation of soil contaminated by petroleum. Surfactants are studied and employed extensively in the field of ex-situ washing, which could remediate petroleum-contaminated soil to increase the solubility of petroleum pollutants and promote them to transfer from soil to water. Surfactants are special substances which are both hydrophobic and hydrophilic.In the present study, surfactants were used to treat the petroleum contaminated soil with ex-situ washing and to investigate the effect of different systems with various mass ratios of anionic and nonionic surfactants and condition parameters on removal efficiency. The oil components in soil before and after surfactant washing were analyzed by means of three-dimensional excitation emission matrix fluorescence spectrum. The influence of ultrasonic auxiliary on washing was investigated and the mechanisms were analyzed through GC-MS and FTIR.The results showed that the capability of enhancing water solubility of petroleum of Tw-80was better than that of SDS and the efficiency was best when the ratio of surfactant SDS/Tw-80was50-60. As the concentration of surfactant increased, removal efficiency of oil gradually increased, and removal rate changed slowly when the concentration reached4g/L. The removal efficiency of oil was significantly influenced by temperature and increased along with the increment of temperature. The analysis based on three-dimensional excitation emission matrix fluorescence spectrum showed that high temperature was helpful for polycyclic aromatic compounds removal. Increasing the liquid-solid ratio improved the oil removal efficiency, but could not remove oil in certain components. The removal efficiency of oil increased along with the increment of the oil content and particle size of soil. The improvement of pH brought active and distinct efforts to the efficiency in cleaning petroleum-contaminated soil, and was helpful to remove the heavy fractions and tricyclic aromatic compounds of oil. The removal efficiency of oil was influenced by inorganic additions. NaCl, CaCl2and MgCl2reduced efficiency in cleaning petroleum-contaminated soil while Na2SO4, Na2CO3, NaHCO3, Na2SiO3and Na3PO4increase the efficiency.Oil removal rate with ultrasonic time and power increased. The ultrasonic assisted cleaning could improve cleaning effect by helping dealt with difficult leaching parts of oil. Based on the analyses of GC-MS and FTIR, it was found that ultrasound was helpful to remove acetophenone and aromatic nitro compounds of oil.