The removal of heavy metals in wetland microcosms: effects of bed depth, plant species, and metal mobility

The present study deals with comparative evaluation of three different plants species, i.e. Canna indica L., Typha angustifolia L. and Cyperus alternifolius L. planted vertical constructed wetlands (CWs) microcosms for Cu, Cr, Co, Ni and Zn removal from aqueous solution. The effects of depth of the gravel beds were also studied in order to explore possibilities of development of compact constructed wetlands. Linear regression analysis was carried out for predicting the final removal efficiencies by variation of the treatment time and the bed depth of filter materials. To determine the removal mechanism and mobility of heavy metals in constructed wetlands, accumulation of these metals in gravel, roots, stem and leaves of plant species were investigated. Results demonstrate that the wetland bed depth has significant, direct effect on final heavy metal removal efficiencies. Considering three different plant species, Zn removal was found to be highest (99.3% in T. angustifolia planted CWs in 72 h of treatment time), and Co removal was found to be lowest (54.6% in T. angustifolia planted CW in 72 h of treatment time).