Cadmium removal capability and growth characteristics of Iris sibirica in subsurface vertical flow constructed wetlands

Due to the increasingly serious river pollution of heavy metals, especially cadmium (Cd), the Cd pollution issues have aroused more and more political and academic attentions. In this study, microcosmic subsurface vertical flow constructed wetlands (MVFCWs) were planted with Iris sibirica to treat simulated polluted river water with different concentrations of Cd. The objective of this study was to investigate the Cd removal capacity of I. sibirica, plant growth characteristics and plant uptake, in order to fill the blank in the research of I. sibirica purification mechanism of Cd polluted water and meet the needs of the actual constructed wetland project. The plants grew well under any Cd treatments over the study period. The maximum Cd content in belowground parts was 1669.4 mg/kg and in aboveground parts 12.8 mg/kg on a dry weight basis when exposed to 6 mg/L Cd for 50 days. The maximum bioconcentration factor (BCF) values for root and shoot tissues were 323.2 and 3.8 respectively, obtained for 3 mg/L Cd, which indicated that the plants can play an important role for removal of Cd through phytoextraction. The test results showed that the average removing rate of Cd from the wastewater could reach 91.8%. High removal efficiency in the study proved that wastewater polluted by Cd could be treated effectively using MVFCWs with I. sibirica plant.