Bioremoval of Direct Red from aqueous solution by Pseudomonas putida and its adsorption isotherms and kinetics

Synthetic dyes are widely used in textile, food, paper and cosmetic industries. The effluents of these industries are highly coloured and the disposal of these wastes into receiving waters causes damage to the environment and can possess toxicity to human and aquatic life. The adsorptive removal of Direct Red 28 (DR) from aqueous solution by Pseudomonas putida MTCC 4910 was investigated. The effect of pH (4-9) and NaCl concentrations (1 mM-1 M) on the adsorptive removal of DR was investigated. There was no change in the adsorption of DR on bacterial cells observed at different pH and NaCl concentrations. The effects of initial dye concentration, initial inoculums size, contact time and temperature on the sorption of DR on cell surface were investigated. The interactions were assayed with respect to pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion kinetic models by linear regression methods, and were found to follow closely the pseudo-second-order. Equilibrium data also were fitted by linear regression methods through Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. The equilibrium process was fitted well to Freundlich model, which indicates the multilayer adsorption of DR on bacterial cell surface.