No abstract

Cost comparison in the field of wastewater treatment is a difficult task, particularly concerning sewages charges in different countries. German wastewater management is, for one thing, known to be very efficient, yet, for another, comparatively costly on an international scale. In this context, the marginal conditions typically prevailing in the field of sewage treatment in Germany should be mentioned: dense population and industrialization with high export-oriented production rates, high-profile purification requirements enforced by law. To establish a valid cost comparison, it is necessary to include both the investment and the operating expenses within the scope of the overall annual costs. The major factors impacting the different cost types are represented. Only if these factors are taken into account and quantified, will cost comparison be fair and lead to useful results. Ten hints for cost minimization are given to serve as a guideline for successful and responsable cost reduction. Cost transparency is the prerequisite for the possibility to develop saving potentials while simultaneously securing the social and political acceptance of the charges levied, and to compare the different plants with one another. Experience from Ruhrverband, a water management association for an entire catchment area, being responsible for planning, building and operation of 94 wastewater treatment plants and other plants for water quantity and water quality management, is reported.

The principles of high-rate denitrification are explained. In the experimental section of the paper the results of nine lab-scale experiments are described and compared with data gained from reviewed literature. The tests were performed in continuous flow stirred-tank and wash-out reactors under mesophilic and thermophilic conditions. The experimental results confirm that high-rate denitrification is an extremely efficient process. Removal rates of up to 25 kg NOx-Nel./ (m3·d) were achieved with the activated sludge systems. The nitrate sludge loading was found to be the significant design parameter for the process if there is an excess of organic substrate. The maximum rate achieved by thermophilic bacteria was 10 kg NOx-Nel./(kg MLVSS·d) which exceeded by 33 % that for mesophilic organisms. Due to this, in the wash-out reactors the thermophilic system was superior to the mesophilic at system-related, inevitably similar MLVSS concentrations. But because of a temperature-dependent type of growth (thermophilic: disperse; mesophilic: flocculating), in the case of systems with recycling of biomass, higher removal rates (per volume) were obtained for the mesophilic reactors.

The water quality management of Ruhr River Association is challenged by the dual use pattern, i. e. drinking water supply and wastewater discharge simultaneously into the same river. In the past 10 years accidental or illegal pollution occurred statistically every twenty days. Identification of water pollutants (and polluters) was often impossible because water samples could not be secured for analysis in time. The water quality surveillance system could be extended with financial support of the European Union by another two automated monitoring stations equipped with sophisticated on-line analysators (e. g. for ammonia, chromium, chlorophyll fluorescence) and biomonitors using water fleas and mussels as detectors. Monitoring strategies, methods, techniques and costs for buildings, equipment and operation are reported. Experience and results obtained so far let assume that the integrated water quality monitoring is able to prove its merits concerning reconnaissance of accidental water pollution and subsequent early warning of water works.

The Ruhr, with an average flow of 80.5 m3/s at its mouth, is a comparatively small tributary to the Rhine River that has to perform an important task: to secure the water supply of more than 5 million people and of the industry in the densely populated region north of the river. The complex water management system and network applied by the Ruhrverband in the natural Ruhr River Basin has been developed step by step, over decades since 1913. And from the beginning, its major goal has been to achieve optimal conditions for the people living in the region. For this purpose, a functional water supply and wastewater disposal infrastructure has been built up. The development of these structures required and still requires multi-dimensional planning and performance. Since the river serves as receiving water and at the same time as a source of drinking water, the above-standard efforts of Ruhrverband for cleaner water also help to conserve nature and wildlife. Ruhrverband has summed up its environmental awareness in the slogan: "For the people and for the environment". This basic water philosophy, successfully applied to the Ruhr for more than 80 years, will be continued in accordance with the new European Water Framework Directive, enacted in 2000, which demands integrated water resources management in natural river basins, by including the good ecological status of surface waterbodies as an additional goal.