Costs and Economic Efficiency
In the previous sections, mention was made of the various technical possibilities, the operational tasks of maintenance and cleaning, the inspection including evaluation of the condition of the sewer and the structural maintenance (sewer repairs) that had to be fulfilled and the sewers to be renovated or replaced by means of investment measures.
For this reason, the requirement for economic efficiency can not only refer to the construction measures but also to comprehensive requirement-oriented operation. The influence of the economic efficiency, however, assumes transparency in the costs, which finally leads to the necessity of attaching the costs and results of the execution of the work to defined objects and to use them to monitor the fulfilment of the tasks. This can refer as well to the costs and the results of the individual sewer cleaning process as also to the costs and results of particular construction procedures for restoring a technical nominal condition. The constant need for the functionality of a sewer network leads to the fact that all services are repeated at stated intervals.
In order to monitor operational tasks and to recognise the costs arising from this, it is necessary to structure the network into independent part-installations. Sections of the sewer, manholes and laterals are well suited for this purpose because they are usually the object of individual tasks and represent the sewer record with which not only the technically-oriented base data are documented but are also available as a basis for cost monitoring.
The monitoring of the operational tasks, as well as the determination and planning of rehabilitation investments, are based on feedback information from the completion of these operational tasks. As a rule, the amount of data requires the utilization of data processing. The recognition of the professional and economical interconnections between the
- operational tasks of cleaning, inspection and the
- structural rehabilitation by means of repair, renovation and replacement
leads to substantial processing and organizational limiting conditions. Not only the individually used technology for the operational objects but also the organisation of the flow of the work has a substantial influence on the economic efficiency of the operational management of a sewer network.
The costs of wastewater collection are also differentiated for the calculation of fees into operational costs and utility period as well as into calculated costs for investments such as write-off and charging of interest. The relative importance results from their share of the communal sewage fees. Pecher et. al. [Peche95] give for the operating costs resulting from personnel and professional costs (including construction maintenance) a share of 40 - 45 % of the fees, while the investment for write-off and interest lead to a share of the fees of up to 60 %.
As it is hardly possible to provide average costs for all services, cost ranges and their main influencing factors will be mentioned in the following for particular points of view. Furthermore, mention will be made of current developments for improving the economic efficiency by controlling the operational costs and the investments and for testing the economic efficiency of investments.