Hidrológiai Közlöny 1971 (51. évfolyam)

1. szám - Dr. Szebellédy Lászlóné: A vízminőség szerepe és változásai csővezetékekben

52 Hidrológiai Közlöny 1971. 1. sz. Special Conference Number, Szebellédy, L. Beyond tho deterioration of taste and odour, the most disturbing phenomenon is, that the further development of the moss cover—which has already attained a thickness of several centimeters — is favoured by darkness and the flowing fresh water rich in nutrients and oxygen. The moss cover is responsible for the faet that the conveying capacity of the pipeline decreased by more than ten percent (10%), and is likely to become clogged altogether as a result of rapid growth. This was experienced at the Dunaújváros industrial pipeline, where the pipe of 800 mm diameter was completely clogged in a few vears. Investigations performed on the Mohács—Pécs pipeline have demonstrated that river water must not be eonveved over long distances even for industrial purposes. When conveying river water the danger of a cover developing in the pipeline is always present, resulting in a loss of conveying capacity, accompanied by an increase of organoleptie effeets. The only solution to this problem consists in the treatment of surface water at the point of diversion, so that only sterile water, or drinking water for domestic supply should be fed into the pipeline. Investigations during the past 30 years supplied the data used by L. Ncmedy, for demonstrating the changes in the bacterial quahty of water in the distribution network in Budapest. Quahty studies permit on the one hand natural waters to be quahfied, and on the other hand, to decide on the method of treatment required to meet quahty specifications. Sanitary requirements are of paramount importance in drinking water and in industrial waters of drinking quahty. In the case of other uses, it is rather the chemical composition, which is significant. In quality studies related to distribution networks, bacterial checks should be emphasized for this reason. Problems related to the interpretation of bacterial water quahty should therefore, be considered and the bacterial parameters drinking water defined first before a more detailed treatment of the subject. The water flowing in the distribution network is likely to change continually its physical, chemical and biological quahty. Owing to the continual exchange no thermal, dynamic or biological equilibrium is possible in the network and the changes in quality are direct reflections of changed external and internál conditions. Quahty changes in the network are sometimes observable even to humán organs. However, bacterial changes remain imperceptible and are impossible to trace even by microbiological methods. It is generally recognised, that regardless of treatment and the method of conveyance, bacteria are always present in the network water. Consequently, this is necessarily the starting basis of any investigation of the bacterial quality of water in the network. Sterile samples are encountered in rare cases only. The absence of bacteria applies even in such cases to the particular sample only and no more remains to be done than to extrapolate the bacteria count obtained for a sample of not more than 300 millilitre to the entire volume contained in the pipe section under study. Quite obviously, the count obtained for a sample which is but a fraction of the water in the network, can be interpreted only statistically as an information on water quahty. Since sample volumes are standardized, the only method for improving the reliability of quahty analyses in the network consists in increasing the number of samples and in checking the values obtained by repetition. The percentual distribution of individual bacteria types by categories is beleived to present the best approximation to the average water quality. Bacterial water quality is composed of an increasing number of parameters. Naturally, during the routine checking of the network, only somé of the parameters are required, but presently the determination of bacteria according to type is often more important than the totál count or the Colicount. During the 30-year period studied, quahty was found to deteriorate gradually, which is in agreement with experience gained elsewhere. This can be explained by the two-fold effect of industrialization, since the quahty of natural waters is affected by the rapid growth of industry, accompanied by a similarly rapid growth in demand. When the counts of bacteria and Coli are plotted, the two curves are seen to intersect in 1957, with the totál count showing higher values thereafter, which is a welcome phenomenon from the aspect of sanitation, although there is a slight increase alsó in the Coli-count. As an explanation it may be offered, that Coli bacteria are less resistant to chlorine, than the saprophyte bacteria, and in response to repidly growing demands, surface water was used increasingly and the feed of chlorine was intensified by the Municipal Water Works. Concerning the bacterial quahty of raw water and water in the network, it is eoncluded that up to 1961 the quahty of raw water was invariably inferior, whereas later the bacteria count of network water was higher. In the over 100 years old network, typical changes of quahty were repeatedly observed. Such changes have been reported alsó abroad, however, without offering any acceptable explanation. ' The changes in bacterial quahty of network water are caused by a great number of both external and internál factors, and these are closely related to the physical, chemical and other biological properties of the water supphed. The verified and assumed factors influencing the bacterial quahty in the network, are classified into internál factors, changes in hydraulic conditions and external factors. Internál factors are defined as those existing in the water produced, before its beingfedinto the network and which themselves are responsible for changes in the quahty of water conveyed. A higher organic content, the occurence of certain chlorine-resistent bacteria are mentioned as examples for these. Decayed organisms serve partly as nutrients, and contain partly enclosed bacteria, while in somé cases the prolifieation of bacteria may be promoted alsó by the method of treatment. Concerning