Summary:The treatment of water from eutrophic lakes is disturbed by extensive development of plankton, which is caused by particulate algogenic organic substances and frequently also by dissolved ones. They are released by excretion, diffusion, cell destruction, separation of cell wall substances and metabolic processes in the course of the cellular reproduction in dependence on the physiological state of the algae. At a sufficient dosage of metallic salts as a flocculant, the extracellular organic substance (EOS) may act as an anionic flocculation aid in the concentration range of 1 ... 2 mg/l C. There is decisive the mass ratio: Me (metal as flocculant)/EOS (as TOC).Below a mass ratio Fe : TOC=2 ... 3 the EOS disturbs the process of flocculation and filtration.
l a c k u n g s h i l f s m i t t e l z u s a t z schwach k a t i o n i s c h k a t i o n i s c hFa hr weiseO F a n ? -
-t C h l o r e l l a18 Acta Iiydrocllinl., Bd. Hieraus lassen sich folgende Schliisse ableiten :-Die EOS aus der hochmolekularen Fraktion stort den Flockungs-und FlockenabtrennprozeB starker als die EOS der niedermolekulnren Fraktion. -Bei den Grun-und Blaualgen stort der hochmolekolare Anteil der EOS mit zunehmendem Kulturalter starker.-Besonders aosgeprkgt sind storende Eigenschaften der EOS der spatstationaren Wachstumsphasen der Blaualge Psewlanabaena, der G r k a l g e Dicfyosphaerium sowie der Kieselalgen Xelosira und Achnnnthes.-Von den niedermolekularen Substmzen weist nur die EOS der logarithmischen Wachstumsphase der Kieselalge Fragilaria ein ebenso stark storendes Verhalten auf.-Ein Zusammenhang des Storeffektes der EOS mit den verschiedenen Algenklassen ist nicht vorhanden.
Be.stimmung der Ladunqs~onzentrationDie Restinimiiiig der Ladungsdichte von Partikeln bzw. der Ladungskonzeiitratioii einer Wasserprobe erfolgt durch Zugabe eiiies entgegengesetzt geladenen Polymers oder Polyelektrolyten bis zur Ladungsneut ralisation. Zur Bestimmung der negativen Ladungskonzentration der im Wasser gelosteii EOS wird eiii kat,ionischer PolyActs hydrochiin. hydrobiol. 17 (1989) 3 251 Tiibellr fi. EC)S-Konxeiitr;ition~ri (rng/l TOC), die r.rfnrtlerlicth sind, uni cine St.ornng d e~ Plockungsprozcsws auszulijscn, dargrst.cllt durch die Erhohung der Kcsttriibung im Filt.rat (von en. 0,25 m-l n i i f 0.5 in -1 ) (Versurlie mit. der ,.kleinen" Flocb-nngstestapparstur) (1989)
s t a t i o n a r e PhaseAbh. 9. Abhangigkeit des Zusntzes a n Pe-LII-
The implications of energy input (G value) and energy input time (t value) as well as the Gt value (Camp number) resulting from the orthokinetic particle aggregation as part of the adsorption coagulation with charge neutralization were investigated in the laboratory using a direct filtration test apparatus with a stirred reactor developed by the Wahnbach Reservoir Association. The tests were carried out at a constant particle concentration. The water was flocculated with 5 mg/l Fe3+ at pH 6. In compliance with literature references, an optimum removal of turbid matter by means of this direct filtration apparatus was achieved at G values of around 40 s−1, t values of 15-30 min and within a Gt range between 30,000-60,000 which corresponds to a GCt range of 60-120 according to Ives. Only in this range are the G values of 30-50 s−1 compatible with t values.
By comparison it was shown that these values are in reasonable agreement with the results of our tests implemented on a full-scale direct filtration with two successive stirred reactors. Optimum direct filtration conditions were found to occur within a G range of 30-60 s−1, at t values of 15-20 min and within a Gt range between 15,000-40,000. From this comparison it can be concluded that results of hydrodynamic investigations into orthokinetic aggregation, which were obtained with the described laboratory floc filtration test apparatus, may well be applied as guide values in full-scale direct filtration processes.
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