Hidrológiai Közlöny 1971 (51. évfolyam)

1. szám - Varró István: Felszíni vizek tisztításának korszerű módszerei és anyagai

Special Conference Number, Szebellédy, L. Hidrológiai Közlöny 1971. 1. sz. 41 chemical flocculants is necessarily unsatisfaetory if the conventional method of visual observation is adopted. By measuring the magnitude of the Zeta-potential better results are bound to accrue and at the same time the necessary chemical feed can be adjusted accurately. The magnitude of the zeta-potential can be influenced bv both mineralic and cation-active eoagulants. Mineralic eoagulants have the drawback of reducing the alkalinitv and pH of water, necessitating further treatment. Of these large quantities must be used, in contrast to cationic eoagulants, which change the electric charge of the colloids in small quantities already and obviate the need for further treatment. The opinion is expressed that the combined application of inorganic eoagulants and cationic flocculants may be advantageous for waters where treatment is found difficult. Individual experiments are deseribed in detail together with the results obtained. The conclusions are largelv correct, as is the observation that more chemicals are needed for treatment with alumínium- or iron compounds only, which is of an adverse effect on the quality of effluent and requires additiorial treatment in order to avert corrosion. The use of auxiliary eoagulants and flocculants is bound to strict conditions and this is whv they cannot be always applied with the desired result. Preliminary experiments should be performed before any application. Occassionally sanitarv restrictions must be expected when treating drinking water. The kinetics of the coagulation are dealt with in the paper by L. Zacek. In the course of his experiments the following methods were applied for arriving at the results: 1. conductometry, 2. measurement of the optical properties of the solution, 3. of the duration of filtration, 4. of the settling velocitv, 5. of the sludge volume, 6. the adhesion angle of sludge, 7. the absorption capacity of sludge. It is not intended to go into the details of the various processes, these being deseribed adequately in the paper. From these experiments he eoncluded: 1. At lower temperát üres the process of coagulation is stronglv influenced by the reduced hvdrolysing ability of the coagulant. The higher pH of water, the higher salts content, the addition of the coagulant, further greater pollutant volumes and higher temperatures will increase the rate of coagulation. In the paper a striking demonstration is given oí the various factors which affect the process of coagulation. Attempts should always be made to obtain optimum results in clarification. A detailed analysis of flow conditions in sludge curtain clarifiers is presented in the verv interesting and instructive paper submitted by Proffessor I. Te.sarik. The main conclusions can be summarised as follows: In floating sludge curtain clarifiers flow conditions depend on the design, i. e., the completed structure, on hydraulic and technological factors. The hydraulic factors are: the settling of suspended solids, their behaviour, the settling of liquid flocs. The technological factors include the quality of water, the amount and quality of coagulant. The settled slurry may be regarded as fluidized, flocculated precipitate, to which the generál equations of fluidization apply. Flocs are regarded as ellipsoids of revolution, with the Reynolds numbers of chemically precipitated flocs ranging from 0.4 to 100. In the experiments with the sludge curtain method the surface velocitv water 0.8, 1.0, 1.2, 1.4 and 1.6 m/sec. The model made of plastic, was 3 ni high at a diameter of 0.3 m. Clarifiers are grouped in the following manner: equipment for the mechanical stirring of the sludge bed, hydraulicallv fluidized sludge bed clarifiers, reactors with sludge-slurry recirculation and finally clarifiers with non-uniform settling basins. Special attention is devoted to clarifiers with hydraulicallv induced flow. At the conical outflow ports of the tanks vortices haye been observed to develop, which were propagated towards to sludge surface. The precipitate appearing on the sludge surface and the water entering the sludge compartment may cause eruptions. The quantity of the suspension entering the sludge concentrator can be computed as that of a dense fluid flowing into water over the erest of a weir. It is eoncluded finally that the minimum depth of the water layer above the sludge must not be less than one-half the distance of the collecting troughs. The paper seems to be very well documented. The determination of the hvdraulically correct design of clarifiers is dealt with in the paper submitted by L. Ivicsics. The causes for poor flow conditions can be deteeted often with the help of scale models only. Although the design costs are increased thereby, this is offset many times during subsequent practical operation. Increased attention should be devoted by the designers to the hydraulically correct design of clarifiers. Remediai measures are suggested in this highly interesting paper. One of the conclusions is worthy of being quoted separately: A rule of generál validity and applying to all types of clarifiers is that a uniform distribution of velocity can be realized easier if changes in the direction of flow are minimized and kept small. At points where a change is inevitable, a guiding element should be provided. The hydraulic effect thereof can be predicted on the basis of model tests only, if the hydraulic consequences of guiding elements are known. These are not always necessarily beneficial to clarification. It is for this reason that attempts should be made at the designing of clarifiers in which the water is forced to change direction as little as possible.