Probleme der Kühlwasserversorgung großer Blockeinheiten aus wasserwirtschaftlicher Sicht

Die Versorgung großer Blockeinheiten von Dampfkraftwerken mit Kühlwasser ergibt eine Reihe schwieriger Probleme, die vor allem aus der Forderung nach einer wassersparenden Technologie und der Vermeidung umweltfeindlicher Produkte resultieren. Für eine wirksame Lösung werden drei Möglichkeiten beschrieben: — Die Optimierung des chemischen Status für das gesamte Kühlwasserregime, — die Wiederverwendung betriebsinterner Abwässer, — die Anwendung von Sparschaltungen für die bedarfsgerechte Versorgung der Nebenkühlstellen mit Brauchwasser. Die derzeit technologische Ausführbarkeit bzw. die Grenzen und Randbedingungen ihrer Anwendbarkeit werden diskutiert.     

Sedimentchemische Untersuchungen in Küstengewässern der Deutschen Demokratischen Republik Teil 17. Spezielle Untersuchungen zur Dynamik der Oberflächensedimente eines flachen Boddengewässers (Barther Bodden)

Repeated samples from the top 5cm of sediment in a homogeneous network of 100 sampling stations in the Barth bodden (mean depth—1.8 m) are analysed for dry weight, organic matter (loss on ignition), grain size distribution, total phosphorus and iron which is soluble in hydrochloric acid. The distribution of mineral and mud sediments (organic matter > 5%) follows the bottom topography: trays, closed basins and channels show the respective muddy concentrations; spits, ground waves and windexposed uplifts from depressions are mostly mineralic. The water depth has only a subordinate effect on distribution. After unquiet meteorological and hydrographic situations mainly the fine-grained material is redistributed. As comparative investigations over four years show, due to this the distribution pattern is not changed fundamentally, so that the distribution of mainly mineralic, muddy and intermediate transition ranges can be mapped, unless this would be done according to surveys under extreme hydrographic and meteorological conditions. The individual parameters of the sediment quality show significant correlations between each other.     

Ausbreitung eines Abwasserauftriebstrahls in einem See Verifikation eines mathematischen Modells in der Natur

The object in view—namely the recording of the trajectory of a buoyant jet in stratified lake and the comparison of this trajectory with that predicted by a mathematical model developed at the VAW—was achieved to a great extent. The field experiments were performed in the summer of 1981 in Lake Hallwil. The comparison shows that, given the same conditions, the results obtained from the mathematical model agree with the measured quantities. Although the final layer where the jet levels appears to be at a greater depth than predicted, the horizontal and vertical spreading of the jet and its dilution accord well with the theory.     

Reduzierung von Bakterien- und Coliphagen-Konzentrationen auf der Fließstrecke eines Klärwerksableiters

Reduction of the Concentration of Bacteria and Coliphages along the Flowing Stretch of a Treated Sewage Channel The efficiency of surface waters to eliminate E. coli, fecal streptococci, Salmonella spp., and coliphages was evaluated in a small river which receives treated wastewater and which is rich in submerged macrophytes. The study took place between April and December, 1994. Total colony count, BOD₅, O₂ concentration and water temperature were determined in the river as well. As the river does not receive additional water downwards along its 17.2 km course, dilution effects could be ruled out as the cause for the elimination of the microorganisms. The reduction is assumed to happen rather due to sedimentation, grazing, and adsorption to the submerged waterplants. Immediately after discharge of the wastewater, the river water contained about 10⁵ cfu/100 mL E. coli and 10⁴ cfu/100 mL fecal streptococci, about 1000 pfu/100 mL coliphages, and, as a rule, was positive for salmonella in 10 mL. The reduction of E. coli, fecal streptococci, salmonella, clostridia, and coliphages at the end of the course was 1 to 2 orders of magnitude. This reduction took place mainly within the first 4.7 km, a part in which, due to low flowing velocities, suspended solids settle down efficiently. Besides, at the end of this part the submerged waterplants are especially abundant. The reduction of suspended solids correlated positively with that of BOD₅, bacteria, and coliphages. The reduction of microorganisms was not sufficient to fulfill the requirements of the European Community guidelines for bathing waters and for surface waters used as drinking water source. The regenerating capacity of surface waters is not sufficient to eliminate pathogens from convenionally treated wastewater. Therefore, tertiary treatment is necessary to keep receiving waters reasonably free from pathogens.     

Zur Rolle der Stickstoffixation im Stoffhaushalt eines geschichteten Sees

In the dimict lake Arend (5.1 km², 146 hm³, 49.5 m z_max), nitrogen is production-limiting with concentrations below the detection limit during the production period. Phytoplankton achieves biomasses of up to 18 mg/l fresh matter, essential contributions being made by Aphanizomenon with 2 mg/l and Anabaena with up to 10 mg/l. Nitrogen fixation was measured by the ethine reduction technique (acetylene reduction) during periods of the occurrence of heterocystforming Cyanophyceae and achieved peak values up to 6.59 μg N² · h^?1 · l^?1 or 14.87 m^?2 · h^?1 g N₂ · m^?2 · h^?1. The rates of fixation show a safe correlation with the biomass of heterocyst-containing Cyanophyceae (r = 0.88), their development beginning at values below the N : P-ratio of 2.66.     

Die chemische Zusammensetzung des Sestons in inneren Küstengewässern der DDR (Darß–Zingster Boddengewässer,südliche Ostsee)

Investigations were made on 27 seston samples of the years of 1978, 1979 and of the first half-year of 1982 from a station in the Zingster Strom. The mean contents – as mg/g dry matter – are: ash-free dry matter 569, C_total 284, C_inorg. 14, N_total 29, P_total 3.6, Fe_HCl-soluble 13. From them resulted the following weight quotients: C : N = 9.9 ± 2.4, C : P = 83 ± 21, N : P = 8.4 ± 1.8, Fe : P = 3.6 ± 1.0. The mean proportion of carbohydrate and the mean protein content amount to 170 and 180 mg/g, resp., dry matter. All parameters show pronounced dependences on seasonal and hydrographic situations, mainly the effects of wind on the very shallow water being of primary importance to the distribution and nature of seston.