Particle reduction study of flocculation mixing by means of grids

Abstract

A flocculation study was completed by means of a vertically oscillating grid mixing device. Five types of single grids with different solidity ratios were vertically oscillated inside a 2 L jar to promote floc aggregation. Kaolin was used as the simulated turbid particles and alum was applied as the chemical coagulant. The method of measurement was completed based on the particle reduction represented by the settled water turbidity. It was found that low turbidity readings could be achieved at a wide range of average volume velocity gradient [Formula: see text], especially in the case of high solidity ratio types of grids. This indicates that the grid mixing had a stable performance and was not greatly affected by mixing variations in the vessel. The floc aggregation and erosion rate coefficient analysis showed that the grid mixing produced particle contacts with low break-up rate. A general relationship among [Formula: see text], flocculation performance parameters, and grid physical characteristics was found, indicating that the flocculation performance was easily controlled. This study has shown the potential of grids as a mixing device to produce an excellent mixing environment for floc aggregation.Key words: flocculation, grid, solidity ratio, kaolin, alum, [Formula: see text], turbidity.