Destabilization and Aggregation in Turbulent Pipe Flow
The application of hydrolyzing aluminium and iron salts in chemical water and wastewater treatment requires a rapid and uniform distribution of the chemicals in the raw water. This can be attributed to the short reaction times involved in the formation of hydroxocomplex species and their adsorption onto the particle surface, which are in the range of 10-4-1 s. However, coagulation experiments in stirred continuous flow reactors do not allow defined reaction times on this order of magnitude to be adjusted. Therefore, a pipe flow reactor for particle destabilization and aggregation investigations has been constructed, permitting a minimum defined reaction time of 0.05 s. This plug flow type reactor has been used to investigate the destabilization kinetics of silica particles with aluminium and prepolymerized aluminium under controlled flow conditions during the very first reaction phase.
The results show that aluminium hydroxocomplex species with a maximum destabilization potential axe formed within an interval of less than 0.1 s. Increased reaction times result in the formation of hydrolysis species, characterized by a decreasing destabilization efficiency. After 6 s, the hydrolysis reaction is terminated and sweep coagulation is the dominating process. There are indications that pre-polymerized aluminium products are more stable after dosing and dilution than polymeric species of Al3+, formed during the hydrolysis reaction after dosing. The importance of high-intensity mixing during the destabilization phase is emphasized by these results. A comparison with data from technical scale plants leads to the conclusion that coagulation process efficiency can be improved with a proper design of the mixing device for the chemicals.
KeywordsHydrolysis Phosphorus Filtration Hydroxide Sedimentation
Unable to display preview. Download preview PDF.
- Levenspiel, O.: Chemical Reaction Engineering. Wiley, New York 1972Google Scholar
- Letterman, R.D., Quon, J.E., Gemmell, R.S.: Influence of Rapid-Mix Parameters on Flocculation. J. AWWA 65 (1973) 716–722Google Scholar
- Amirtharajah, A., Mills, K.M.: Rapid-Mix Design for Mechanisms of Alum Coagulation. J. AWWA 74 (1982) 210–216Google Scholar
- Klute, R., Dierschke, M.: Particle Destabilization in Pipe Flow: The Effect of Aluminium Hydrolysis Species. Z. Wasser-Abwasser-Forschung (1990) (in press)Google Scholar
- Klute, R.: Rapid Mixing in Coagulation Processes - Design Criteria. In: Chemical Water and Wastewater Treatment (A. Grohmann, H.H. Hahn, R. Klute (eds.)). Fischer, Stuttgart/New York 1985Google Scholar
- Dittmann, W., Grohmann, A., Klute, R., Wiesmann, U.: Mixing Systems for Pipe Reactors in Water Treatment. Vom Wasser 70 (1988) 129–140Google Scholar
- Hahn, H.H., Stumm, W.: Coagulation by Al(III): The Role of Adsorption of Hydrolyzed Aluminium in the Kinetics of Coagulation. Advances in Chemistry Series No. 79, Adsorption from Aqueous Solution (1968) 91–111Google Scholar
- Amirtharajah, A.: Design of Rapid-Mix Units. In: Water Treatment Plant Design for the Practising Engineer (R.L. Sanks (ed.)). Ann Arbor Science, Ann Arbor, Mich., 1978Google Scholar
- Dittmann, W., Grohmann, A., Klute, R., Wiesmann, U.: Vergleichende Untersuchungen über den Einfluß von Mischprozessen auf die Wirkung von Flok- kungsmitteln bei der Wasseraufbereitung. Report BMFT 02-WT 438, Federal Ministry of Research, Bonn, West-Germany (1989)Google Scholar
-  O’Melia, C.R., Stumm, W.: Aggregation of Silica Dispersion by Iron(III).
- ∅degaard, H., Fettig, J., Ratnaweera, H.: Coagulation with Prepolymerized Metal Salts. In: Proceedings of the 4th Gothenburg Symposium (H.H. Hahn, R. Klute (eds.)). Springer, Berlin Heidelberg New York 1990Google Scholar
- Seyfried, A.: (Unpublished data, 1990)Google Scholar
- Ventresque, C., Bablon, G.: New Coagulant Injection Process. In: Pretreatment in Chemical Water and Wastewater Treatment (H.H. Hahn, R. Klute, (eds.)). Springer, Berlin Heidelberg New York 1988Google Scholar
- Chao, J.-L., Stone, B.G.: Initial Mixing by Jet Injection Blending. J. AWWA 71 (1979) 570–573Google Scholar
- Grohmann, A., Hässelbarth, U., Langer, W.: Hochgeschwindigkeitsinjektion bei der Wasseraufbereitung. Vom Wasser 49 (1977) 267–275Google Scholar
- Stendahl, K.: Colloid Destabilization in Practice. In: Chemical Water and Wastewater Treatment (A. Grohmann, H.H. Hahn, R. Klute (eds.)). Fischer, Stuttgart/New York 1985Google Scholar
- Bratby, J.: Coagulation and Flocculation. Uplands Press Ltd., Croydon, England, 1980Google Scholar
- Faison, T.K., Davis, J.C., Achenbach, P.R.: Performance of Square-Edge Orifices and Orifice-Target Combination as Air Mixers. National Bureau of Standards, Building Science Series 12, Washington, 1967Google Scholar
- Vrale, L., Jorden, R.M.: Rapid Mixing in Water Treatment. J. AWWA 63 (1971) 52–58Google Scholar