Biosorption of Cu 2+ and Ni 2+ by Arthrospira platensis with different biochemical compositions

This study employed for the first time carbohydrate-enriched dry and living biomass of A. platensis as biosorbent for copper or nickel ions. The results show that the various biomass compositions of A. platensis obtained from cultivation under different phosphorus concentrations had a diverse effect on Cu2+ and Ni2+ biosorption capacity. The experiments with dry biomass show that the accumulation of carbohydrates slightly improved the biosorption capacity for nickel, but significantly improved the biosorption capacity for copper. In contrast, the experiments with living biomass show that the accumulation of carbohydrates decreased the biosorption capacity for both metals. A. platensis showed greater biosorption capacity for Ni2+ than for Cu2+. For all biomass types investigated, the pseudo-second order kinetics model fitted better the experimental data, but underestimated slightly the early time data (first 15 min). It was observed that the intra-particle diffusion was not a limited process, and that intra-particle diffusion model described well the experimental data for the first 15 min. Also, it was observed that the Freundlich model represents better the biosorption onto living biomass due to the presence of possible bioaccumulation, whereas, the Langmuir model fits better the experimental data with dry biomass. The results show that the main sorption mechanisms involved were ion exchange and complexation. In general, the carbohydrate-enriched biomass contributed to a weak ion-exchange sorption.Summarization: This study is focused on copper and nickel biosorption onto Arthrospira platensis biomass of different biochemical compositions. Four types of A. platensis were employed, namely: (1) typical dry biomass (TDB), (2) carbohydrate-enriched dry biomass (CDB), (3) typical living biomass (TLB), and (4) carbohydrateenriched living biomass (CLB). The CDB was produced using a cultivation mode where phosphorus was the limiting nutrient. The biosorption of both metals investigated was shown to be very fast. Most of the metal sorption capacity of the biomass was filled within 15–30 min, and equilibrium was achieved within 30–60 min. The cultivation conditions (nutrient repletion or depletion) did not affect the pattern of copper and nickel biosorption kinetics. The capacity for copper ions biosorption was significantly positively affected by the accumulation of carbohydrates in the dry biomass, but was negatively affected by the accumulation of carbohydrates in the living biomass. For nickel ions, the alteration of biomass had a little but positive effect on the dry biomass, and a greater negative effect (about 30% lower biosorption capacity) on the living biomass. Living biomass exhibited a higher biosorption capacity than dry biomass, for both metals. The biosorption of copper and nickel onto A. platensis biomass occurred mainly due to the mechanisms of ion exchange and complexation, and less to physical adsorption.Παρουσιάστηκε στο: Chemical Engineering Journa