Numerical Simulation Study Of BAF Aeration Pipe System And Design Optimization

Biological aeration filter(BAF), as a bio-film treatment process with good effluent quality, adjustable load capability and occupying less space, has been widely used in the field of sewage treatment. This study was designed to solve the problems of lower aeration efficiency and high energy consumption of a wastewater treatment plant with BAF reactor. It is presented in this paper multilevel numerical simulations of BAF based on the basic equations of fluid mechanics, Eulerian multiphase flow model, porous media model and the k-? turbulence model. First, it is simulated the two-dimensional flow in three kinds of aeration pipelines which are ring-shaped unilateral and center dendritic shaped respectively. By analyzing the simulated velocity and pressure fields, it is found that deadend zone appears at the four corners of ring-shaped pipe aeration. This problem can not be solved by increasing the inflow rate or reducing ring size. Without increasing total energy consumption, unilateral and center dendritic pipelines increase aeration efficiency significantly. By the comparison of three-dimensional gas-liquid two-phase flow simulation of the BAF with or without filter, it is found that porous filter functions to increase air volume ratio vertically and promote its uniform distribution horizontally. Finally, a small scale gas-liquid two-phase flow simulation of flows through grain size increase due to biofilm growth was studied. By analyzing the velocity and turbulent kinetic energy distribution before and after the filter particle diameter increase, it is concluded that filter biofilm thickening reduces porosity between the particles, air and water velocity between the particles increase, and the turbulent kinetic energy increases also,resulting in more suspended solids being washed to the upper filter, exacerbating the upper filter media congestion and causing more head loss. These will provide valuable options for the selection and optimization of aeration systems as well as treatment process of wastewater treatment plants with BAF.