The hydrodynamic characteristics of small hydrophobic activated carbon particles were determined in air flowing through both fixed and fluidized bed layers and water flowing through an inverse fluidized bed. Based on experimental data the Ergun-equation was corrected. A new relationship is proposed to predict the pressure drop in a fixed bed with gas flowing by using the minimum fluidizing velocity (umf) and particle terminal velocity (ut). Apparent density of oven-dried activated carbon increases with filling the internal pores by water. After the bed density reaches the density of water, the system switches from an inverse fluidized layer into the classical fluidized state. Finally, it has been demonstrated that the Reynolds number (Remf) at umf associated with the original Archimedes number (Ar) for gas-solid fluidized system and the modified Ar numbers characterizing the inverse fluidized beds lie on identical curves.