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, 4000 mg/L Tween 80 (TW80), and/or 0.04 mol/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 15.3 h during TW80, TW80/CA, TW80-CA, and CA/TW80 flushing and those of copper (II) at 2.7, 3.3, 3.3, and 14.0 h 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.     

Characterization of polycyclic aromatic hydrocarbons degradation and arsenate reduction by a versatile Pseudomonas isolate

A Pseudomonas isolate, designated PAHAs-1, was found capable of reducing arsenate and degrading polycyclic aromatic hydrocarbons (PAHs) independently and simultaneously. This isolate completely reduced 1.5 mM arsenate within 48 h and removed approximately 100% and 50% of 60 mg l⁻¹ phenanthrene and 20 mg l⁻¹ pyrene within 60 h, respectively. Using PAHs as the sole carbon source, however, this isolate showed a slow arsenate reduction rate (4.62 μM h⁻¹). The presence of arsenic affected cell growth and concurrent PAHs removal, depending on PAH species and arsenic concentration. Adding sodium lactate to the medium greatly enhanced the arsenate reduction and pyrene metabolism. The presence of the alpha subunit of the aromatic ring-hydroxylating dioxygenase (ARHD) gene, arsenate reductase (arsC) and arsenite transporter (ACR3(2)) genes supported the dual function of the isolate. The finding of latter two genes indicated that PAHAs-1 possibly reduced arsenate via the known detoxification mechanism. Preliminary data from hydroponic experiment showed that PAHAs-1 degraded the majority of phenanthrene (>60%) and enhanced arsenic uptake by Pteris vittata L. (from 246.7 to 1187.4 mg kg⁻¹ As in the fronds). The versatile isolate PAHAs-1 may have potentials in improving the bioremediation of PAHs and arsenic co-contamination using the plant-microbe integrated strategy.