Zinc biosorption from aqueous solution by a halotolerant cyanobacterium Aphanothece halophytica

We have investigated the characteristics of zinc biosorption by Aphanothece halophytica. Zinc could be rapidly taken up from aqueous solution by the cells with an equilibrium being reached within 15 min of incubation with 100 mg L-1 ZnCl2. The adsorbed zinc was desorbed by treatment with 10 mM EDTA. The presence of glucose, carbonyl cyanide m-chlorophenylhydrazone (CCCP), and N,N'-dicyclohexylcarbodiimide (DCCD) did not affect the uptake of zinc. The specific uptake of zinc increased at low cell concentration and decreased when cell concentration exceeded 0.2 g L-1. The binding of zinc followed Langmuir isotherm kinetics with a maximum zinc binding capacity of 133 mg g(-1) and an apparent zinc binding constant of 28 mg L-1. The presence of an equimolar concentration of Mn2+, Mg2+, Co2+, K+, or Na+ had no effect on zinc biosorption, whereas Ca2+, Hg2+, and Pb2+ showed an inhibitory effect. The biosorption of zinc was low at a pH range from 4 to 6, but increased progressively at pH 6.5 and 7.