Removal of heavy metal ions from drinking water by alginate-immobilised Chlorella sorokiniana

This paper investigates the potential of alginate-immobilised Chlorella sorokiniana for removing Cu2+, Ni2+ and Cd2+ ions from drinking water solutions. The effects of initial metal concentrations, contact times and temperatures on the biosorptions and removal efficiencies of the tested metals were investigated at initial pH values of 5, and pH effects were studied within the range of 3-7. When studying the effects of initial metal concentrations, the highest experimental removal yields achieved for Cu2+, Ni2+ and Cd2+ ions were 97.10, 50.94 and 64.61 %, respectively. The maximum biosorption capacities obtained by the Langmuir isotherm model for the biosorptions of Cu2+, Ni2+ and Cd2+ ions by alginate-immobilised C. sorokiniana were found to be 179.90, 86.49 and 164.50 mg/g biosorbent, respectively. The experimental data followed pseudo-second-order kinetics. At an initial metal concentration of 25 mg/L, immobilised algae could be used in at least 5 successive biosorption-desorption cycles. SEM and EDS analyses revealed that the metals bonded to the biosorbent. Bi- and multi-metal systems of Cu2+, Ni2+ and Cd2+ were investigated at initial metal concentrations of 30, 50 and 100 mg/L. The removal of Cd2+ as well as Ni2+ in such systems was negatively affected by the presence of Cu2+. The removal efficiency for Cu2+ in multi-metal systems decreased by 5-7 %, whilst in the cases of Cd2+ and Ni2+ the efficiencies decreased by up to 30 %. Nevertheless, the results obtained show that alginate-immobilised C. sorokiniana can efficiently remove the metals tested from polluted drinking water sources.