Adsorption of methylene blue dye from the aqueous solution via bio-adsorption in the inverse fluidized-bed adsorption column using the torrefied rice husk

In this work, the inverse fluidized-bed bio-adsorption column is applied for the first time and is demonstrated using the torrefied rice husk (TRH) for the removal of methylene blue from the solution. The bio-adsorbents were characterized by BET, FI-IR, and SEM. The inverse fluidized-bed adsorption column using TRH becomes saturated in the 95-min continuous adsorption, during which the breakthrough time is 22 min, the overall MB removal (R) is 84%, and the adsorption capacity (Q_exp) on the TRH is 6.82 mg g⁻¹. These adsorption characteristics are superior to those in the fixed-bed adsorption column (R of 52% and Q_exp of 2.76 mg g⁻¹) at a lower flow rate (100 vs. 283 cm³ min⁻¹). Torrefaction of RH significantly increases the surface area (28 vs. 9 m² g⁻¹) and enhances the surface functional groups, leading to an improved maximum equilibrium adsorption amount from 21.5 to 38.0 mg g⁻¹ according to Langmuir model in the batch adsorption system. Besides, the increased Q_exp on the TRH is also obtained in the inverse fluidized-bed (5.25 vs. 2.77 mg g⁻¹, 89% higher) and the fixed-bed (2.76 vs. 1.53 mg g⁻¹, 80% higher) adsorption columns compared to that on the RH.