Bioaccumulation of Cr(III) ions by Blue-Green alga Spirulina sp. Part I. A Comparison with Biosorption

The paper presents the results of studies on kinetics and equilibrium of bioaccumulation process of Cr(III) ions by blue-green alga Spirulina sp. Bioaccumulation was described as the process that consists of two stages, passive (identical with biosorption) and active (accumulation inside the cells). The passive stage (similarly as biosorption itself) was found to be quick process and the subsequent active stage (accumulation) was much slower and required metabolic activity of cells. The overall equilibrium of bioaccumulation process was reached after ca. 30 hours. The efficiency of bioaccumulation was compared with biosorption performance of cells grown under the same conditions. Two applications of bioaccumulation were discussed: metal ions removal from wastewater and metal ions binding to the biomass to produce biological feed supplement with microelements. The experimental results showed that bioaccumulation capacity was greater than biosorption capacity. Wastewater treated by the process of bioaccumulation contained lower residual metal ions concentration due to equilibrium shift of external (biosorptive) metal ions binding capacity towards lower values, resulting in lower residual metal ions concentration and thus higher treatment efficiencies. If bioaccumulation was considered as the method of biomass enrichment to produce mineral feed supplements for livestock, bioaccumulation enabled to bind more microelements, not only to the surface of cell wall, but also to accumulate inside the cells.