Biosorption of nickel by microalgae

Discharging of electroplating effluent containing nickel (II) ion would imposed severe impacts on the marine ecology. Microalgae were suggested as an efficient and cost-effective alternative in remediating heavy metal problem. The present study thus aimed at examine the capability of microalgae in sequestration and accumulation of Ni2+; determine their biosorption mechanism; and assess their reusability, metal recovery and viability maintenance in nickel biosorption. Optimization of nickel biosorption process was also attempted. Experimental findings demonstrated that the unicellular green algae, Chlorella vulgaris and WWI (primarily identified as Chlorella spp.), showed a promising Ni2+ removal performance. Ni2+ removal efficiency were around 41 - 33 % and over 90 % were demonstrated by C. vulgaris and WWI, respectively, in nickel solution ranged lo-40 μg/ml. Higher removal efficiency was identified when there was lower initial Ni2+ concentration.Nickel removal efficiency of WWI maintained not less than 70 % in 10 cycles of 30 μg/ml Ni2+ treatment, in which each cycle lasted for 24 hours. C. vulgaris was still able to remove about 30 % of ambient Ni2+ in the last cycles. Both of the two algal species were viable after 240-hour Ni2+ treatment. About 80 % of Ni could be regenerated out from algal cells by using chelating agent EDTA or diluted nitric acid. Biosorption of Ni2+ by microalgae was predominant by physical binding on cell wall. Bioaccumulation of Ni2+ became obvious after extracellular adsorption was saturated. Algal cells was demonstrated to offer certain anionic binding sites for Ni2+ binding, by esterification of surface carboxyl groups . After having carboxymethylation of amine groups by sodium iodoacetate, the capacity for Ni sequestration of cell wall was enhanced. However, chemical modification of extracellular amine group exert harmful effect on the viability of algal cells.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 1997