Removal of Cu and Ni by free and immobilized microalgae.

The present investigation evaluated the effectiveness of Chlorella cells in concentrating Cu and Ni in their cells and thereby removing the two metals from solution. The removal efficiency of the two metals by free and immobilized algal cells were further studied. (1) Four types of Chlorella cells, namely Chlorella pyrenoidosa (26) (from Carolina Biological Supplies Company), Chlorella HKBC-1 and-2 (isolated from a polluted stream receiving wastewater from several electroplating factories) and Chlorella HKBC-3 (from a clean water pond) were subjected to different concentrations of Cu and Ni accordingly. It was revealed that Chlorella HKBC-1 was the most tolerant species to Cu and Ni as reflected by their highest values of 48 h and 96 h "Highest no effect concentrations" (The highest concentration of the tested substance that does not inhibit the growth rate of the alga: Cu 2 and Ni 10 mg/l at 48 h, Cu 2 and Ni 5 at 96 h). This was followed by C. pyrenoidosa (26) and then C. HKBC-2 while C. HKBC-3 had the lowest tolerance to the two metals (Cu 0.5 and Ni 2 at 48 h; Cu 0.5 and Ni 1 mg/l at 96 h). (2) It was further revealed that C. HKBC-1 had higher concentration factors and removal efficiencies of Ni (734-963 mg/l, 16.3-18.7%) and C. HKBC-2 had higher concentration factors and removal efficiencies of Cu (2316-2839 mg/l, 53.7-66%) when exposed to lower concentrations of Cu (0.5, 1 and 2 mg/l) and Ni (5, 10 and 13 mg/l). (3) By treating the free and immobilized algal cells (algal cells entrapped in alginate beads) with different concentrations of Cu and Ni, it was observed that free cells had higher concentration factors and removal efficiencies when compared with immobilized cells (free cells: Cu 1577-3056 mg/l, 24.2-71.4%; Ni 355-849 mg/l, 4.8-18.7%; immobilized cells: Cu 453-935 mg/l, 13.9-53.2%; Ni 244-486 mg/l, 3.2-11.9%).