Effect of media volume on mixing of biological aerated filters

Effect of reduced media volume on the mixing of biological aerated filters (BAF) was quantitatively determined. The degree of mixing was evaluated based on Reynolds numbers (Re) while the nonideality of the flow was assessed from information of residence time distribution. At HRTs of 1411, 1111, 781 and 581 min and their, respectively, approximate OLRs of 2, 3, 4, and 6 kg COD·m^–3·d^–1, the Re in the partial-bed were 40300, 36100, 25500, and 40400, respectively, whilst those of the full-bed were 19500, 20500, 11700, and 26400. Porosity of the BAF is a bed characteristic resulting from the balance between the effect of biomass accumulation due to growth and biomass loss due to shear stress, arising from increased organic loadings, gas flow, and increased upflow velocity. The number of tanks, calculated from the residence time distribution data, is either 1 or 2 (rounded up to an integer). This indicates the occurrence of a completely mixed pattern inside both reactors.