Optimization Study of Flocculation Mixing by Means of Grids

The purpose of this study was to optimize flocculation mixing created by single grids. Double and triple biplane grids were vertically oscillated within a standard 2 L jar. The turbulent velocities were measured using a 2D laser doppler anemometer. The particle removal performance was observed based on the settled water turbidity. When a larger number of grids were applied, the same average volume velocity gradient (G) could be achieved at lower vertical grid speeds. A uniform and more gentle mixing was therefore created, producing high particle contacts and low particle breakup. The minimum settled water turbidity was also achieved at lower G values. A larger number of grids, especially of high solidity ratio, produced a wider range of G values with low settled water turbidity. These findings showed that the grid mixing performance could be optimized by applying a larger number of high solidity ratio grids. It was also found that grids, at their best arrangement, had a better performance than a standard flat blade impeller.