ABSTRACT
148This study examined the performance of pilot scale vertical subsurface flow constructed wetlands (VSF-CW) planted with three indigenous plants, i.e. Typha latifolia, Cyperus alternifolius and Cynodon dactylon (L.) Pers., in removing heavy metals from secondary treated refinery wastewater under tropical conditions. The total heavy metal concentrations in the influent amounted to 15.6 mg Cu/L, 13.2 mg Cr/L, 12.4 mg Zn/L, 4.4 mg Pb/L 0.93 mg Cd/L and 68.9 mg Fe/L. The T. latifolia planted VSF-CW had the best heavy metal removal performance, followed by the C. alternifolius planted VSF CW and then the C. dactylon planted VSF-CW. The data indicated that Cu, Cr, Zn, Pb, Cd and Fe were accumulated in the plants at all the three VSF-CWs. However, this accumulation of the heavy metals in the plants accounted for only a rather small fraction (0.09 - 16 %) of the overall heavy metal removal by the wetlands. The plant roots accumulated the highest amount of heavy metals, followed by the leaves and then the stem. Cr and Fe were mainly retained in the roots of T. latifolia, C. alternifolius and C. dactylon (TF < 1), meaning that the Cr and Fe were only partially transported to the leaves of these plants. The concentrations of the six heavy metals investigated in the shoots and roots of the three indigenous plants exceeded reported threshold limits. This study showed that VSF-CWs planted with T. latifolia, C. alternifolius and C. dactylon can be used for the large-scale removal of heavy metals from secondary refinery wastewater under tropical conditions.
