Hidrológiai Közlöny 1971 (51. évfolyam)

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

Hidrológiai Közlöny 1971. 1. sz. 48 The role of, and changes in, water quality in distribution networks By Dr. SZEBELIÉDY, íJSZIŐNÉ (Mrs.) Secfcion Heftd (Research Institute for Water Resources Development, Budapest) In order to meet the growing demands for good quality drinking and industrial water, this must he conveyed often over long distances, or in order to supply the required volume, waters of different quality must be mixed. This is whv increasing significance must be attributed to the circumstance that water is often imported from considerable distances, before it reaches the consumer. During its passage adverse changes may occur in quality, giving rise to a variety of complaints. rfhe changes in quality can be traced back to a variety of causes and consequentlv, as in all problems associated with water quality, experts from different fields of science including engineers, chemists, and biologists, must cooperate in solving them. Difficulties in supply may arise if waters of different quality, of surface and subsurface origin must be mixed to meet the demands. The chemical composition of water may suffer changes within the distribution network as a function of time, temperature, velocity of flow, dissolved gases, etc. The changes in quality that are not due to the pipe material, result usuallv from micro-biological processes, which take place in the presence of organic substences. However, in many cases, substances are dissolved by the water itself from the pipes, or substances dissolved in water are precipitated within the conduit. The bacterial quality and the factors affecting it liave been investigated first in connection with the water supply systems of large communities. It is for this reason that this field has been explored most extensively. Biological tests using the microscope have been introduced lately, so that evaluation by the presence of different microorganisms and by their number became possible. Owing to the ramified nature of the problem, the depth of information in various fields is by no means uniform. This applies especially to problems, where new kinds of pollutants are encountered, or new pipe materials have been introduced. Hovewer, practically, each field is covered by the papers submitted, the only question being, whether or not, the possibilities in each of them are exhausted. In connection with this subject, the following papers have been received: Áll. L. (Hungary) : The role of, and changes in, water quality in pipelines. Figwer E. (Austria) : Plastic pipes in contemporary distribution networks. Görög J. (Hungary) : The role of, and changes in, water quality in pipeiines. Literáthy P. (Hungary) : Changes of quality in the Mohács — Pécs pipeline. Majorlaki J. (Hungary) : Changes of water quality in the Mohács—Pécs pipeline. Némedy L. (Hungary) : Factors affecting the bacterial quality of water in the Budapest distribution network. Serek M. (CSSR) : Variations of quality in distribution networks and measures for their reduction. Schiefner K., Hegyessy L., Pénzes M. (Hungary): The quality of surface water with special regard to (he sanitary aspects of water supply. Szabó Z. (Hungary) : The significance of microsediment tests in drinking- and industrial water supply. The paper submitted by L. Áll will be considered first, as it presents a comprehensive rewiev of all problems dealt with in detail by the other authors. The water demand of major industrial agglomerations and cities cannot be met in generál from local resources. The producing areas are situated consequently at increasing distances from the consumers. Appreciation ot this fact lead necessarilv to the development of régiónál supply-systems. Encouraged by experiences gained abroad, the first régiónál supply system has been completed recently in North—Hungary. In the initial stage, water was produced from subsurface resources, but later on, surface waters were alsó utilized first by groundwater recharging, later by direct treatment. Owing to the particular characteristics of the system, several problems related to water quality were encountered, of which the two most important ones were — the changes in quality due to the mixing of waters produced by different technologies, and — the influenee of facilities serving the storage and conveyance of water. The producing plants in the Borsod Régiónál Water Works can be classified into three groups, namely: plants drawing on bank-filtered water, plants drawing on bank-filtered water, with groundwater recharging, and intakes from watercourses. Water is conveyed in several instances over many kilometres from the treatment plánt to the consumers. At normál flow velocities the time of residence in the pipeline may be considerable and so may be the adverse changes in quality. This is the reason why quality is checked at several points of the distribution network. Practical experiences are listed in the paper, which illustrate strikingly the changes of water quality. At the plants drawing on bank filtered water, temperatures remain below 13 to 14 Centigrades, even in the warmest periods, whereas, at surface intakes, for instance from reservoirs, the rangé of fluctuation is from 0,2 to 20 Centigrades. Consequently the temperature of bank-filtered water is practically constant within the network, while that of surface water may fluctuate as much as 5 to 6 Centigrades, depending on the season. With rising temperatures the quantity of dissolved gases will decrease in water. In warm periods the dissolved oxigén content was found to be 2 to 4 mg/lit only, at the same time that of bank-fii-