The spatial variability of oxygen transfer in Biological Aerated Filter (BAF) is key to improving model accuracy but remains underexplored. This is the first spatially resolved characterization of gas–liquid transfer parameters in a large-scale pilot BAF under clear-water, biofilm-free conditions. Porosity ∊ and gas hold-up (εG) profiles were measured using pressure and oxygen sensors. Oxygen transfer was quantified using stationary and dynamic methods, with modeling to estimate the transfer coefficient (kLa) across reactor zones.
Measured εG and kLa were significantly higher in the bed zone, which comprises 29% of the reactor working volume but accounts for 71.7% of oxygen flux. The bed also showed a stronger dependence of εG on gas velocity, revealing limits of reactor-scale correlations in capturing bed-scale dynamics. Under tested conditions, ∊, εG, and kLa were uniform throughout the bed. Correlations developed for εG and kLa in the bed support BAF model refinement.