Table 7342 Classification Of Polyelectrolyte Flocculants

Type Ionic Charge Examples

Anionic Negative Hydrolyzed Polyacrylamides, polyacrylic acid, poly-

acrylates, and polystyrene sulfonate Cationic Positive Polyalkylene polyamines, polyethylenimine, polydi-

methylaminomethyl polyacrylamide, polyvinyl-benzyl trimethyl ammonium chloride, and polydimethyl diallyl ammonium chloride Nonionic Neutral Polyacrylamides and polyethylene oxide

Miscellaneous Variable Alginic acid, dextran, guar gum, and starch derivatives sufficiently different to permit separation. Sand and grit particles are heavy and compact. They can have effective densities more than twice that of water. Biological solids and hydrated inorganic precipitates are hydrophilic, i.e., associated with surface-bound and internally contained water. Their densities can be only slightly greater than that of water. The density of water is affected slightly by temperature and more significantly by salt content.

The salt content and pH of suspending water affect the surface charge of the SS. The sign, magnitude, and distribution of this surface charge strongly influence the type and quantity of the flocculant to be used. Negatively charged solids can be flocculated by cationic flocculants; positively charged solids can be flocculated by anionic floc-culants. Negatively charged solids can also be coagulated by inorganic cations and then flocculated by an anionic flocculant.

The size, shape, and concentration of solid particles also affect flocculation and settling. Large particles settle faster than small particles. Irregularly shaped particles settle slower than smooth, spherical particles. Flocculation effectiveness is reduced if the solids concentration is low (<50 mg/l) since the probability for contact among particles is reduced. Settling is hindered at high solids concentrations (>2000 mg/l) because of excessive interparti-cle contact. Most suspensions subjected to settling in water and wastewater treatment settle freely, with the exception of concentrated biological sludges.

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