Hexavalent Chromium (VI) Removal Efficiency From Petroleum Refinery Effluent Using Hybrid Constructed Wetlands Planted with <i>Arundo donax</i> L. in Erbil, Iraq

This work assessed the efficacy of A. donax L. (giant reed) in outdoor hybrid-built wetland (HCW) experiments for the removal of the Cr (VI), from KCPS refinery effluents (32 km southwest of Erbil, Iraq). Results showed that A. donax L. macrophyte experienced an excellent adaptation and tolerance of the highly polluted effluent by Cr (VI), based on their significant biomass output and perfect survival rate over the entire 91-day experiment. The Cr (VI) concentrations taken from the outlet samples of HCWs (planted with A. donax L.) ranged from (0.04 to 0.12 mg/l), with a mean value of (0.07 ± 0.057 mg/l), which approached the Cr (VI) safe limit set by international guidelines. The HCWs planted with A. donax L. showed a high Cr (VI) removal rate of (88.12%) with a removal capacity of (3.34 mg/day/g). The highest accumulated Cr (VI) concentration was (925.11 mg/plant) in roots, (193.71 mg/plant) in stems and (115.1 mg/plant) in leaves. The phytoextraction potential of A. donax L. by both bioaccumulation factor (BAF) and translocation factor (TF) also underwent evaluation. Bioaccumulation factor values of (14.24), (8.46) and (68.02) were calculated for stems, leaves and roots, respectively, and the TF value was (0.33), proposing that A. donax L. has a good capacity of Cr (VI) phytostabilization from the KCPS refinery effluent, as revealed in elevated BAF (>1) and TF value (< 1) in plant parts, which showed that the A. donax L. is not a Cr-hyperaccumulator under these conditions of the experiment.