Column Flushing of Phenanthrene and Copper (II) Co-Contaminants from Sandy Soil Using Tween 80 and Citric Acid

The clean-up of soils co-contaminated with heavy metals and organic compounds is a contemporary issue of remediation efforts. Column flushing was conducted to investigate the performance of nonionic surfactant and/or organic acid solutions, 4000mg/L Tween 80 (TW80), and/or 0.04mol/L citric acid (CA), to enhance the simultaneous removal of phenanthrene and copper (II) from the co-contaminated sandy soil. The flushing effects were compared when TW80, CA, TW80 after CA (CA/TW80), CA after TW80 (TW80/CA), and a mixture of TW80 and CA (TW80-CA) were used as flushing agents. The maximum concentrations of phenanthrene in effluent solutions occurred at 3.3, 4.7, 5.3, and 15.3h during TW80, TW80/CA, TW80-CA, and CA/TW80 flushing and those of copper (II) at 2.7, 3.3, 3.3, and 14.0h during CA, CA/TW80, TW80-CA, and TW80/CA flushing, respectively. Phenanthrene was mainly desorbed through partitioning into TW80 micelles in aqueous phase while copper (II) was effectively removed through complexation with CA. The removal efficiencies were up to 81.5%, 5.9%, 99.9%, 91.6%, and 99.8% for phenanthrene, and 0.1%, 76.7%, 85.7%, 78.1%, and 84.4% for copper (II) by TW80, CA, TW80/CA, TW80-CA, and CA/TW80. However, it took a long time to use TW80/CA and CA/TW80 to clean phenanthrene and copper (II) efficiently. The overall removal efficiencies of contaminants in the soil column increased with flushing time in the Sigmoidal Model. The results indicated that a combination of TW80 and CA has potential for in situ clean-up of heavy metals and polycyclic aromatic hydrocarbons (PAHs) from co-contaminated soils.