Das Entwässerungsverhalten von Klärschlamm in Gegenwart von Polyelektrolyten

Untersuchungen zur Wechselwirkung von Klarschlamm mit wohldefinierten synthetischen Polyelektrolyten unterschiedlicher Ladung, Molmasse und Molekulgeometrie wurden mittels Zeta- und Stromungspotentialmessungen und Polyelektrolyttitrationen vorgenommen. Dabei konnten verschiedene Mechanismen der Klarschlammflockung aufgezeigt und deren Auswirkung auf das Entwasserungsverhalten des Schlamms uberpruft werden. Je nach Flockungsverfahren (kationische Monoflockung, anionisch-kationische und kationisch-anionische Dualflokkung) sowie Kettenlange und Verzweigungsgrad der eingesetzten Polyelektrolyte werden unterschiedliche Mechanismen der Schlammentwasserung (Verbruckung, Mosaikhaftungsmechanismen, Einschlusflockung infolge von Poly-elektrolytkomplexbildung) diskutiert. Fur ein gegebenes Flockungsmittel lassen sich somit bei Kenntnis des Mechanismus der Wechselwirkung optimale Verfahrensweisen zur Klarschlammentwasserung vorhersagen. Dewatering Behaviour of Sludge in the Presence of Polyelectrolytes Interactions of sludge particles with well defined synthetic polyelectrolytes of different charge, molecular mass, and molecular geometry were investigated by means of zeta- and streaming potential measurements and polyelectrolyte titrations. Different mechanisms of flocculation were discussed with regard to the dewatering behaviour of the sludge. In dependence on the flocculation procedure (cationic monoflocculation, anionic-cationic, and cationicanionic dual flocculation) as well as on the chain length and branching of the polyelectrolytes used, different mechanisms of sludge dewatering were discussed: Polyanions are not adsorbed on the sludge particles and lead to a decline of the dewatering results. Linear short chain polycations result in a flocculation after surface charge neutralization of the particles according to a patch mechanism. Long chain linear polycations cause a bridging of the particles leading to a flocculation without charge neutralization of the aggregates formed. With branched polycations, a flocculation according to a patch mechanism is observed. These polycations form sludge particle aggregates which are surface charge neutralized at the flocculation point. In anionic-cationic dual flocculations using long chain polycations, an inclusion flocculation due to polyanion-polycation complex formation is the predominating mechanism. The cationic-anionic dual flocculation with complete covering of the particles with polycations in the first step can be discussed by a patch mechanism quite similar to an anionic monoflocculation of cationic particles. By knowing the mechanism of interaction for a given flocculation agent, an optimal sludge dewatering procedure can be predicted.