It is well known that turbulence can be used as a measure of the effectiveness of promoting flocculation, an extensively used and most important method of water treatment. Although the overall turbulence should be the integration of the turbulence intensity at each individual point in the flocculator rather than an average velocity gradient, the average velocity gradient has generally been employed as the turbulence parameter in assessing flocculation efficiency and designing the flocculation process as it can be evaluated relatively simply. With the use of Computational Fluid Dynamics (CFD), this study was able to provide the value of turbulence at any point in a channel flocculator. Comparisons between the model simulation and the experimental results obtained from Laser Doppler Anemometry (LDA) show that the model can reproduce the main features of flow in flocculators. The relationships between turbulence and velocity and the nominal velocity and the number of channels in a hydraulic flocculator, as found in this study, could substantially save the lead time and the costs of new flocculator designs. The effect of the geometry of the flocculator on flocculation efficiency was also studied. A modified Argaman's equation (1968) is proposed to calculate the flocculation in relation to turbulence in an accurate and easy way based on the relationships mentioned above. Aggregation and breakup constants during flocculation were determined by experiments. Flocculation and settling performance under various flow rates, initial concentrations, retention times, coagulants, flocculator geometry and arrangements of settling were also investigated in the laboratory and the flocculation experimental results were used to verify the corresponding modelling. The flocculation efficiency in terms of not only turbidity removal but also floc characteristics was investigated by means of video imaging techniques.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:653968 |
| Date | January 1999 |
| Creators | Liu, Jie |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12441 |
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