Numerical Simulation Of Solid-liquid Two Phase Flow Of Baf And Experimental Study

Due to the fast development of industrialization and urbanization in China,it has led to discharge more and more industrial wastewater and domestic sewage.For solving the increasingly great problem of wastewater treatment, not onlymore wastewater treatment plants need to be built, but also more efficientmethods of wastewater treatment be considered. So, a kind of effective and deepwastewater treatment equipment--biological aerated filter (BAF) was developedwidely applied in recent years. However, the filter material in traditionalbiological aerated filter is fixed which easily causes silting, biofilm aging andhigh efficiency back-washing.In this thesis, a fluidized state biological aerated filter is proposed to solveabove problem. Choosing suitable operation parameters makes the filter materialin fluidized state. Increasing the turbulent intensity of the flow field contributesto the dropping and update of the ageing biofilm on filter material, then thesuspended material won’t accumulate and silt, which helps keep the stability andefficiently running of the biological aeration filter. In order to make the filtermedia in reasonable fluidized state, the computational fluid dynamics methodwas employed to select parameters. The Euler-Euler two-fluid model and k-εturbulence model was also used to simulate two-phase movement condition inbiological aeration filter. The flow field, particle concentration distribution andparticle axial velocity distribution at the condition of different wastewatervelocities, different particle sizes, different particle densities and different initialfilling heights of filter media were studied, the influence of the parameters wasalso analyzed. Based on simulation results the appropriate operation parameterswere selected for the preparation of the experiments.To verify the effect of the method and the selected parameters of biologicalaerated filter in treating wastewater, a test bench was designed and built.Experiments were conducted by the parameters chosen in the simulation. Theresults show that the filter material keep in steady fluidized state and thewastewater COD removal efficiency of different concentrations can reach morethan80%，the highest up to89.3%. Compared with the traditional biological aerated filter with fixed filter material, the COD removal efficiency remainsrelatively high and steady, the problem of silt and biofilm aging was also solved.It also saved the backwash progress which helps increasing the stability ofbiological aerated filter. The experiments confirmed the advantage of theproposed method in this paper, which also verified the correctness andsuperiority of the application of two-phase flow simulation in biological aeratedfilter.