Biosorption valorization of floating and submerged macrophytes for heavy-metal removal in a multi-component system

This study comprises the comparative evaluation of floating (Azolla filiculoides) and submerged (Hydrilla verticillata) macrophytes for potential biosorption of Cu(II), Cr(VI), As(III) and Pb(II) from aqueous solution in a multi-component study. Statistically valid Plackett–Burman design of experiments was employed with four heavy metals at two different levels by varying their initial concentration in the range 10-50 mg L−1 for both the macrophytes. The maximum removal efficiency for Pb(II) was obtained for both the biosorbents, i.e., Azolla sp. (81.4%) and Hydrilla sp. (84.3%) within 4 h of the experimental runs, with an initial concentration of 10 mg L−1 of all the heavy metals. Followed by Pb(II) removal, a declining trend for the removal (%) for Cu(II), As(III) and Cr(VI) was obtained, for all the experimental runs. Also, the minimum removal (%) for all the experimental runs was attained at 25 mg L−1 (maximum) for all the heavy-metal concentration level. The removal efficiency (%) trends follow the order: Pb(II) > Cu(II) > As(III) > Cr(VI) for both the biosorbents. Analysis of variance and Student’s t test of the metal bioremoval revealed that main (individual) effect due to the metals was highly significant (P value < 0.05) on each other’s removal. Student’s t test results revealed that both Pb(II) and Cu(II) strongly inhibited both Cu(II) removal (P value < 0.01), while Cr(VI) has only inhibitory effect on Pb(II) removal. Henceforth, all these results simultaneously depicted good potential of the aquatic macrophytes for the biosorption capability of heavy metal and the effect of individual metals on each other’s removal in the multi-component system.