Bewertung zentraler und dezentraler Abwasserinfrastruktursysteme
- Evaluation of centralised and decentralised infrastructure systems for sewage disposal
Herbst, Heinrich Bernhard; Dohmann, Max (Thesis advisor)
Aachen : Publikationsserver der RWTH Aachen University (2008)
Dissertation / PhD Thesis
Aachen, Techn. Hochsch., Diss., 2008
Since nearly 160 years central sewage systems are built to discharge surface water as well as domestic and industrial wastewater in Central Europe. With the beginning of the 20th century the wastewater increasingly became treated in central sewage treatment plants. Today approx. 96% of the population in Germany is connected to a central sewage disposal system and the remaining part to local sewage treatment plants. The existing technical sewage installations have to be maintained and adapted to changing basic conditions, e.g. legal, demographical and climatical changes. Waste water can be considered as a valuable source containing carbon as energy source as well as phosphorus, nitrogen and potassium as nutrients. Treated wastewater can serve as a substitute for water utilisations that do not need drinking water quality. A consequent utilisation of the sewage water and its recyclable material is realised in new ecological sanitation systems. Thereby an efficient separation and collection of the different flows of the domestic wastewater - toilet wastewater (black water) faeces (brown water), urine (yellow water) and the remaining domestic wastewater (greywater) is realised directly in situ. These systems require a complex sanitary technique as well as a specialised process engineering for the recovery of nutrients and for the wastewater treatment, considering the specific ingredients of the different partial wastewater flows. Important criteria for the elaboration or modification of sewage disposal systems are the efficiency, the cost-effectiveness as well as pollution abatement and the protection of resources. The fulfilment of these criteria and a multitude of applicable proceedings are needed to define an objective valuation for the decision in favour of a central or decentralised infrastructure system. The valuation of infrastructure systems is nowadays carried out with regard to the sustainability of a system taking in consideration economical, ecological and social aspects. Hitherto existing valuation models show the following deficits: • extreme expenses in time and effort; thus applicable for scientific purposes only, • lacking transferability due to project defined valuation • no consideration of industrial wastewater in the valuation of new ecological sanitation systems • subjective valuation due to application of ordinal valuation methods • mostly no consideration of existing infrastructural elements • mostly no consideration of social criteria, like acceptance or future oriented aspects (demographic and climatic changes) The absence of a practice oriented valuation model for the evaluation that is scientifically founded and simple to apply for sewage infrastructure systems has given the motif for this thesis. Economical, ecological and social criteria were developed for the new multidimensional evaluation system with practical relevance. The essential characteristics of this new evaluation model are: • Functional specification and cardinal valuation of criteria by calculation of a validation number • Criteria are objectified by the calculation of a validation number • Adaptation of criteria as well as their functional coherence considering all project related conditions • High variability of evaluation criteria facilitates a wide application • Consideration of abstracted settlement systems • Incorporation of the disposal of industrial wastewater • Evaluation of existing infrastructural elements or infrastructural systems considering their system efficiency • Valuation of existing infrastructural elements or systems in the case of a possible system change • Consideration of future demographical and climatic developments • Amplification of the model by elements of water supply and regional planning are possible, e.g. energy supply, telecommunication and social institutions. One community area serves as an example for the manageability and informal value of the validation model. As result of this application shall be mentioned: • The evaluation should only be done by specialists in municipal water management. • A change of the validation of criteria should only be done having experience in evaluation of infrastructural systems of wastewater. • The final result has to be verified by a sensitivity analysis of the weighting factors. • The amount of work is suitable. The presented model enables engineers and scientists of municipal water management and regional planning to compare different sewage structure systems under the aspect of sustainability on the basis of local conditions. The application of this evaluation system is not limited to Central Europe because the high variability of the criteria allows an adaptation to the specific conditions of any country.