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. 51 rient supply and the removal of metabolism products. Micro-organisms are capable of thriving on nutriens in very low coneentration. Of the substances dissolved in water, the coneentration of iron and oxygen, further the equilibrium of lime and carbonic-acid are decisive for the prolification of iron bacteria. An interesting example for silting under the combined effect of carbon dioxidé, agressive carbonic-acid, iron compounds and favourable temperature can be found in the gas-washing system of ammónia plants. The temperature of water is around 30 Centigrades, and is thus highly favourable for the prolification of micro-organisms. Cultures of iron bacteria are developped in the round 1 m thick top layer of the tower packed with Raschig rings, and adhering to the silt particules suspended in water, they form a gelatinous precipitate of large volume, which restricts the flow of gas and can be removed by manual labour at high cost only. The control, that is prevention or remouval of flocs and incrustation in pipehnes, presents a complex problem. Relying on the results of investigations into microbiological problems related especially to cooling systems and to petróleum industry the following methods of control have been suggested: Removal and dispersion of precipitates by adding compounds, containing lignine-sulphonate and modifietl tannic acid, further poly-electrolvtes, for preventing flocculation and for promoting their dissolving, substances forming celates, the main function of which is to oxidize metallic precipitates. Inexpensive acid treatment, though effective— is detrimental to the equipment and is therefore not recommended. üf the microcides, the application of nonoxidizing biocides has alsó proved succesfull, besides the familiar practice of using chlorine. Good results have been reported with 4—valent ammónium salts, sodium—penta-chlorophenolate and taurine derivatives, in concentrations of a few mg/lit. Aside from their biocide properties these ammónium salts are effective for corrosion control, too, but their application may be restricted by water uses on the recipient into which they are discharged. Similar phenomena and problems have been encountered during the investigation of the 43 km long Mohács—Pécs pipeline, through which the town of Pécs is supplied with drinking water. The two papers by Literáty and Majorlaky, are devoted to this problem. Severe shortages of drinking water occured in Pécs in the early 1950-ies. The yield of springs and well-fields was reduced as a consequence of miningoperations, so that the use of surface water presented the only alternative. The demand for drinking water was accompanied by the demand of the thermal power station, the latter having been solved by an intake from the Danube, constructed in 1960 — 1962, and the Mohács—Pécs pipeline. Of the round 40 000 cu.m/day industrial water arriving through the pipeline, about 10 000 cu.m were treated at the municipal plánt to drinking quality. Sufficient water was now available, but the quality was poor due to odour — and taste complaints. The origin thereof was investigated by several institutions. The supply system, including the clarifier at Mohács, the pipeline and the structures at the treatment plánt were subject to a detailed chemical and biological analvsis performed in 1968 69, by the Research lnstitute for Water Resources Development. Investigations were extended to the Danube and Sio-rivers, as it was assumed that wastes released periodically on the Sio-river is one of the factors responsible for taste — and odour complaints. Samples were taken each month for one year, including periods when wastewaters released from the industrial effluent reservoir at Királyszentistván were present in the Mohács section of the Danube. Chemical and biological tests performed for determining water quality included analyses on micro-pollutants as well. From the results of these investigations it is concluded that owing to the high degree of dilution the polluting influence of the chemical wastes released from the Királyszentistván reservoir is no more perceptible at Mohács, and thus neither at Pécs. The secondary effect reflected by changes in the biological life in the Sio and Danube rivers alike ,was found to be considerable. The changes in water quality within the pipeline are controlled by the micro-organisms of Danube origin, present in the mosses adhereing to the pipe wall. Conditions are favourable for the formation of a similar cover. The quality of raw water undergoes no substantial change in the course of settling at Mohács, only the suspended content is reduced. Danube water of high dissolved oxygen content is thus fed into the pipeline, in which biological activity is promotecl by the meta-phosphate added in order to control pipe corrosion. The cover developed in the pipeline was found to induce favourable changes in the chemical components of water, the organic pollution is reduced. Increased biological activitv and the reduction of organic pollution is reflected positively by the decrease of dissolved oxygen and oxygen-comsumption observed in the pipeline. In summer months this reduction was more pronounced. Besides the removal of organic substances the process of nitrification could alsó be traced. The quantity of ammonium-nitrogen was reduced, whereas that of nitráté—nitrogén was increased. On the other hand, an intensification of organoleptic effects must be anticipated by the metabolism products of micro-organisms, resulting from increased biological activity. Unfortunately, owing to the lack of exact composition and to the low coneentration, these are difficult to detect by chemical methods; however, from the results it is concluded that the taste ond other complaints in the drinking water are due mainly to the metabolism products of micro-organisms; the majority of which originate in the pipeline.