Vízügyi Közlemények, 1969 (51. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(71) roxides and accelerate flocculation. Substances having cationic properties can be used without a basic flocculant as well. At the Budapest laboratory of the Research Institute for Water Resources Development experiments have been conducted for treating the water of the Soroksár Danube branch —the closed branch along the left-hand side of the island downstream of Budapest—with the help of auxiliary coagulants. The basic coagulant was aluminium sulphate. In the experiments activated silicic acid, carboxv-methyl celluloze polyakrylamide and sodium alginate were used. Settling efficiency has been evaluated, by optical measurement of relative turbidity. The optimum application rates of individual chemicals have been determined separately. Hereafter, these optimum application rates were used in comparing various chemicals. Experimental runs have been conducted in winter and summer alike, so that results are available for both 20 and 0 С water. The optimum application rate of activated silicic acid bas been determined at these two temperatures in the manner illustrated in Figs. 9 and 10. Curves of similar shape have been obtained for the other chemicals as well. Individual chemicals have been compared in Figs. 11 and 12, indicating the superiority of activated silicic acid at both winter and summer temperatures. EUTROPHICATION OF SURFACE WATERS IN HUNGARY By Dr. L. Felföldi] (For the Hungarian text see pp. 352) According to the degree of saprobity, trophitg and toxicity the biological indices, phenomena and variations of water quality can be classified into three groups. The degree of saprobity is raised by non-toxic, organic pollution. In such waters heterotrophic living organisms prolificate, which oxidize the organic pollutants of water, consuming its reserves of dissolved oxygen thereby. Organic pollutants are mineralized by these heterotrophic organisms into anorganic compounds, the most important of which are phosphorus and nitrogen compounds which in turn serve as nutrients for plants (algae, aquatic plants, seaweed). The degree of trophity is increased by the accumulation of similar plant nutrients in the lake. The rise of the degree of trophity is called eutrophication, the reasons for which may be natural (natural eutrophication) and atropogeneous (artificial eutrophication). Changes which under natural conditions may take several thousand years may be accelerated by artificial nutrient supply enough to require no more than five- or ten years to become noticeable. The causes of excessive nutrient supply are urbanization, the increasing application of fertilizers and synthetic detergents, higher rates of soil erosion due to agricultural cultivation, but first of all the discharge of both raw and treated domestic wastes. The recipient is first polluted by untreated wastes, enrichment following subsequently, while treated sewage and agricultural wastes first results in enrichment and then pollute surface waters. As a result of eutrophication aquatic plants (algae, seaweed) start to prolificate at extremely high rates in the recipient. Especially the monocell algae may give rise by decay after "blooming" odour complaints, prevent recreational use of the water, while the blooming of toxic algae may be determinal to aquatic and land life alike. Filters and other structures of diversion works may be clogged by large masses of algae, so that, in general the aesthetic and economic value of water is impaired by eutrophication. Without even mentioning sanitary problems, the resulting consequences may be as grave as that of discharging untreated wastes into the recipient. Among the causes of eutrophication the time factor is also of significance. A well definable relationship has been found to exist between the cell prolification of algae and the length of time for which water is retained in the bed, backwater reach, etc. This time factor, mentioned also by Pearson, is also of considerable practical significance, as it offers an explanation for the fact that no eutrophication occurs on the upper, rapid reaches of rivers, whereas stored water volumes are greatly susceptible thereto.