This study identified polymer attachment sites in three types of sludge for different molecular weight and charge density cationic polymers. Conditioned and unconditioned sludge samples were treated with cationized ferritin (CF) to label anionic charged sites on the surface of sludge particles. Sludge surfaces were examined using transmission electron microscopy. The presence of CF indicates an anionic site not attached to polymers. For increasing polymer molecular weight, comparison of micrographs of samples conditioned with similar polymer doses showed an increase in CF attachment. Therefore polymer attachment was seen to decrease with increasing polymer molecular weight. At extremely high polymer dosages, the presence of CF indicates that anionic sites have not been saturated by polymers. These results imply the molecular weight (chain length) and structure of polymers may determine the mechanisms of polymer action. No appreciable differences were observed for sludges conditioned with polymers of various charge densities.

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