Continuous fixed-bed column study for removal of Congo red dye from aqueous solutions using Nelumbo nucifera leaf adsorbent

The adsorption of Congo red (CR) dye from aqueous solutions is conducted in a continuous fixed-bed column by using agricultural biomass of Nelumbo nucifera leaf adsorbent. The column performance is evaluated by varying the adsorbent bed height (2.5-5 cm), influent dye concentrations (10-50 mg L-1), and inlet flow rate (1-5 mL min(-1)). Column experimental data confirmed that the breakthrough characteristics of the adsorption system are dependent on bed height, flow rate, and initial adsorbate concentration. The results show that the decolourisation efficiency and equilibrium uptake (q(e)) of CR decreases with increasing flow rate and increases with increasing bed height and influent adsorbate concentration. The maximum absorption efficiency (83.12%) was obtained using 5 cm bed height, 15 mg L-1 inlet adsorbate concentration, and 1 mL min(-1) flow rate. The increased flow rate and initial adsorbate concentration lead to a shorter column exhaustion time. The length of mass transfer zone increased with increasing bed height. Various mathematical models are applied to column experimental data to predict the breakthrough curve and to evaluate the column capacity and kinetic constants of the models. The correlation between the experimental and theoretical data is quantified by calculating the regression coefficients for the Thomas and Yoon-Nelson models, an R-2 >= 0.954 at various operating conditions was obtained, which shows that the trend of experimental data fits well and the overall system kinetics are limited by solid-liquid interphase mass transfer. The N. nucifera leaf fine powder adsorbent is proven to be capable of removing CR efficiently from aqueous solutions in continuous fixed-bed systems at low flow rate and higher bed depth and it can be used effectively in wastewater treatment.