Hidrológiai Közlöny 1971 (51. évfolyam)

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

Special Conference Number, Szebellédy, L. Hidrológiai Közlöny 1971. 1. sz. 49 tered waters was 6 to 7 mg/lit. The content of free carbon dioxidé changed accordingly. In drinking water, where the hme-earbon dioxidé equilibrium is guaranteed, quality is known to meet the requirements. However, this equilibrium is a function of pressure and temperature. It is frequently observed that in water, in which lime and carbon dioxid are in equilibrium at the point of produetion, this balance is disturbed in the course of long transportation and the water tends to become corrosive. The disturbance of equilibrium may occur alsó in zones where waters of different origin are mixed and owing to the increased carbon dioxidé content, the water may become enriched with iron if conveyed in steel pipes. Allowance has been made for all these experiences during design and operation, and attempts are made to minimize the operation of terminál pipelines, ot to transform them to closed-loop systems, in order to eliminate the possibility of stagnation. For new conduits corrosion resistant pipe materials, such as asbestos-ceinent or plastic, are used increasingly. Besides the phvsical and chemical alterations mentioned above, problems are due alsó to the organic content of waters. This applies especially to surface water, in which biological activity is most pronounced in the summer season. In header pipes little oppotunity is offered for the prolifieation of hving organisms, owing to the usually high velocity of flow and to the decreasing trend of temperature. Considerable problems are due, however, to quality changes occuring in the storage basins of the system. Extended times of residence favour the development and prolifieation of hving organisms. Various strains of Colibacteria were found to survive for extended periods and under favourable temperature conditions may even prolificate in originally perfect water. In water of 9 Centigrades temperature the Colieount was observed to increase within 10 days to above the allowable limit, whereas at 18,5 Centigrades this occured during four days already. The conclusions arrived at therefrom, are as follows: — operational practices must be such as to prevent the stagnation of water, — it is essential to make provisions for the regular flushing and disinfection of the network, — great care should be devoted to the regular supervision of existing facilities and to the realization of the necessary modifications, — the sanitary regulations in force should be strictly observed during the design and operation, expecially in locations, where the disposal of wastes is not perfectly solved, because of the potential entrance of wastewater into empty distribution pipes. The first problem raised in the paper by L. Áll, namely the changes in quality resulting from the mixing of waters of different origin, in considered alsó by M. Serek, who deseribed the experiences gained during the design of the mixed system supply network of Brno. The quality of water was found to fluctuate in distribution networks supplied from two or more sources, where the water produced by individual plants was of different quality. Fluctuation may occur in time, if the quality varies at the same consumer, and it may be local if different consumers receive water of different quality. A method is given for the mathematical modelling of quality fluctuations in similar networks. Such models can be conceived by adapting the mathematical models used for the hydraulic simulation of transiant phenomena. The resulting water quality is estimated by the mixing law, or it is determined experimentally in a laboratory. Computations are performed on digital computers. The measures aiming at the reduction of fluctuation may have the objective of minimizing fluctuations in time, variations with location, or both simultaneously. Different methods serving this purpose are deseribed, with special regard to the distribution network of Brno, the inanguration of which is scheduled for 1974. Severe problems are caused by corrosion in the network, due to quality changes resulting from the mixing of different waters, changes in temperatures and other factors. The use of corrosion resistant materials may be the answer to these problems. Plastic-pipes are eminently suited for corrosion control. The growing popularity of plasticpipes is reflected by the figures quoted from Austrian practice by E. Figwer. Plastic-pipes have been introduced in 1954, using round 154 tons. In 1969 round 10 000 tons of plastic pipe have been used. Polyethylene and hard PVC are the materials predominantly applied. Experiences gained with the use of plastic-pipes are deseribed in detail with reference to data published in the literature. Great significance is attributed to the circumstance, that plastic pipes meet all relevant sanitary specifications and are non-toxic. Pipes of hard PVC are preferred. Concerning the role of metál stabilizers in the produetion of hard PVC pipes for distributing drinking water, conflicting opinions prevail in different countries. In Europe, with the exception of Francé, a certain percentage of lead is considered allowable, while in somé countries zinc derivatives are alsó permissible. In Francé only calcium is allowed for thermal stabilization. In the U. S. all zine derivatives are considered allowable. The influence of stabilizers on the quahty of water has been studied extensively, with special attention to lead and heavy metals. It is eoncluded, that no more than 0.1 mg/ht. lead was dissolved from hard PVC-pipes made with lead as the stabilizing agent. Plastic-pipes are consequently considered harmless, from both the sanitary and toxicological point of view. It is not intended to question the future role of plastic pipes, but it should be remembered, that according to data published in the relevant literature, specifications have been issued in several countries, restricting the quahty of plastic-pipes that can be used for distributing drinking water. In 1952 representatives of the Plastic Industry in the U. S. have invited the National Sanitation