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designed to be large enough to have a retention time of more than 7 h under conditions of maximum flow. A non-return valve at the base of the tank provides a connection with the pumping station. |
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6.4.1
Cost Considerations |
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Compared with conventional sewerage systems, our low-cost shallow sewerage system proved to be very cheap. We were able to make an accurate comparison of costs because we were designing a conventional sewerage system at the same time as this project was underway. This was for the mainly agricultural settlement of Bryta, which is situated in Edessa Prefecture, 140 km north of Thessaloniki. The design population was 750 people. The peak flow factor was 1.8. The length of sewer was 4830 m, and PVC pipe was used with a minimum diameter of 200 mm and a maximum diameter of 315 mm. |
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The cost analysis of the 'internal' network of Finikia (Table 6.1) includes the construction cost of the sewers and two pumping stations. The 'external' network cost represents sewer costs and the costs of the other two pumping stations. The cost analysis is based on 1993 prices. The cost comparison between the conventional sewerage network of Bryta Community and the shallow sewerage system constructed in Finikia (Table 6.2) demonstrates the economy of the latter. |
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| Table 6.1 Cost analysis of the Finikika low-cost sewerage system |
| | Item | | | Internal | External | Total (percentage) | | Earthworks | 4954500 | 1674430 | 6628930 (23.4) | | Pipes | 9961500 | 3687695 | 13649195 (48.3) | | Pumping stations | 4420056 | 3257790 | 7677846 (27.1) | | Inspection chambers | 320000 | | 320000 (1.2) | | Total | 19656056 | 8619915 | 28275971 (100) | | Cost per m | 9270 | 12367 | 10038 |
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