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−1) and metal (from 100 to 800 mg l−1) were tested. Low biomass levels (Xo ⩽ 2 g l−1) ensured metal removal up to 98% only at Cd0= 100 and 200 mg l−1, while Xo ⩾ 2.0 g l−1 were needed at Cd0 = 400 mg l−1 to achieve satisfactory results. Whereas Xo = 4.0 g l−1 was effective to remove up to Cd0 = 500 mg l−1, a further increase in metal concentration (Cd0 = 600 and 800 mg l−1) 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−1 and then to 4.0 g l−1, 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−1.