Modeling the aeration efficiency of a passively aerated vertical-flow biological filter

摘要

A model aimed at calculating the aeration efficiency of a passively aerated biological vertical bed unit is presented. The model allows the calculation of the mass of air that would flow via convection into the vertical bed, therefore enabling the prediction of the maximal capacity of the bed as an aerobic biological reactor. Aeration efficiency, defined as the volume of air that would enter the bottom of the bed as a function of the volume of water that is drained from it, is predicted in the model as a function of the mean particle size of the gravel media, and the diameter and number of the aeration tubes installed. The model was calibrated in the laboratory and verified using results from a pilot scale vertical bed treating secondary municipal wastewater effluents. The principal model equation is: E-PAVB =N D-p(p)4/ (N D-p(p)4+ 0.285(p)D (2)(r)delta(2)), where E-PAFB =efficiency of the passive air pump (-); N-p=number of aeration pipes (-); D-p=aeration pipes' diameter (m); p=medium porosity (-); and D-r=vertical bed diameter (m).