Flocculation-Sedimentation Performance Model for Laminar-Flow Hydraulic Flocculation with Polyaluminum Chloride and Aluminum Sulfate Coagulants

Abstract

Mechanistically based scalable algorithms for design and operation of hydraulic flocculators were developed in this research based on observations of residual turbidity for a range of influent turbidities (5–500 NTU) and coagulant doses (0.01–0.15 mM Al), for two hydraulic residence times (800 s and 1,200 s) and for two coagulant types (polyaluminum chloride and aluminum sulfate). Kaolin clay was used as a model colloid to create synthetic raw water turbidities. Data were obtained over a range of sedimentation capture velocities using a bench-scale laminar-flow tube flocculator and quiescent settling column. Tap water with a pH of approximately 7.6 was used for all experiments. Seemingly disparate results were unified through creation of a composite dimensionless parameter that considers collision potential in the flocculator and coagulant surface coverage of colloids. One adjustable model parameter was used to fit data (