A new approach for scaling up fixed-bed adsorption columns for aqueous systems: A case of antibiotic removal on natural adsorbent

The scaling up of adsorption columns is a crucial step toward the removal of emerging pollutants from domestic and industrial wastewaters. In this study, a fixed-bed column to remove sulfamethoxazole packed with sugarcane bagasse was scaled up from laboratory (D_L = 2.2 cm) to pilot unit (D_P = 4.4 cm) using a scaling factor (K = 2). In addition to the basic similarity rules for scaling, three new criteria were proposed for the mass adsorbent, flow rate, and bed volume. Then, three lab-scale tests at flow rate of 5 mL/min and bed heights of 15, 25, and 35 cm were transferred to the pilot-scale column at flow rate of 20 mL/min and bed heights of 30, 50, and 70 cm, respectively. The breakthrough curves and the fixed-bed parameters (residence time t_R, saturation time t_s, adsorption capacity q_e, volume of solution treated V_ef, and removal percentage %R) obtained in both scales were compared to define their effect with the increase of scale. Finally, a mechanistic model was proposed to predict the breakthrough curves in both columns. The results exhibited that the breakthrough curves in the pilot-scale prolonged in time with higher breakthrough and saturation times than the laboratory breakthrough data. Additionally, t_R, t_s, and V_ef changed in function of the K value used: t_s and t_R doubled their value in the pilot column or t_RP=Kt_RL; V_ef was eight times higher in the pilot column than the lab-column or V_efP=K³V_efL; q_e and %R remained constant in both scales; these results were corroborated with the predicted breakthrough curves. Besides, the mechanistic model predicted with great precision the breakthrough data in both scales (R²>0.9), which means that the model can be used confidently for scaling up purposes. This study demonstrated new criteria which can be easily applied to scale up adsorption columns whit results that showed a correlation between both scales.