The continuous adsorption of a cationic dye (Methylene Blue, MB) on surface-modified rice husk was investigated. First, rice husk was submitted to ultrasound-assisted, supercritical CO2 and NaOH treatments. The adsorbents were characterized. Then, the continuous adsorption was optimized by response surface methodology (RSM), using raw rice husk as the adsorbent. Finally, under the optimal conditions, breakthrough curves were obtained using all adsorbents and the models were used to interpret these curves. The optimal bed performance was reached at a flow rate of 5 mL min(-1) and an initial MB concentration of 10 mg L-1. Under these conditions, the breakthrough time was 109 min, the length of the mass transfer zone was 20.1 cm, and the maximum capacity of the column was 1.55 mg g(-1). All surface modifications were able to improve the rice husk characteristics in relation to the MB adsorption. Consequently, the bed performance was significantly improved when the surface-modified adsorbents were used. The breakthrough times were 109, 240, 155, and 385 min, respectively, when raw rice husk, UA-rice husk, SCO2-rice husk, and NaOH-rice husk were used. The length of the mass transfer zone was 20.1, 7.9, 15.9, and 9.3 cm for raw rice husk, UA-rice husk, SCO2-rice husk, and NaOH-rice husk, respectively. The dynamic models were able to fit the adsorption data and provided physically consistent parameters.