Chromium binding capacity of Lyngbya putealis exopolysaccharides

This paper presents the chromium adsorptive potential of polysaccharide produced by a novel cyanobacterium Lyngbya putealis HH-15. Batch mode experiments were performed to determine the adsorption equilibrium and the equilibrium data was applied to different two-parameter models (Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, Flory–Huggins, and Brunauer, Emmer & Teller (BET) model). The highest coefficient of determination (0.9925) for Langmuir and BET models indicates best fitness of these models in explaining the sorption as a multilayer process. Effect of different variables like initial metal ion concentration (10–100 mg/L), pH (2–6) and temperature (25–45 °C) on chromium adsorption of exopolysaccharides (EPS) were also examined, using Box–Behnken design model. Very high value of regression coefficient between the variables and the response (R2 = 0.9982) indicates excellent evaluation of experimental data by second-order polynomial regression model. The response surface method indicated that 30–40 mg/L initial chromium concentration, pH 2 and 45 °C temperature were optimal for biosorption of chromium by the cyanobacterial exopolysaccharides. Adsorption capacity of EPS increased from 45 to 157 mg/g of EPS as initial Cr(VI) concentration increased from 10 to 30 mg/L. Surface adsorption of the metal at surface of EPS was confirmed through scanning electron microscopy.