Vízügyi Közlemények, 1996 (78. évfolyam)

2. füzet - Rövidebb tanulmányok, közlemények, beszámolók

Keverés a koagulációban és a flokkulációban 243 The colloid destabilization can occur due to adsorption of hydrolysis species or sweep coagulation which are dependent upon pH and couagulant concentration (Fig. 1.). During coagulation the £ potential but total charge neutralization cannot be carried out due to the different type of colloids and their distribution of size an shape. The simplified hydrolysis is shown by (2). The short reaction times require effective rapid mixing. The alum polymer formation can be characterized by the ligandum number (3). The flocculation (slow mixing) aims the floc-aggregate formation by transport processes such as the perikinetic and orthokinetic flocculation and the collision of the settling particles. The floes can be characterized by several parameters in terms of size, shape, density (4)-(7). The aggregate formation is likely to happen in for levels: primary particle, flocculi, floe and flocaggregate. The aggregate structure is determined by the flocculi hence G of slow mixing effects only the aggregate size. The structure depends on the G t value of rapid mixing. The floe strenght characterizes the floe resistance (8). (9) shows the floe diameter as a function of time. The author describes the three different types of flocculation: the random, concact and pellet flocculation. Most of the mixing processes require turbulent flow characteristics which can be modeled either by the Eulerian or the Lagrangian view. The aim of mixing is twofold: to decrease the average concentration gradient by convective transport (macromixing) and to decrease the concentration fluctuation by diffusion (micromixing). Fig. 2.; (10). The role of micromixing can be fundamental in coagulation. In aigated mixers the scale of turbulence varies widely, while in plug flows and static mixers it is more even. The author describes the importance of the multiphase and the laminar mixing. For the characterization of reactors the determination of mixing time, 0(11) and the Reynolds number-Power number function (12)—(13), Fig. 3., is useful. Modeling th emixing processes of reactors is necessary in order to produce parameters required by design and operation. Due to the complexity of these models a feasible possibility can be the application of the residence time distribution theory which is described by the author (14)~(24), Fig. 4. The theoretical outlet concentration can be calculated using (25). Modeling the ffect of micromixing is also possible by this theory (26H30), Fig. 5. The residence time distribution theory is efficient enough to determine the boundary product concentration in caseof certain reactors although research is needed to define their distribution functions. The author gives a summary on the applicable rapid mixers and flocculators. In case of coagulation there are hydraulic mixers and mechanical mixers Presently the design is based on rules of thumb( applying only G and G-t) the flexibility in terms of operation is essential. There are hydraulic flocculators and mechanical flocculators of which design process the same rule applies. In the summary the author emphasizes the importance of the reactor kinetic view, the process analysis and the numerical models in the field of coagulation and flocculation.