Removal of toxic pollutants from produced water by phytoremediation: Applications and mechanistic study

In this study, a greenhouse experiment of complete randomized design with three replications was conducted to investigate the potential of Medicago sativa, Zea mays, Helianthus annus, Sorghum bicolor, Phragmites australis and Caroxylon imbricatum in the removal of toxic pollutants from a produced water (PW). The collected local oil-refinery wastewater was also characterized physically and chemically. The concentration of the total dissolved solids (TDS), chloride, sodium, boron ions and sodium adsorption ratio were 300 g/L, 122 g/L, 61 g/L, 0.038 g/L and 139.9 meq/L, respectively. Results showed that except M. sativa, tolerated up to 10% diluted PW with a 30% decrease in length and biomass compared to control treatment, all other plants could not survive. However, Caroxylon imbricatum tolerated up to 20% diluted PW without any significant differences in the morphological characteristics. The Fourier transform infrared (FTIR) results for C. imbricatum tissues showed that cellulose structure had the greatest role in the metal adsorption and transportation inside the plant tissue. This conclusion is verified by the shifting or disappearance in transmission bands at 1028, 1334, 2852 and 2921 cm(-1). After PW treatment, the soil with sandy-loam texture used in this study showed a huge accumulation of sodium ions up to 17.6 x 10(3) mg/Kg. The organic contents of the PW were below the detection limits of the gas chromatography (GC) and ultra-performance liquid chromatography (UPLC) instruments. The results of polycyclic aromatic hydrocarbons (PAHs) extraction showed accumulation of less polar PAHs in 30% irrigated soil.