Apparatus for Observation and Analysis of Floc Blanket Formation and Performance

AbstractFloc blankets are fluidized beds of aggregated suspended particles utilized in some upflow sedimentation tanks for drinking water treatment. Floc blankets can significantly enhance particle removal and may reduce operation and maintenance costs. An experimental apparatus was built with the goal of developing an understanding of floc blanket physics and to establish a mechanistic basis for optimizing floc blanket performance. Visual insights into floc blanket mechanics are obtained by analyzing transmitted light intensity through a 1.3-cm-thick section of a floc blanket. Floc blankets were formed under simulated raw water conditions of 100 nephelometric turbidity units (NTU), an alum coagulant dose of 45 mg/L (4.1 mg/L as Al), and at sedimentation tank upflow velocities ranging from 0.4 to 1.8 mm/s. This study presents nondestructive methods for measuring floc blanket concentration and position of the floc-water interface, steady-state performance data from the experimental apparatus, and the effect of upflow velocity on solids concentration in a floc blanket.