Cadmium biosorption on Spirulina platensis biomass

Dry biomass of Spirulina platensis re-hydrated for 48 h was employed as a biosorbent in tests of cadmium(II) removal from water. Various concentrations of biomass (from 1 to 4 g l 121) and metal (from 100 to 800 mg l 121) were tested. Low biomass levels (Xo 64 2 g l 121) ensured metal removal up to 98% only at Cdo = 100 and 200 mg l 121, while Xo 65 2.0 g l 121 were needed at Cdo = 400 mg l 121 to achieve satisfactory results. Whereas Xo = 4.0 g l 121 was effective to remove up to Cdo = 500 mg l 121, a further increase in metal concentration (Cdo = 600 and 800 mg l 121) led to progressive worsening of the system performance. At a given biomass levels, the kinetics of the process was better at low Cd2+ concentrations, while, raising the adsorbent level from 1.0 to 2.0 g l 121 and then to 4.0 g l 121, the rate constant of biosorption increased by about one order of magnitude in both cases and the adsorption capacity of the system progressively decreased from 357 to 149 mg g 121