Co2+, Cu2+, and Zn2+ Accumulation by Cyanobacterium Spirulina platensis

Abstract

The Spirulina platensis biomass was characterized for its metal accumulation as a function of pH, external metal concentration, equilibrium isotherms, kinetics, effect of co-ions under free (living cells, lyophilized, and oven-dried) and immobilized (Ca-alginate and polyacrylamide gel) conditions. The maximum metal biosorption by S. platensis biomass was observed at pH 6.0 with free and immobilized biomass. The studies on equilibrium isotherm experiments showed highest maximum metal loading by living cells (181.0 ± 13.1 mg Co2+/g, 272.1 ± 29.4 mg Cu2+/g and 250.3 ± 26.4 mg Zn2+/g) followed by lyophilized (79.7 ± 9.6 mg Co2+/g, 250.0 ± 22.4 mg Cu2+/g and 111.2 ± 9.8 mg Zn2+/g) and oven-dried (25.9 ± 1.9 mg Co2+/g, 160.0 ± 14.2 mg Cu2+/g and 35.1 ± 2.7 mg Zn2+/g) biomass of S. platensis on a dry weight basis. The polyacrylamide gel (PAG) immobilization of lyophilized biomass found to be superior over Ca-alginate (Ca-Alg) and did not interfere with the S. platensis biomass biosorption capacity, yielding 25% of metal loading after PAG entrapment. The time-dependent metal biosorption in both the free and immobilized form revealed existence of two phases involving an initial rapid phase (which lasted for 1–2 min) contributing 63–77% of total biosorption, followed by a slower phase that continued for 2 h. The metal elution studies conducted using various reagents showed more than 90% elution with mineral acids, calcium salts, and Na2EDTA with free (lyophilized or oven-dried) as well as immobilized biomass. The experiments conducted to examine the suitability of PAG-immobilized S. platensis biomass over multiple cycles of Co2+, Cu2+, and Zn2+ sorption and elution showed that the same PAG cubes can be reused for at least seven cycles with high efficiency.