Vízügyi Közlemények, 1969 (51. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(72) The most effective method for controlling eutrophication is to prevent wastes from being discharged into the recipients, or to remove the nutrient substances during wastes treatment (Hie third stage of treatment). Attempts at the restoration of the water quality of lakes where eutrophication already occurred, involve necessarily serious engineering and other measures, such as the vigorous development of fisheries, the removal of algae and other bulky aquatic (liants, the dredging of decaying silt, aeration of deep, low-oxygen water layers, the release thereof, or their dilution with fresh water, but first of all a thorough understanding of the hydrological and biological conditions of rivers and lakes must be gained before any measure can be implemented in the hope of success. The problem of artificial eutrophication is not a too serious problem yet in Hungary. In some reservoirs algal blooming has been observed to recur regularly each year and difficulties have been encountered at some intake works diverting water from watercourses, or lakes. Nevertheless, the condition of Lake Velence, the lake in Central Europe, where eutrophication is gravest, and disquieting phenomena observed on Lake Balaton (plankton invasions since 1Ü49, the appearance of irregular epibiontae on the surface of Crustaceae, the rising content of organic substances in the bay of Keszthely, the spreading of seaweed and occasional algal blooming) necessitate the study of eutrophication. STUDIES INTO THE OIL POLLUTION OF SURFACE- AND SUBSURFACE WATERS By Mrs. L. Szebellédy, Dr., and P. Literathy (For the Hungarian text see pp. 363) The two basic problems dealt with in this paper are concerned with the sampling and analytical methods used in the determination of the oil content in surfaceand subsurface waters, as well as with oil pollution over the Hungarian reach of the Danube river. The difficulties in sampling are due mainly to the circumstance that oils are encountered in water in a variety of forms, depending on the origin of oil pollution. Thus oil may be present in water as an emulsion, as an adsorbed layer on suspended sediment, or as a film floating on the surface. In view of the fact that neither domestic, nor foreign standard specifications contain hints on the particulars of sampling, authors have been prompted to develop sampling devices suitable for retrieving samples from the surface film and from subsurface layers alike. During their work several recognized methods for determining the oil content have been tested with the conclusion that at small oil concentrations, these methods—with a few exceptions —do not yield reliable results. For this reason it was found necessary to develop a new method, in which the crucial operation — the extraction of oil from water —has been solved by means of the oil adsorbent EKO —PERL 33. For the determination of oil two methods, i.e., desorption and heat treatment have been applied. The former of the two is recommended at low oil concentrations, whereas the latter at high concentrations and at low suspendedmatter contents. Besides quantitative determination, an analytical method has also been developed for the qualitative separation of oils, using a Derivatograph of Hungarian manufacture, suitable for performing thermic analyses. Using the sampling and analytical methods developed the present state of oil pollution along the Danube river has been surveyed. Surface waters, thus also the Danube, are exposed to a wide variety of oil pollutions. These may originate from the wastes of oil refineries, further from different phases of handling, transportation, storage and use. The results of this survey have indicated that the Danube carries a considerable polluting load of oil already as it enters Hungarian territory. This load corresponds to about 190 tons of oil daily. Different plants of the oil industry in Hungary —namely Szőny, Almásfüzitő, Százhalombatta, Csepel — and from among other industrial operations the Dunaújváros Steel Works contrib-