Cationic Polyacrylamide (CPAM) — Frequently Asked Questions

They are sequential steps, not alternatives. A coagulant such as alum or PAC neutralises particle surface charge so fine particles can approach one another, producing small fragile microflocs. A flocculant such as CPAM then bridges those microflocs: its long chains adsorb onto two or more particles at once, binding them into large, dense, strong agglomerates that settle quickly and dewater well.

By charge density and molecular weight, matched to the sludge. Highly negative organic sludges need higher charge density to neutralise them; very high molecular weight gives the strongest bridging and the largest flocs. The only reliable method is jar testing against the actual sludge, since the optimum varies with solids type, concentration and the upstream treatment.

Because the outside of each particle hydrates instantly and forms a gel skin that water cannot penetrate, leaving dry powder trapped inside. The remedy is to wet the powder slowly into vigorously stirred water, ideally through a proper eductor or dispersion funnel, never by tipping it in. Undissolved lumps never recover and represent wasted product.

Typically a day or two. Polyacrylamide solutions degrade over time through chain scission caused by shear, heat and contamination, and a degraded solution flocculates poorly because the bridging depends on chain length. Make-up should be sized to daily consumption, and excessive pumping or recirculation of the made-up solution should be avoided.