Biosorption of selected heavy metals by green algae, spirogyra species and its potential as a pollution biomonitor

Abstract

Control of heavy metal pollution is becoming increasingly important as industrialization becomes the main economic activity of many nations. A number of strategies have been employed to control environmental pollution. The aim of this work was to study the biosorption parameters of green algae for cadmium, chromium, copper and lead and the possibility of using the algae as a biomonitor of environmental pollution by the selected metals. Biosorption studies were conducted to determine the adsorption parameters (pH, contact time and adsorption capacity) of the selected metals in model aqueous solutions using green algae, spirogyra species. The optimum pH values were found to be 5.0, 5.5, 5.8, and 5.9 for lead, cadmium, chromium and copper, respectively. The adsorption process was second order and fitted the Langmuir isotherm better than the Freundlich isotherm. Adsorption capacities on green algae were found to be 22.52, 35.59, 38.19and 94.34 mg/g for cadmium, copper, chromium and lead, respectively. The time required for quantitative uptake of each metal from model solution was investigated over a period of 140 minutes for all metals and found to be 15 minutes for cadmium, 40 minutes for chromium and copper and 50 minutes for lead. The optimum initial concentrations for metal adsorption ranged from 500 – 700 mg/L. Adsorption kinetics of the metals on green algae were also investigated. The experimental data was tested using first and second order kinetic models and was found to follow second order kinetics. The algae was also used as biomonitor of water pollution by the selected heavy metals. Concentration of the selected metals was determined in algae and in the parent water. The results in both samples by ICP – OES were 1.81 ± 0.11, 12.08 ± 1.80, 17.14 ± 0.155 and 64.33 ± 0.35 μg/L in water and 2.30 ± 0.09, xiii 12.17 ± 0.20, 25.61 ± 0.74 and 60.50 ± 1.57 μg/g for cadmium, lead, copper and chromium in algae, respectively. The average concentration factors were Cd (2547.01), Cr (367.02), Cu (1843.59) and Pb (7154.95). These results point to the dominance of sorption process vis-à-vis diffusion in metal uptake. This is seen in the fact the algae can maintain a high internal concentration of metal against the large concentration gradient between it and the water. This demonstrates the potential of green algae as both a biosorbent and biomonitor of water pollution by the selected heavy metals.