Biosorption of Direct Red 28 (Congo Red) from Aqueous Solutions by Eggshells: Batch and Column Studies

The feasibility of using eggshells as a low-cost biosorbent for the removal of Direct Red 28 (DR 28) from aqueous solutions was studied in batch and dynamic flow modes of operation. The effect of biosorption process variables such as particle size, solution pH, initial dye concentration, contact time, temperature, feed flow rate, and bed height were investigated. Both the Langmuir and Freundlich isotherm models exhibited excellent fit to the equilibrium biosorption data. Optimum pH (6.0), particle size (<250 mu m), initial dye concentration (50 mg g(-1)), temperature (313 K), and contact time (240 min) gave maximum monolayer biosorption capacity of 69.45 mg g(-1) which was higher than those of many sorbent materials. Pseudo-second-order kinetic model depicted the biosorption kinetics accurately. Thermodynamic study confirmed the spontaneous and endothermic nature of the biosorption process. Breakthrough time increased with increase in the bed height but decreased with increase in flow rate. Overall, batch and continuous mode data suggest the applicability of eggshells as an environment friendly and efficient biosorbent for removal of DR 28 from aqueous media.