Removal of Ni and Cu from single and binary metalsolutions by free and immobilized Chlorella vulgaris

The potential of calcium alginate-entrapped Chlorella vulgaris in removing Ni and Cu from single and binary metal solution was determined. Almost complete removal of test metals from the solution by Chlorella beads (biomass concentration, 100 mg dry weight I–1) was achieved within 1 h when metal concentration was <10 mg I–1. The metal sorption capacity of free and immobilized biomass from binary metal solution was also determined using 3-D plots. The presence of the secondary metal (Cu and Ni) inhibited the sorption of the primary metal (Ni and Cu) by free as well immobilized cells but inhibition in sorption of Ni due to Cu was stronger than inhibition of Cu sorption by Ni. The total metal (Ni + Cu) sorbed from the binary metal solution by free as well as immobilized cells always remained lower than the total sorption of individual metals from their respective single metal solutions, thereby suggesting competition between Ni and Cu for the common binding sites on Chlorella. Better fitness of equilibrium metal sorption data to the Freundlich than the Langmuir model suggests multilayer adsorption of test metals onto the cell surface. Higher Kf and qm (Freundlich and Langmuir constants, respectively) for Cu than Ni sorption suggested that the test alga has a greater affinity for Cu than for Ni. It may be possible to use Chlorellabeads for complete removal of Ni and Cu from dilute solutions having their concentrations below 10 mg I–1.