Polymer flocculation mechanism in animal slurry established by charge neutralization

Flocculation and filtration of animal manure is practically and environmentally beneficial. However, the flocculation mechanism in manure need to be clarified to use the technique efficiently rather than relying on trial-and-error. Manures were flocculated with polyacrylamides. Floc size, dewaterability, dry matter and turbidity were measured. At optimal polymer volume, the charge neutralization was determined, i.e. amount of negative manure particle charge neutralized by positive polymer charge. The optimal cationic polymer properties were linear and very high molecular weight, which caused efficient particle catching. And it had medium charge density, which caused efficient particle attachment. The required charge neutralization was 5–23% (15% for the optimal polymer). Polymer bridging proved the dominant flocculation mechanism; patch flocculation may be slightly significant for some polymers, while coagulation proved insignificant. Manure’s high ionic strength, high dry matter content and highly charged small molecules caused bridging to be more dominant in manure than in other typically flocculated media.

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► Mechanism upon manure flocculation is identified by observing charge neutralization.
► Proved: necessary to neutralize 5–23% of manure particle charges by polymer charges.
► Mechanism: Polymer bridging dominant, while patch flocculation slightly.
► Polymer bridging proved more dominant than in previously observed media.
► Contrast: manure’s high ionic strength, dry matter and charge on small particles.