Vízügyi Közlemények, 1971 (53. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(40) levee height and the hauling distance of the material. The method of construction for combined levee sections is shown in Fig. 6, indicating the 5 stages of work. The economics of construction work on navigation and reclamation canals is analysed on the basis of technological diagrams in Section 3. The first of Lhese is shown in Fig. 7. The examples quoted in the analyses are taken from the canal construction work performed in the Vojvodina territory. The method of analysis is illustrated with reference to the diagram shown in Fig. 7, representing a cross-section of a typical section of the Bega — Temes Canal. The diagram is representative of both the volume and organization of construction. For obtaining information on the depth of the groundwater table and for eliminating its influence it is essential to excavate a pilot ditch, for which an asymetrical arrangement is considered. The unit costs of different land-based and floating earthmoving machines are compared on the basis of different technological diagrams illustrated in Figs. 8 to 11. Economical limits for the use of individual machines are derived therefrom subsequently. In conclusion the unit cost of earthmoving is demonstrated to depend primarily on the complexity of the technological diagram controlled by the dimensions of the cross-section, but also on the composition of the soil, its mechanical properties and on the depth of the groundwater table under the terrain level. The two graphs reproduced in Fig. 13 indicate the unit cost of earthmoving for a canal of compound cross-section excavated a) in clayey sand soil and b) in sandy clay soil. Unit costs are given in terms of the canal cross-section and the depth of the groundwater table. EXPERIENCES GAINED IN TECHNOLOGICAL STUDIES ON FLOCCULANTS USED IN WATER TREATMENT By Lajos Bulkag, Civ. Engr. (For the Hungarian text see pp. 175) According to their method of operation clarifiers can be classified into three large groups, namely a) horizontal flow-, b) counter flow- and c) vertical upward flow basins. The development of horizontal flow-types points to multi-level designs. In the vertical upward-flow, countercurrent clarifiers sludge settles downward against the upward flowing water, whereas in the uniform-flow types sludge skimming is adopted. The surface load in horizontal-flow and countercurrent clarifiers is around 0.5 mm/sec, while in uniform-flow types it is about twice as high. After the description of the main clarifier types the designs realized in Hungary so far are analysed. Hydraulic conditions are evaluated on the basis of the passage hydrograph determined by feeding lithium salt as tracer material. Such hydrographe are shown in Fig. 20 for six different clarifiers. Accordingly, the compartment (Fig. 18) and the uniflow (Fig. 7) types were found to behave poorly, in that the dropping branch of the hydrograph was delayed, while the others proved suitable. The technological behaviour of the basins was evaluated on the basis of the reduction attained in suspended matter, turbidity and oxygen consumption. Very good results have been attained with the Mélyépterv (Fig. 19), Candy (Fig. 12) and two-level ( Fig. 3 ) types. On the basis of investment costs related to 1 cu.m/day treatment capacity the Candy, and Corridor ( Fig. 13) types proved superior, but the specific costs are relatively low also in the case of the Pulsator ( Fig. 16) and Cyclofloc ( Fig. 17) type clarifiers. The circumstance that no scraper equipment is required for removing tlie sludge, may be mentioned as a special advantage of the first three types. For the efficient operation of clarifiers it is essential to ensure a uniform velocity distribution at the inflow, further in the case of basins with a circular plan the concentric arrangement of all parts affecting the flow of water. If the suspended content of the water to be treated is low (less than 25 mg/litre), it may be desirable to increase the sludge concentration artificially. If operated correctly, the clarifier should reduce the suspended content to below 15 mg/litre. It is essential to maintain continuously a uniform load on the clarifier, i. е., fluctuations in demand must