Abstract
FBBR （Fluidized Bed Biofilm Reactor） method is one of the most popular method to remove organic pollutants and ammonia in the wastewater. FBBR involves introducing small free floating media into the aeration tanks where they provide a large surface area to which biological growths attach. The deposition of the media in the aeration tanks cause some serious failure in the wastewater plant. We measured the critical tractive velocity of sponge media in full-scale FBBR aeration tanks operating in various conditions and researched the actual situation for deposition in the full-scale FBBR aeration tank. Sponge media used in FBBR were found to be large in dimensionless critical tractive shear stress and needed much bottom shear stress to be re-suspended compared with gravel particles. The empirical equation was obtained to derive the critical tractive velocity from the easily measurable terminal settling velocity. In the full-scale FBBR aeration tank, the deposition of sponge media was actually observed where the CFD simulated velocity was smaller than the critical tractive velocity.
