Comparison of technology, costs and environmental benefit of wastewater treatment plants in mountainous areas in the alps

Abstract 
Keywords
Cost analysis 
Benefit analysis 
Priority Ranking
Conclusions
References

Abstract

In the course of the current EU-Life project 15 demonstration treatment plants at mountain refuges have been installed and their performance has been monitored during the project period of 46 months (http://www.uibk.ac.at/c/c8/c815/life/intro.html ). Beside technological issues the ecological benefit of the treatment works has been evaluated against their economical effort (ecobalance). After the determination of 10 boundary conditions (e.g. energy supply, altitude, means of transport) of a refuge the expected technical effort and the costs can be estimated. The influence of each boundary condition on the total costs is evaluated by a simple effort-weights-classification system. The actual costs of the installation of the treatment plant related to the determined effort-weights result in effort specific costs and are a parameter for the cost-effectiveness of the considered treatment plant. A similar system allows the quantification of the ecological benefit of the treatment plant. Here the weights of a potential wastewater emission (depending on the organic load, the annual load and the water demand) are multi-plied with the sensitivity of the site.

Keywords

On-site treatment, mountains, ecobalance, public funding, ecological benefit, economic effort

Cost analysis

It is difficult for both parties – the building owner and the public authority – to evaluate relatively high investment costs of small wastewater treatment plants WWTPs in the mountains. The cost effectiveness of municipal WWTPs usually is assessed by the cost per load unit (person equivalent) and therefore the design load is a sufficient evaluation parameter. In remote areas treatment plants of the same size can show significant cost variations because local boundary conditions influence not only the appropriate type of treatment strategy but also the costs. All 15 WWTPs of the Life project have been constructed concerted at the same time and allow a systematic cost analysis. For this reason 10 boundary conditions have been considered which are defined in the ÖWAV Guideline 1 “Wastewater treatment in the mountains” (Austrian Water- and Waste-Management Association, 2000) in more details. These boundary conditions are combined as influencing factors of the investment costs using uniform units. This means that each boundary condition is described by a weight classification of expected difficulties a certain project has to deal with. The amount of weights (1, 2 or 3 weights) of a boundary condition is a measure of the required technical or economical effort caused by a local boundary condition. The sum of weights of all boundary conditions of a planned treatment plant represents the expected effort.

 

Tab. 1: Suggested weight classification to characterise the effort caused by 10 boundary conditions

Effort E =  Total of weights (1 - 10)

In order to demonstrate this calculation one site – the refuge Konstanzer Hütte – is picked out as an example: The design load is 110 PE (++), the specific water demand is 100 l/PE (+), the annual organic load amounts to 230 kg BOD (++), the altitude is 1708 m a.s.l. (-), the refuge is located at a creek with rather high discharge therefore the site shows no significant sensitivity or hazard (+), the required treatment efficiency of 80 % BOD is average (++), there is no operation during the winter season (-), the energy supply by a small water power station is sufficient (-), the refuge is accessible by a lorry (-) and the already existing septic tanks and storage tanks are re-useable (-). Consequently the expected effort E for the installation of the biological treatment plant is summed up to 8 effort-weights (+). The investment costs of 41500 € divided by the effort E results in the effort-specific costs of about 5000 €. This amount represents the economical effort under consideration of the local situation. Operating cost are not eligible and therefore they are not considered here. The advantage of such a simple effort calculation is based on its quick and transparent application. Of course this inquiry is a compromise in accuracy but it enables a comparison of different sites. The effort-specific costs are a clear indicator of the economic efficiency of the analysed treatment plant. The cost analysis of all 15 Life treatment plants (Fig.1) represent a cost-database for an evaluation of future investments. As a further consequence public flat rate funding according to the effort weights might be considered. In comparison to the common cost-proportional funding administration and supervision would be simplified.

Benefit analysis

An evaluation of the efficiency of an investment should always include an analysis of the benefits for the environment and these benefits should be in a reasonable relationship with the expenses. Following this intention the Austrian water authorities have released specific wastewater emission standards for isolated sites in mountain regions. The legal requirements are lower than for municipalities considering the fact that that they are more difficult and more expensive to achieve. The benefit for the environment is determined by the potential damage prevented by the installed treatment plant. The potential damage is represented by the maximum load (boundary condition 1), the specific flow (2), the annual organic load or sludge production (3), the geo-hydraulic sensitivity of the site (5) and the climatic situation or altitude (4). According to this enumeration only the first 5 out of 10 boundary condition need to be considered. To stress the significance of the sensitivity of the site (5) the weights from this boundary condition are multiplied with the sum of weights: Benefit B = Total of weights (1 - 4) x weights (5) The environmental benefit of the wastewater treatment plant Konstanzer Hütte is calculated by this equation: B = (2+1+2+0) + 1 = 5 Benefit-specific costs are investment costs related to the benefit B (Fig.1). In some cases the effort-specific costs differ significantly from the benefit-specific costs. For instant low effort-specific and high benefit specific costs mean a budget-priced construction of a treatment plant with low environmental relevance. The suggested simple evaluation procedure requires only basic data and no detailed investigations.

Fig.1: Investment costs of all 15 Life treatment plants related to the effort and the environmental benefit of their installation.

Priority Ranking

Limited public funding of water protection measures should be utilised efficient and these measures should be ranked according to their urgency. Both goals are expressed by the benefit/effort ratio. This ratio can be defined as a priority with a value greater than 1 indicating high priority. Lower values indicate less relevance of the measure. It is important that the priority is calculated exclusively from the effort- and benefit-weights without knowledge of the actual investment costs. This fact allows a priority ranking before the start of the planning of the treatment plant and before a detailed cost estimation. The Office of the Government of Tyrol (section Water Management) administrates a database about ca. 1000 touristic sites in the mountains which has been elaborated on-site by a detailed questionnaire. The suggested approach to calculate the priority as a benefit/effort ratio has been installed tentatively. After programming different query routines the weights of all 10 boundary conditions could be determined automatically from the database. Only 20 % of the sites provided not sufficient data in terms of information about the sensibility of the site and they have been neglected. Fig.2 presents the results of the analysis and the graduation of 5 priority classes.

 
 

Fig. 2: Priority ranking of treatment plants of 773 analysed touristic sites which are administrated in a database of the Office of the Government of Tyrol.

Conclusions

Water law and public funding are two political tools to regulate and support wastewater treatment in mountainous regions. In case the public subsidisation of the treatment plants is based on the actual weights of the constraints and not on the costs more cost-efficient systems are promoted. The ecobalance can serve for an objective priority ranking of required on-site treatment plants.

References

ÖWAV (Austrian Water and Waste Management Association), 2000: Wastewater treatment in mountainous areas (in German, English, French and Italian). Guideline 1, Vienna Wett, B., Becker, W., Ingerle, K. 2000: Comparison of technology, costs and environmental benefit of wastewater treatment plants in mountainous areas in the Alps. EU-Life-project homepage: http://www.uibk.ac.at/c/c8/c815/life/intro.html

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