Settling velocity distribution of microalgal biomass from urban wastewater treatment high rate algal ponds

The aim of this study was to evaluate the settling velocity distribution of microalgal biomass with and without flocculant (Tanfloc SG). Microalgal biomass was obtained from two experimental wastewater treatment high rate algal ponds (HRAPs) operated with 4 and 8days of hydraulic retention time. Two sets of dynamic sedimentation tests were carried out using a water elutriation apparatus. In the first set, most of the biomass of the 8days-HRAP (63%) had settling velocities between 16.5 and 4m/h, while most of the biomass of the 4days-HRAP (65%) had settling velocities between 16.5 and 1m/h. In the second set, most of the biomass from both HRAPs (60% from the 8days-HRAP and 80% from the 4days-HRAP) had settling velocities between 6.5 and 0.4m/h. In this second set, settling velocities of 6.5m/h, compared to 10% and 14% of microalgal biomass without flocculant for the 8days- and 4days-HRAPs, respectively. With flocculant, a very small amount of biomass (3% for the 4days-HRAP and 8% for the 8days-HRAP) had settling velocities of