The effect of synergistic phytoremediation and bacterial isolates on removal of polycyclic aromatic hydrocarbons (PAHs) from contaminated soil

Having carcinogenic and toxic effects, aromatic hydrocarbons cause serious damage to the environment and living organisms. These compounds are mainly discharged into the soil. For the remediation of contaminated soils, biological methods utilizing the efficient microorganisms isolated from the oil-contaminated soils as well as resistant plants are preferred. The aim of this study was to assess the effect of Conocarpus erectus and Pseudomonas aeruginosa on the removal efficiency of polycyclic aromatic hydrocarbons (PAHs) from contaminated and saline soils of the salt separation pond of a desalination unit during 275 days under non-laboratory condition. The study was conducted in a factorial experiment with two factors based on completely randomized design with three replications. The factors used in this experiment included four treatment types (plant, bacteria, plant-bacteria cultivated in the soil, and soil with no plant and bacteria (control)) and the concentration of contaminant (Bangestan crude oil) with 5 levels (0, 0.5, 1, 2.5, and 5 wt%). As hydrocarbon concentrations increased at all five levels, the percentage of PAHs removal, the dry weight of roots and shoots, and chlorophyll contents decreased. At 0 and 1 % concentrations, the highest percentages of removal were obtained as 99.43, 59.89, and 57.01 for bacteria-plant treatment and separate bacterial and plant treatments, respectively (p≤0.05). The plant and the bacteria showed almost equal efficiency in the removal of oil hydrocarbons (p≤0.05). Bacterial treatments led to increased chlorophyll content as well as higher dry weight of roots and shoots compared with the treatments without bacteria (p≤0.05). Results indicated that individual treatments of plant and bacteria had a positive effect on the decomposition rate of PAHs. However, the rate was more positively influenced by the synergistic activity of the bacteria and plants (p≤0.05).