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Wastewater treatment is of great financial concern in many states of Germany. In the rural areas of the Saarland (German state at the border to Luxembourg and France) investments for wastewater treatments in the next years will mount up to 400 mio. €. Nevertheless, decision makers are still left with the question, if these investments result in an effective and sustainable water treatment. To answer this question, the ministry of environment, related authorities and the University of the Saarland (Geographical Institute) started a Project to investigate seven small headwater catchments with predominantly Triassic series of Muschelkalk. Aims of this study were the following: (i) the description of the spatial variability of water chemistry upstream and downstream of small villages (in these villages only mechanically treated waste water is discharged into the brooks), (ii) calculation of nutrient loads of differently managed catchments (predominantly woodland, meadows or fields) and (iii) the relative importance of non-point pollution sources to point pollution sources. Results indicated that spatial variability of nitrate concentration during base-flow conditions was quite similar in intensively used agricultural areas. Nitrogen fluxes were predominantly controlled hydrologically. The nitrogen load (kg N per ha) from non-point pollution sources amounts from 32.5 to 43 kg N / ha * a in intensively used agricultural areas. This load, forecast to one square-km, is equal to the N-load of 800 " 1000 population equivalents. Thus, non-point pollution sources are a major part of the overall nitrogen pollution in the rural areas. The results are important criterias for the sewage disposal plan of the Saarland (disposal plans are obligate according to German water law) and can serve as a first part of a river basin management according to the European Water Framework Directive. To lower non-point N-pollution changes in agricultural management practices are necessary.
Der Aufbau einer Klassifikation von Einzugsgebieten (EZG) auf Basis des Abflussverhaltens und der Gebietseigenschaften sowie die Regionalisierung von Abflussparametern sind Kernthemen der Hydrologie. Die Ziele dieser Arbeit sind der Aufbau einer Klassifikation für EZGs mit hoher räumlicher Auflösung nach dem Abflussverhalten und der Gebietseigenschaften, die Identifikation abflussrelevanter, physiogeografischer und klimatischer Gebietseigenschaften und die Regionalisierung von Abflussverhalten und Modellparametern auf Basis von Klassifikationen. Dabei wird untersucht, ob sich 53 häufig benachbarte und z.T. ineinander geschachtelte Einzugsgebiete in Rheinland-Pfalz für eine Klassifikation eignen und wie das Abflussverhalten für die Beurteilung von Ähnlichkeiten beschrieben werden kann. Das Abflussverhalten der EZGs wird mit einer großen Anzahl von Ereignis-Abflussbeiwerten je EZG und Abflussdauerlinien (Flow-Duration Curves) der EZGs beschrieben, die das Abflussverhalten umfassend und mit einer ausreichenden Trennschärfe abbilden. Gebietseigenschaften, die das Abflussgeschehen dieser EZG dominieren, sind langjährige, mittlere Niederschlagssummen, die mittlere potentielle Verdunstung, die Topografie und die Speichermöglichkeiten im EZG. Für den Aufbau und die Anwendung der EZG-Klassifikationen wird ein hierfür entwickeltes Verfahren eingesetzt, dass auf Selbstorganisierenden Merkmalskarten (Self-Organizing Maps, SOM) basiert. Vorteile dieses Verfahrens gegenüber vielen konventionellen Verfahren sind Qualitätsmaße, die datenbasierte Bestimmung wichtiger Parameter, aussagestarke Visualisierungen der Ergebnisse und die Klassifikation und Regionalisierung mit einer Methode. Die Auswertung von zwei separaten Klassifikationen, nach dem Abflussverhalten und nach den physiogeografischen und klimatischen Gebietseigenschaften, stellen einen direkten Zusammenhang zwischen Abfluss- und Gebietseigenschaften her. Der Überschneidungsbereich der beiden Klassifikationen ist die Grundlage für die Übertragung von Abflussinformationen auf unbeobachtete Gebiete (Regionalisierung). Die Ergebnisse zeigen, dass die Methode der Clusteranalyse, Klassifikation und Regionalisierung mit SOM und den genannten Abfluss- und Gebietskennwerten geeignet ist, EZGs mit einer hohen räumlichen Auflösung treffend und detailliert zu klassifizieren sowie Abflussparameter zu regionalisieren.
Evaluation of desalination techniques for treating the brackish water of Olushandja sub-basin
(2014)
The groundwater of Olushandja sub-basin as part of Cuvelai basin in central-northern Namibia is saline with TDS content varying between 4,000ppm to 90,000ppm. Based on climatic conditions, this region can be classified as a semi-arid to arid region with an annual rainfall during summer time varying between 200mm to 500mm. The mean annual evaporation potential is about 2,800mm, which is much higher than the annual rainfall. The southern block of this sub-basin is of low population density. It has not been covered by the supply networks for electricity and water. Therefore, the inhabitants are forced to use the untreated groundwater from the hand-dug wells for their daily purposes. This groundwater is not safe for human consumption and therefore needs to be desalinated for that purpose. The goal of this thesis has been to select a suitable desalination technology for that region. The technology to be selected is from those which use renewable energy sources, which have capacity of production from 10m3 to 100m3 per day, which are simple and robust against existing harsh environmental conditions and have already been implemented successfully in some place. Based on these criteria, the technologies which emerged from the literature are: multistage flashing (MSF), multi effect distillation (MED), multi effect humidification (MEH), membrane distillation (MD), reverse osmosis (RO) and electro dialysis reversed (ED). Out of these technologies, RO & ED are based on membrane techniques and MSF, MED & MEH use thermal processes whereas MD technology uses a hybrid process of thermal and membrane techniques for desalinating the water. For evaluation of technical performance, environmental sustainability and financial feasibility of the above mentioned desalination techniques, the following criteria have been used: gained output ratio, recovery rate, pretreatment requirements, sensitivity to feed water quality, post treatment, operating temperature, operating pressure, scaling and fouling potential, corrosion susceptibility, brine disposal, prime energy requirement, mechanical and electrical power output, heat energy, running costs and water generation costs. The data regarding the performance standards of the successfully implemented desalination techniques have been obtained from the literature of performance benchmarks. The Utility Value Analysis Tool of the Rafter-Group of Multi-Criteria Analysis (MCA) has been used for measuring the performance score of a technology. To perform the utility analysis, an evaluation matrix has to be constructed through the following procedures: selection of the decision options (or assessment groups), identification of the evaluation criteria, measurement of performance and transformation of the units. Then the criteria under the objective groups are assigned a level of importance for determining their weights.To perform the sensitivity analysis the level of importance of a criterion is changed by giving more weight or rate to the assessment group of interest (or study). Within the assessment group of interests, the best performing desalination technology has been selected according to the outcome of the sensitivity analysis. The important conclusions of this study are the identification of the capabilities of thermal and membrane based small scale desalination technologies and their applicability based on site specific needs. The sensitivity analysis indicates that the MED technology is the most environmental friendly technology that uses minimum energy and produces least concentrated brine for disposal. The ED technology has emerged to be technically suitable, but it is only applicable when source water has less than 12.000 ppm salt content. The MSF process has favorable thermal efficiency and it is insensitive to feed water quality. Its major drawbacks are energy needs and post treatment requirements that affected its net score. The MD and MSF process have scored the lowest for the technical and economic assessment groups and are concluded not to be suitable for Olushandja sub-basin. The MEH process is cheaper and technically more appropriate than the MED in the two assessment groups. Based on the above mentioned evaluations, this study concluded that Olushandja sub-basin needs more data collection on the geological profile, distinctive identification of aquifers and evidence on the interaction between the aquifers. From the best available data obtained, it could not be established with certainty where the highest level of salinity can be found in the profile, or how the geological profile is layered. More data on ground water quality for spatial overview of the trends and pattern of the sub-basin will be useful in drawing better conclusion on the specific desalination technology needed which is suitable for a specified village or living space.