Parameters affecting steady-state floc blanket performance

A laboratory-scale reactor was used to simulate a water treatment process sequence of rapid mix, hydraulic flocculation, upflow clarification with a floc blanket, and lamellar sedimentation to accomplish removal of colloidal particles. This study focused on variables affecting performance of the floc blanket including: provision of hydraulic flocculation, raw water turbidity, coagulant dose, upflow velocity through the floc blanket, and bulk density and solids concentrations of the floc blanket. An upflow clarifier velocity between 1.0 and 1.3 mm s⁻¹ produced the best floc blanket performance for turbidities studied between 10 and 200 NTU while an upflow velocity between 0.6 and 0.8 mm s⁻¹ produced the best floc blanket performance at 500 NTU. The results show that overall particle removal efficiency improved with increasing hydraulic flocculator residence time and energy dissipation rate. Particle removal efficiency improved with increasing floc blanket depth for floc blanket depths between 15 and 75 cm. Lamellar sedimentation with a capture velocity of 0.12 mm s⁻¹ is a key component in improving clarifier performance when utilizing a floc blanket.