MODELING SEPARATION OF FLOCCULANT PARTICLES IN HORIZONTAL-FLOW GRAVEL-BED

Vertical-or horizontal-how gravel beds can be used in water treatment as roughing filters. To improve its performance, the horizontal-flow r oughing filtration (HRF) process was modified in an earlier study by a pplying a constant dose of 1 mg Al(III)/l coagulant (''direct'' horizo ntal-how roughing filtration). After rapid mixing, the destabilized su spension is passed on to the horizontal-flow gravel bed, which is divi ded into two or three compartments. The first compartment, here referr ed to as the gravel bed, contains the largest grain size (15-25 mm dia meter) and acts as a combined flocculator and settler. A mathematical model for the gravel bed was developed based on an analogy with a para llel plate settler in which both the sedimentation and flocculation pr ocesses are incorporated. An experimental methodology was derived for applying the model to different suspension types using column settling tests. The model was validated experimentally. The procedure develope d here would allow the optimization of design and operation of the gra vel bed for different raw water characteristics and for different proc ess conditions.