Heavy metals removal from dumpsite leachate by algae and cyanobacteria

Abstract

A living consortium of green algae (Ankistrodesmus) and cyanobacteria (Nostoc and Anabaena) was tested for the removal of heavy metal ions (Fe (II), Cu (II), Pb (II), Cr (VI) and Zn (II)) from dumpsite leachate under natural climatic conditions. Metal removal experiment was performed at 5 and 10 mg L−1 initial metal concentration in leachate and 0.8 and 1.6 g L−1 of biomass doses. Metal removal was in the order of Pb > Cu > Zn > Fe > Cr. Among all the metals algae and cyanobacteria removed the highest amount of Pb (7.03 ± 0.6 mgg−1) at 10 mgL−1 initial metal concentration and algal dose of 0.8 gL−1 and, the lowest amount of Cr metal (0.98 ± 0.6 mgg−1) was taken up at 5 mgL−1 initial metal concentration and 1.8 gL−1 of biomass dose. Metal removal by unit biomass mass (mgg−1) increases with an increase in initial metal concentration in leachate and decrease in biomass concentration however, the removal rates (percent removal per unit time) of metal ions has positive relationship with the initial biomass concentration. With an increase in initial metal concentration, the chances of collision between metal ions and available cations at the cell surface of biomass increases, resulting in increased metal uptake until the equilibrium is achieved after which the metal uptake remains constant. At small initial doses relatively a large number of adsorption sites at cell walls of algae and cyanobacteria are exposed, shifting the sorption equilibrium toward the biomass side resulting in rapid saturation of binding sites and increased bio sorption capacity of algae and cyanobacteria. This study reveals that living consortium of algae and cyanobacteria can be used as potential organisms for heavy metal removal from dumpsite leachate under natural climatic conditions.