Selecting polymers for direct filtration

Cationic polymers with low to medium molecular weights and high charge densities are ideally suited for direct filtration. Rapid mixing at a velocity gradient of 300‐650 sec‐1 for 3–6 min is necessary before filtration. In most cases slow flocculation may be avoided. Modified jar tests with high intensity mixing followed immediately by particle size distribution analysis should be the method of choice for selecting polymers for direct filtration. For optimum filtration, an optimum floc size distribution exists that depends on filter and particulate characteristics.