Biological Aerated Filter (BAF) has been global applied in secondary and tertiary wastewater treatment process in the past decades. As the increasing application of BAF, it was required to get deeper understanding of the operational discipline, parameter optimization and structural characteristics of BAF to improve the treatment efficiency and to operate stability constantly. In this paper, a physical filtration equation of clean filter bed was established firstly based on an average porosity ratio equation and Kozeny-Carman filtration equation. And then the influence of biological oxidation and biofilm development were introduced, of which the Eckenfelder mode and oxygen transfer were considered, to induce a hybrid physical- biologically equation to describe the headloss development in the BAF.

In order to evaluate the feasibility of the hybrid physical– biologically filtration equation of Biological Aerated Filter (BAF) developed previously, the parameters of the filtration equations were determined through the numerical simulation and experimental fitting, and the empirical formula was carried out finally. The results showed that experimental data were in agreement with the simulated data very well, illustrated that the determined parameter was reasonable and the equation can be used to forecast the headloss development of the tested filter.