Mixing Intensity and Polymer Sludge Conditioning

Experiments were performed on samples of alum, activated, and primary sludges to determine if these sludges, conditioned with polymers under high stress, would provide good filterability. Tests were conducted using a variable speed mixer with root mean square velocity gradient (G) values ranging from $250-2\text{,}030{\sec }^1$ with both anionic and cationic high molecular weight polymers. Capillary suction time (CST) was used to measure relative changes in filterability. Results indicated that readily dewatered sludges can be obtained when subjected to high‐stress mixing conditions. The standard jar test apparatus was found to be inadequate when predicting polymer dose requirements when high‐stress dewatering processes are used. The most significant parameters governing high‐stress conditioning were determined to be polymer dose and total mixing energy input (Gt). It was discovered that once an optimum Gt had been established for a given polymer dose, any combination of G and t, within a ideal range of G to t ratios, could be used with no appreciable loss in filtering performance.