Cd(II) sorption by Nostoc sp. JRD1: Kinetic, thermodynamic and isotherm studies

Abstract

The present work describes the biosorption of Cd 2 + by a cyanobacterium isolated from water of an effluent reservoir of Hindustan Paper Corporation Limited, Jagiroad, India polluted with different heavy metal ions. The novelty of the study lies in the fact that an extensive literature search did not yield any report of biosorption by any cyanobacterium isolated from paper mill effluent. The molecular identification technique established the cyanobacterium as a Nostoc sp. and was named Nostoc sp. JRD1. The organism showed relatively high tolerance to Cd 2 + as a 24 h Cd 2 + (0.5 ppm) exposure showed no significant changes in its morphology and ultrastructure under bright-field, scanning and transmission microscopic study. Cd 2 + binding to its cell surface was confirmed by SEM-EDX investigation and FTIR analysis identified the functional groups involved in Cd 2 + binding. Cd 2 + biosorption by live biomass of the organism from aqueous solution was a function of initial inoculum size and metal ion concentration, pH, temperature and shaking rate and under optimized conditions the organism biosorbed 94% Cd 2 + from a solution supplied with 0.5 ppm Cd 2 + within 24 h. Of this total removed Cd 2 + , 89.5% was adsorbed on the cell surfaces while 7.2% was internalized. Kinetic study revealed Cd 2 + biosorption to be instantaneous (5–30 min) and fitted best in the pseudo-first-order kinetic model with q e cal value of 41.8 mg/g. Thermodynamic study indicated the process of biosorption as energetically favorable with a negative Δ G value and was exothermic in nature. Cd 2 + biosorption followed Langmuir isotherm best with a R 2 value of 0.98, and a maximum biosorption capacity, Q max of 24.7 mg/g. Almost similar Cd 2 + removal (92%) was found in a photo-bioreactor study compared to the removal scenario in a small conical flask (94%). The various outcomes of the study suggested that live Nostoc sp. JRD1 biomass is extremely suitable as biosorbent for removal of Cd 2 + from contaminated waters. • Morphological and ultrastructural studies confirmed Cd 2+ tolerance of Nostoc sp. JRD1. • The isolate could remove 94% Cd 2+ from a solution containing 0.5 ppm Cd 2+ . • Kinetic, thermodynamic & biosorption studies showed Cd 2+ sorption to be favorable. • Conditions Optimization enhanced biosorption percentage significantly. • Scanty information on any cyanobacteria isolated from paper mill effluent.