Hidrológiai Közlöny 1971 (51. évfolyam)

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

46 Hidrológiai Közlöny 1971. 1. sz. Special Conference Number, Szebellédy, L. highly oxidizjng substance, ozone together with activated carbon, is most effective in removing phenole taste from water. In combination they represent furthermore the most successful solution for destroying the cancerogeneous substances in water. Organic compounds of iron and manganese can be removed with good efficiency. Operational experience gained with the use of ozone for disinfection is reported alsó by K. Berger. The assumption that where ozone is used for •disinfection, bacteria tend to prohfieate again in the distribution network is dismissed on the grounds of actual experience. Similar phenomena have been observed alsó with water disinfected by other means before introduction into the network. The prolification of bacteria within the pipes can be suppressed by the addition of chlorine gas. Free chlorine present in concentrations from 0.01 to 0.02 mg/lit is claimed to be sufficient for this purpose. Water containing ozone should not be chlorinated, since owing to the oxidizing effect, bactericide chlorine compounds cannot be detected. The free-chlorine concentration of 0.01 to 0.02 mg/üt appears to be slightly low and difficult to determine in practice. 0.05 to 0.1 mg/üt seems to be a safer rangé. Another problem in disinfection technology is considered in the paper by Mrs. L. Yasváry, who dealt with the destruction of the Coxsakie A2 virus with hypochloric acid. This is required in sanitary specifications. According to investigations at +5 Centigrade temperature the exposure required is 20 minutes to non-dissociated hypochloric acid of at least 0.3 mg/ht concentration. In waters containing no ammónia the necessary concentration of hypochloric acid can be maintained without any difficulty, but when disinfecting waters containing ammónia, different chloramine compounds may be förmed, depending on the relative proportions of ammónia present in water and of chlorine added. The effect of chlorination may be influenced decisively by these, since the different chloramine compounds förmed differ in their effect and may give rise sometimes to taste and odour complaints. In the orthotolydine method the totál active chlorine is determined, regardless of the particular chlorine compounds present. Hypochloric acid is highly bactericide, does not lend taste and odour to water and is decomposed but slowly in water. In the presence of ammónia the addition of chlorine leads to the formation of monochloramine, the disinfecting effect of which is poorer. Even poorer is dichloramine, while trichloramine has a very moderate disinfecting effect, moreover it lends objectionable taste and odour to water. This is the reason why in the interest of thorough and safe disinfection the chlorine compounds förmed during chlorination must be determined separately. This can be performed by titration, or by the amperometric method. Disinfection is thus seen to be a delicate operation. The importance of regular laboratory checks is alsó emphasised. In his paper "The application of contemporary treatment methods in watersupply" S. Valló listed the different methods used for treating surface water and the experiences gained with them. Attention is focussed on problems attendant to intakes from artificial reservoirs (taste- and odour effects, variations in quality with time, etc.) and on methods for improving the efficiency of rapid filters. The results attained at the Hydraulic Planning Office in the field of water treatment are reflected by the paper, the principal merit of which is the publication of a wealth of information on different topics. Development The expected trends in the development of water treatment technology are outlined in the paper by K. E. Oehler, who found that the principal difference between older and modern processes lies essentially in the extensive modernization and automation of treatment and the introduction of new chemicals. The primary objective of future development is the production of good drinking water at reasonable prices. As it is impermissible to attempt no more than the observation of loosely established allowable limits, it is equally unwarranted to apply highly sophisticated methods of treatment devised to remove even unexpected pollutions. The less polluted the surface water is, the lower the cost of converting it to drinking quality. An enormous drawback of highly developed civilization is the growing pollution of environment, affecting surface waters as well. Among these oils, detergents, pesticides and other substances toxic to Man must be mentioned. To quote the author verbally: "An attempt will be made at forecasting development in different methods of water treatment". Auxiliary flocculants have been developed in recent times only, so that further development may be expected in this field. The application of computere may well result in the automatic optimization of flocculation. Input values are turbidity, the level of pH, the residual quantities ofcoagulants (Fe and A1 ions) and occasionally specific pollutants, as e. g. phenole. The feed of various chemicals will be automatically controlled. In filters the major parameters are filter design, granulometry of the filter material, shape of particles and the filtering velocity. Filtration velocity is in generál 5 m/hour, but values as high as 15 m/hour will alsó be possible in somé cases. In the more distant future velocities of 50 m/hour may alsó be attainable, preferably with multi-layer filters. Molecular filtration, reversed osmosis are known to be suited for removing salts and substances causing turbidity. For the quality of filtered water the maintenance of a constant differential head on the filter would be of advantage. For the treatment of surface waters the method developed by Mrs. Bozzay and partners has been introduced. This consists of using micro-sand for increasing the weight of flocs, so that the settling and clarifying effect can be improved. In verticalflow clarifiers nozzles were used by Hásselbarth