Development of Parametric Numbers in Filter-bed Flocculation

Abstract

This paper reviews the various geometric and hydrodynamic representations of flow in granular beds and proposes a model for prediction of the parameters that are pertinent in flocculation process in a filter bed – the velocity gradient G, residence time tr and the product Gtr. The proposed model is applied to direct filtration data and compared to actual measurements taken from the filter beds. The results indicate that values of the flocculation parametric numbers obtainable in the filter beds are quite similar to those used in conventional flocculation practice. This finding clearly discounts the commonly held view that the setbacks experienced in the use of direct filters (e.g. poor effluent quality, turbidity breakthrough, etc) are due to insufficient flocculation in the filter bed. Such setbacks are probably due to the limited pore volume in the filter bed that would necessitate the settlement of flocculated water to reduce the sediment load applied to the filter.