Removal kinetics and treatment efficiency of heavy metals and other wastewater contaminants in a constructed wetland microcosm: Does mixed macrophytic combinations perform better?

Abstract

Eight constructed wetland microcosms have been designed using various combinations of three different macrophytes in single as well as mixed planting units. The removal efficiency of major water quality parameters such as biological oxygen demand, total phosphorus, soluble reactive phosphorus, ammonium, nitrate and nitrite-nitrogen and heavy metals was evaluated at three retention times. The potential of selected macrophytes for heavy metals uptake was also studied in terms of bioconcentration factor, translocation factor, aerial tissue concentration factor and root concentration factor. Constructed wetland microcosm unit designed using Pistia stratiotes and Phragmites karka exhibited higher removal potential with maximum decay constants for most of the heavy metals and other wastewater contaminants. Maximum translocation and bioconcentration factors were also expressed by Pistia stratiotes and Phragmites karka for Zn (0.69 and 1.69 respectively). However, the maximum root concentration factor and aerial tissue concentration factors were observed in Pistia stratiotes for Cu (0.35) and Zn (0.10) respectively. The paper reports significantly higher removal of wastewater contaminants including heavy metals in mixed species planting as compared to single species. The removal efficiencies for all metals studied in different constructed wetland microcosm units ranged from 43.80 to 63.67%, 75.92–92.07% and 82.17–98.58% for 3, 7 and 14 days retention time respectively. Relative higher values of decay constants were observed for Cr, Cd and Mn. However, the correlation studies between removal efficiencies of heavy metals and several other parameters exhibited significant variation over time.