Hidrológiai Közlöny 1971 (51. évfolyam)
1. szám - Varró István: Felszíni vizek tisztításának korszerű módszerei és anyagai
44 Hidrológiai Közlöny 1971. 1. sz. Special Conference Number, Szebellédy, L. cals are not fed into the reactor, but into a preliminary mixer, where violent mechanical agitation for 2 to 3 minutes is used to ensure throrough mixing. The method proved entirely successful, since the density of the eontact flocs and thus their settling properties improved and practically no suspended matter remained in suspension. In order to prevent the comminution of eontact flocs an auxiliary flocculant on polyacryl basis is used. With this method of clarification pretreated water of good quality was obtained — unaffected by weather conditions and season. In the clarified water the residual iron ion content was only 0.1 to 0.2 mg/lit and this consisted of iron(III) sulphate, the main flocculating agent. The filtrate was completely iron free. After presetthng, for further treatment a small amount of additional flocculant (secondary flocculant) is added, accomjiained by ozone treatment. Surprisinglv, as a result of the combined application of the secondary flocculant and ozone, the number of residual suspended particles of 5 micron diameter was reduced to 50/litre. Without secondary treatment figures 100 to 1000 times as high were obtained. These good results were obtained with double-laver filters, füled with hydro-anthracite. The velocity of filtration was 12 to 15 m/hour. The filter required flushing at 5 to 6 day intervals. The use of activated carbon filters is alsó considered necessary, besides the use of ozone. In this manner the objectionable odour- and taste substances can be removed completely from water. Cancerogeneous polycyclic materials are retained in 98.5% by the filter. Pesticides can be retained by the activated carbon filter only. Bv similar sophisticated treatment methods good-quality drinking water can be produced from surface water. The main conclusion arrived at from the paper is that increasing difficulties must be anticipated when attempting to develop a suitable technology for the treatment of surface waters. At the same time is seems permissible to state that experiments with pilot-scale plants are essential for the solution of more exacting problems. The complex application of chemicals, the filter velocity of 12 to 15 m/hour and the flushing period of 5 to 6 davs are of special interest. The sludge accumulating in settling reactors contains a variety of organic and inorganic, live and lifeless substances. Changes in the quality thereof and their influenee on the quaüty of the treated effluent have been investigated by Mfs. J. Bozzav. In vertical-flow settling basins somé of the sludge is recirculated in order to obtain a higher sludge concentration. Investigations have shown sludges of high organic content to undergo within a few clays alterations of highly adverse consequences for the quality of treated water. According to the results obtained, in the water affected by the decomposing sludge there is an increase of the ammónia content, the oxygen consumption, alkalinity and germ count. The prolification of Pseudomonas aeruginosa and Streptococcus faecalis must be expected. The process of decomposition is accompanied by the development of intensive odour. It is concluded that the high sludge concentration necessary for clarification must beensured by using chemically and biologically indifferent substances. It will be perceived from the foregoing that when producing drinking water, extensive checks must be performed for protecting the quality of water. Iinprovement oí the quality oí drinking water A complex treatment problem is deseribed alsó in the paper by I. Podhorsky entitled "Increasing the hardness of water". Waters stored at higher elevations contain as a rule little dissolved salts, their hardness is low and üttle carbonic acid is present in them. Difficulties are encountered in the treatment of such water, corrosion is caused in the distribution network and iron dissolved from the pipes is present in the water supplied to the consumer. For preventing corrosion phenomena the alkalinity and pH of water must be adjusted to a value corresponding to the dissolved calcium-carbonate balance in the water. The alkalinity of water must be raised to at least 0.6, but for the sake of safety 0.7, or even 0.8 may be indicated. Under such conditions the water is close to the lime-carbonic acid balance, i. e., it is on the limit, where the precipitation, or dissolving of lime is equally possible. In this respect the dissolved oxygen content of water becomes alsó important for averting corrosion damages. The value thereof should be at least 5 to 6 mg 0 2/üt, at which the protective layer in the pipe becomes stable. Another requirement is that the water should have a hardness of at least 2 Germán degrees, which is above the lime-solving limit of water free of carbonic acid. This adjustment can be accomplished by the addition of calcite, lime, or acidic materials (e. g. H 2S0 4, Cl 2, A1 2(S0 4) 3•18 H 20, etc.), occasionally carbonic acid. At thé Ossining treatment plánt finely ground calcite, chlorine and alumínium sulphate was used for raising the hydrogén-carbonate ion content. In this way not only the water was stabilized, but effective coagu lation was attained during treatment. Foreign experiments and results are alsó mentioned in the paper. The method of treatment deseribed appears to be sound. It would be interesting to attempt mixing .of these very soft waters with such having a higher natural hardness. This, it is believed, would better meet the biological requirements, since e. g. the presence of magnesium is essential in drinking water for the phvsiological action of enzymes. In No. 12, 1968 of "Die Wasserwirtschaft" H. Anders objected positivelv to the use of soft waters, since a deficiency of Ca and Mg may be detrimental to the cordial musele of persons suffering from circulation disturbance. F. B. Straub in his book "Biochemie" (1960) underlined the important role of magnesium in enzyme effects. These enzv-
