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In this study, the evergreen Iris sibirica plant was planted in a constructed wetland during the low-temperature season. Microcosmic subsurface vertical flow constructed wetlands (MVFCWs) were fed with simulated Cd polluted river water for three months under different Cd supply and the seasonal growth changes and Cd uptake ability of Iris sibirica were investigated. The treatment performance of MVFCWs and removal mechanisms and distribution of Cd were evaluated. The amount of rhizospheric microorganisms (bacteria, fungi, and actinomyces) and the enzyme activities (urease, sucrase, alkaline phosphatase and catalase) were also monitored. Iris sibirica proves to be a good accumulator of Cd with the highest accumulation of Cd in below-ground parts of 443.3 mg/kg when exposed to 8 mg/L Cd for three months. Under 1, 2, 4 and 8 mg/L Cd supply in low-temperature seasons, the MVFCWs exhibit average Cd removals of 94.9%, 97.4%, 95.6% and 96.2%, respectively. The predominant removal process of Cd in MVFCWs is substrate adsorption, which accounts for about 50% of Cd removal. Under the same Cd supply, the removal rates of Cd, amount of rhizospheric microbes and activities of enzymes in planted wetland are higher than those in unplanted wetland.

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.