Hidrológiai Közlöny 1971 (51. évfolyam)

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

50 Hidrológiai Közlöny 1971. 1. sz. Special Conference Number, Szebellédy, L. Foundation to investigate any potential changes caused by plastic-pipes in waterquality. Certain plastics were found tó contain toxic substances, such as lead, cadmium, strontium, lithium, stibium, etc., in quantities exceeding the values perrnitted in the U. S. standard for drinking water. Lead was found to be dissolved in quantities ranging from 0.3 to 2.0 mg/lit. whereas the limit perrnitted in the relevant U. S. standard is 0.05 mg/lit. Besides metals, taste—and odour complaints may be caused in somé instances by phenole, and plastics of poor quality may cause colour complaints in water. Investigations, extended bver 17 years, have lead to the conclusion, that the plastics tested and approved by the National Sanitation Foundation, can safely be used in distribution networks, while no approval is granted to plastics of unknown composition or to such, containing toxic substances. The papers considered so far dealt with problems of technical-chemical character. Such devoted to problems of more involved chemical-biological natúre will be considered subsequently. Water better than drinking quality is required in somé industries, especially the pharmaceutical, textile and food industry. Teehnologieal specifications there may call for standards of quality which are difficultto satisfy. In teresting ideas are raised in this context, by J. Görög. The limits, mentioned in different standards, indicate allowable values for factors affecting water quality. As pointed out repeatedly in this report, water must be regarded as a multi-component dynamic system subject to continual changes, the transformation of which is started in the distribution network already, and may depend on the time of residence there. The extent of transformation will depend on the temperature, velocity, chemical composition—primarily oxigén and carbon-dioxide — of water. No mention is made of the determination of these latter in various standard specifications and directives. This statement by J. Görög appears to be importent in view of the problem of quality changes in the network. Dissolved substances may be precipitated in the form of solids as a result of biological, or non-biological action. These solids may either form a dense layer or loose, suspended adhearing flocs. The compounds forming inorganio crusts are mainly calcium-carbonate, calcium-phosphate, calcium-sulphate, salts of magnesium, silica and iron oxidé. The precipitation of carbonates is one of the mostly explored problems associated with changes in water quality. Inorganic solid compounds may be dissolved localy and accumulate by precipitation at other points in the network, where a change in the temperature or composition of water occurs. Loose flocs are either suspended in water, or adhering to the pipe walls and form hardly soluble substances with the inorganic solids. Flocculation may be promoted by micro-organisms prolificating in water, by clay, silt, organic debris, coagulants and remains of substances added for corrosion control. The most significant change is — however — due to the micro-organisms present in water. The biological environment composed of characteristic micro-organisms is specific of everv reservoir and distribution network. The composition and character thereof is controlled by the nutriens dissolved in water, together with environmental factors, of which temperature and light are the most important ones. Owing to their intense metabolism and rapid prolification, bacteria play the most significant role of the micro-organisms encountered in pipes and conduits conveying water. Two groups are of special interest, namely the pathogenie organisms and iron bacteria, which give rise to considerable chemical alteriations. Pathogenie organisms remain virulent in clear drinking water for extended periods of time and survive there longer than in properly treated wastewater discharged into rivers. In fact in the latter case, the bacterium count is considerably reduced by the dissolved oxygen of flowing water, by solar radiation, the purifying effect of bacteriophag protozoa, and antiseptic substances present in water. Many publications have been devoted to the circumstances and defects by which pathogenie bacteria may be introduced into drinking water. However, the activity of iron bacteria is even more difficult to control. The mass appearence of iron bacteria poses severe problems in any industrial use of water. Ferrous flocs in water cause colour complaints in textile mills, in the food-industry, while in the chemical industry conduits may be clogged, the efficiency of heat exchangers may be reduced and iron bacteria cause severe corrosion in any pipeline, or container made of ferrous materials. Damages due to micro-organisms are especially severe in the petroleum-industry, where waters are high in hydrocarbons and sulphate ion. The severity of the problems is reflected by the rapid increase in the number of papers during the last decade, devoted to micro-biological corrosion within and outside the pipelines in the petróleum industry. It is of fundamental importance to obtain clear understanding of the factors controlling the prolification of micro-organisms in pipelines. The dominant factors are temperature and the nutriens available. Within the same water system, temperature fluctuations are usually restricted to a rather narrow rangé. In industrial plants, water is often re-circulated and consequently it may be heated to temperatures of 20 to 40 Centigrades, which highly favours the prolification of microorganisms. In generál, water temperature is one of the factors limiting the mass prolification of bacteria. When investigating water used in the chemical industry, it is advisable to consider separately closed and semi-open recirculation systems, in the latter of which, water is in contact with the athmosphere. Optimum conditions for continued prolification of micro-organisms within the pipehne are offered by flowing water ensuring constant nut-