Analysis of Biosorption Parameters, Equilibrium Isotherms and Thermodynamic Studies of Chromium (VI) Uptake by a Nostoc sp. Isolated from a Coal Mining Site in Meghalaya, India

Abstract

A cyanobacterium isolated from a water sample collected from a coal mine in the West Khasi Hills of Meghalaya, India, and identified as Nostoc sp. (accession no. KX814344) using 16S rRNA analysis showed a high tolerance to chromium. It was shown to be able to grow in the presence of 15 ppm Cr, which is 30 times the highest Cr concentration recorded in the area. Cr biosorption by the cyanobacterium was optimum at pH 6.0 with 3 µg mL−1 biomass. The sorption showed a linear correlation with increasing metal concentration, gradually reaching saturation. An energy dispersive X-ray study verified Cr binding on the cyanobacterial biomass, and FTIR analysis revealed many negatively charged functional groups on the cell surface, which aided in metal binding. Thermodynamic studies showed the biosorption process to be energetically favorable: − 0.479, − 0.665, and − 0.852 kJ mol−1 at temperatures of 293, 303, and 313K, respectively. Sorption isotherm data fit the Langmuir isotherm best, indicating the monolayer nature of the Cr sorption. The organism’s maximum sorption capacity was as high as 20 mg of Cr per g of biomass. The separation factor calculated from the Langmuir isotherm was < 1, signifying favorable interaction between the cyanobacterial biomass and the Cr ions.