Adsorptive removal of cadmium ions by Spirulina platensis dry biomass

Cadmium is one of the most toxic substances found in aquatic ecosystems. This metal tends to accumulate in photosynthetic plants and fish and is transferred to humans causing many diseases. It has to be removed from our environment to reduce any health risks. Dry biomass of the microalga (cyanobacterium) Spirulina platensis was used as biosorbent for the removal of cadmium ions (Cd(2+)) from aqueous solutions. The effects of different levels of pH (3-9), biomass concentration (0.25-2 g), temperature (18-46 °C), metal concentration (40-200 mg/l) and contact time (30-120 min) were tested. Batch cultures were carried out in triplicate in an orbital shaker at 150 rpm. After centrifuging the biomass, the remaining levels of cadmium ions were measured in the supernatant by Atomic Absorption Spectrometer. Very high levels of removal, reaching up to 87.69% were obtained. The highest percentage of removal was reached at pH 8, 2 g of biosorbent, 26 °C, and 60 mg/l of cadmium concentration after 90 min of contact time. Langmuir and Freundlich isotherm models were applied to describe the adsorption isotherm of the metal ions by S. platensis. Langmuir model was found to be in better correlation with experimental data (R (2) = 0.92). Results of this study indicated that S. platensis is a very good candidate for the removal of heavy metals from aquatic environments. The process is feasible, reliable and eco-friendly.