Gravity separation of biomass washed‐out from an aerated submerged filter

Abstract

Settling velocities and some geometric characteristics of biomass washed out from an aerated submerged biological filter (ASBF) were determined by a multi‐exposure photographic method and an image analysis system. The geometric mean value of the projected area diameter and the mean value of the settling shape factor of the particle aggregates studied were 580 μm and 0.45, respectively. The frequency of aggregate sizes and settling shape factors fitted in the log‐normal distribution and the normal distribution, respectively. The settling velocities increased as a fractional power of the projected area diameters with the power law coefficient of 0.85. The mean settling velocity was 2.11 mm s^‐1. The particle aggregates size and the terminal settling velocity increased with the increasing organic loading rate of the ASBF. The average values of the dry density, density, effective density and porosity of the biomass studied, were 1.43 g cm^‐3, 1.017 g cm^‐3, 0.020 g cm^‐3, and 0.95, respectively. The aggregate density decreased and the aggregate porosity increased with an increase in the aggregate size.